Neuromusculoskeletal interfacing of lower limb prostheses

Doctoral thesis, 2021

The method of bone-anchored attachment of limb prostheses via a percutaneous skeletal extension was developed to circumvent commonly reported problems associated with the conventional method of socket attachment. In addition to the direct structural connection, the percutaneous implant may serve as a conduit for bidirectional communication between muscles and nerves within the residual limb and the prosthesis. Implanted electrodes recording myoelectric activity within the residual limb can be used to infer the user’s movement intent and may thus be used to provide intuitive control of the prosthesis in real time. Sensory feedback from the prosthesis can be provided back to the user by neurostimulation via implanted neural electrodes, thus closing the control loop. Together the skeletal, neural, and muscular interfaces form a neuromusculoskeletal interface. This technology is currently being evaluated in a clinical trial on individuals with upper limb amputation, but it has not yet been used in the lower limb.

The aim of this thesis has been to translate the concept of neuromusculoskeletal interfacing to the lower limb. An additional aim has been to reduce the limitations on high impact activities, that exist on current available systems for bone-anchored attachment of limb prostheses. To achieve these aims, a new design of the neuromusculoskeletal interface was developed where the structural capacity was increased with respect to current versions of the implant system to accommodate increased loads for highly active usage by individuals with lower limb amputation. In order to set adequate design requirements, investigations were conducted to determine the load exposure of bone-anchored implant systems during a number of loadbearing activities. Structural verification of the neuromusculoskeletal interface has been performed using numerical simulations as well as physical testing in static and dynamic conditions. The first steps towards clinical implementation of the lower limb neuromusculoskeletal interface have been taken by the development of a clinical research protocol that has been approved by the Swedish Ethical Review Authority.