MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Journal of Biomechanics' source. Thu, 09 Feb 2012 14:07:53 +0100 http://www.medworm.com/index.php?rid=5624510&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929012000036%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624510 Tue, 24 Jan 2012 19:15:55 +0100 5624510 http://www.medworm.com/index.php?rid=5624538&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007676%2Fabstract%3Frss%3Dyes Abstract: The joint fluid mechanics and transport of wear particles in the prosthetic hip joint were analyzed for subluxation and flexion motion using computational fluid dynamics (CFD). The entire joint space including a moving capsule boundary was considered. It was found that particles suspended in the joint space are drawn into the joint gap between prosthesis cup and head during subluxation, which was also documented by ; Journal of Biomechanics 40, 1676–1685), however, wear particles remain in the joint gap. Wear particles leave the joint gap during flexion and can finally migrate to the proximal boundaries including the acetabular bone, where the particle deposition can cause osteolysis according to the established literature. Thus, the present study supports the theory of polyeth... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624538 Mon, 09 Jan 2012 05:00:00 +0100 5624538 http://www.medworm.com/index.php?rid=5624515&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007846%2Fabstract%3Frss%3Dyes Abstract: Embolic coiling is the most popular endovascular treatment available for cerebral aneurysms. Nevertheless, the embolic coiling of wide-neck aneurysms is challenging and, in many cases, ineffective. Use of highly porous stents to support coiling of wide-neck aneurysms has become a common procedure in recent years. Several studies have also demonstrated that high porosity stents alone can significantly alter aneurysmal hemodynamics, but differences among different stent configurations have not been fully characterized. As a result, it is usually unclear which stent configuration is optimal for treatment. In this paper, we present a flow study that elucidates the influence of stent configuration on cerebral aneurysm fluid dynamics in an idealized wide-neck basilar tip aneurysm model... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624515 Mon, 09 Jan 2012 05:00:00 +0100 5624515 http://www.medworm.com/index.php?rid=5624514&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007858%2Fabstract%3Frss%3Dyes In this study, mechanical response of fresh bovine brain tissue was studied using the two modified Kolsky bar techniques. Radial deformation behavior of annular specimens, which are typically used to characterize the dynamic uniaxial compressive response of biological tissues, was examined using a modified Kolsky bar and a high speed camera to collect images while the specimen deforms at an axial strain rate of 2000s−1. The high-speed images revealed inhomogeneous specimen deformation possibly brought about by radial inertia and causing a multi-axial stress state. To acquire valid stress–strain results that can be used to produce constitutive behavior of the soft materials, a novel torsion technique was developed to obtain pure shear response at dynamic loading rates. Experimental resu... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624514 Mon, 09 Jan 2012 05:00:00 +0100 5624514 http://www.medworm.com/index.php?rid=5624511&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007408%2Fabstract%3Frss%3Dyes This study investigates the role of cutaneous feedback on maximum voluntary force (MVF), finger force deficit (FD) and finger independence (FI). FD was calculated as the difference between the sum of maximal individual finger forces during single-finger pressing tasks and the maximal force produced by those fingers during an all-finger pressing task. FI was calculated as the average non-task finger forces normalized by the task-finger forces and subtracted from 100 percent. Twenty young healthy right-handed males participated in the study. Cutaneous feedback was removed by administering ring block digital anesthesia on the 2nd, 3rd, 4th and 5th digits of the right hands. Subjects were asked to press force sensors with maximal effort using individual digits as well as all four digits togeth... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624511 Fri, 06 Jan 2012 05:00:00 +0100 5624511 http://www.medworm.com/index.php?rid=5624543&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007731%2Fabstract%3Frss%3Dyes In the original article “Acknowledgement” was incorrect. The Acknowledgement is given below: This research was funded through support from the Saskatchewan Health Research Foundation (SHRF), Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Institutes of Health Research (CIHR) and the Canadian Arthritis Network (CAN). (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624543 Wed, 04 Jan 2012 05:00:00 +0100 5624543 http://www.medworm.com/index.php?rid=5624518&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007470%2Fabstract%3Frss%3Dyes In this study, a model has been created to study posture strategies in such situations. A 3D mechanical model consisting of eight rigid segments and 30 muscle groups is used in which varying moment arms along the ranges of motion and biarticular muscles are considered. The method is based on static optimization, both to solve the load sharing in the muscle system and to choose posture strategy. The optimization computes the specific posture with minimal required effort (level of muscle activations), while fulfilling constraints containing subject specific ranges of motion, muscle strength/weakness and external support if present. Anthropometry and strength were scaled to each individual, based on reported pediatric anthropometry and strength values, combined with each individual's physical... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624518 Wed, 04 Jan 2012 05:00:00 +0100 5624518 http://www.medworm.com/index.php?rid=5624516&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100769X%2Fabstract%3Frss%3Dyes Abstract: The purpose of this study was to assess the relationship of accelerometer output, in counts (ActiGraph GT1M) and as raw accelerations (ActiGraph GT3X+ and GENEA), with ground reaction force (GRF) in adults. Ten participants (age: 29.4±8.2yr, mass: 74.3±9.8kg, height: 1.76±0.09m) performed eight trials each of: slow walking, brisk walking, slow running, faster running and box drops. GRF data were collected for one step per trial (walking and running) using a force plate. Low jumps and higher jumps (one per second) were performed for 20s each on the force plate. For box drops, participants dropped from a 35cm box onto the force plate. Throughout, three accelerometers were worn at the hip: GT1M, GT3X+ and GENEA. A further GT3X+ and GENEA were worn on the left and right wrist, res... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624516 Wed, 04 Jan 2012 05:00:00 +0100 5624516 http://www.medworm.com/index.php?rid=5624520&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007469%2Fabstract%3Frss%3Dyes Abstract: In vitro pre-clinical testing of total knee replacement (TKR) devices is a necessary step in the evaluation of new implant designs. Whole joint knee simulators, like the Kansas knee simulator (KKS), provide a controlled and repeatable loading environment for comparative evaluation of component designs or surgical alignment under dynamic conditions. Experimental testing, however, is time and cost prohibitive for design-phase evaluation of tens or hundreds of design variations. Experimentally-verified computational models provide an efficient platform for analysis of multiple components, sizes, and alignment conditions. The purpose of the current study was to develop and verify a computational model of a dynamic, whole joint knee simulator. Experimental internal–external and valg... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624520 Tue, 03 Jan 2012 05:00:00 +0100 5624520 http://www.medworm.com/index.php?rid=5624517&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007615%2Fabstract%3Frss%3Dyes Conclusions: The pubovisceral muscle enthesis and the muscle near the perineal body are the regions of greatest strain thereby placing them at highest risk for stretch-related injury. Decreasing perineal body tissue stiffness significantly reduced tissue stress and strain, and therefore injury risk, in those regions. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624517 Tue, 03 Jan 2012 05:00:00 +0100 5624517 http://www.medworm.com/index.php?rid=5624523&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007433%2Fabstract%3Frss%3Dyes Abstract: In clinical arthrographic examination, strong hypertonic contrast agents are injected directly into the joint space. This may reduce the stiffness of articular cartilage, which is further hypothesized to lead to overload-induced cell death. We investigated the cell death in articular cartilage while the tissue was compressed in situ in physiological saline solution and in full strength hypertonic X-ray contrast agent HexabrixTM. Samples were prepared from bovine patellae and stored in Dulbecco’s Modified Eagle’s Medium overnight. Further, impact tests with or without creep were conducted for the samples with contact stresses and creep times changing from 1MPa to 10MPa and from 0min to 15min, respectively. Finally, depth-dependent cell viability was assessed with a confocal mi... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624523 Fri, 30 Dec 2011 05:00:00 +0100 5624523 http://www.medworm.com/index.php?rid=5549528&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007524%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549528 Thu, 29 Dec 2011 11:21:02 +0100 5549528 http://www.medworm.com/index.php?rid=5624519&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007494%2Fabstract%3Frss%3Dyes Abstract: The notching phenomenon is one of the major concerns with reversed total shoulder arthroplasty. Repetitive contact between the humeral implant and the scapula (mechanical notching) produces progressive abrasion of the implant if the moving part is made of polyethylene. Its debris may then lead to active osteolysis (biological notching). Inversion of bearing materials, i.e. Glenosphere made of polyethylene and humeral Inlay made of metal, aims at the reduction of this phenomenon. However, the question arises if the tribological behavior would then be different.On an experimental setup, the gravimetric wear of both material configurations was measured after loading and moving over 500,000 cycles. The abrasion of the polyethylene Inlay due to mechanical notching was calculated by me... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624519 Thu, 29 Dec 2011 05:00:00 +0100 5624519 http://www.medworm.com/index.php?rid=5624512&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007421%2Fabstract%3Frss%3Dyes Abstract: Elderly frequently present variable degrees of osteopenia, sarcopenia, and neuromotor control degradation. Severely osteoporotic patients sometime fracture their femoral neck when falling. Is it possible that such fractures might occur without any fall, but rather spontaneously while the patient is performing normal movements such as level walking? The aim of this study was to verify if such spontaneous fractures are biomechanically possible, and in such case, which conditions of osteoporosis, sarcopenia, and neuromotor degradation could produce them. To the purpose, a probabilistic multiscale body-organ model validated against controlled experiments was used to predict the risk of spontaneous fractures in a population of 80-years old women, with normal weight and musculoskeletal... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624512 Wed, 28 Dec 2011 05:00:00 +0100 5624512 http://www.medworm.com/index.php?rid=5624522&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007445%2Fabstract%3Frss%3Dyes The objective of this study was to spatially quantify the viscoelastic parameters of the intervertebral disc throughout degeneration, including the as yet unreported residual stress/strain. This required the development of a hybrid confined/in situ indentation methodology, which preserves the disc structural morphology. At four locations of the disc (anterior-AF, right and left lateral AF, and NP) stress-relaxation tests were performed using the hybrid confined/in situ indentation method, which utilizes the vertebral endplate as the porous indenter tip. This method allows the endplate to remain interwoven with the disc tissue, retaining its native orientation. Healthy disc tissue exhibited significantly higher residual stress values compared to both moderate and severe degeneration in all ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624522 Mon, 26 Dec 2011 05:00:00 +0100 5624522 http://www.medworm.com/index.php?rid=5624513&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100741X%2Fabstract%3Frss%3Dyes Abstract: Reductionist approaches have provided little insight on the fatigue experienced by humans during activities of daily living. Some of the reasons for this lack of progress include the persistence of outdated concepts, the misinterpretation of experimental recordings, and a failure to embrace a global perspective on fatigue. This paper summarizes the three examples of these limitations that were discussed in the 2011 Muybridge Award lecture: motor unit types and muscle fatigue, myoelectric manifestations of fatigue, and fatigue and fatigability. Although the motor units in a population do exhibit a range of fatigability values, there are not distinct groups of motor units and the concept that some motor units are resistant to fatigue emerged from protocols in which motor units were... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624513 Mon, 26 Dec 2011 05:00:00 +0100 5624513 http://www.medworm.com/index.php?rid=5624521&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007457%2Fabstract%3Frss%3Dyes Abstract: Despite the findings that peak anterior shear load is highly correlated with low-back pain reporting, very little research has been conducted to determine how vertebral shear injury potential is influenced. The current study quantified the combined effects of vertebral joint compression and flexion/extension postural deviation from neutral on ultimate shear failure. Ninety-six porcine cervical specimens (48C3–C4, 48C5–C6) were tested. Each specimen was randomly assigned to one of twelve combinations of compressive force (15%, 30%, 45%, or 60% of predicted compressive failure force) and flexion/extension postural deviation (extended, neutral, or flexed). Vertebral joint shear failure was induced by applying posterior shear displacement of the caudal vertebra at a constant rate... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624521 Fri, 23 Dec 2011 05:00:00 +0100 5624521 http://www.medworm.com/index.php?rid=5624526&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007238%2Fabstract%3Frss%3Dyes This article employs three computational fluid methodologies, of varying levels of complexity with coupled 0D boundary conditions, to simulate the haemodynamics within a patient-specific aorta. The most comprehensive model is a full FSI simulation. The simplest is a rigid walled incompressible fluid simulation while an alternative middle-ground approach employs a compressible fluid, tuned to elicit a response analogous to the compliance of the aortic wall. The results demonstrate that, in the context of certain clinical questions, the simpler analysis methods may capture the important characteristics of the flow field. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624526 Thu, 22 Dec 2011 05:00:00 +0100 5624526 http://www.medworm.com/index.php?rid=5624539&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007500%2Fabstract%3Frss%3Dyes Abstract: The purpose of this study was to investigate whether neuromuscular adaptations at the site of injury or neural adaptation remote to the injury are affected in individuals with chronic ankle instability (CAI). Electromyography data were collected from the peroneus longus (PL) and tibialis anterior during an ankle joint reaction time task in 12 participants with unilateral CAI and 12 healthy control participants. Following an auditory cue, time to onset of muscle activity (pre-motor time) and time from onset of muscle activity to movement (motor time) were measured during rapid ankle eversion and dorsiflexion. Reaction time for ankle eversion on the affected side was significantly slower in the CAI group than the control group, due to significantly slower motor time for the PL. Cha... