Causes and prevention--0) Biomechanics

Twenty-five years ago John Charnley proclaimed the three basic conceptions for successful hip replacement arthroplasty 1. His recognition that low friction at the prosthetic bearing surface could greatly decrease the chances of component loosening from bone, that 316L stainless steel, ultra high molecular weight polyethylene and methylmethacrylate self curing bone cement were biocompatible and caused little or no tissue inflammation in either bulk of particulate form, and that methylmethacrylate bone cement could durably fix prosthetic components to bone have been foundational to the development of joint replacement techniques that bring comfort and increased independence to well over 250,000 patients each year. While it is worthwile to reflect on our failures and to rectify our design and usage short comings, we should maintain confidence and be pleased about the great majority of long term durable successes. Loosening with subsequent progressive development of increasing pain, disability, and deformity is the single most frequent cause of failure of total joint replacement arthroplasty. Accordingly, most attention will be paid to biomechanical factors in prosthetic component loosening. It is of importance to generalise from experiences with a group of patients treated with primary arthroplasty since this is a group that should expect good results. The others: the young with monarticular arthritis; those who have had prior failed arthroplasties; those with prior infection or with unusual pathologies such as neuropathic or Charcot joints each represent very special cases with far greater risks of failure. Every one of these patients is unique, and while many of the generalisations reviewed here may be of value in management of these patients, they must in addition, have individual consideration by a