Functional outcome of knee arthroplasty is dependent upon the evaluation method employed

It is becoming increasingly important to evaluate surgical procedures beyond pain relief and implant survival. Patient satisfaction and objective functional assessment is now as relevant. The aim of this study was to establish the functional differences and patient perceptions between unicompartmental knee replacement (UKR) and total knee replacement (TKR). In a prospective study 52 TKR patients were compared to 24 UKR (at preoperative, 3, 6 months and 1 year postoperative). The disease specific KSS and Womac (pain and function subscores), the generic SF36 (pain, function and patient perception subscores) and the Dynaport^®Knee Test, a validated performance-based knee test using accelerometers to score function during activities of daily living, was utilized. Preoperative UKR patients had significantly higher KSS function and the Dynaport^®Knee Test (P < 0.05), but despite being younger, with different indication, they were not different to TKR with regards to function and pain subscores of Womac and SF36. Regarding preoperative perception, UKR patients reported better physical and social function but subjectively felt worse than TKR patients regarding health, emotion and mental status (n.s.). At one year, postoperative perception scores for both groups increased significantly, with UKR retaining functional lead and UKR patients also felt superior regarding health, emotion and mental status (n.s.). Postoperative recovery regarding KSS, Womac, and SF36-pain was steep only during the first 3 months with near equal values for both TKR and UKR. It was found that SF36-Function recovery was not significant, but UKR also scored higher than TKR. Only functional scores by the Dynaport^®Knee Test showed continued improvement and maintained the functional advantage of UKR patients throughout recovery. UKR and TKR patients have different age demographics, indications and perceptions, but clinical outcome scores do not equally capture these differences, especially with regards to function. Postoperative functional benefits of UKR seem to be due mainly to the superior preoperative conditions. Appreciation of recovery with generic, disease specific and functional measurements appears invaluable.