Gait Following Transcutaneous Osseointegrated Limb Replacement in Swine; A Pilot Study

Abstract

It is currently estimated that one in 142 people in the US are living with an amputation. For lower-limb amputees, the socket prosthetic presents a number of clinically-recognized issues at the socket-to-stump interface, including blisters, sores, swelling, and heterotopic ossification. A novel alternative to the socket has been developed and implemented in over 250 patients in Europe alone. This new approach involves an implant anchored in bone (osseointegrated) that passes through the skin (transcutaneous) and attaches to an external prosthetic, eliminating the socket and the problems that accompany it. This innovative solution has not yet been approved in the US due to a lack of human clinical trials, a high infection rate in Europe, and the lack of a permanent seal at the skin-to-implant interface. To further investigate infection and wound healing at the stoma site, an animal model must be developed. This pilot study is also the first step to obtaining FDA approval in the US. A hind leg amputation was performed by an orthopedic surgeon on four adult Yucatan Mini Pigs. The length of the study varied for each animal: 5, 8, 10, and 11 weeks post-surgery. Specific aim I was to develop and validate a surgical procedure and perform a trans-tibial hind leg amputation, during which a titanium implant was inserted through the skin into the tibial canal. A prosthetic was attached at 2 days post-op. The objective of specific aim II was to promote wound healing while preventing infection. The wound was cleaned and the dressings were changed every 2-4 days. Two methods of wound cleaning were investigated: H2O2+H2O solution vs. soap+H2O solution. Bacterial swabs were collected at each dressing change to monitor the wound for infection. Infection was successfully prevented in all animals; soap+H2O was proven to be a sufficient method for cleaning the wound and preventing infection. The objective of specific aim III was to collect and compare gait parameters to investigate changes in weight distribution and gait kinetics. Gait parameters were collected pre- and at various time points post-surgery using a force plate and motion capture system to observe changes and trends. There was no significant difference in the load distribution between the front legs or the load distribution between the back legs pre-surgery. Loading of the amputated leg decreased by over 50% in all animals, while the intact-side front leg compensated by increasing weight bearing. Muscle contracture was present in the semitendinosus and semimembranosus muscles of the amputated leg of all animals and was measured by an overall decrease in the maximum angle between the prosthetic and the ground. Results from this pilot study will be used in developing and implementing a full animal study for this novel transcutaneous osseointegrated (TOI) solution to the socket prosthetic. This animal model should become the standard for the future testing of TOI prostheses as an option for lower-limb amputees.