In the US military, amputation is estimated to represent 7.4% of major extremity injuries sustained during war. For people needing to have part of their leg amputated, the process of learning to walk again using a prosthetic limb is difficult and people are often unable to return to their original level of activity. Most prosthetic limbs for lower limb amputations fit the remaining limb into a socket. Use of a socket prosthetic often comes with disabling discomfort, pain, and skin breakdown. Alternatively, a relatively new approach called osseointegration involves surgically placing a bone-anchored implant into the bone at the base of the remaining limb. The osseointegrated implant extends from the base of the remaining limb and then directly connected to a prosthetic limb. This approach removes pressure on the skin of the remaining limb and is assumed to enable people to walk and move better than compared to using a socket prosthetic. The problem is that comparison of walking mechanics and other bodily movements between those that have a prosthetic lower limb connected via an osseointegrated implant and those that have a socket is largely unexplored. It is unclear how well the hip muscles that support the limb with the amputation can recover to enable individuals to walk with their original ability.

Furthermore, the risk of needing a hip replacement on the same limb as an osseointegrated implant could result in extensive surgery if there is not enough room along the shaft of the femur to house both the osseointegrated implant and hip replacement implant. Hip muscle loss is related to risk for hip degeneration, potentially creating an additional risk following amputation if hip muscle is lost during amputation process and not recovered during post-surgical rehabilitation.

In order to assess the walking mechanics and effects on hip function that accommodate lower limb osseointegrated prosthetics, we propose a study comparing walking mechanics from motion analysis and hip muscle health from MRI (magnetic resonance imaging) between osseointegrated and socket transfemoral amputees who are at least 2 years following final surgery with no outstanding complications. This study will take us 2 years to complete. Over the first year, we will recruit eight civilian transfemoral osseointegration subjects that are completing participation in a pilot study where they received the two-stage osseointegrated surgery and will return to UCSF (University of California, San Francisco) for routine clinical follow-ups. Motion analysis and MRI data will be collected on these eight osseointegration patients and eight similarly aged transfemoral socket subjects. Data collection will be complete by the first quarter of the second year. Data analysis will be complete by the third quarter of the second year with final reports done by end of second year. Results from this work stand to (1) report the biomechanical outcomes of lower limb osseointegrated prosthetics in comparison to conventional socket prosthetics, (2) clarify the role of muscle function on biomechanical outcomes in lower limb amputees and explore the related risk for hip replacement on the affected side for transfemoral osseointegration, (3) inform targeted rehabilitation approaches for improving walking mechanics, and (4) motivate the development of regenerative therapeutics for muscle recovery.