Advances in Improving the Longevity of Total Joint Replacement Surgery
There exists no warranty period that an artificial joint may remain functional after its placement. It all depends on the patient and the techniques in its placement. Most artificial joint prosthesis can last for 15 to 20 years. With the recent advances in the materials and design of the joint prosthesis and in the precision of its implantation, artificial joint prosthesis can last even longer.
The use of high molecular weight polyethylene in the manufacturing of the acetabulum cup has been the source of wear particles in the joint. These minute wear debris can give rise to an inflammatory response in its neighborhood and is a cause of bone absorption surrounding the prosthesis, resulting in loosening of the prosthesis. The current trend is to replace this polyethylene with dense, highly cross- linked ultrahigh molecular weight polyethylene or ceramic materials for the acetabulum cup and with an especially coated articular surface, so that friction and thus wear particles are much minimized. The metallic implant is now specially treated: either porous coated or hydroxy-appatite coated so as to facilitate the growth of new bone on the surface of the implant, improving the fixation of the stem to the host bone. The chance of loosening of the prosthesis is thus minimized. New materials that can promote growth of new bone directly on its surface, such as Tantalum are being researched, so as to improve its fixation to the host bone.
Apart from the materials, advances are also achieved on the precision of implantation surgery that contributes to its longevity.
An experienced orthopaedic surgeon can achieve aligning of the axis of prosthesis, say in the knee, within 3 degrees of error. A gross malalignment may affect the range of movement of the artificial joint, resulting in stiffness or even subluxation, and later loosening from the host bone. With the use of intra-operative computer scanning and navigation tools, the precision can be improved to within one degree. Furthermore, the accumulation of the navigation data on its orientation on the host bone and the tension of the soft tissues can be a basis of future references and research in perfecting the navigation techniques. Patient Specific Instrumentation and Implant (PSI) can be prepared by pre-operative scanning of the patient’s diseased joint. This technique not only can shorten the operation time, a tailor-made implant can also help to settle any mismatching of the prosthesis with the host bone.
Dr. TANG, Wai-man