Abstract
In order to find the incidence of loosening of the femoral component after total knee arthroplasty (TKA) for rheumatoid patients and to clarify the relationship between the radiographic findings and loosening, 168 knee joints in 112 rheumatoid patients who received cementless TKA have been reviewed. The mean age of patients at surgery was 56.1 years (range: 22-75) . The average follow-up period was 5.5 years (range: 2-16) . Depending on the time, five different prostheses were used, such as the Mark- II (Okayama University, Kodama-Yamamoto), Mark- III (Okayama University, Kodama-Yamamoto), KC-1 (Kyoto Ceramics), Ortholoc- II (Whiteside), and Ortholoc modular knee system (Whiteside) . Twen-ty femoral components were revised because of loosening. The incidence of loosening of the femoral component (11.9%) was statistically equivalent to that of the tibial component (8.3%) . The cumulative survival rates of the Mark- II and Mark-III were 93.5% at the 5th post-operative year, 82.1% at the 10th post-operative year, and 54.3% at the 15th post-op-erative year; that of the KC-1 was 94.7% at the 5th post-operative year, 59.5% at the 10th post-operative year, and 44.7% at the 11th post-operative year; that of the Ortholoc- II was 87.8% at the 5th post-operative year, 79.8% at the 6th post-operative year; and that of the Ortholoc modular knee system was 100% at a mean 29.9 post-operative month (38 months maximum) . Migration of the femoral component in 15 joints, and the radiolucent zone with-out migration in 5 joints, were the radiological findings based on which revision surgery was decided. In respect to migration of the femoral component, posterior tilt and sinking were common findings in all five prostheses; no tendency was found dependent on a particular prosthesis. Radiolucency was recognized in 56.7% of all the joints. The incidence of revision surgery correlated with extension of the radiolucent zone around the femoral component. Radiolucency, located between the anterior flange and the anterior cortex of the femoral condyle, was recognized in 41.1% (anterior radiolucency) . It was more remarkable here than in other zones of interface between the femoral component and the femoral condyle. Anterior radiolucency was found in all five prostheses. Anterior radiolucency was radiographically classified into six types. It was found that revision surgery was performed more frequently in joints which demonstrated radiolucency of the following two of the six types: one that was parallel to the anterior flange with continuity to the anterior chamfer, and another that was also parallel to but without continuity to the anterior chamfer. The thickness of the radiolucent zone in the latter type was more than 2 mm. No relationship was observed between the installation angle and loosening of the femoral component. In summary, the author concludes that radiolucency is a common finding for the cementless TKA in rheumatoid patients, the presence of a thick anterior radiolucent zone would suggest the possibility of the necessity of revision surgery of the femoral component for actual or potential loosening.