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624539 Mon, 19 Dec 2011 05:00:00 +0100 5624539 http://www.medworm.com/index.php?rid=5624536&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006890%2Fabstract%3Frss%3Dyes Abstract: Unilateral lower limb prosthesis users display temporal, kinematic, and kinetic asymmetries between limbs while ascending and descending stairs. These asymmetries are due, in part, to the inability of current prosthetic devices to effectively mimic normal ankle function. The purpose of this study was to provide a comprehensive set of biomechanical data for able-bodied and unilateral transtibial amputee (TTA) ankle–foot systems for level-ground (LG), stair ascent (SA), and stair descent (SD), and to characterize deviations from normal performance associated with prosthesis use. Ankle joint kinematics, kinetics, torque–angle curves, and effective shapes were calculated for twelve able-bodied individuals and twelve individuals with TTA. The data from this study demonstrated the ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624536 Mon, 19 Dec 2011 05:00:00 +0100 5624536 http://www.medworm.com/index.php?rid=5624531&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007184%2Fabstract%3Frss%3Dyes Abstract: ATP is actively released into the extracellular environment from a variety of cell types in response to mechanical stimuli. This is particularly true in bone where mechanically induced ATP release leads to immediate early gene activation to regulate bone remodelling; however there is no consensus as to which mechanical stimuli stimulate osteoblasts the most. To elucidate which specific type(s) of mechanical stimuli induce ATP release and gene activation in human osteoblasts, we performed an array of experiments using different mechanical stimuli applied to both monolayer and 3D cultures of the same osteoblast cell type, SaOS-2. ATP release from osteoblasts cultured in monolayer significantly increased in response to turbulent fluid flow, laminar fluid flow and substrate strain. N... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624531 Mon, 19 Dec 2011 05:00:00 +0100 5624531 http://www.medworm.com/index.php?rid=5624528&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007226%2Fabstract%3Frss%3Dyes Abstract: The hyoid bone is a unique bone in the skeleton not articulated to any other bone. The hyoid muscles, which attach to the hyoid bone, may play a role in neck mechanics, but analysis of their function requires quantifying hyoid bone mechanics. The goal of this study was to obtain the detailed kinematics of the hyoid bone over a large range of flexion-extension motion using radiographs at 5 postures. The position of the hyoid bone in the sagittal plane was characterized with respect to head, jaw, and vertebral movements. Sex differences in hyoid kinematics were also investigated. We hypothesized that (1) the position of the hyoid bone in the sagittal plane is linearly correlated with motion of the head, jaw, and vertebrae, and (2) the hyoid position, size, and kinematics are sex-sp... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624528 Mon, 19 Dec 2011 05:00:00 +0100 5624528 http://www.medworm.com/index.php?rid=5624527&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007263%2Fabstract%3Frss%3Dyes Abstract: The acetabular labrum is believed to have a sealing function. However, a torn labrum may not effectively prevent joint fluid from escaping a compressed joint, resulting in impaired lubrication. We aimed to understand the role of the acetabular labrum in maintaining a low friction environment in the hip joint. We did this by measuring the resistance to rotation (RTR) of the hip, which reflects the friction of the articular cartilage surface, following focal and complete labrectomy. Five cadaveric hips without evidence of osteoarthritis and impingement were tested. We measured resistance to rotation of the hip joint during 0.5, 1, 2, and 3 times body weight (BW) cyclic loading in the intact hip, and after focal and complete labrectomy. Resistance to rotation, which reflects articul... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624527 Mon, 19 Dec 2011 05:00:00 +0100 5624527 http://www.medworm.com/index.php?rid=5624524&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007275%2Fabstract%3Frss%3Dyes This study was designed to determine the effects of ball radius on friction. Generic models of metal-on-metal TDA were manufactured with ball radii of 10, 12, 14 and 16mm, with a radial clearance of 0.015mm. A simulator was used to test each sample in flexion–extension, lateral bending and axial rotation at frequencies of 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2Hz under loads of 50, 600, 1200 and 2000N, in new born calf serum. Frictional torque was measured and Stribeck curves were plotted to illustrate the lubrication regime in each case. It was observed that implants with a smaller ball radius showed lower friction and showed boundary and mixed lubrication regimes, whereas implants with larger ball radius showed boundary lubrication only. This study suggests designing metal-on-metal T... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624524 Mon, 19 Dec 2011 05:00:00 +0100 5624524 http://www.medworm.com/index.php?rid=5512157&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007305%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512157 Sat, 17 Dec 2011 07:23:24 +0100 5512157 http://www.medworm.com/index.php?rid=5624537&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006828%2Fabstract%3Frss%3Dyes We present a robust and computationally inexpensive method to estimate the lengths and three-dimensional moment arms for a large number of musculotendon actuators of the human lower limb. Using a musculoskeletal model of the lower extremity, a set of values was established for the length of each musculotendon actuator for different lower limb generalized coordinates (joint angles). A multidimensional spline function was then used to fit these data. Muscle moment arms were obtained by differentiating the musculotendon length spline function with respect to the generalized coordinate of interest. This new method was then compared to a previously used polynomial regression method. Compared to the polynomial regression method, the multidimensional spline method produced lower errors for estima... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624537 Fri, 16 Dec 2011 05:00:00 +0100 5624537 http://www.medworm.com/index.php?rid=5624525&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007251%2Fabstract%3Frss%3Dyes Abstract: The aim of this study was to identify kinematic and dynamic variables related to the best tumble turn times (3mRTT, the turn time from 3-m in to 3-m out, independent variable) in ten elite male swimmers using a three-dimensional (3D) underwater analysis protocol and the Lasso (least absolute shrinkage and selection operator) as statistical method. For each swimmer, the best-time turn was analyzed with five stationary and synchronized underwater cameras. The 3D reconstruction was performed using the Direct Linear Transformation algorithm. An underwater piezoelectric 3D force platform completed the set-up to compute dynamic variables. Data were smoothed by the Savitzky–Golay filtering method. Three variables were considered relevant in the best Lasso model (3mRTT=2.58−0.425RD+0... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624525 Fri, 16 Dec 2011 05:00:00 +0100 5624525 http://www.medworm.com/index.php?rid=5624540&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007172%2Fabstract%3Frss%3Dyes Abstract: Ascending stairs is a challenging activity of daily living for many populations. Frontal plane joint dynamics are critical to understand the mechanisms involved in stair ascension as they contribute to both propulsion and medio-lateral stability. However, previous research is limited to understanding these dynamics while initiating stair ascent from a stand. We investigated if initiating stair ascent from a walk with a comfortable self-selected speed could affect the frontal plane lower-extremity joint moments and powers as compared to initiating stair ascent from a stand and if this difference would exist at consecutive ipsilateral steps on the stairs. Kinematics data using a 3-D motion capture system and kinetics data using two force platforms on the first and third stair tread... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624540 Thu, 15 Dec 2011 05:00:00 +0100 5624540 http://www.medworm.com/index.php?rid=5624542&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006865%2Fabstract%3Frss%3Dyes Abstract: Based on the hypothesis that diabetic foot lesions have a mechanical etiology, extensive efforts have sought to establish a relationship between ulcer occurrence and plantar pressure distribution. However, these factors are still not fully understood. The purpose of this study was to simultaneously record shear and pressure distributions in the heel and forefoot and to answer whether: (i) peak pressure and peak shear for anterior–posterior (AP) and medio-lateral (ML) occur at different locations, and if (ii) peak pressure is always centrally located between sites of maximum AP and ML shear stresses. A custom built system was used to collect shear and pressure data simultaneously on 11 subjects using the 2-step method. The peak pressure was found to be 362kPa±106 in the heel an... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624542 Wed, 14 Dec 2011 05:00:00 +0100 5624542 http://www.medworm.com/index.php?rid=5624541&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007287%2Fabstract%3Frss%3Dyes Abstract: Previous studies have used radiostereometric analysis (RSA) to assess the integrity and mechanical properties of repaired tendons and ligament grafts. A conceptually similar approach is to use CT imaging to measure the 3D position and distance between implanted markers. The purpose of this study was to quantify the accuracy and repeatability of measuring the position and distance between metallic markers placed in the rotator cuff using low-dose CT imaging. We also investigated the effect of repeated or variable positions of the arm on position and distance measures. Six human patients had undergone rotator cuff repair and placement of tantalum beads in the rotator cuff at least one year prior to participating in this study. On a single day each patient underwent nine low-dose CT... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624541 Wed, 14 Dec 2011 05:00:00 +0100 5624541 http://www.medworm.com/index.php?rid=5624530&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007196%2Fabstract%3Frss%3Dyes Abstract: The purpose of this study was to establish the region of stability of balance control using the center of mass (COM) acceleration and to characterize age-related differences during sit-to-stand (STS) movement. Whole body motion data were collected from 10 young and 10 elderly subjects while performing STS at their self-selected manners. In addition, young subjects were asked to perform another block of trials with their trunk purposely bent forward prior to seat-off. With the use of a single-link-plus-foot inverted pendulum model, boundaries for the region of stability were determined based on the COM position at seat-off and its instantaneous velocity or its peak acceleration (ROSv or ROSa, respectively). No significant group differences were detected in COM velocities at seat-o... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624530 Wed, 14 Dec 2011 05:00:00 +0100 5624530 http://www.medworm.com/index.php?rid=5624532&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006920%2Fabstract%3Frss%3Dyes Abstract: We investigated the influence of inter-electrode spacing on the degree of crosstalk contamination in surface electromyographic (sEMG) signals in the tibialis anterior (target muscle), generated by the triceps surae (crosstalk muscle), using bar and disk electrode arrays. The degree of crosstalk contamination was assessed for voluntary constant-force isometric contractions and for dynamic contractions during walking. Single-differential signals were acquired with inter-electrode spacing ranging from 5mm to 40mm. Additionally, double differential signals were acquired at 10mm spacing using the bar electrode array. Crosstalk contamination at the target muscle was expressed as the ratio of the detected crosstalk signal to that of the target muscle signal. The crosstalk contamination ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624532 Mon, 12 Dec 2011 05:00:00 +0100 5624532 http://www.medworm.com/index.php?rid=5624529&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011007214%2Fabstract%3Frss%3Dyes Abstract: The development of atherosclerosis is correlated to the accumulation of lipids in the arterial wall, which, in turn, may be caused by the build-up of low-density lipoproteins (LDL) on the arterial surface. The goal of this study was to model blood flow within a subject specific human aorta, and to study how the LDL surface concentration changed during a cardiac cycle. With measured velocity profiles as boundary conditions, a scale-resolving technique (large eddy simulation, LES) was used to compute the pulsatile blood flow that was in the transitional regime. The relationship between wall shear stress (WSS) and LDL surface concentration was investigated, and it was found that the accumulation of LDL correlated well with WSS. In general, regions of low WSS corresponded to regions ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624529 Mon, 12 Dec 2011 05:00:00 +0100 5624529 http://www.medworm.com/index.php?rid=5624533&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006877%2Fabstract%3Frss%3Dyes Conclusion: ETER does not restore the normal AT and therefore leads potential of annular dilatation. The anterior leaflet prolapse has a greater potential of annular dilatation than the posterior leaflet prolapse after ETER. Annuloplasty is recommended to maintain long-term ETER efficacy. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624533 Thu, 08 Dec 2011 05:00:00 +0100 5624533 http://www.medworm.com/index.php?rid=5549552&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100618X%2Fabstract%3Frss%3Dyes Abstract: The effects of fluid–structure interactions (FSI) and pulsation on the transport of low-density lipoprotein (LDL) through an arterial wall are analyzed in this work. To this end, a comprehensive multi-layer model for both LDL transport as well as fluid–structure interaction (FSI) is introduced. The constructed model is analyzed and compared with the existing results in the limiting cases. Excellent agreement is found between the presented model and the existing results in the limiting cases. The presented model takes into account the complete multi-layered LDL transport while incorporating the FSI aspects to enable a comprehensive study of the deformation effect on the pertinent parameters of the transport processes within an artery. Since the flow inside an artery is time-de... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549552 Thu, 08 Dec 2011 05:00:00 +0100 5549552 http://www.medworm.com/index.php?rid=5549545&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006361%2Fabstract%3Frss%3Dyes Abstract: We develop a model of transport and growth in epithelio-mesenchymal interactions. Analysis of the growth of an avascular solid spheroid inside a passive mesenchyme or gel shows that sustained volumetric growth requires four generic mechanisms: (1) growth factor, (2) protease, (3) control of cellularity, and (4) swelling. The model reveals a bifurcation delineating two distinct morphogenetic regimes: (A) steady growth, (B) growth arrested by capsule formation in the mesenchyme. In both morphogenetic regimes, growth velocity is constant unless and until a complete capsule forms. Comprehensive exploration of the large parameter space reveals that the bifurcation is determined by just two ratios representing the relative strengths of growth and proteolytic activity. Growth velocity i... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549545 Thu, 08 Dec 2011 05:00:00 +0100 5549545 http://www.medworm.com/index.php?rid=5549544&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006543%2Fabstract%3Frss%3Dyes Abstract: This work presents a validation of a fluid–structure interaction computational model simulating the flow conditions in an in vitro mock heart chamber modeling mitral valve regurgitation during the ejection phase during which the trans-valvular pressure drop and valve displacement are not as large. The mock heart chamber was developed to study the use of 2D and 3D color Doppler techniques in imaging the clinically relevant complex intra-cardiac flow events associated with mitral regurgitation. Computational models are expected to play an important role in supporting, refining, and reinforcing the emerging 3D echocardiographic applications. We have developed a 3D computational fluid–structure interaction algorithm based on a semi-implicit, monolithic method, combined with an ar... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549544 Mon, 05 Dec 2011 05:00:00 +0100 5549544 http://www.medworm.com/index.php?rid=5549538&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006725%2Fabstract%3Frss%3Dyes Abstract: The spatial dimensionality of the vocal fold vibration is a common challenge in creating parsimonious models of vocal fold vibration. The ideal model is one that is accurate, with the lowest possible computational expense. Inclusion of full 3D flow and structural vibration typically requires massive amounts of computation, whereas reduction of either the flow or the structure to two dimensions eliminates certain aspects of physical reality, thus making the resulting models less accurate. Previous 2D models of the vocal fold structure have utilized a plane strain formulation, which is shown to be an erroneous modeling approach since it ignores influential stress components. We herein present a 2D/3D hybrid vocal fold model that preserves three-dimensional effects of length and lon... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549538 Mon, 05 Dec 2011 05:00:00 +0100 5549538 http://www.medworm.com/index.php?rid=5549532&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006816%2Fabstract%3Frss%3Dyes Abstract: Recent studies have demonstrated that actin filaments are not crucial for the short-term stability of tubular membrane protrusions originating from the cell surface. It has also been demonstrated that prominin nanodomains and curvature inducing I-BAR proteins could account for the stability of the membrane protrusion. Here we constructed an axisymmetric model of a membrane protrusion that excludes actin filaments in order to investigate the contributions of prominin nanodomains (rafts) and I-BAR proteins to the membrane protrusion stability. It was demonstrated that prominin nanodomains and I-BAR proteins can stabilize the membrane protrusion only over a specific range of spontaneous curvature. On the other hand, high spontaneous curvature and/or high density of I-BAR proteins co... