The Bi-Surface total knee arthroplasty: minimum 10-year follow-up study

The Bi-Surface Knee System (Japan Medical Material, Kyoto, Japan), which has a unique ball-and-socket joint and whose femoral component is made from alumina ceramic, was designed to improve deep knee flexion and long-term durability after total knee arthroplasty. The purpose of this study was to review the clinical results of a minimum 10-year follow-up. Between 1989 and 1997, 507 total knee arthroplasties were carried out in 371 patients. Forty three patients (56 knees) were lost to follow-up. The mean age of the patients at operation was 68.5 years, and the patients were followed up for a mean of 11.7 years. The knees were evaluated on the basis of Knee Society knee score and functional score, radiographs, and Kaplan-Meier survivorship analysis. The knee score was improved from 38.9+/-17.4 points preoperatively to 93.3+/-7.8 points at the latest follow-up (p<0.001). The functional score was improved from 34.9+/-19.3 points to 52.7+/-24.1 points (p<0.001). The mean range of flexion was improved from 118.7+/-21.7 degrees to 124.2+/-20.8 degrees (p<0.001). The critical angle, which means the border to gain more range of flexion postoperatively, was 130.1 degrees. Kaplan-Meier survivorship at 10-year was 95.9% with any operation or radiographic failure as the end point. The corresponding rate was 97.4% with revision of any component as the end point. No ceramic component fracture occurred. The present study demonstrates that good range of flexion was maintained for a long time after total knee arthroplasty with excellent durability. The Bi-Surface Knee System appears to have achieved its design objectives.