REVIEW OF 20 YEARS OF EXPERIENCE

Costs and risks of implantation of prosthetic knee joints are analyzed in this retrospective study. From 1974-1993 514 primary and 34 revisi on arthroplasties were done in this hospital, all by the same surgeon. 98% of the patient protocols were available and analyzed, but no syst ematic follow-up was attempted. 82% of the patients were female; mean age at operation was 74 years. Joint destruction was caused by osteoar thritis in 75%, aseptic osteonecrosis in 10%, rheumatoid arthritis in 9% and posttraumatic arthritis in 3.5%. 75% of the patients were obese and had a body mass index >25 kg/m(2). Non-constrained unicompartment al type prostheses were used in 66%, the non-constrained multicompartm ental type in 10% and the constrained total rotation knee (Engelbrecht ) in 24%. Hospital mortality rate was 0.55% due to myocardial infarcti on and pulmonary embolism. 3 patients died of septic prosthetic joint infections 5, 7 and 7 1/2 years after surgery. Peri-operative morbidit y, typical of the age group above 70 years, was mainly due to cardiova scular and thromboembolic events and gastrointestinal bleeding. Early infection during the first postoperative year was encountered in 3 con strained total knees, but none in non-constrained type. The calculated operative infection rate was 2.4% for the constrained type, zero for the non-constrained type, and 0.5% for the whole series. Late prosthet ic infections occurred in 8 patients up to 12 years after surgery. In comparing non-constrained unicondylar and hinged types of joint replac ement, the non-constrained sledge prosthesis involves considerably low er costs in terms of duration of surgery, hospital stay, blood loss, p rice of the implant, infection rate and difficulties of revision arthr oplasty. Lower costs and risks favour the smaller unicondylar implant for use in localized degenerative or necrotic destruction, particularl y of the medial compartment of the knee. Semi-constrained total condyl ar systems are used for more extensive degeneration without evident in stability. The indication for hinged endoprostheses is restricted to r evision arthroplasty and grossly unstable knees.