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549532 Mon, 05 Dec 2011 05:00:00 +0100 5549532 http://www.medworm.com/index.php?rid=5549531&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100683X%2Fabstract%3Frss%3Dyes Abstract: The Achilles' tendon moment arm (ATma) is a critical quantity in that it defines the triceps surae's ability to generate a moment on the calcaneus, which is then transferred to the foot. This measure has been primarily acquired two-dimensionally in small male populations. Thus, the primary purpose of this study was to establish the first in vivo three-dimensional measures of the ATma, measured non-invasively during dynamic activity in a large normative population, inclusive of both males and female subjects (n=20). Subjects were each placed supine in a 1.5T MRI and asked to repeat a simulated toe-raise while a full sagittal-cine-phase contrast (dynamic) MRI dataset was acquired. From these data, the 3D and 2D ATma was calculated. The ATma was scaled by the distal tibial width, ba... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549531 Mon, 05 Dec 2011 05:00:00 +0100 5549531 http://www.medworm.com/index.php?rid=5624535&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006853%2Fabstract%3Frss%3Dyes This study highlights the importance of the collagen fibril organization, especially that indicated by split-line patterns, for the weight-bearing properties of articular cartilage. Osteoarthritic changes of cartilage in the medial femoral condyle created a possible failure point in the lateral femoral condyle. This study provides further evidence on the importance of the collagen fibril organization for the optimal function of articular cartilage. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624535 Fri, 02 Dec 2011 05:00:00 +0100 5624535 http://www.medworm.com/index.php?rid=5624534&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006841%2Fabstract%3Frss%3Dyes Abstract: The interphalangeal (IP) finger joints coordinate as a mechanism when the deep flexor is active. This mechanism is created by the complex finger extensor apparatus (EA) – a confluence of end tendons of one or two extensors, radial and ulnar interossei, and lumbrical – which inserts as a single structure into both the middle and distal phalanges. Although the IP-coupling principle was well demonstrated more than half a century ago, the detailed relationship between EA morphology and IP coupling remains not well described. Main reasons are that by dissection the EA's fiber network loses functional consistency, while fibers becoming taut or slack beyond measuring resolutions complicate measuring functional fiber motions. To circumvent these difficulties, we present a two dimensi... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5624534 Fri, 02 Dec 2011 05:00:00 +0100 5624534 http://www.medworm.com/index.php?rid=5549530&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006889%2Fabstract%3Frss%3Dyes Abstract: Radial force (Fr) distributions describe grip force coordination about a cylindrical object. Recent studies have employed only explicit Fr tasks, and have not normalized for anatomical variance when considering Fr distributions. The goals of the present study were (i) to explore Fr during tangential force production tasks, and (ii) to examine the extent to which anatomical registration (i.e. spatial normalization of anatomically analogous structures) could improve signal detectability in Fr data. Twelve subjects grasped a vertically oriented cylindrical handle (diameter=6cm) and matched target upward tangential forces of 10, 20, and 30N. Fr data were measured using a flexible pressure mat with an angular resolution of 4.8°, and were registered using piecewise-linear interpolatio... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549530 Fri, 02 Dec 2011 05:00:00 +0100 5549530 http://www.medworm.com/index.php?rid=5549555&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006750%2Fabstract%3Frss%3Dyes Abstract: A finite elements model was developed in order to evaluate the combined influence of the head lateral microseparation and the cup abduction angle on the contact pressure in Ceramic-on-Ceramic Total Hip Arthroplasty. The model's parameters were those used on the Leeds II hip simulator. A 32mm head diameter and a 30μm radial clearance was used. The cup was positioned with an abduction angle ranging from 45° to 90°. The medio-lateral microseparation varied from 0 to 500μm. A load of 2500N was applied through the head centre. For 45° abduction angle, edge loading appeared above a medial–lateral separation of 30μm. Complete edge loading was obtained for a 60μm medial–lateral separation. Under edge loading conditions, the contact area was found to be elliptical. For 45° abd... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549555 Mon, 28 Nov 2011 05:00:00 +0100 5549555 http://www.medworm.com/index.php?rid=5549554&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006713%2Fabstract%3Frss%3Dyes In this study, an experimental apparatus and fixation methodology was developed to accommodate cadaver osteoligamentous head–neck complexes from around birth (perinatal) to full maturation (adult) [cervical length: 2.5–12.5cm; head breadth: 6–15cm; head length: 6–19cm] and sequentially test the whole cervical spine in tension, the upper cervical spine in bending and the upper cervical spine in tension. The experimental apparatus and the fixation methodology provided a rigid casting of the head during testing and did not compromise the skull. Further testing of the intact skull and sub-cranial material was made available due to the design of the apparatus and fixation techniques utilized during spinal testing. The stiffness of the experimental apparatus and fixation technique are re... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549554 Mon, 28 Nov 2011 05:00:00 +0100 5549554 http://www.medworm.com/index.php?rid=5549534&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006798%2Fabstract%3Frss%3Dyes In this study, we investigate the effect of three OFF parameters on osteocyte activity in vitro and hypothesize that COX-2, RANKL, and OPG mRNA expression in osteocytes are sensitive to the OFF parameters: peak shear stress amplitude (0.5Pa, 1Pa, 2Pa, and 5Pa), oscillating frequency (0.5Hz, 1Hz, and 2Hz), and total flow duration (1h, 2h, and 4h). Our findings demonstrate that COX-2 mRNA levels are elevated in osteocytes subjected to higher peak shear stress amplitudes and longer flow durations, while RANKL/OPG mRNA levels decreased to a minimum threshold in response to higher peak shear stress amplitudes, faster oscillating frequencies, and longer flow durations. These findings suggest that dynamic fluid flow with higher peak shear stress amplitudes, faster oscillating frequencies, and lon... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549534 Mon, 28 Nov 2011 05:00:00 +0100 5549534 http://www.medworm.com/index.php?rid=5549529&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006907%2Fabstract%3Frss%3Dyes Abstract: Cell–substrate interaction is examined in a two-dimensional mechanics model. The cell and substrate are treated as a shell and an elastic solid, respectively. Their interaction through adhesion is treated using nonlinear springs. Compared to previous cell mechanics models, the present model introduces a cohesive force law that is dependent not only on cell–substrate distance but also on internal cell-membrane stress. It is postulated that a living cell would establish focal adhesion sites with density dependent on the cell-membrane stress. The formulated mechanics problem is numerically solved using coupled finite elements and boundary elements for the cell and the substrate, respectively. The nodes in the adhesion zone from either side are linked by the cohesive springs. The... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549529 Mon, 28 Nov 2011 05:00:00 +0100 5549529 http://www.medworm.com/index.php?rid=5549543&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006737%2Fabstract%3Frss%3Dyes Abstract: Biomechanical properties of cells have been identified as an important factor in a broad range of biological processes. Based on measurements of mechanical properties by atomic force microscopy (AFM) particularly cell elasticity has been linked with human diseases, such as cancer. AFM has been widely used as a nanomechanical tool to probe the elasticity of living cells, however, standard methods for characterizing cell elasticity are still lacking. The local elasticity of a cell is conventionally used to represent the mechanical property of the cell. However, since cells have highly heterogeneous regions, elasticity mapping over the entire cell, rather than at a few points of measurement, is required. Using human aortic endothelial cells (HAECs) as a model, we have developed in t... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549543 Thu, 24 Nov 2011 05:00:00 +0100 5549543 http://www.medworm.com/index.php?rid=5549533&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006804%2Fabstract%3Frss%3Dyes Abstract: The success of a total hip arthroplasty is strongly related to the initial stability of the femoral component and to the stress shielding effect. In fact, for cementless stems, initial stability is essential to promote bone ingrowth into the stem coating. An inefficient primary stability is also a cause of thigh pain. In addition, the bone adaptation after the surgery can lead to an excessive bone loss and, consequently, can compromise the success of the implant. These factors depend on prosthesis design, namely on material, interface conditions and shape. Although, surgeons use stems with very different geometries, new computational tools using structural optimization methods have been used to achieve a better design in order to improve initial stability and therefore, the impla... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549533 Thu, 24 Nov 2011 05:00:00 +0100 5549533 http://www.medworm.com/index.php?rid=5512169&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006634%2Fabstract%3Frss%3Dyes In this study the model-simulated behavior in case of several abnormal reflex settings was compared to the clinical features of dystonia: abnormal posture, sustained muscle contraction, increased stiffness, diminished voluntary control and activity-aggravation.The simulation results were rated to criteria based on characteristic features of dystonia. Three abnormal reflex scenarios were tested: (1) increased reflex sensitivity—increased sensitivity of both the agonistic and antagonistic reflex pathways; (2) imbalanced reflex offset—a static offset to the reflex pathways on the agonistic side only; and (3) imbalanced reflex sensitivity—increased sensitivity of only the agonistic reflex pathways.Increased reflex sensitivity did not fully account for the features of dystonia, despite di... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512169 Wed, 23 Nov 2011 05:00:00 +0100 5512169 http://www.medworm.com/index.php?rid=5512158&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006622%2Fabstract%3Frss%3Dyes Abstract: Obesity is widely recognized as a major public health problem due to its strong association with a number of serious chronic diseases including hyperlipidemia, hypertension, type II diabetes and coronary atherosclerotic heart disease. During the development of obesity, the positive energy balance involves recruitment of new adipocytes from preadipocytes in adipose tissue, which have proliferated and differentiated. Given that cells in adipose tissues are physiologically exposed to compound mechanical loading: tensile, compressive and shear strains/stresses, which are caused by bodyweight loads as well as by weight-bearing, it is important to determine whether the adipose conversion process is influenced by mechanical stimulations. In this article we provide a comprehensive review... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512158 Wed, 23 Nov 2011 05:00:00 +0100 5512158 http://www.medworm.com/index.php?rid=5549542&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006671%2Fabstract%3Frss%3Dyes Abstract: Squeaking is reported for ceramic-on-ceramic hip arthroplasty, and risk factors leading to this phenomenon have been investigated empirically in the past, this way giving hints to when this phenomenon occurs. The aim of this study is to present an experimentally validated explanation for the dynamical mechanism underlying the squeak, i.e. a description of what happens when noise is generated.First the kinematics of the ceramic bearing couple in relative motion are reconsidered. The relative motion at the contact zone can be understood as superposition of relative rotation and translation. The relative weight of both components depends substantially on the instantaneous load vector, which primarily determines the position of the contact area, and the instantaneous relative rotatio... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549542 Mon, 21 Nov 2011 05:00:00 +0100 5549542 http://www.medworm.com/index.php?rid=5512173&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006063%2Fabstract%3Frss%3Dyes Abstract: Human embryonic stem cells (hESC) and hESC-derived cardiomyocytes (hESC-CM) hold great promise for the treatment of cardiovascular diseases. However the mechanobiological properties of hESC and hESC-CM remains elusive. In this paper, we examined the dynamic and static micromechanical properties of hESC and hESC-CM, by manipulating via optical tweezers at the single-cell level. Theoretical approaches were developed to model the dynamic and static mechanical responses of cells during optical stretching. Our experiments showed that the mechanical stiffness of differentiated hESC-CM increased after cardiac differentiation. Such stiffening could associate with increasingly organized myofibrillar assembly that underlines the functional characteristics of hESC-CM. In summary, our findin... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512173 Mon, 21 Nov 2011 05:00:00 +0100 5512173 http://www.medworm.com/index.php?rid=5549553&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006786%2Fabstract%3Frss%3Dyes Abstract: Intervertebral disc degeneration, a leading cause of low back pain, poses a significant socioeconomic burden with a broad array of costly treatment options. Mechanical loading is important in disease progression and treatment. Connecting mechanics and biology is critical for determining how loading parameters affect cellular response and matrix homeostasis. A novel ex-vivo experimental platform was developed to facilitate in-situ loading of rabbit functional spinal units (FSUs) with relevant biological outcome measures. The system was designed for motion outside of an incubator and validated for rigid fixation and physiologic environmental conditions. Specimen motion relative to novel fixtures was assessed using a digitizer; fixture stiffness exceeded specimen stiffness by an ord... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549553 Fri, 18 Nov 2011 05:00:00 +0100 5549553 http://www.medworm.com/index.php?rid=5549541&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006683%2Fabstract%3Frss%3Dyes Abstract: The aim of the present study was to quantify to what extent the scar tissue formation following the transfer of flexor carpi ulnaris (FCU) to the distal tendon of extensor carpi radialis (ECR) affects the force transmission from transferred FCU in the rat. Five weeks after recovery from surgery (tendon transfer group) and in a control group, isometric length–force characteristics of FCU were assessed for progressive stages of dissection: (i) with minimally disrupted connective tissues, (ii) after full dissection of FCU distal tendon exclusively, and (iii) after additional partial dissection of FCU muscle belly.Total and passive length–force characteristics of transferred and control FCU changed significantly by progressive stages of dissection. In both groups, tendon dissecti... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549541 Fri, 18 Nov 2011 05:00:00 +0100 5549541 http://www.medworm.com/index.php?rid=5549536&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006762%2Fabstract%3Frss%3Dyes Abstract: Previous studies of the mechanical work performed during uphill and downhill walking have neglected the simultaneous negative and positive work performed by the leading and trailing legs during double support. Our goal was to quantify the mechanical work performed by the individual legs across a range of uphill and downhill grades. We hypothesized that during double support, (1) with steeper uphill grade, the negative work performed by the leading leg would become negligible and the trailing leg would perform progressively greater positive work to raise the center of mass (CoM), and (2) with steeper downhill grade, the leading leg would perform progressively greater negative work to lower the CoM and the positive work performed by the trailing leg would become negligible. 11 heal... