Abstract-Prosthetic gel liners are often prescribed for persons with lower-limb amputations to make the prosthetic socket more comfortable. However, their effects on residual limb pressures and gait characteristics have not been thoroughly explored. This study investigated the effects of gel liner thickness on peak socket pressures and gait patterns of persons with unilateral transtibial amputations. Pressure and quantitative gait data were acquired while subjects walked on liners of two different uniform thicknesses. Fibular head peak pressures were reduced (p = 0.04) with the thicker liner by an average of 26 +/-21%, while the vertical ground reaction force (GRF) loading peak increased 3 +/-3% (p = 0.02). Most subjects perceived increased comfort within the prosthetic socket with the thicker liner, which may be associated with the reduced fibular head peak pressures. Additionally, while the thicker liner presumably increased comfort by providing a more compliant limb-socket interface, the higher compliance may have reduced force and vibration feedback to the residual limb and contributed to the larger vertical GRF loading peaks. We conclude that determining optimal gel liner thickness for a particular individual will require further investigations to better identify and understand the compromises that occur between user perception, residuallimb pressure distribution, and gait biomechanics.

Background Reduced-stiffness components are often prescribed in lower-limb prostheses, but their efficacy in augmenting shock absorption has been inconclusive. Objectives To perform a systematic variation of longitudinal prosthetic stiffness over a wide range of values and evaluate its effect on shock absorption during gait. Study Design Repeated-measures crossover experiment. Methods 12 subjects with a unilateral transtibial amputation walked at normal and fast self-selected speeds. Longitudinal prosthetic stiffness was modified by springs within a shock absorbing pylon: NORMAL (manufacturer-recommended), 75% of normal (MEDIUM), 50% of normal (SOFT), and RIGID (displacement blocked). The variables of interest were kinematic (stance-phase knee flexion and pelvic obliquity) and kinetic (prosthetic-side ground reaction force (GRF) loading peak magnitude and timing). Results No changes were observed in kinematic measures during gait. A significant difference in peak GRF magnitudes between MEDIUM and NORMAL (p = 0.001) during freely selected walking was attributed to modified walking speed (p = 0.008). GRF peaks were found to be statistically different during fast walking, but only between isolated stiffness conditions. Thus, altering longitudinal prosthesis stiffness produced no appreciable change in gait biomechanics. Conclusions Prosthesis stiffness does not appear to substantially influence shock absorption in transtibial prosthesis users.

Currently, it is unknown whether changing prosthetic limb stiffness affects the total limb stiffness and influences the shock absorption of an individual with transtibial amputation. The hypotheses tested within this study are that a decrease in longitudinal prosthetic stiffness will produce (1) a reduced total limb stiffness; and (2) reduced magnitude of peak impact forces and increased time delay to peak force. Fourteen subjects with a transtibial amputation participated in this study. Prosthetic stiffness was modified by means of a shock-absorbing pylon (SAP) that provides reduced longitudinal stiffness through compression of a helical spring within the pylon. A sudden loading evaluation device (SLED) was built to examine changes in limb loading mechanics during a sudden impact event. No significant change was found in the peak force magnitude or timing of the peak force between prosthetic limb stiffness conditions. Total limb stiffness estimates ranged Institutional Review: This study was approved by the Northwestern University Institutional Review Board. Written informed consent was obtained from each subject prior to participation. Participant Follow-Up:The authors do not plan to inform participants of the publication of this study. However, participants have been encouraged to check our Web site for updated publications. Disclaimer:The opinions contained in this publication are those of the grantee and do not necessarily reflect those of the Department of Education. U.S. Department of Veterans Affairs VA Author ManuscriptVA Author Manuscript VA Author Manuscript from 14.9 -17.9 kN/m and was not significantly different between conditions. Thus, the prosthetic-side total limb stiffness was unaffected by changes in prosthetic limb stiffness. The insensitivity of the total limb stiffness to prosthetic stiffness may be explained by the mechanical characteristics (i.e., stiffness and damping) of the anatomical tissue within the residual limb.

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