PROJECT SUMMARY/ABSTRACT More than two million people live with limb loss in the United States, nearly one-third of whom express dissatisfaction regarding their socket prosthesis fit. To address socket-based issues, osseointegration is offered as a secondary procedure with a direct connection of the prosthesis to the residual limb through a bone-anchored implant. The direct prosthesis-to-bone connection offers a novel potential benefit to postural control through improved osseoperception (sensation of mechanical stimulation of bones), proprioception (knowledge of the static and dynamic body positioning), and prosthetic limb control. Up to 67% of patients with transfemoral amputation fall at least once annually leading to diminished self-efficacy, fear of falling, and physical activity avoidance. How individuals maintain postural control, an important objective in fall prevention, after osseointegration remains uninvestigated. This F32 study will test a conceptual framework for the impact of prosthesis osseointegration directly on postural control and indirectly through osseoperception and proprioception through a two independent-groups cross-sectional design in 30 patients with unilateral transfemoral amputation (osseointegrated-prosthesis group (n = 15) and socket-prosthesis group (n=15)). Aim 1: Osseoperception and proprioception. Osseoperception will be evaluated with a variable frequency and amplitude vibration platform to identify sensation thresholds. Proprioception will be evaluated with standing joint position reproduction of the knee. Aim 2: Standing and walking postural control. Standing control will be measured using center of pressure trajectories during eyes-opened and eyes-closed standing. Walking control will be measured by step length and width asymmetry and variability. Aim 3: Anticipatory and reactive postural control. Anticipatory control will be measured during the anticipatory postural adjustment phase of gait initiation. Reactive control will be measured with reaction time during standing treadmill perturbations requiring a single recovery step. This proposal will be impactful to the clinical care of people with transfemoral amputations because (1) prosthesis osseointegration offers a unique path to increased osseoperception and proprioception, (2) the effects of prosthesis osseointegration on postural control are largely unknown (3) we will comprehensively evaluate postural control, and (4) we will compare outcomes from individuals with an OI-prosthesis to those with a socket-fit prosthesis without significant fit problems. Achieving these aims will improve our ability to provide targeted postural control training, target decreased fall risk, and improve health outcomes for this new and growing population of people with prosthesis bone-anchored implants. The proposed research and training plan are impactful to Dr. Tracy’s preparation to engage in an effective independent research career centered on the study of postural con...