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549536 Fri, 18 Nov 2011 05:00:00 +0100 5549536 http://www.medworm.com/index.php?rid=5512179&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006105%2Fabstract%3Frss%3Dyes This study developed two RSA methods for automate the estimation of the prosthetic pose and decrease the nonorthogonality-induced error. The predicted results were validated by both simulative and experimental tests and compared with reported findings in the literature. The outcome revealed that the feature-recognized method automates pose estimation and significantly increases the execution efficiency up to about 50 times in comparison with the literature counterparts. Although the nonorthogonal images resulted in undesirable errors, the outline-optimized method can effectively compensate for the induced errors prior to fine registration. The superiority in automation, efficiency, and accuracy demonstrated the clinical practicability of the two proposed methods especially for the numerous... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512179 Thu, 17 Nov 2011 05:00:00 +0100 5512179 http://www.medworm.com/index.php?rid=5549556&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006531%2Fabstract%3Frss%3Dyes Abstract: Subject-specific finite element models have been used to predict stress-state and fracture risk in individual patients. While many studies analysed quasi-axial loading configurations, only few works simulated sideways load configurations, such as those arising in a fall. The majority among these latter directly predicted bone strength, without assessing elastic strain prediction accuracy. The aim of the present work was to evaluate if a subject-specific finite element modelling technique from CT data that accurately predicted strains in quasi-axial loading configurations is suitable to accurately predict strains also when applying low magnitude loads in sideways configurations. To this aim, a combined numerical–experimental study was performed to compare finite element predicte... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549556 Mon, 14 Nov 2011 05:00:00 +0100 5549556 http://www.medworm.com/index.php?rid=5549551&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006555%2Fabstract%3Frss%3Dyes This study examines the elastic and viscoelastic shear behavior of both diabetic and non-diabetic plantar tissue. Previously compression tested plantar tissue specimens (n=54) at six relevant plantar locations (hallux, first, third, and fifth metatarsal heads, lateral midfoot, and calcaneus) from four cadaveric diabetic feet and five non-diabetic feet were utilized. Per in vivo data (i.e., combined deformation patterns of compression followed by shear), an initial static compressive strain (36–38%) was applied to the tissue followed by target shear strains of 50% and 85% of initial thickness. Triangle waves were used to quantify elastic parameters at both strain levels and a stress relaxation test (0.25s ramp and 300s hold) was used to quantify the viscoelastic parameters at the upper st... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549551 Mon, 14 Nov 2011 05:00:00 +0100 5549551 http://www.medworm.com/index.php?rid=5549549&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006567%2Fabstract%3Frss%3Dyes This study presents a total of 41 tension tests performed on spleen parenchyma coupons and 29 tension tests performed on spleen capsule/parenchyma coupons. Standard dog-bone coupons were obtained from fresh human spleen and tested within 48h of death. Each coupon was tested once to failure at one of the four loading rates to investigate the effects of rate dependence. Load and acceleration data were obtained at each of the specimen grips. High-speed video and optical markers placed on the specimens were used to measure local displacement. Failure stress and strain were calculated at the location of failure in the gage length of the coupon. The results of the study showed that both the spleen parenchyma and the capsule are rate dependent, with higher loading rates yielding higher failure st... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549549 Mon, 14 Nov 2011 05:00:00 +0100 5549549 http://www.medworm.com/index.php?rid=5549548&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100666X%2Fabstract%3Frss%3Dyes This study investigated whether people with low back pain (LBP) reduce variability of movement between the pelvis and thorax (trunk) in the transverse plane during gait at different speeds compared to healthy controls. Thirteen people with chronic LBP and twelve healthy controls walked on a treadmill at speeds from 0.5 to 1.72m/s, with increments of 0.11m/s. Step-to-step variability of the trunk, pelvis, and thorax rotations were calculated. Step-to-step deviations of pelvis and thorax rotations from the average pattern (residual rotations) were correlated to each other, and the linear regression coefficients between these deviations calculated. Spectral analysis was used to determine the frequencies of the residual rotations, to infer the relation of reduced trunk variability to trunk sti... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549548 Mon, 14 Nov 2011 05:00:00 +0100 5549548 http://www.medworm.com/index.php?rid=5549540&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006695%2Fabstract%3Frss%3Dyes The objective of this study was a quantitative validation of the accuracy of the KAdM in patients with knee OA, when estimated with an ambulatory-based method (AmbBM) versus a laboratory-based method (LabBM). AmbBM is employing the IFS and a linked-segment model, while LabBM is based on a force plate and optoelectronic marker system. Effects of ground reaction force (GRF), centre of pressure (CoP), and knee joint position measurement are evaluated separately. Twenty patients with knee OA were measured.The GRFs showed differences up to 0.22N/kg, the CoPs showed differences up to 4mm, and the medio-lateral and vertical knee position showed differences to 9mm, between AmbBM and LabBM. The GRF caused an under-estimation in KAdM in early stance. However, this effect was counteracted by differen... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549540 Mon, 14 Nov 2011 05:00:00 +0100 5549540 http://www.medworm.com/index.php?rid=5549539&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006701%2Fabstract%3Frss%3Dyes We examined effects of walking speed and age on the pattern and variability of inter-joint coordination. Gait analyses of 10 young and 10 elderly adults were performed with different self-selected speeds, including a preferred, faster, and slower speed. Continuous relative phase (CRP), derived from phase planes of two adjacent joints, was used to assess the inter-joint coordination. CRP patterns were examined with cross-correlation measures and root-mean-square (RMS) differences when comparing ensemble mean curves of the faster or slower speed to preferred speed walking. Variability of coordination for each participant was assessed with the average value of all standard deviations calculated for each data point over a gait cycle from all CRP curves, namely the deviation phase (DP). For hip... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549539 Mon, 14 Nov 2011 05:00:00 +0100 5549539 http://www.medworm.com/index.php?rid=5549537&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006749%2Fabstract%3Frss%3Dyes The objectives of the present study were to investigate the relationship between axial SOS and tendon's nonlinear elasticity, measured in standard laboratory conditions, and to evaluate if tendon's mass density and cross-sectional area (CSA) affect the SOS level. Axial SOS was measured during in vitro cycling of 9 equine superficial digital tendons. Each tendon's stiffness was characterized with a tangent modulus (the continuous derivative of the true stress/true strain curve) and an elastic modulus (the slope of this curve's linear region). Tendon's SOS was found to linearly vary with the square root of the tangent modulus during loading; tendon's SOS level was found correlated to the elastic modulus's square root and inversely correlated to the tendon's CSA, but it was not affected by te... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549537 Mon, 14 Nov 2011 05:00:00 +0100 5549537 http://www.medworm.com/index.php?rid=5512168&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006154%2Fabstract%3Frss%3Dyes Abstract: It has been widely observed that atherosclerotic stenosis occurs at sites with complex hemodynamics, such as arteries with high curvature or bifurcations. These regions usually have very low or highly oscillatory wall shear stress (WSS). In the present study, 3D sinusoidally pulsatile blood flow through the models of internal carotid artery (ICA) with different geometries was investigated with computational simulation. Three preferred sites of stenoses were found along the carotid siphon with low and highly oscillatory WSS. The risk for stenoses at these sites was scaled with the values of time-averaged WSS and oscillating shear index (OSI). The local risk for stenoses at every preferred site of stenoses was found different between 3 types of ICA, indicating that the geometry of ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512168 Mon, 14 Nov 2011 05:00:00 +0100 5512168 http://www.medworm.com/index.php?rid=5549535&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006774%2Fabstract%3Frss%3Dyes Abstract: An increasing number of tissue banks have begun to focus on gamma irradiation and freeze–thaw in the reconstruction of anterior cruciate ligaments using allografts. The purpose of this study was to evaluate the biomechanical properties of human tendons after exposure to gamma radiation and repeated freeze–thaw cycles and to compare them with fresh specimens. Forty flexor digitorum superficialis tendons were surgically procured from five fresh cadavers and divided into four groups: fresh tendon, gamma irradiation, freeze–thaw and gamma irradiation+freeze–thaw. The dose of gamma irradiation was 25kGy. Each freeze–thaw cycle consisted of freezing at −80°C for 7 day and thawing at 25°C for 6h. These tendons underwent 4 freeze–thaw cycles. Biomechanical properties were... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549535 Fri, 11 Nov 2011 05:00:00 +0100 5549535 http://www.medworm.com/index.php?rid=5512187&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006117%2Fabstract%3Frss%3Dyes Abstract: Handball is one of the top four athletic games with highest injury risks. The jump shot is the most accomplished goal shot technique and the lower extremities are mostly injured. As a basis for ankle sprain simulation, the aim of this study was to extend the ankle region of an existing musculoskeletal full-body model through incorporation of three prominent lateral ankle ligaments: ligamentum fibulotalare anterius (LFTA), ligamentum fibulotalare posterius (LFTP), ligamentum fibulocalcaneare (LFC). The specific objective was to calculate and visualise ligament force scenarios during the jumping and landing phases of controlled jump shots. Recorded kinematic data of performed jump shots and the corresponding ground reaction forces were used to perform inverse dynamics. The calculat... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512187 Thu, 10 Nov 2011 05:00:00 +0100 5512187 http://www.medworm.com/index.php?rid=5549559&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100652X%2Fabstract%3Frss%3Dyes Abstract: Two-dimensional methods have been applied to determine the Achilles tendon moment arm in previous studies, although the talocrural joint rotates in three-dimension. The purpose of this study was to develop a method for determining the Achilles tendon moment arm in three-dimensions (3DMA). A series of sagittal ankle images were obtained at ankle positions of −20°, −10° (dorsiflexed position), 0° (neutral position), +10°, +20°, and +30° (plantarflexed position). The talocrural joint axis was determined as the finite helical axis of the ankle joint over 20° of displacement, and the 3DMA was determined as the shortest distance from the talocrural joint axis to the line of action of the Achilles tendon force. The corresponding 2DMA was determined with the center of rotation... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549559 Mon, 07 Nov 2011 05:00:00 +0100 5549559 http://www.medworm.com/index.php?rid=5549550&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006348%2Fabstract%3Frss%3Dyes Abstract: The integrity of bone–cement interface is essential for the long-term stability of cemented total joint arthroplasty. Although several studies have been carried out on bone–cement interface at continuum level, micromechanics of the interface has been studied only recently for tensile and shear loading cases. Fundamental studies of bone–cement interface at microstructural level are critical to the understanding of the failure processes of the interface, where multiple factors may contribute to failure. Here we present a micromechanical study of bone–cement interface under compression, which utilised in situ mechanical testing, time-lapsed microcomputed tomography (CT) and finite element (FE) modelling. Bovine trabecular bone was used to interdigitate with bone cement to ob... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549550 Mon, 07 Nov 2011 05:00:00 +0100 5549550 http://www.medworm.com/index.php?rid=5512165&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006312%2Fabstract%3Frss%3Dyes Abstract: Damage accumulation underlies tendinopathy. Animal models of overuse injuries do not typically control loads applied to the tendon. Our in vivo model in the rat patellar tendon allows direct control of the loading applied to the tendon. Despite this advantage, natural variation among tendons results in different amounts of damage induced by the same loading protocol. Our objectives were to (1) assess changes in the initial mechanical parameters (hysteresis, stiffness of the loading and unloading load-displacement curves, and elongation) after fatigue loading to identify parameters that are indicative of the induced damage, and (2) evaluate the relationships between these identified initial damage indices with the stiffness 7 day after loading. Left patellar tendons of adult, fema... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512165 Mon, 07 Nov 2011 05:00:00 +0100 5512165 http://www.medworm.com/index.php?rid=5374869&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006610%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374869 Fri, 04 Nov 2011 17:44:00 +0100 5374869 http://www.medworm.com/index.php?rid=5374849&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006427%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374849 Fri, 04 Nov 2011 17:43:59 +0100 5374849 http://www.medworm.com/index.php?rid=5512170&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006166%2Fabstract%3Frss%3Dyes Abstract: Previous research has quantified differences in head and spinal kinematics between children and adults restrained in an automotive-like configuration subjected to low speed dynamic loading. The forces and moments that the cervical spine imposes on the head contribute directly to these age-based kinematic variations. To provide further explanation of the kinematic results, this study compared the upper neck kinetics – including the relative contribution of shear and tension as well as flexion moment – between children (n=20, 6–14yr) and adults (n=10, 18–30yr) during low-speed ( (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512170 Fri, 04 Nov 2011 04:00:00 +0100 5512170 http://www.medworm.com/index.php?rid=5512163&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006385%2Fabstract%3Frss%3Dyes Abstract: Patients with subtalar joint instability may be misdiagnosed with ankle instability, which may lead to chronic instability at the subtalar joint. Therefore, it is important to understand the difference in kinematics after ligament sectioning and differentiate the changes in kinematics between ankle and subtalar instability. Three methods may be used to determine the joint kinematics; the Euler angles, the Joint Coordinate System (JCS) and the helical axis (HA). The purpose of this study was to investigate the influence of using either method to detect subtalar and ankle joints instability. 3D kinematics at the ankle and subtalar joint were analyzed on 8 cadaveric specimens while the foot was intact and after sequentially sectioning the anterior talofibular ligament (ATFL), the ca... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512163 Fri, 04 Nov 2011 04:00:00 +0100 5512163 http://www.medworm.com/index.php?rid=5549547&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006300%2Fabstract%3Frss%3Dyes Abstract: Aging is associated with the loss of muscle volume (MV) and force leading to difficulties with activities of daily living. However, the relationship between upper limb MV and joint strength has not been characterized for older adults. Quantifying this relationship may help our understanding of the functional declines of the upper limb that older adults experience. Our objective was to assess the relationship between upper limb MV and maximal isometric joint moment-generating capacity (IJM) in a single cohort of healthy older adults (age≥65 years) for 6 major functional groups (32 muscles). MV was determined from MRI for 18 participants (75.1±4.3 years). IJM at the shoulder (abduction/adduction), elbow (flexion/extension), and wrist (flexion/extension) was measured. MV and IJM ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549547 Wed, 02 Nov 2011 04:00:00 +0100 5549547 http://www.medworm.com/index.php?rid=5549546&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006324%2Fabstract%3Frss%3Dyes Abstract: Humans use equal push-off and heel strike work during the double support phase to minimize the mechanical work done on the center of mass (CoM) during the gait. Recently, a step-to-step transition was reported to occur over a period of time greater than that of the double support phase, which brings into question whether the energetic optimality is sensitive to the definition of the step-to-step transition. To answer this question, the ground reaction forces (GRFs) of seven normal human subjects walking at four different speeds (1.1–2.4m/s) were measured, and the push-off and heel strike work for three differently defined step-to-step transitions were computed based on the force, work, and velocity. To examine the optimality of the work and the impulse data, a hybrid theoretica... