Preoperative considerations and how I perform a fixed bearing Lateral Unicompartmental Knee Arthroplasty

Background: Lateral unicompartmental knee arthroplasty (LUKA) remains underutilized compared to total knee arthroplasty for treating isolated lateral compartment osteoarthritis (OA), despite its potential to preserve joint kinematics and cruciate ligament integrity. While population-based data suggest that approximately 10% of knee OA involves the lateral compartment, surgical utilization rates reported in arthroplasty registries remain historically low.

Objective: This article describes the clinical indications, radiographic assessment, biomechanical principles, and specific surgical techniques required to achieve successful outcomes in LUKA.

Key Points: Appropriate patient selection requires bone-on-bone lateral OA, a functionally intact anterior cruciate ligament, and a correctable valgus deformity indicating a competent lateral collateral ligament. Contraindications include inflammatory arthritis, severe patellofemoral OA, and significant flexion contractures exceeding 20 degrees. Biomechanically, the lateral compartment exhibits greater physiological laxity in flexion compared to the medial side; therefore, surgical balancing should not aim for symmetric gaps. Technical precision is required for the sagittal tibial cut, often performed via a partial vertical split of the patellar tendon, and for femoral component positioning to avoid patellar impingement. Fixed-bearing implants with cementless femoral and cemented tibial fixation are utilized to resurface the compartment while restoring the patient's pre-disease alignment.

Conclusion: LUKA is a viable, bone-sparing alternative to total knee arthroplasty for isolated lateral OA. Success depends on strict adherence to selection criteria, preservation of natural ligamentous tension, and specialized surgical techniques that accommodate the unique kinematic properties of the lateral compartment.