Unicompartmental knee arthroplasty: long-term results

Unicompartmental knee arthroplasty has been controversial since its introduction in the early 1970s. Some initial reports suggested that medial compartment replacement did not yield good enough early results to be a viable long-term option, although lateral compartment replacement seemed to be promising. By the early 1980s, however, good initial results were being published for medial and lateral replacements and enthusiasm for the procedure began to increase. Refinements were made in patient selection, surgical technique, and prosthetic design. Ten-year followup studies were reported that showed survivorship was slightly less than that reported for total knee arthroplasty but acceptable considering the theoretically conservative nature of unicompartmental surgery. Unicompartmental knee arthroplasty now can be characterized as a procedure with a reliable 8- to 10-year outcome in properly selected patients with osteoarthritis who receive a skillfully implanted proper design. Unicondylar knee arthroplasty can be an attractive alternative to osteotomy or total knee arthroplasty especially some middle-aged women. Approximately all studies with followups of 10 years or greater show that unicompartmental knee arthroplasty will have inferior survivorship to total knee arthroplasty whether from loosening, prosthetic wear, or secondary degeneration of the opposite compartment in the second decade. Recently published 10-year results from two centers (one using a mobile-bearing design, the other using a fixed-bearing design) are comparable with those of total knee arthroplasty. This suggests that enhanced second-decade survivorship and therefore an expansion of the indications for unicompartmental knee arthroplasty are possibilities.