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549546 Mon, 31 Oct 2011 04:00:00 +0100 5549546 http://www.medworm.com/index.php?rid=5512180&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006099%2Fabstract%3Frss%3Dyes Abstract: Conventional bone plates are commonly used for surgical mandibular fracture fixation. Improper alignment between bone segments, however, can result in malocclusion. Current methods of fixation require a surgeon to visually align segments of bone and affix a metal plate using bone screws, after which little can be done to adjust alignment. A method of adjusting fracture alignment after plate placement, without screw removal, presents an improvement over costly and risky revision surgery. A modified bone plate has been designed with a deformable section to give surgeons the ability to reduce misalignments at the fracture site. The mechanics of deformation for various adjustment mechanisms was explored analytically, numerically, and experimentally to ensure that the adjustable plate... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512180 Mon, 31 Oct 2011 04:00:00 +0100 5512180 http://www.medworm.com/index.php?rid=5512178&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006245%2Fabstract%3Frss%3Dyes Abstract: Controversy on superiority of pulsatile versus non-pulsatile extracorporeal circulation in cardiac surgery still continues. Stroke as one of the major adverse events during cardiopulmonary bypass is, in the majority of cases, caused by mobilization of aortic arteriosclerotic plaques that is inducible by pathologically elevated wall shear stress values. The present study employs computational fluid dynamics to evaluate the aortic blood flow and wall shear stress profiles under the influence of antegrade or retrograde perfusion with pulsatile versus non-pulsatile extracorporeal circulation. While, compared to physiological flow, a non-pulsatile perfusion resulted in generally decreased blood velocities and only moderately increased shear forces (48Pa versus 20Pa antegradely and 127... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512178 Mon, 31 Oct 2011 04:00:00 +0100 5512178 http://www.medworm.com/index.php?rid=5512175&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006178%2Fabstract%3Frss%3Dyes Abstract: To improve the treatments for low back pain, new designs of total disk replacement have been proposed. The question is how well these designs can act as a functional replacement of the intervertebral disk. Four finite element models were made, for four different design concepts, to determine how well they can mimic the physiological intervertebral disk mechanical function. The four designs were a homogenous elastomer, a multi-stiffness elastomer, an elastomer with fiber jacket, and a hydrogel with fiber jacket. The best material properties of the four models were determined by optimizing the model behavior to match the behavior of the intervertebral disk in flexion–extension, axial rotation, and lateral bending. It was shown that neither a homogeneous elastomer nor a multi-stif... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512175 Mon, 31 Oct 2011 04:00:00 +0100 5512175 http://www.medworm.com/index.php?rid=5512171&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006142%2Fabstract%3Frss%3Dyes Abstract: Lymphatic capillary drainage of interstitial fluid under both steady-state and inflammatory conditions is important for tissue fluid balance, cancer metastasis, and immunity. Lymphatic drainage function is critically coupled to the fluid mechanical properties of the interstitium, yet this coupling is poorly understood. Here we sought to effectively model the lymphatic-interstitial fluid coupling and ask why the lymphatic capillary network often appears with roughly a hexagonal architecture. We use homogenization method, which allows tissue-scale lymph flow to be integrated with the microstructural details of the lymphatic capillaries, thus gaining insight into the functionality of lymphatic anatomy. We first describe flow in lymphatic capillaries using the Navier–Stokes equatio... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512171 Mon, 31 Oct 2011 04:00:00 +0100 5512171 http://www.medworm.com/index.php?rid=5549557&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006373%2Fabstract%3Frss%3Dyes This study highlights the importance of defining muscle paths in multiple postures in order to properly define the changing curvature of a muscle path due to soft tissue deformation with posture. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549557 Fri, 28 Oct 2011 04:00:00 +0100 5549557 http://www.medworm.com/index.php?rid=5512184&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006087%2Fabstract%3Frss%3Dyes This study presents a method to create a statistical model of kinetic waveform data. A PCA based statistical model was created of the tibiofemoral joint loads for level gait of preoperative TKR patients using data predicted from a musculoskeletal model. A reconstruction test showed that, using principal components (PCs) representing 95% variance, the median root-mean-squared (RMS) error was (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512184 Wed, 26 Oct 2011 04:00:00 +0100 5512184 http://www.medworm.com/index.php?rid=5512181&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100635X%2Fabstract%3Frss%3Dyes Abstract: To examine the region specificity within the rectus femoris (RF) for knee extension and hip flexion force directions, three force components around the ankle were measured during intramuscular electrical stimulation applied to six parts of the RF: a proximal and medial part, a proximal and lateral part, a middle and medial part, a middle and lateral part, a distal and medial part, and a distal and lateral part. As a result, the exerted force directions in all of the subjects were variable in all regions, and the proximal region of the RF was the dominant contributor to the hip flexion moment. In addition, the force in the lateral region of the RF, rather than that in the medial region, denoted the lateral direction. These results suggest that divergent regions of muscle fibers wi... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512181 Wed, 26 Oct 2011 04:00:00 +0100 5512181 http://www.medworm.com/index.php?rid=5512176&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006075%2Fabstract%3Frss%3Dyes Abstract: Durability and kinematics are two critical factors which must be considered during total knee replacement (TKR) implant design. It is hypothesized, however, that there exists a competing relationship between these two performance measures, such that improvement of one requires sacrifice with respect to the other. No previous studies have used rigorous and systematic methods to quantify this relationship. During this study, multiobjective design optimization (MOO) using the adaptive weighted sum (AWS) method is used to determine a set of Pareto-optimal implant designs considering durability and kinematics simultaneously. Previously validated numerical simulations and a parametric modeller are used in conjunction with the AWS method in order to generate a durability-versus-kinemati... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512176 Wed, 26 Oct 2011 04:00:00 +0100 5512176 http://www.medworm.com/index.php?rid=5512167&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006191%2Fabstract%3Frss%3Dyes Abstract: Force-induced deformation of tissues is transduced to the cytoskeletal (CSK) network within cells via focal adhesions. Previous studies have characterized transfer of strains of less than 15% from the substrate to the cell, using mitochondria as surrogate markers for CSK deformation. However, it is unclear if intracellular strains determined from mitochondrial displacement accurately reflect CSK network deformation. Furthermore, previous studies have not characterized substrate–CSK network strain transfer for strain magnitudes exceeding 15%, as can occur in vivo and in cell culture studies. Here, we developed and characterized a texture correlation algorithm to address the image distortion problem caused by large strain. We then used this algorithm to characterize large compres... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512167 Wed, 26 Oct 2011 04:00:00 +0100 5512167 http://www.medworm.com/index.php?rid=5549558&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006336%2Fabstract%3Frss%3Dyes Abstract: Damage development in cemented acetabular reconstructs has been studied under a combined cyclic loading block representative of routine activities in a saline environment. A custom-made environmental chamber was designed and installed on the Portsmouth hip simulator to allow testing of acetabular reconstructs in a wet condition for the first time. Damage was monitored and detected by scanning at selected loading intervals using micro-focus computed tomography (μCT). The preliminary results show that, although, as in dry cases, debonding at the bone–cement interface defined the failure of the cement fixation, the combination of mechanical loading and saline environment significantly affected the damage initiation and development, with drastically reduced survival lives of the r... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5549558 Mon, 24 Oct 2011 04:00:00 +0100 5549558 http://www.medworm.com/index.php?rid=5512188&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006294%2Fabstract%3Frss%3Dyes The authors regret that the last name of the author, Lewis Gerace-Fowler, was incorrect. The correct name is Lewis H. Fowler-Gerace. The authors would like to apologise for any inconvenience caused. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512188 Mon, 24 Oct 2011 04:00:00 +0100 5512188 http://www.medworm.com/index.php?rid=5512185&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006221%2Fabstract%3Frss%3Dyes Abstract: Foot and toe clearance (TC) are used regularly to describe locomotor control for both clinical and basic research. However, accuracy of TC during obstacle crossing can be compromised by typical sample frequencies, which do not capture the frame when the foot is over the obstacle due to high limb velocities. The purpose of this study was to decrease the error of TC measures by increasing the spatial resolution of the toe trajectory with interpolation. Five young subjects stepped over an obstacle in the middle of an 8m walkway. Position data were captured at 600Hz as a gold standard signal (GS-600-Hz). The GS-600-Hz signal was downsampled to 60Hz (DS-60-Hz). The DS-60-Hz was then interpolated by either upsampling or an algorithm. Error was calculated as the absolute difference in T... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512185 Mon, 24 Oct 2011 04:00:00 +0100 5512185 http://www.medworm.com/index.php?rid=5512182&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006270%2Fabstract%3Frss%3Dyes Abstract: Experiments designed to assess balance recovery in older adults often involve exposing participants to repeated loss of balance. The purpose of this study was to investigate the adaptive balance recovery response exhibited by older adults following repeated exposure to forward loss of balance induced by releasing participants from a static forward lean angle. Fifty–eight healthy, community-dwelling older adults, aged 65–80 years, participated in the study. Participants were instructed to attempt to recover with a single step and performed four trials at each of three lean angles. Adaptive recovery responses at four events (cable release, toe-off of the stepping foot, foot contact and maximum knee flexion angle following landing in the stepping leg) were quantified for trials ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512182 Mon, 24 Oct 2011 04:00:00 +0100 5512182 http://www.medworm.com/index.php?rid=5512174&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006257%2Fabstract%3Frss%3Dyes This study evaluated the discriminant capability of stability measures, trunk kinematics, and step kinematics to classify successful and failed compensatory stepping responses. In addition, the shared variance between stability measures, step kinematics, and trunk kinematics is reported. The stability measures included the anteroposterior distance (d) between the body center of mass and the stepping limb toe, the margin of stability (MOS), as well as time-to-boundary considering velocity (TTBv), velocity and acceleration (TTBa), and MOS (TTBMOS). Kinematic measures included trunk flexion angle and angular velocity, step length, and the time after disturbance onset of recovery step completion. Fourteen young adults stood on a treadmill that delivered surface accelerations necessitating mult... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512174 Mon, 24 Oct 2011 04:00:00 +0100 5512174 http://www.medworm.com/index.php?rid=5512172&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006129%2Fabstract%3Frss%3Dyes Abstract: Cell adhesions are modulated by the interactions between cells and their surroundings, among which substrate stiffness plays an important role in mediating cellular behaviors and functions. Little is known, however, about the inherent mechanism of how nascent adhesion nucleation, as the precursor of focal adhesions, is regulated by substrate stiffness. This paper presents a microscopic model to imitate integrin clustering kinetics, where integrin diffusion, activation on elastic substrates, receptor–ligand binding and association dynamics are fully considered. Particularly, the contribution of substrate compliance to the activation energy is analyzed, leading to a description of mechanical energy barrier for stretching a substrate-bound integrin molecule from bent to extended c... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512172 Mon, 24 Oct 2011 04:00:00 +0100 5512172 http://www.medworm.com/index.php?rid=5512166&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006208%2Fabstract%3Frss%3Dyes In this study, muscle morphology measurements were made for major muscles present in the trunk between vertebral levels T6 and L5 using quantitative computed tomography scans from a community-based sample of 100 men and women aged 36–87. We present regression equations to predict trunk muscle CSA and position relative to the vertebral body in the transverse plane from sex, age, height and weight at vertebral levels T6 to L5. Regressions were also developed for predicting anatomical CSA and muscle moment arms, which were estimated using literature data on muscle line of action. This work thus provides a resource for estimating muscle parameters in the general population for musculoskeletal modeling of the thoraco-lumbar trunk. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512166 Mon, 24 Oct 2011 04:00:00 +0100 5512166 http://www.medworm.com/index.php?rid=5512164&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006397%2Fabstract%3Frss%3Dyes The objectives of the present study were to compare the axial speed of sound (SOS) measured in vivo in normal and injured tendons and to investigate their relationship with the tendons' mechanical parameters, in order to assess the potential of quantitative axial ultrasound to monitor the healing of the injured tendons. SOS was measured in vivo in the right fore SDFTs of 12 horses during walk, before and 3.5 months after the surgical induction of a bilateral core lesion. The 12 horses were then euthanized, their SDFTs isolated and tested in tension to measure their elastic modulus and maximal load (and corresponding stress). SOS significantly decreased from 2179.4±31.4m/s in normal tendons to 2065.8±67.1m/s 3.5 months after the surgical induction, and the tendons' elastic modulus (0.90±... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512164 Mon, 24 Oct 2011 04:00:00 +0100 5512164 http://www.medworm.com/index.php?rid=5512162&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006403%2Fabstract%3Frss%3Dyes Abstract: Biomechanical non-invasive interventions have been previously reported to reduce pain and facilitate superior levels of function in patients with medial knee osteoarthritis [OA]. One such treatment is the AposTherapy, a customized program utilizing a foot-worn biomechanical device allowing center of pressure modification and continuous perturbation during gait. The influence of this intervention on objective gait metrics has yet to be determined. The aim of the current study was to prospectively examine changes in kinetic and kinematic parameters in patients enrolled in this treatment program. Twenty-five females with symptomatic bilateral medial compartment knee OA were enrolled in the customized daily treatment program. All patients underwent barefoot gait analysis testing and ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512162 Mon, 24 Oct 2011 04:00:00 +0100 5512162 http://www.medworm.com/index.php?rid=5512186&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100621X%2Fabstract%3Frss%3Dyes Abstract: The present study focuses on the determination of human temporal tendons and deep temporal fascia biomechanical behavior. The tensile and shear loads generated by the temporal muscle are transmitted to the masticatory system by the temporal tendons and muscle fascia. Establishing these connective tissues' biomechanical properties will help to develop proper finite element-based simulations of the human masticatory system, which will allow better understanding of diseases affecting the temporomandibular joint.The tissues were harvested from 8 male fresh cadavers, who were subjected to uniaxial tension tests. Available literature states that different connective tissues undergo identical biochemical, cellular and mechanical changes during senescence. Several mechanical phenomena oc... