A Practical Approach for Evaluation of Socket Pistoning for Lower Limb Amputees

Although fit of the socket-suspension system is critical to lower limb amputees, monitoring of the fit is largely based on user feedback, which is subjective and often unreliable. Pistoning, defined as the relative displacement between the socket and the residual limb, is a well-accepted indicator of the fit of the socket-suspension system. However, opacity and rigidity of everyday prosthetic sockets make measurement of pistoning a challenging task. In this paper, we describe the development of a pistoning evaluation procedure that relies on two motion capture systems: a magnetic motion capture system used to measure the motion of the residual limb and an optical motion capture system used to measure the motion of the socket. Through synchronization of the two motion capture systems, the motion of the residual limb relative to the socket can be determined to derive the amplitude of pistoning. Here, we evaluated the performance of our approach through repeated calibration and a treadmill walking task with an amputee. Results demonstrate that this procedure, which does not rely on radiography unlike some existing methods, can be used to evaluate the fit of amputees' everyday sockets.