Journal of biomechanics
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Journal of biomechanics · Jan 2006
Determination of frictional conditions between electrode array and endosteum lining for use in cochlear implant models.
Frictional conditions between the electrode array (in cochlear implants) and the endosteum lining covering the walls of the interior scala tympani structure strongly influence the sliding behaviour of the electrode array. Friction coefficients, determined by a simple but effective method based on the impending slippage model of electrode arrays sliding over the endosteum lining are reported in this paper. ⋯ Application of lubricants (glycerin and sorbelene) has the potential to lower the friction coefficient for Nucleus standard straight array (0.12 and 0.15) and for the Contour array (0.04 and 0.08). These results are used in finite element models to predict accurately the trajectories of electrode arrays and sliding contact pressures on cochlear structures to evaluate the likelihood of damage sustained during insertion.
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In the standard inverse dynamic method, joint moments are assessed from ground reaction force data and position data, where segmental accelerations are calculated by numerical differentiation of position data after low-pass filtering. This method falls short in analyzing the impact phase, e.g. landing after a jump, by underestimating the contribution of the segmental accelerations to the joint moment assessment. This study tried to improve the inverse dynamics method for the assessment of knee moment by evaluating different cutoff frequencies in low-pass filtering of position data on the calculation of knee moment. ⋯ Because the accelerometer-based method did not result in the expected improvement of the knee moment assessment during activities with high impacts, it is proposed to filter the ground reaction force with the same cutoff frequency as the calculated accelerations. When this precaution is not taken, the impact peaks in the moments can be considered as artifacts. On the basis of these findings, we recommend in the search to biomechanical explanations of chronic overuse injuries, like jumper's knee, not to consider the relation with impact peak force and impact peak moment.
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Journal of biomechanics · Dec 2005
Controlled Clinical TrialLength-tension properties of ankle muscles in chronic human spinal cord injury.
Contracture, or loss of range of motion (ROM) of a joint, is a common clinical problem in individuals with spinal cord injury (SCI). In order to measure the possible contribution of changes in muscle length to the loss of ankle ROM, the active force vs. angle curves for the tibialis anterior (TA) and gastrocnemiussoleus (GS) were measured in 20 participants, 10 with SCI, and 10 gender and age matched, neurologically intact (NI) individuals. Electrical stimuli were applied to the TA and GS motor nerves at incremented angles of the entire ROM of the ankle and the resulting ankle and knee torques were measured using a multi-axis load cell. ⋯ Differences in the passive ROM were consistent with the force-angle changes. The ROM in the dorsiflexion direction was significantly smaller in SCI subjects compared to NI controls (p<0.05) while the plantar flexion ROM was not significantly different (p=0.114). Based upon these results, we concluded that muscle shortening is an important component of contracture in SCI.
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Journal of biomechanics · Dec 2005
Trabecular bone fracture healing simulation with finite element analysis and fuzzy logic.
Trabecular bone fractures heal through intramembraneous ossification. This process differs from diaphyseal fracture healing in that the trabecular marrow provides a rich vascular supply to the healing bone, there is very little callus formation, woven bone forms directly without a cartilage intermediary, and the woven bone is remodelled to form trabecular bone. Previous studies have used numerical methods to simulate diaphyseal fracture healing or bone remodelling, however not trabecular fracture healing, which involves both tissue differentiation and trabecular formation. ⋯ Using finite element analysis and the fuzzy logic for diaphyseal healing, the model simulated formation of woven bone in the fracture gap and subsequent remodelling of the bone to form trabecular bone. We also demonstrated that the trabecular structure is dependent on the applied loading conditions. A single model that can simulate bone healing and remodelling may prove to be a useful tool in predicting musculoskeletal tissue differentiation in different vascular and mechanical environments.