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512186 Thu, 20 Oct 2011 04:00:00 +0100 5512186 http://www.medworm.com/index.php?rid=5512177&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006269%2Fabstract%3Frss%3Dyes Abstract: Upper motor neuron diseases (UMND), such as stroke and spinal cord injury (SCI), are assumed to produce alterations in muscle tissue in association with neural damage. Distinguishing between these two factors is of clinical importance in choosing appropriate therapy. We studied the effect of changes in the gain of the Ia reflex pathway and tissue viscoelasticity on the emergence, frequency, and persistence of ankle clonus: a clinically significant, involuntary oscillatory movement disorder. Monte Carlo simulations were performed to explain our experimental observations in patients with stroke (n=3) and SCI (n=4) using a nonlinear antagonistic muscle model of the human ankle joint. Ia reflex gain was varied by changing motor unit pool threshold and gain, and passive tissue viscosi... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512177 Wed, 19 Oct 2011 04:00:00 +0100 5512177 http://www.medworm.com/index.php?rid=5512159&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006233%2Fabstract%3Frss%3Dyes Abstract: Objective: This review is intended to highlight and discuss discrepancies in the literature of the periodontal ligament's (PDL) mechanical properties and the various analytical models, approaches and assumptions used in simulating its behaviour. The present study then offers to propose a model development that allows for a better phenomenological description of PDL behaviour under static, near clinical, orthodontic loading conditions.Methodology: Searches were performed on biomechanical and orthodontic publications (in databases: Compendex, EMBASE, MEDLINE, PubMed, ScienceDirect and Scopus).Results: The review revealed that significant variations exist, some on the order of six orders of magnitude, in the PDL's elastic constants and mechanical properties. Possible explanations ma... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512159 Wed, 19 Oct 2011 04:00:00 +0100 5512159 http://www.medworm.com/index.php?rid=5512183&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011006130%2Fabstract%3Frss%3Dyes Abstract: Synchronization of data coming from different sources is of high importance in biomechanics to ensure reliable analyses. This synchronization can either be performed through hardware to obtain perfect matching of data, or post-processed digitally. Hardware synchronization can be achieved using trigger cables connecting different devices in many situations; however, this is often impractical, and sometimes impossible in outdoors situations. The aim of this paper is to describe a wireless system for outdoor use, allowing synchronization of different types of – potentially embedded and moving – devices. In this system, each synchronization device is composed of: (i) a GPS receiver (used as time reference), (ii) a radio transmitter, and (iii) a microcontroller. These components a... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512183 Mon, 17 Oct 2011 04:00:00 +0100 5512183 http://www.medworm.com/index.php?rid=5374856&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005872%2Fabstract%3Frss%3Dyes Abstract: Rats use specialized tactile hairs on their snout, called vibrissae (whiskers), to explore their surroundings. Vibrissae have no sensors along their length, but instead transmit mechanical information to receptors embedded in the follicle at the vibrissa base. The transmission of mechanical information along the vibrissa, and thus the tactile information ultimately received by the nervous system, depends critically on the mechanical properties of the vibrissa. In particular, transmission depends on the bending stiffness of the vibrissa, defined as the product of the area moment of inertia and Young's modulus. To date, Young's modulus of the rat vibrissa has not been measured in a uniaxial tensile test. We performed tensile tests on 22 vibrissae cut into two halves: a tip-segment ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374856 Thu, 13 Oct 2011 04:00:00 +0100 5374856 http://www.medworm.com/index.php?rid=5292636&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005951%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292636 Fri, 07 Oct 2011 07:00:04 +0100 5292636 http://www.medworm.com/index.php?rid=5374860&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005550%2Fabstract%3Frss%3Dyes Abstract: The components of prosthetic hip bearings may experience in-vivo subluxation and edge loading on the acetabular socket as a result of joint laxity, causing abnormally high, damaging contact stresses. In this research, edge-loaded contact of prosthetic hips is examined analytically and experimentally in the most commonly used categories of material pairs. In edge-loaded ceramic-on-ceramic hips, the Hertzian contact theory yields accurate (conservatively, 400N. The Hertzian contact theory is shown to be ill-suited to edge-loaded ceramic-on-polyethylene pairs due to polyethylene's nonlinear material behavior. This work elucidates the methods and the accuracy of applying classical contact theory to edge-loaded hip bearings. The results help to define the applicability of the Hertzian... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374860 Mon, 03 Oct 2011 04:00:00 +0100 5374860 http://www.medworm.com/index.php?rid=5374867&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005574%2Fabstract%3Frss%3Dyes Abstract: Standard, beaded radiostereometric analysis (RSA) and markerless RSA often use computed tomography (CT) scans to create three-dimensional (3D) bone models. However, ethical concerns exist due to risks associated with CT radiation exposure. Therefore, the aim of this study was to investigate the effect of decreasing CT dosage on RSA accuracy. Four cadaveric shoulder specimens were scanned using a normal-dose CT protocol and two low-dose protocols, where the dosage was decreased by 89% and 98%. 3D computer models of the humerus and scapula were created using each CT protocol. Bi-planar fluoroscopy was used to image five different static glenohumeral positions and two dynamic glenohumeral movements, of which a total of five static and four dynamic poses were selected for analysis. F... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374867 Fri, 30 Sep 2011 04:00:00 +0100 5374867 http://www.medworm.com/index.php?rid=5374866&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005914%2Fabstract%3Frss%3Dyes Abstract: Magnetic resonance imaging (MRI) could potentially be used to non-invasively predict the strength of an ACL graft after ACL reconstruction. We hypothesized that the volume and T2 relaxation parameters of the ACL graft measured with MRI will predict the graft structural properties and anteroposterior (AP) laxity of the reconstructed knee. Nine goats underwent ACL reconstruction using a patellar tendon autograft augmented with a collagen or collagen–platelet composite. After 6 weeks of healing, the animals were euthanized, and the reconstructed knees were retrieved and imaged on a 3T scanner. AP laxity was measured prior to dissecting out the femur–graft–tibia constructs which were then tested to tensile failure to determine the structural properties. Regression analysis indi... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374866 Fri, 30 Sep 2011 04:00:00 +0100 5374866 http://www.medworm.com/index.php?rid=5374862&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005422%2Fabstract%3Frss%3Dyes The objective of this study was to develop a lumped parameter model, solely based on non-invasive data, allowing the description of the interaction between LV, COA, AS and the arterial system. First, a formulation describing the instantaneous net pressure gradient through the COA was introduced and the predictions were compared to in vitro results. The model was then used to determine LV work induced by coexisting AS and COA with different severities. The results show that LV stroke work varies from 0.98J (no-AS; no-COA) up to 2.15J (AS: 0.61cm2+COA: 90%). Our results also show that the proportion of the total flow rate that will cross the COA is significantly reduced with the increasing COA severity (from 85% to 40%, for a variation of COA severity from 0% to 90%, respectively). Finally, ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374862 Wed, 28 Sep 2011 04:00:00 +0100 5374862 http://www.medworm.com/index.php?rid=5374865&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005938%2Fabstract%3Frss%3Dyes Abstract: Although the interpretability and reliability of joint kinematics depends strongly on the accuracy and precision of determining the anatomical frame (AF) orientation, the exact dependency of joint angle error on AF misalignment is still not clear. To fully understand the behavior, this study uses linear perturbations to quantify joint angle error due to known modifications of the AFs, where the joint angles are calculated according to the Cardanic convention. The result is a functional representation of joint angle error with dependence on nominal joint angles and on the orientations of the alternative AFs relative to the nominal AFs. The results are validated using numerical analysis on knee joint angle data during walking. The derived relationship elucidates results from previo... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374865 Mon, 26 Sep 2011 04:00:00 +0100 5374865 http://www.medworm.com/index.php?rid=5374859&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005859%2Fabstract%3Frss%3Dyes Abstract: The goal of this work was to create a finite element micromechanical model of the myotendinous junction (MTJ) to examine how the structure and mechanics of the MTJ affect the local micro-scale strains experienced by muscle fibers. We validated the model through comparisons with histological longitudinal sections of muscles fixed in slack and stretched positions. The model predicted deformations of the A-bands within the fiber near the MTJ that were similar to those measured from the histological sections. We then used the model to predict the dependence of local fiber strains on activation and the mechanical properties of the endomysium. The model predicted that peak micro-scale strains increase with activation and as the compliance of the endomysium decreases. Analysis of the mo... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374859 Mon, 26 Sep 2011 04:00:00 +0100 5374859 http://www.medworm.com/index.php?rid=5374854&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005926%2Fabstract%3Frss%3Dyes Abstract: Diarthrodial joints are freely moveable joints containing synovial fluid (SF) within a connective tissue joint capsule that allows for low-friction and low-wear articulation of the cartilaginous ends of long bones. Biomechanical cues from joint articulation regulate synoviocyte and cartilage biology via joint capsule strain, in turn altering the composition of SF. Joint flexion is clinically associated with pain in knees with arthritis and effusion, with the nociception possibly originating from joint capsule strain. The hypothesis of this study was that knee fluid volume distribution and joint capsule strain are altered with passive flexion in the rabbit model. The aims were to (a) determine the volume distribution of fluid in the joint at different total volumes and with flexio... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374854 Mon, 26 Sep 2011 04:00:00 +0100 5374854 http://www.medworm.com/index.php?rid=5374853&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005902%2Fabstract%3Frss%3Dyes Abstract: Animal models of ventricular tachypacing (VTP) have been successfully used to reproduce the relevant features observed in patients with atrial fibrillation, such as increased atrial pressure and volume, ion-channel alterations and fibrosis. After performing VTP on a healthy Yorkshire pig, we measured an increase in volume of 60%, a two-fold rise in pressure, and a complex pattern of local mechanical, histological and biochemical changes, including a generalized stiffening of the wall. A protocol recently developed was employed to generate computational models of the porcine left atrium mechanics in healthy conditions and after VTP. Comparison of the stress distribution in the healthy vs. VTP case provided a map of how pressure overload affects and modifies left atrium mechanics. ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374853 Mon, 26 Sep 2011 04:00:00 +0100 5374853 http://www.medworm.com/index.php?rid=5374852&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005896%2Fabstract%3Frss%3Dyes In this study, damage was induced in bovine trabecular bone samples by axial compression, and the effects on the mechanical properties in shear were assessed. The damaged shear modulus, shear yield stress, ultimate shear stress, and energy to failure all depended on induced damage and decreased as the architecture became more rod-like. The changes in ultimate shear strength and toughness were proportional to the decrease in shear modulus, consistent with an effective decrease in the cross-section of trabeculae based on cellular solid analysis. For typical ranges of bone volume fraction in human bone, the strength and toughness were much more sensitive to decreased volume fraction than to induced mechanical damage. While ultimately repairing or avoiding damage to the bone structure and incr... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374852 Mon, 26 Sep 2011 04:00:00 +0100 5374852 http://www.medworm.com/index.php?rid=5374851&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005884%2Fabstract%3Frss%3Dyes In this study, post-stroke atrophy was determined bilaterally in fifteen leg muscles with volumes quantified using magnetic resonance imaging (MRI). All muscle volumes were adjusted to exclude non-contractile tissue content, and muscle atrophy was quantified by comparing the volumes between paretic and non-paretic sides. Non-contractile tissue or intramuscular fat was calculated by determining the amount of tissue excluded from the muscle volume measurement. With the exception of the gracilis, all individual paretic muscles examined had smaller volumes in the non-paretic side. The average decrease in volume for these paretic muscles was 23%. The gracilis volume, on the other hand, was approximately 11% larger on the paretic side. The amount of non-contractile tissue was higher in all paret... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374851 Mon, 26 Sep 2011 04:00:00 +0100 5374851 http://www.medworm.com/index.php?rid=5374857&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005847%2Fabstract%3Frss%3Dyes Abstract: Musculoskeletal computer models are often used to study muscle function in children with and without impaired mobility. Calculations of muscle forces depend in part on the assumed strength of each muscle, represented by the peak isometric force parameter, which is usually based on measurements obtained from cadavers of adult donors. The aim of the present study was twofold: first, to develop a method for scaling lower-limb peak isometric muscle forces in typically-developing children; and second, to determine the effect of this scaling method on model calculations of muscle forces obtained for normal gait. Muscle volumes were determined from magnetic resonance (MR) images obtained from ten children aged from 7 to 13yr. A new mass–length scaling law was developed based on the as... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374857 Thu, 22 Sep 2011 04:00:00 +0100 5374857 http://www.medworm.com/index.php?rid=5374858&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005811%2Fabstract%3Frss%3Dyes Abstract: The morphological change of cellular apoptosis initiates from the change of membrane roughness. In order to identify cellular apoptosis in its early stage, atomic force microscope was adapted to reveal the change of membrane roughness in unprecedented details, providing an image in nanometer-scaled resolution. The mouse monocyte/macrophage cell line RAW 264.7 was the subject studied and subjected to apoptotic induction by hydrogen peroxide. A finding of the qualitative correlation between cell membrane roughness and oxidative stress level is disclosed stating that roughness is increasing with the increasing level of oxidative stress. