Clinical outcome of unicompartmental knee arthroplasty and influence of alignment on prosthesis survival rate.

INTRODUCTION: Various factors that affect the longevity of unicompartmental knee arthroplasty (UKA) include patient activity level, habitus, competence of cruciate ligaments, postoperative alignment, implant positioning and ligament balancing. The purpose of this study was to evaluate the clinical outcome of the open standard UKA and establish the influence of radiological alignment on the survivorship of the prosthesis.

METHODS: We consecutively reviewed the results of 20 open standard UKAs performed in 17 patients between 1996 and 2000. A single implant type, the Press Fit Condylar Unicompartmental Knee System (DePuy, Leeds, UK), was used in all patients. All patients were evaluated clinically using the Knee Society Rating. Implant positioning and limb alignment were recorded in the standing long leg anteroposterior and lateral radiographs, and various angles were measured.

RESULTS: The alignment of the prosthesis was found to be good in 19 out of 20 operated knees. One knee with malalignment of prosthesis had to be revised at 23 months follow-up. There was a significant increase in Knee Society Rating of all patients, at a follow-up of 4-8 years. The Kaplan-Meier survival rate using revision to total knee arthroplasty as an endpoint was 91.7 percent.

CONCLUSION: The long-term outcome of UKA is influenced by positioning and alignment of the prosthesis. With proper patient selection and surgical technique, the outcome of UKA can be definitely improved.