ALUMINA VERSUS POLYETHYLENE IN TOTAL KNEE ARTHROPLASTY

The cementless alumina total knee prosthesis, which uses alumina in the portions coming in contact with the bone and a combination of alumina and ultra-high molecular-weight polyethylene (UHMWPE) in the sliding portions, is referred to as a total condylar. Alumina total knee arthroplasty was performed on 137 patients, including 103 rheumatoid arthritis (RA) and 34 osteoarthrosis (OA) patients, from January 1982 to February 1985. The follow-up period was seven years 11 months and four years ten months, respectively. At follow-up evaluation, 108 patients were available for clinical and roentgenographic examinations, amounting to a 79% follow-up rate. At follow-up examination, 67 joints (62%) were completely pain free and 28 joints (26%) caused slight pain on bearing weight. Walking ability was recovered moderately in RA and markedly in OA. In RA, 14 of 84 knees were cemented and one knee was treated with loosening. Of 72 cementless implantations, 55 sustained displacing distally and one sustained loosening in the tibia, whereas 31 sustained displacing proximally and six sustained loosening in the femur. In OA, 21 cementless knees had 17 displacings in the tibia, and ten displacings and two loosenings in the femur. Scanning electron microscopy (SEM) observation of the UHMWPE surface in tibial plates revealed smoothing and burnishing. Alumina is far superior to metal for the sliding part, although it is not always best for the portion in contact with the bone. To resolve these problems, for cementless fixation, anchoring portions of Ti alloy and alumina implants were covered with beads and coated with hydroxyapatite. For cement fixation, "the interface bioactive bone cement technique" interposing hydroxyapatite granules between bone and cement was performed.