Lateral unicompartmental knee arthroplasty through a medial approach. Surgical technique.

BACKGROUND: Unicompartmental knee arthroplasty of the medial compartment has excellent long-term clinical outcomes. Arthritis isolated to the lateral compartment is much less common; subsequently, the clinical outcomes of the treatment of that condition are less frequently reported. Most commonly, the lateral compartment is approached through a lateral arthrotomy. The purpose of this study was to determine the midterm results of lateral unicondylar replacement through a medial arthrotomy in patients with primary osteoarthritis or posttraumatic arthritis.

METHODS: From 1991 to 2004, forty-nine lateral unicompartmental knee arthroplasties were performed in forty-five patients by a single surgeon. One patient was excluded from the study because of a severe underlying neurologic condition. Lateral unicompartmental replacement was performed in thirty-eight knees with primary osteoarthritis and in ten knees with posttraumatic arthritis secondary to a tibial plateau fracture. Retrospective chart reviews and radiographic evaluations were performed, and Knee Society scores were determined.

RESULTS: The average Knee Society knee and function scores improved from 39 and 45 points, respectively, preoperatively to 89 and 80 points at an average of 5.2 years postoperatively. Preoperative alignment averaged 10 degrees of valgus, which was corrected to an average of 6.2 degrees of valgus postoperatively. There were no revisions and no notable soft-tissue complications. The mean postoperative knee and function scores were significantly better for patients with primary osteoarthritis (95 and 86 points, respectively) than they were for those with posttraumatic arthritis (74 and 65 points).

CONCLUSIONS: Lateral unicompartmental knee replacement through a medial approach provided durable and reliable short to midterm results. This approach is safe, effective, and extensile, making it a viable alternative to a lateral approach. The outcomes of lateral unicompartmental replacement in patients with posttraumatic arthritis can be expected to be inferior to those in patients with primary osteoarthritis.