Objective/Hypotheses and Specific Aims: The primary aim of this proposal is to determine whether a PFE can be used to predict foot preference and mobility outcomes with corresponding commercial prosthetic feet in people with a unilateral transtibial amputation (TTA). Secondarily, the investigators aim to determine whether a brief trial of commercial prosthetic feet would be able to similarly predict longer-term foot preference and mobility outcomes with those feet.

Study Design: The investigators will use a participant blinded cross-over study with repeated measurements. Participants with TTA will be enrolled at each of the three study sites: two VA sites (Puget Sound and Minneapolis), and one Department of Defense site (Center for the Intrepid). Participants will complete up to 6 visits. After an initial assessment visit, participants will be assigned to the high or low mobility group, and then during visit 2 they will be randomized to use the PFE in three foot modes or the three corresponding actual (commercially available) feet during walking tests in the laboratory. During visit 3 participants will repeat the procedures in the other condition (e.g., PFE if Day 2 included actual feet testing). At the end of visit 3 participants will be fit with one of the actual feet and wear it at home and in the community for approximately two weeks. At visit 4 participants will be fit with the next actual foot and repeat the 2 week use window. The same process will be followed for the final foot at visit 5, and the study foot will be returned at visit 6. Participants' preference, satisfaction and perceived mobility, and functional mobility will be measured and compared across all foot conditions (emulated and actual). After participants complete the procedures detailed above, they may be eligible to be invited to participate in follow-up phone interviews. A subset of participants may also be invited to participate in follow-up biomechanical data collection comparing the PFE foot conditions to the respective actual prosthetic feet during walking. Additionally, a subset of participants may also be invited to participate in follow-up data collection comparing prosthetic foot conditions of different stiffness categories.

Objectives and Rationale: Using a prosthesis allows many who experience lower leg amputation to regain functional abilities, but walking may be more difficult, and a sub-optimal prosthesis can substantially restrict participation in desired activities. Selecting an optimal prosthetic foot is an important aspect of maximizing mobility and the achievement of functional goals for people with lower leg amputation, however there is limited evidence to guide this process. The current prosthetic prescription process relies on clinician experience and typically does not allow people with a leg amputation to easily try out different prosthetic feet. The investigators have developed a customizable robotic prosthetic foot that mimics the mechanical properties of commercially available prosthetic feet without physically changing feet. This 'prosthetic foot emulator' (PFE) can be attached to the prescribed prosthetic socket and worn like a regular prosthetic foot within the laboratory or clinic, providing people with leg amputations the opportunity to quickly 'test-drive' many prosthetic foot designs within a single test session. Trial and error with actual commercial prosthetic feet can be inefficient given the time and expense required for the purchasing and fitting of prosthetic feet. The PFE could provide a means to explore a range of feet in a very short period of time. This study will evaluate the ability of the emulator to accurately reproduce the experience of wearing several commercially available (actual) prosthetic feet. The investigators will test whether brief in-laboratory experiences with emulated or actual feet can accurately predict longer-term foot preference, satisfaction, and walking ability in the community. The investigators will also evaluate the experiences of prosthetic foot prescription practices using qualitative methods from follow-up phone interviews with participants. Finally, the investigators will evaluate biomechanical outcomes during walking between the PFE and actual prosthetic feet to examine the ability of the emulator to accurately reproduce the experience of walking with the actual feet. Results from this study may provide evidence to support a new approach to prosthesis prescription and could resolve longstanding uncertainty in the prescription process for prosthetic feet.

Inclusion Criteria:

• has a unilateral (one leg) transtibial (below-knee) amputation
• has used a prosthetic limb for walking for at least six months
• has a comfortably fitting prosthetic socket
• be able to walk with a prosthetic limb sufficiently to participate in the experiment walking trials
• be age 18 to 89 years

Exclusion Criteria:

• contralateral limb or upper limb amputation
• are unable to use test feet for any reason (e.g., excessively long residual limb that is not compatible with wearing study prosthetic feet)
• unable to walk under the minimal necessary study walking conditions in order to complete the study procedures without undo stress
• currently pregnant (determined via self-report during screening)
• current surgical, neurological, rheumatologic, or lower limb musculoskeletal problem that significantly impairs ambulation (e.g., current ulcer, terminal illness, lower extremity joint replacement)
• weight greater than 250lbs.
• inadequate cognitive or language function to consent to participate
• currently incarcerated