Load Mechanics In External And Bone-Anchored Prostheses

There are at least 3 million people globally who need prosthetic treatment. The number of people who receive lower limb amputations could be on the rise with the occurrence of the ageing problem. Prosthetic replacement is one of the most significant rehabilitation programs for those who lose their limbs. A lower-limb prosthesis is conventionally attached to the residual limb by a socket. Although this approach has been used for over 50 years, residual limb pain and soft tissue breakdown occur commonly. Poor socket fit applying excessive pressure to the pressure-intolerable residual limb has been suggested to be the main cause of the problems. On the other hand, a few teams are developing a surgical approach for directly anchoring a prosthesis to the femur using a titanium implant (osseointegration). One of the most advanced fixation systems currently available includes an implant and an abutment. The proximal end of the abutment is attached to the implant while its distal end protrudes through the soft tissue allowing attachment of the external prosthesis. The absence of prosthetic socket can alleviate the skin problems and residual limb pain. Improved sensory feedback and greater hip range of motion are the other advantages. However, occasional mechanical failures of fixation have been reported. Loosening of implants after long term usage might be a potential issue due to the load transfer from the bone to the implant (stress shielding), although there is no data available in the literature indicating the incidence yet. Residual limb pain, mechanical failures of the fixation and the potential problems of implant loosening are all related to mechanical loading. To improve the quality of external and bone-anchored lower-limb prostheses, it is important to study the load applied to them. This article presents our studies performed at The Hong Kong Polytechnic University and Queensland University of Technology investigating the load mechanics in both types of prostheses