Implant load during running on a transtibial bone anchored prosthesis: A multibody modelling case study

A bone-anchored prosthesis (BAP) offers a promising approach to solve socket-related problems for persons with a lower leg amputation, with the added benefit of direct load transfer. In the recent years, implants utilized in BAPs performed well in daily living activities such as walking. However, it is unknown if high impact activities, such as running, are safe. This case study determined the forces and moments acting on the implant during walking on a daily use prosthesis (DUP) and running on a DUP and a running specific prosthesis (RSP). A single unilateral transtibial BAP user with a press-fit osseointegration implant performed trials at varying speeds on an instrumented split belt treadmill. Kinematics were reconstructed from marker data using multi-body modelling, forces and moments were computed using inverse dynamics. Running on the RSP resulted in 40% smaller peak anteroposterior force and 38% smaller peak sagittal moment compared to walking on a DUP. However, peak axial force was 59% higher during running. Running on the RSP resulted in higher sagittal moment during late stance compared to running on the DUP, but smaller peak compression force. These results indicate an acceptable load for the user, as bending moments tend to be more harmful than axial loads. However, further analysis is needed to better understand the mechanical implications of this difference on bone stress. The results of this study suggest that running might pose less risk for mechanical failure of the bone-implant system than earlier perceived.