Micromovement of the Tibial Component in Successful Knee Arthroplasty, Studied by Roentgen Stereophotogrammetry

Abstract

During recent years arthroplasty of human joints with endoprostheses has become an accepted mode of treatment of destructive joint diseases of different kinds. Pertaining to the knee joint, with which this report will deal, there has been a rapid development since the method was introduced in its modern form in 1971 (1). The first, perhaps not ideal designs have been replaced by other, more refined ones. The infections, initially very numerous, are now less frequent. One remaining problem, however, with this kind of therapy is the occurrence of mechaniccal loosening of the prosthetic components. In knee joint arthroplasty this almost exclusively involves the tibial component, with a reported frequency of up to 20% (2,3). The prosthetic components are bonded to the bone by cement, and around this cement a radiolucent zone develops with great regularity, in some reports the incidence of which is 100% (4). In the context of mechanical loosening much interest has come to be focused on this radiolucent zone, which is known to consist of connective tissue, fibrous tissue or even fibro-cartilage (5,6). To assess prosthetic movements of the magnitude that could be allowed, for example, by this zone, with its possibly inferior load-bearing characteristics, conventional radiography is insufficient. Multiple blind measurements of films taken with an exact reproducable technique in Lund, shows that the accuracy is not greater than ± 1.5 degrees (7). Therefore, roentgen stereophotogrammetry combined with kinematic analysis introduced by Selvik in 1974 (8) has been used to study the behaviour of the tibial component in a number of knee arthroplasties in a more precise way. Since the beginning of 1981 the method is used in every knee arthroplasty which is performed for gonarthrosis at the Lund University Hospital.