Micromotion and Push-Out Evaluation of an Additive Manufactured Implant for Above-the-Knee Amputees

In comparison to through-knee amputees the outcomes for above-the-knee amputees are relatively poor; based on this novel techniques have been developed. Most current percutaneous implant-based solutions for transfemoral amputees make use of high stiffness intramedullary rods for skeletal fixation, which can have risks including infection, femoral fractures, and bone resorption due to stress shielding. This work details the cadaveric testing of a short, cortical bone stiffness-matched subcutaneous implant, produced using additive manufacture, to determine bone implant micromotion and push-out load. The results for the micromotions were all <20 μm and the mean push-out load was 2,099 Newtons. In comparison to a solid control, the stiffness-matched implant exhibited significantly higher micromotion distributions and no significant difference in terms of push-out load. These results suggest that, for the stiffness-matched implant at time zero, osseointegration would be facilitated and that the implant would be securely anchored. For these metrics, this provides justification for the use of a short-stem implant for transfemoral amputees in this subcutaneous application. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2104-2111, 2019.