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374858 Wed, 21 Sep 2011 04:00:00 +0100 5374858 http://www.medworm.com/index.php?rid=5374855&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005793%2Fabstract%3Frss%3Dyes Abstract: The present study concerns the simulation and analysis of the flow field in the upper human respiratory system in order to gain an improved understanding of the complex flow field with respect to the process affecting drug delivery for medical treatment of the human air system. For this purpose, large eddy simulation (LES) is chosen because of its powerful performance in the transitional range of laminar and turbulent flow fields.The average gas velocity in a constricted tube is compared with experimental data () and numerical data from Reynolds-averaged Navier–Stokes (RANS) equations coupled with low Reynolds number (LRN) κ–ω model () and LRN shear–stress transport κ–ω model (), for model validation. The present study emphasizes on the instantaneous flow field, where... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374855 Wed, 21 Sep 2011 04:00:00 +0100 5374855 http://www.medworm.com/index.php?rid=5374864&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005471%2Fabstract%3Frss%3Dyes Abstract: This paper reports on a small-scale bending method for human hair. The test sample, which is elliptical in cross-section, is fixed to a hollow steel needle using resin to form a cantilever. A loading probe is used to subject this to a lateral load, where the load is applied parallel to either the long or short axis of the elliptical cross-section. From these tests, load–displacement relationships for the hair were obtained. From the experimental data and analysis, we found that the structural elasticity determined is independent of the direction of bending, and precise measurements of the structural elasticity of human hair with scattering of less than 5% were realized using this test scheme. Finally, changes in the structural elasticity of hair due to hair treatments were dete... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374864 Mon, 19 Sep 2011 04:00:00 +0100 5374864 http://www.medworm.com/index.php?rid=5374863&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100563X%2Fabstract%3Frss%3Dyes Abstract: In experiments turbulence has previously been shown to occur in intracranial aneurysms. The effects of turbulence induced oscillatory wall stresses could be of great importance in understanding aneurysm rupture. To investigate the effects of turbulence on blood flow in an intracranial aneurysm, we performed a high resolution computational fluid dynamics (CFD) simulation in a patient specific middle cerebral artery (MCA) aneurysm using a realistic, pulsatile inflow velocity. The flow showed transition to turbulence just after peak systole, before relaminarization occurred during diastole. The turbulent structures greatly affected both the frequency of change of wall shear stress (WSS) direction and WSS magnitude, which reached a maximum value of 41.5Pa. The recorded frequencies we... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374863 Mon, 19 Sep 2011 04:00:00 +0100 5374863 http://www.medworm.com/index.php?rid=5374861&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005434%2Fabstract%3Frss%3Dyes Abstract: Clinical studies suggest that aneurysm aspect ratio (AR) is an important indicator of rupture likelihood. The importance of AR is hypothesized to arise from its influence on intra-aneurysmal hemodynamics. It has been conjectured that slower flow in high AR sacs leads to a cascade of biological activities that weaken the aneurysm wall (). However, the connection between AR, hemodynamics and wall weakening has never been proven. Animal models of saccular aneurysms provide a venue for evaluating this conjecture. The focus of this work was to evaluate whether a commonly used elastase induced aneurysm model in rabbits is suitable for a study of this kind from a hemodynamic perspective. In particular, to assess whether hemodynamic factors in low and high AR sacs are statistically diffe... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374861 Mon, 19 Sep 2011 04:00:00 +0100 5374861 http://www.medworm.com/index.php?rid=5374850&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005860%2Fabstract%3Frss%3Dyes Abstract: The menisci of the knee are structures integral to the long term health of the knee joint. The primary function of these tissues is to distribute load across the tibiofemoral joint by increasing the congruency of the joint, thereby decreasing the resultant stress experienced by the articular cartilages. The menisci also play a secondary role in stabilizing the joint, particularly in the anterior cruciate ligament deficient knee, and also have roles in joint lubrication and proprioception. Also, an oft-cited role of this tissue is that of a shock absorber. We will review the literature supporting this shock absorption paradigm and describe the limitations and errors in the conclusions made by these studies. Consequently, we will show that the literature is inconclusive with no sup... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5374850 Mon, 19 Sep 2011 04:00:00 +0100 5374850 http://www.medworm.com/index.php?rid=5292650&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005501%2Fabstract%3Frss%3Dyes Conclusion: There is a significant modification in biomechanical properties between ruptured aneurysm, presenting a soft tissue and unruptured aneurysms, presenting a rigid material. This finding strongly supports the idea that a biomechanical risk factor based assessment should be utilized in the to improve the therapeutic decision making. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292650 Mon, 19 Sep 2011 04:00:00 +0100 5292650 http://www.medworm.com/index.php?rid=5292638&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005823%2Fabstract%3Frss%3Dyes Abstract: This paper compares geometry-based knee axes of rotation (transepicondylar axis and geometric center axis) and motion-based functional knee axes of rotation (fAoR). Two algorithms are evaluated to calculate fAoRs: Gamage and Lasenby's sphere fitting algorithm (GL) and Ehrig et al.'s axis transformation algorithm (SARA). Calculations are based on 3D motion data acquired during isokinetic dynamometry. AoRs are validated with the equivalent axis based on static MR-images. We quantified the difference in orientation between two knee axes of rotation as the angle between the projection of the axes in the transversal and frontal planes, and the difference in location as the distance between the intersection points of the axes with the sagittal plane. Maximum differences between fAoRs r... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292638 Mon, 19 Sep 2011 04:00:00 +0100 5292638 http://www.medworm.com/index.php?rid=5292647&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005513%2Fabstract%3Frss%3Dyes Abstract: The noninvasive measurement of finite strains in biomaterials and tissues by magnetic resonance imaging (MRI) enables mathematical estimates of stress distributions and material properties. Such methods allow for non-contact and patient-specific modeling in a manner not possible with traditional mechanical testing or finite element techniques. Here, we employed three constitutive (i.e. linear Hookean, and nonlinear Neo-Hookean and Mooney–Rivlin) relations with known loading conditions and MRI-based finite strains to estimate stress patterns and material properties in the articular cartilage of tibiofemoral joints. Displacement-encoded MRI was used to determine two-dimensional finite strains in juvenile porcine joints, and an iterative technique estimated stress distributions an... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292647 Thu, 15 Sep 2011 04:00:00 +0100 5292647 http://www.medworm.com/index.php?rid=5292639&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100580X%2Fabstract%3Frss%3Dyes Abstract: Percutaneous osseointegrated prostheses are being investigated as an alternative strategy to attach prosthetic limbs to patients. Although the use of these implants has shown to be promising in clinical trials, the ability to maintain a skin seal around an osseointegrated implant interface is a major challenge to prevent superficial and deep periprosthetic infections.The specific aim of this study was to establish a translational load-bearing ovine model to assess postoperative limb compensation and gait symmetry following a percutaneous osseointegrated implant. We tested the following hypotheses: (1) the animals would return to pre-amputation limb loads within 12-months; (2) the animals would return to a symmetrical gait pattern (stride length and time in stance) within 12-month... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292639 Thu, 15 Sep 2011 04:00:00 +0100 5292639 http://www.medworm.com/index.php?rid=5292656&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005616%2Fabstract%3Frss%3Dyes In this study, the accuracy and robustness of this measurement for clinical usage was assessed. The validation experiments were conducted in an RSA setup with a phantom setup of a knee in a vertical orientation. 72 RSA images were created using different variables for knee orientations, two prosthesis types (fixed-bearing Duracon knee and fixed-bearing Triathlon knee) and accuracies of the reconstruction models. The measurement error was determined for absolute and relative measurements and the effect of knee positioning and true seperation distance was determined. The measurement method overestimated the separation distance with 0.1mm on average. The precision of the method was 0.10mm (2⁎SD) for the Duracon prosthesis and 0.20mm for the Triathlon prosthesis. A slight difference in error... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292656 Mon, 12 Sep 2011 04:00:00 +0100 5292656 http://www.medworm.com/index.php?rid=5292644&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005628%2Fabstract%3Frss%3Dyes Abstract: Mechanical properties of the cell nucleus play an important role in maintaining the integrity of the genome and controlling the cellular force balance. Irregularities in these properties have been related to disruption of a variety of force-dependent processes in the cell, such as migration, division, growth or differentiation. Characterizing mechanical properties of the cell nucleus in situ and relating these parameters to cellular phenotypes remain challenging tasks, as conventional micromanipulation techniques do not allow direct probing of intracellular structures. Here, we present a framework based on light microscopic imaging and automated mechanical modeling that enables characterization of the compressibility of the nuclear interior in situ. Based entirely on optical meth... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292644 Mon, 12 Sep 2011 04:00:00 +0100 5292644 http://www.medworm.com/index.php?rid=5292637&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005835%2Fabstract%3Frss%3Dyes We present a procedure to generate a comprehensive computational model of the left atrium, including physiological loads (blood pressure), boundary conditions (pericardium, pulmonary veins and mitral valve annulus movement) and mechanical properties based on planar biaxial experiments. The model was able to accurately reproduce the in vivo dynamics of the left atrium during the passive portion of the cardiac cycle. A shift in time between the peak pressure and the maximum displacement of the mitral valve annulus allows the appendage to inflate and bend towards the ventricle before the pulling effect associated with the ventricle contraction takes place. The ventricular systole creates room for further expansion of the appendage, which gets in close contact with the pericardium. The tempora... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292637 Mon, 12 Sep 2011 04:00:00 +0100 5292637 http://www.medworm.com/index.php?rid=5203914&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005689%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203914 Sun, 11 Sep 2011 03:22:45 +0100 5203914 http://www.medworm.com/index.php?rid=5292657&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005598%2Fabstract%3Frss%3Dyes Abstract: The fundamental nature of impact testing requires a cautious approach to signal processing, to minimize noise while preserving important signal information. However, few recommendations exist regarding the most suitable filter frequency cut-offs to achieve these goals. Therefore, the purpose of this investigation is twofold: to illustrate how residual analysis can be utilized to quantify optimal system-specific filter cut-off frequencies for force, moment, and acceleration data resulting from in-vitro upper extremity impacts, and to show how optimal cut-off frequencies can vary based on impact condition intensity. Eight human cadaver radii specimens were impacted with a pneumatic impact testing device at impact energies that increased from 20J, in 10J increments, until fracture o... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292657 Fri, 09 Sep 2011 04:00:00 +0100 5292657 http://www.medworm.com/index.php?rid=5292641&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005653%2Fabstract%3Frss%3Dyes Abstract: To study the effects of increase in the degree of stenosis severity and subsequent complexity of hemodynamic patterns on hemodynamic parameters, experimental investigations and numerical simulations were performed. The correlations between the large negative Stress Phase Angle (SPA), the low mean Wall Shear Stress (WSS) and high Oscillatory Shear Index (OSI) were investigated at the distal shoulder and post-stenotic regions as the outcomes of elevated stenosis severity. Models included non-Newtonian fluid flow in stenotic arteries with 30–80% symmetrical stenoses. To study the interactions between pulsatile WSS and pulsatile wall circumferential stress (WCS) acting on endothelial cells, SPA as the phase difference between WSS and WCS waves was used. Moreover, the distribution o... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292641 Fri, 09 Sep 2011 04:00:00 +0100 5292641 http://www.medworm.com/index.php?rid=5512160&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005562%2Fabstract%3Frss%3Dyes Abstract: The primary cilium is a non-motile singular cellular structure that extends from the surface of nearly every cell in the body. The cilium has been shown to play numerous roles in maintaining tissue homeostasis, through regulating signaling pathways and sensing both biophysical and biochemical changes in the extracellular environment. The structural performance of the cilium is paramount to its function as defective cilia have been linked to numerous pathologies. In particular, the cilium has demonstrated a mechanosensory role in tissues such as the kidney, liver, endothelium and bone, where cilium deflection under mechanical loading triggers a cellular response. Understanding of how cilium structure and subsequent mechanical behavior contributes to the roles that cilium plays in ... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512160 Wed, 07 Sep 2011 04:00:00 +0100 5512160 http://www.medworm.com/index.php?rid=5292649&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005537%2Fabstract%3Frss%3Dyes This study reports on modulation of toe clearance and toe clearance variability in response to changes in ground inclination, paving type, and shoe sole geometry. Toe clearance and toe clearance variability for ten healthy young adults were calculated two-fold: a) for the commonly-used position on the foremost part of the sole of the shoe and b) for the lowest of a total of 7 sole positions, located between the metatarsals and the toe tip across the entire width of the sole. Utilizing a full-factorial design we found that toe clearance was affected by ground inclination, paving type, and sole geometry regardless of the computational method used (with p-values (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292649 Wed, 07 Sep 2011 04:00:00 +0100 5292649 http://www.medworm.com/index.php?rid=5292645&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005604%2Fabstract%3Frss%3Dyes Abstract: Preterm newborn infants may develop respiratory distress syndrome (RDS) due to functional and structural immaturity. A lack of surfactant promotes collapse of alveolar regions and airways such that newborns with RDS are subject to increased inspiratory effort and non-homogeneous ventilation. Pressure oscillation has been incorporated into one form of RDS treatment; however, how far it reaches various parts of the lung is still questionable. Since in-vivo measurement is very difficult if not impossible, mathematical modeling may be used as one way of assessment. Whereas many models of the respiratory system have been developed for adults, the neonatal lung remains essentially ill-described in mathematical models. A mathematical model is developed, which represents the first few ge... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292645 Wed, 07 Sep 2011 04:00:00 +0100 5292645 http://www.medworm.com/index.php?rid=5292642&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005641%2Fabstract%3Frss%3Dyes Abstract: Wearable hip protectors (padded garments) represent a promising strategy to decrease impact force and hip fracture risk during falls, and a wide range of products are currently marketed. However, little is known about how design features of hip protectors influence biomechanical effectiveness. We used a mechanical test system (simulating sideways falls) to measure the attenuation in femoral neck force provided by 26 commercially available hip protectors at three impact velocities (2, 3, and 4m/s). We also used a materials testing machine to characterize the force–deflection properties of each device. Regression analyses were performed to determine which geometric (e.g., height, width, thickness, volume) and force–deflection properties were associated with force attenuation. A... