CONVERSION OF FAILED MODERN UNICOMPARTMENTAL ARTHROPLASTY TO TOTAL KNEE ARTHROPLASTY

Between January 1983 and January 1991, 29 patients (31 knees) with a f ailed Robert Brigham metal backed knee arthroplasty (Johnson & Johnson , Raynham, MA) underwent revision to a total knee arthroplasty (TI(A). Twenty-five patients had osteoarthritis, three avascular necrosis, an d one rheumatoid arthritis. The average patient age was 72.3 years (ra nge, 49-88 years), and the average weight was 179 lb. (range, 112-242 lb.). The interval between the primary and secondary index procedures averaged 62 months (range, 7-106 months), and mean postrevision follow -up period was 45 months (range, 24-104 months). The primary mechanism of failure of the UKA was tibial polyethylene wear in 21 knees and op posite compartment progression of arthritis in 10 knees. Sixteen knees had particulate synovitis with dense metallic staining of the synoviu m. At revision, the posterior cruciate ligament was spared in 30 knees and substituted in 1 knee. Restoration of bony deficiency at revision required cancellous bone-graft for contained defects in seven knees, tibial wedges in foul knees, and femoral wedges in two knees. No defec ts received structural allografts. The data suggest that failed, moder n unicompartmental knee arthroplasty can successfully be converted to TKA. In most cases, the posterior cruciate ligament call be spared and bone defects corrected with simple wedges or cancellous grafts. Moreo ver, the results of revision of failed unicompartmental knee arthropla sty are superior to those of failed TKA and failed high tibial osteoto my and comparable to the authors' results of primary TKA with similar- length follow-up periods. Although these results are encouraging, long er-term follow-up evaluation is required to determine survivorship of these revision arthroplasties.