A low-cost, easy-to-use fit monitor of socket-suspension systems for lower limb amputees For lower limb amputees, the use of prosthetic legs is critical to remain active and live independently. Interface between the residual limb and the prosthetic leg, usually a prosthetic socket with related suspension system (SSS), only works well if the SSS is fit appropriately. To maintain an appropriate SSS fit, repeated interventions from both amputees and clinicians are necessary; otherwise, the SSS fit deteriorates due to fluctuation of amputees’ residual limb volume caused by long term factors, such as body weight changes, and short-term factors, such as impact during locomotion. Currently, all interventions are guided by amputees’ haptic sensation, which is not a reliable information source for regulation of the SSS fit. Guided by this inaccurate information source, interventions are often not effectively or timely, and deterioration of the SSS fit is often ignored until side effects become severe. These unfavorable side effects include unexpected stress concentrated on the residual limb, abnormal gait patterns, increased risk of secondary conditions such as back pain, and skin abrasions that are painful and difficult to heal. Objective of the proposal is to develop a novel SSS fit monitor to track the SSS fit based on kinematic features of pistoning, which describes the relative motion between the residual limb and the prosthetic socket. We will accomplish our study objectives by pursuing three specific aims. Aim 1: Identify phase-dependent kinematic features of pistoning, which are sensitive to change of SSS fit, on multiple locations on the residual limb; Aim 2: Design a sensor array to track pistoning motions in 3D space; and Aim 3: demonstrate the capability to monitor SSS fit during walking on amputee subjects using the developed SSS fit monitor. All these efforts will help us to reach our long-term goal: help amputees and clinicians to improve their capability to manage the interface between the residual limb and their prosthetic legs.