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292642 Wed, 07 Sep 2011 04:00:00 +0100 5292642 http://www.medworm.com/index.php?rid=5292640&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005665%2Fabstract%3Frss%3Dyes Abstract: Slip-induced falls in gait often have devastating consequences. The purposes of this study were 1) to select the determinants that can best discriminate the outcomes (recoveries or falls) of an unannounced slip induced in gait (and to find their corresponding threshold, i.e., the limits of recovery, which can clearly separate these two outcomes), and 2) to verify these results in a subset of repeated-slip trials. Based on the data collected from 69 young subjects during a slip induced in gait, nine different ways of combining the center of mass (COM) stability, the hip height, and its vertical velocity were investigated with the aid of logistic regression. The results revealed that the COM stability (s) and limb support (represented by the quotient of hip vertical velocity to hip... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292640 Wed, 07 Sep 2011 04:00:00 +0100 5292640 http://www.medworm.com/index.php?rid=5512161&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005495%2Fabstract%3Frss%3Dyes The objective of this systematic literature review is to provide an overview for direct in vivo human bone strain measurement studies and place the strain results within context of current theories of bone remodeling (i.e. mechanostat theory). We employed a standardized search strategy without imposing any time restriction to find English language studies indexed in PubMed and Web of Science databases that measured human bone strain in vivo. Twenty-four studies met our final inclusion criteria. Seven human bones were subjected to strain measurements in vivo including medial tibia, second metatarsal, calcaneus, proximal femur, distal radius, lamina of vertebra and dental alveolar. Peak strain magnitude recorded was 9096με on the medial tibia during basketball rebounding and the peak strai... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5512161 Fri, 02 Sep 2011 04:00:00 +0100 5512161 http://www.medworm.com/index.php?rid=5292653&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005446%2Fabstract%3Frss%3Dyes Abstract: In the table contact phase of gymnastics vaulting both dynamic and static friction act. The purpose of this study was to develop a method of simulating Coulomb friction that incorporated both dynamic and static phases and to compare the results with those obtained using a pseudo-Coulomb implementation of friction when applied to the table contact phase of gymnastics vaulting. Kinematic data were obtained from an elite level gymnast performing handspring straight somersault vaults using a Vicon optoelectronic motion capture system. An angle-driven computer model of vaulting that simulated the interaction between a seven segment gymnast and a single segment vaulting table during the table contact phase of the vault was developed. Both dynamic and static friction were incorporated w... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292653 Fri, 02 Sep 2011 04:00:00 +0100 5292653 http://www.medworm.com/index.php?rid=5292643&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005586%2Fabstract%3Frss%3Dyes The objective of this study was to develop a methodology that would integrate a motion analysis-based kinematic foot model with a computational model of the ankle to determine dynamic ankle ligament strains during external foot rotation. Six subjects performed single-legged, internal rotation of the body with a planted foot while a marker-based motion analysis was conducted to track the hindfoot motion relative to the tibia. These kinematic data were used to drive an established computational ankle model. Ankle ligament strains, as a function of time, were determined. The anterior tibiofibular ligament (ATiFL) experienced the highest strain at 9.2±1.1%, followed by the anterior deltoid ligament (ADL) at 7.8±0.7%, averaged over the six subjects. The peak ATiFL strain occurred prior to pea... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292643 Fri, 02 Sep 2011 04:00:00 +0100 5292643 http://www.medworm.com/index.php?rid=5292646&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005525%2Fabstract%3Frss%3Dyes In this study, propagation of severe, linear, and diffuse damage was examined in trabecular bone cores from the femoral head of younger (61.3±3.1 years) and older (75.0±3.9 years) men and women. Using a two-step mechanical testing protocol, damage was first initiated with static uniaxial compression to 0.8% strain then propagated at a normalized stress level of 0.005 to a strain endpoint of 0.8%. Coupling mechanical testing with a dual-fluorescent staining technique, the number and length/area of propagating cracks were quantified. It was found that the number of cycles to the test endpoint was substantially decreased in older compared to younger samples (younger: 77,372±15,984 cycles; older: 34,944±11,964 cycles, p=0.06). This corresponded with a greater number of severely damaged tra... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292646 Thu, 01 Sep 2011 04:00:00 +0100 5292646 http://www.medworm.com/index.php?rid=5292658&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005549%2Fabstract%3Frss%3Dyes In conclusion, the mechanical properties of the biopsies were mainly determined by the cement porosity and the cement material properties. The study showed that bone tissue inside the biopsies was mechanically “switched off” such that load was carried essentially by the porous PMMA. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292658 Mon, 29 Aug 2011 04:00:00 +0100 5292658 http://www.medworm.com/index.php?rid=5292648&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005483%2Fabstract%3Frss%3Dyes This study quantified head impact exposure in collegiate football, providing data that is critical to advancing the understanding of the biomechanics of concussive injuries and sub-concussive head impacts. (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292648 Mon, 29 Aug 2011 04:00:00 +0100 5292648 http://www.medworm.com/index.php?rid=5292652&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005458%2Fabstract%3Frss%3Dyes Abstract: Traction force generated at focal adhesions (FAs) of cells plays an essential role in regulating cellular functions. However, little is known about how the traction force at each FA changes during cell stretching. Here we investigated dynamic changes in traction force at FAs during macroscopic stretching of porcine aortic smooth muscle cells (SMCs) cultured on elastic micropillar substrates. SMCs were cultured on polydimethylsiloxane (PDMS)-based substrates with a micropillar array, and stretched approximately in the direction of their major axis and then released by stretching and relaxing the substrates. This stretch–release cycle was repeated twice with cell strain rates of 0.3%/15s up to a 3% strain, and the deflection of the PDMS micropillars was measured simultaneously to... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292652 Thu, 25 Aug 2011 04:00:00 +0100 5292652 http://www.medworm.com/index.php?rid=5292651&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100546X%2Fabstract%3Frss%3Dyes Abstract: Cellular mechanics is known to play an important role in many cellular functions including adhesion, migration, proliferation, and differentiation. Human mesenchymal stem cells (hMSCs) demonstrate unique mechanical properties distinct from fully differentiated cells. This observation suggests that the stem cell mechanics may be modulated to regulate the hMSCs' lineage commitment. Specifically, ERM (ezrin, radixin, moesin) proteins are known to mediate the membrane–cytoskeleton adhesion, cell elasticity, actin cytoskeleton organization, and therefore could serve as potential targets for modulation of the cellular mechanics. Combining silencing RNA, atomic force microscopy, and laser optical tweezers, the role of the ERM proteins involved in the regulation of stem cell biomechani... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292651 Thu, 25 Aug 2011 04:00:00 +0100 5292651 http://www.medworm.com/index.php?rid=5203918&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005215%2Fabstract%3Frss%3Dyes Abstract: A fundamental understanding of the mechanical properties of the extracellular matrix (ECM) is critically important to quantify the amount of macroscopic stress and/or strain transmitted to the cellular level of vascular tissue. Structural constitutive models integrate histological and mechanical information, and hence, allocate stress and strain to the different microstructural components of the vascular wall. The present work proposes a novel multi-scale structural constitutive model of passive vascular tissue, where collagen fibers are assembled by proteoglycan (PG) cross-linked collagen fibrils and reinforce an otherwise isotropic matrix material. Multiplicative kinematics account for the straightening and stretching of collagen fibrils, and an orientation density function cap... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203918 Mon, 22 Aug 2011 04:00:00 +0100 5203918 http://www.medworm.com/index.php?rid=5292654&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005276%2Fabstract%3Frss%3Dyes This study aimed to design and validate the measurement of ankle kinetics (force, moment, and power) during consecutive gait cycles and in the field using an ambulatory system.An ambulatory system consisting of plantar pressure insole and inertial sensors (3D gyroscopes and 3D accelerometers) on foot and shank was used. To test this system, 12 patients and 10 healthy elderly subjects wore shoes embedding this system and walked many times across a gait lab including a force-plate surrounded by seven cameras considered as the reference system. Then, the participants walked two 50-meter trials where only the ambulatory system was used.Ankle force components and sagittal moment of ankle measured by ambulatory system showed correlation coefficient (R) and normalized RMS error (NRMSE) of more th... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292654 Fri, 19 Aug 2011 04:00:00 +0100 5292654 http://www.medworm.com/index.php?rid=5203916&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005240%2Fabstract%3Frss%3Dyes Abstract: Quantifying the time course of load-induced changes in arterial wall geometry, microstructure, and properties is fundamental to developing mathematical models of growth and remodeling. Arteries adapt to altered pressure and flow by modifying wall thickness, inner diameter, and axial length via marked cell and matrix turnover. To estimate particular biomaterial implications of such adaptations, we used a 4-fiber family constitutive relation to quantify passive biaxial mechanical behaviors of mouse carotid arteries 0 (control), 7–10, 10–14, or 35–56 days after an aortic arch banding surgery that increased pulse pressure and pulsatile flow in the right carotid artery. In vivo circumferential and axial stretches at mean arterial pressure were, for example, 11% and 26% lower, re... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203916 Fri, 19 Aug 2011 04:00:00 +0100 5203916 http://www.medworm.com/index.php?rid=5203921&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100460X%2Fabstract%3Frss%3Dyes Abstract: The relationship between bony spinal column and spinal cord injury during an injury event is not well understood. While several studies have measured spinal canal occlusion during axial impact, there has been limited work done to quantify the spinal cord compression or deformation during simulated injury. Because the cord is a viscoelastic solid it may provide resistance to bone fragments, ligaments or other elements that move into the canal and impinge it during column injury. This would differentiate the measurement of cord compression from the measurement of occlusion of an empty canal. In the present study, a novel method of visualizing and quantifying spinal cord deformation during dynamic head-first impact of ex vivo human cervical spine specimens (N=6) was developed. A rad... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203921 Tue, 16 Aug 2011 04:00:00 +0100 5203921 http://www.medworm.com/index.php?rid=5203917&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005239%2Fabstract%3Frss%3Dyes Abstract: Muscle fascicles curve during contraction, and this has been seen using B-mode ultrasound. Curvature can vary along a fascicle, and amongst the fascicles within a muscle. The purpose of this study was to develop an automated method for quantifying curvature across the entirety of an imaged muscle, to test the accuracy of the method against synthetic images of known curvature and noise, and to test the sensitivity of the method to ultrasound probe placement. Both synthetic and ultrasound images were processed using multiscale vessel enhancement filtering to accentuate the muscle fascicles, wavelet-based methods were used to quantify fascicle orientations and curvature distribution grids were produced by quantifying local curvatures for each point within the image. Ultrasound image... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203917 Tue, 16 Aug 2011 04:00:00 +0100 5203917 http://www.medworm.com/index.php?rid=5124305&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS002192901100529X%2Fabstract%3Frss%3Dyes (Source: Journal of Biomechanics) Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5124305 Sat, 13 Aug 2011 06:57:34 +0100 5124305 http://www.medworm.com/index.php?rid=5292655&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005264%2Fabstract%3Frss%3Dyes Abstract: We investigated the changes in the technical ability of force application/orientation against the ground vs. the physical capability of total force production after a multiple-set repeated sprints series. Twelve male physical education students familiar with sprint running performed four sets of five 6-s sprints (24s of passive rest between sprints, 3min between sets). Sprints were performed from a standing start on an instrumented treadmill, allowing the computation of vertical (FV), net horizontal (FH) and total (FTot) ground reaction forces for each step. Furthermore, the ratio of forces was calculated as RF=FHFTot−1, and the index of force application technique (DRF) representing the decrement in RF with increase in speed was computed as the slope of the linear RF-speed rel... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5292655 Fri, 12 Aug 2011 04:00:00 +0100 5292655 http://www.medworm.com/index.php?rid=5203924&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011004982%2Fabstract%3Frss%3Dyes Abstract: The purpose of this study was to clarify how foot deformation affects the relationship between triceps surae muscle–tendon unit (MTU) length and ankle joint angle. For six women and six men a series of sagittal magnetic resonance (MR) images of the right foot were taken, and changes in MTU length (the displacement of the calcaneal tuberosity), foot arch angle, and ankle joint angle were measured. In the passive session, each subject's ankle joint was secured at 10° dorsiflexed position, neutral position (NP), and 10° and 20° plantar flexed positions while MR images were acquired. In the active session, each subject was requested to perform submaximal isometric plantar flexions (30%, 60%, and 80% of voluntary maximum) at NP. The changes in MTU length in each trial were estima... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203924 Thu, 11 Aug 2011 04:00:00 +0100 5203924 http://www.medworm.com/index.php?rid=5203922&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005227%2Fabstract%3Frss%3Dyes Abstract: A model is presented for describing the Amputee Independent Prosthesis Properties (AIPP) of complete assemblies of trans-tibial prosthetic components distal to the socket. This new AIPP model includes features of both lumped parameter and roll-over models and describes prosthesis properties that are of importance in stance phase, including prosthetic foot geometry, normal stiffness, shear stiffness, and damping (energy dissipation). Methods are described for measuring the parameters of the AIPP model using a custom test-rig, commercial load-cell, and a motion capture system. Example data are presented for five pylon angles reflecting the shank angles seen in normal gait. Through the inclusion of measured AIPP in future in-vivo studies comparing different prostheses more generic i... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203922 Thu, 11 Aug 2011 04:00:00 +0100 5203922 http://www.medworm.com/index.php?rid=5203923&cid=s_38490_61_f&fid=38490&url=http%3A%2F%2Fwww.jbiomech.com%2Farticle%2FPIIS0021929011005185%2Fabstract%3Frss%3Dyes Abstract: Ankle sprains are common during sporting activities and can have serious consequences. Understanding of injury mechanisms is essential to prevent injuries, but only two previous studies have provided detailed descriptions of the kinematics of lateral ankle sprains and measures of kinetics are missing. In the present study a female handball player accidentally sprained her ankle during sidestep cutting in a motion analysis laboratory. Kinematics and kinetics were calculated from 240Hz recordings with a full-body marker setup. The injury trial was compared with two previous (non-injury) trials. The injury trial showed a sudden increase in inversion and internal rotation that peaked between 130 and 180ms after initial contact. We observed an attempted unloading of the foot from 80ms... Journal of Biomechanics journals http://www.medworm.com/rss/comments.php?id=5203923 Tue, 09 Aug 2011 04:00:00 +0100 5203923