Early post-operative biomechanical assessment of joint replacements

Abstract

Recent early failures of newly introduced joint replacement prostheses, involving many patients, point to the need for further improvements in methods of preclinical testing. Randomly controlled bilateral clinical trials of a new device against an established device can greatly reduce the numbers of patients at risk. During such a trial, Roentgen Stereophotogrammetric Analysis (RSA) methods can be used to detect excessive early wear of the new prosthesis. Early measurement of dynamically inducible micromotion (DIMM) has been found to be predictive of mid-term migration of the implant; excessive migration has been found to be predictive of later loosening. DIMM has the advantage that it depends only on the instantaneous mechanics of the chosen activity and on the instantaneous mechanical properties of the tissues and implant and of the interfaces between them. The further improvements in our understanding of musculoskeletal mechanics needed to allow the calculation of DIMM are outlined.