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The influence of polyurethane cosmeses on the mechanical performance of transfemoral prostheses

Cairns, Nicola and Murray, Kevin (2013) The influence of polyurethane cosmeses on the mechanical performance of transfemoral prostheses. In: ISPO 2013 World Congress, 2013-02-04 - 2013-02-07, HICC.

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Abstract

Transfemoral prostheses are often covered with a flexible Polyurethane foam cosmesis to provide an aesthetic finish and protect the mechanical components. Despite its flexibility, the cosmesis is known to hinder prosthetic joint movement and alter amputee gait particularly in the swing phase. In fact amputees can be advised to keep the limb in full flexion for a period of time when the limb is first issued in order to stretch the cosmesis and reduce its impact on joint movement. Over time the cosmesis ruptures, typically in the knee area, due to repeated material flexure during gait. Although the cosmesis limitations are evident in clinical practice, the information is largely anecdotal; the impact of the polyurethane cosmesis on the function of the prosthesis has not been addressed in the scientific literature. The aim of this study was to determine if the cosmesis affects the mechanical performance of the prosthesis and consequently alters amputee gait. Three transfemoral amputees were voluntarily recruited for the study (Strathclyde University ethics approval) conducted in a gait analysis laboratory using a VICON (MODEL?) motion analysis system. Temporal gait parameters and joint angles were recorded as the subjects walked at a self-selected speed along a 12 metre level surface under two test conditions: without wearing a cosmesis and wearing a newly fitted cosmesis. Surface markers were attached to the prosthesis or cosmesis at standardised landmarks for kinematic measurement. Differences were measured in the swing phase gait parameters with and without a cosmesis. This is likely to reduce over time as the cosmesis wears. Consequently longitudinal adjustments may be required to accommodate for the cosmesis effect on the mechanical performance of the prosthesis. The findings pose the question why the advanced prosthetic components optimally set up for each amputee are covered with a cosmesis which hinders their operation?