Background: Lower limb amputees experience chronic health challenges such as residual limb skin problems, low back pain, and osteoarthritis. These problems are exacerbated by high physical activity levels and by poor prosthetic socket fit. Prosthetists believe that limiting residual femur and skin motion will improve force coupling and thereby address these problems. However, there are no data demonstrating how changes in socket design affect residual femur and skin motion, and, by extension, lead to improved patient-reported outcomes.

Objective/Hypothesis: Goal of this research is to improve the current socket design optimization process that involves trial and error and relies heavily on the prosthetist's experience and intuition by using a quantitatively informed optimization process. The hypothesis is that modifiable in-socket mechanics, i.e. residual femur motion, skin strain, and pressure within the socket, are related to socket design and patient outcomes, and can be estimated using readily available clinical measurements.

Specific Aims: First aim is to identify the key characteristics of in-socket mechanics that are related to physical function and patient-reported comfort and function. The second aim is to identify readily available clinical measurements that are associated with the in-socket mechanical characteristics that are related to outcomes. The purpose of this aim is to correlate our laboratory findings from Aim 1 with more conventional modalities for clinical assessment.

Research Strategy: Preliminary data demonstrates the feasibility of the proposed research plan and will progress to a pilot clinical trial. The two aims will involve 30 transfemoral amputees. A highspeed biplane radiography system is used to image the residual limb while participants walk on a dual-belt instrumented treadmill both in their current socket and in sockets with purposely altered volume, brim height, cross-sectional geometry, and stiffness. Three-dimensional (3D) skin motion within the socket will be determined by tracking the motion of 40 to 50 small metal beads placed in a grid pattern on the skin of the residual limb before donning the socket. Residual femur motion within the socket will be determined with submillimeter accuracy using a validated tracking process that matches subject-specific bone models obtained from CT to the biplane radiographs. Discrete in-socket pressure will be recorded at four locations using pressure sensing pads. Readily available clinical measurements will be collected as well, including gait analysis, foot loading patterns, ground reaction forces, residual limb tissue stiffness, and hip range of motion hip strength. Each participant will complete clinical questionnaires to qualitatively evaluate comfort, fit, and overall satisfaction after wearing each socket. The different socket modifications are intended to affect the in-socket mechanics of the residual limb, physical function and patient-reported outcomes (Aim 1). These relationships will be assessed using a generalized linear model. Correlation between the research grade measurements and accessible clinical measures (Aim 2) will be evaluated using bivariate correlation analyses. The information gained in Aims 1 and 2 will be used to develop a quantitatively-informed socket optimization process, wherein the clinical measurements associated with in-socket mechanics will be used to inform socket design optimizations.