Background. Individuals with above-knee amputation (AKA) experience significant mobility limitations due to a combination of factors, including diminished proprioception in the affected limb, that contribute to gait asymmetry, metabolically inefficient movements, and atypical joint loading patterns that have been associated with chronic secondary injuries, such as osteoarthritis and degenerative joint disease. Therefore, increasing gait symmetry, improving balance, and increasing walking efficiency, commonly referred to as gait retraining, is an essential component of rehabilitation for individuals with AKA. Traditional gait retraining is typically limited to a therapist providing verbal cues based on subjective observations to instruct the patient to correct his/her movements to achieve a desired outcome. Biofeedback (BFB) has been gaining attention as a potential tool for supplementing traditional gait retraining by using wearable sensors to quantify a patient's motion and communicate instructions back to the user through externally applied stimuli. Recent research in BFB applications has demonstrated its potential as a rehabilitation tool for several types of mobility impairment, but the effectiveness of BFB as a training tool for improving functional outcomes in individuals with above-knee amputations remains unknown. The proposed research will evaluate the effects of BFB training on the functional mobility of individuals with AKA, and aligns with the Orthotics and Prosthetics Function Focus Area.

Objectives \& Hypothesis. The overarching goal driving this proof-of-concept clinical trial is to develop best-practices for incorporating BFB training into gait retraining protocols for individuals with AKA to improve functional outcomes and decrease the prevalence of secondary injury. This study tests the hypothesis that vibrotactile BFB will increase gait symmetry, decrease gait deviations, and improve gait efficiency in above-knee prosthesis users immediately following BFB training; moreover, that these improvements will persist for a minimum of thirty minutes after the cessation of BFB stimuli.

Specific Aims. Specific Aim 1 will test whether short-term BFB training on late stance-phase hip extension produces discernible improvements in overall mobility scores and gait efficiency relative to pre-training levels that persist after the cessation of BFB stimuli. Specific Aim 2 will test whether a single BFB training session produces significant decreases kinematic gait deviations and increases limb loading symmetry relative to pre-training levels that persist after the cessation of BFB stimuli. For both specific aims, the training effects of BFB will be evaluated for (1) efficacy of real-time BFB stimuli, and (2) retention training-induced gait changes after BFB is no longer applied.

Study Design. Forty experienced above-knee prosthesis users will be recruited from the Palo Alto VA (n=20) and University of California Orthopaedic Institute (n=20). Participants will all undergo two types of gait training, in randomized order: traditional (CTRL) and biofeedback (BFBK). Prior to each type of training, participants will be instrumented with a wearable motion capture system and heart rate monitor. They will then perform a two-minute-walk-test (2MWT) to establish a baseline suite of functional outcome levels, including the Physiological Cost Index and gait Symmetry Indices. During BFBK training, BFB will be provided by small vibrating motors when participants have achieved the target amount of hip extension. CTRL training will consist of traditional verbal cuing. After each training phase, participants will undergo an additional 2MWT to quantify the effects of each training type on the outcome measures. For the BFBK phase, participants will undergo two additional 2MWT tests without BFB at 15 and 30 minutes after training to measure training retention. Repeated measures analysis of variance will be used conducted to identify differences in each of the outcome measures between the four time points (pre-test, post-test, 15-minutes, 30-minutes).