Medial unicompartimental knee arthroplasty : Indications and limits

Background: Medial unicompartmental knee arthroplasty (UKA) serves as an intermediary surgical intervention between osteotomy and total knee arthroplasty (TKA). Despite historical concerns regarding failure rates and restrictive selection criteria established in 1989, advancements in tribology and surgical technique have improved clinical outcomes to levels comparable with TKA.

Objective: This article evaluates the evolution of indications and contraindications for medial UKA, examining the impact of patient factors and surgeon experience on long-term implant survivorship.

Key Points: Modern evidence suggests that traditional contraindications, including age under 60, obesity, and asymptomatic patellofemoral chondrosis, do not significantly compromise outcomes. While inflammatory arthritis remains a definitive contraindication, ACL deficiency may be managed successfully in specific older populations. Optimal results are strongly correlated with surgical volume, specifically when UKA constitutes 20–50% of a surgeon's total knee replacement caseload. Technical precision is critical, as axial alignment must avoid overcorrection to prevent lateral compartment degeneration or undercorrection leading to polyethylene wear. The Unicompartmental Indication Score (UIS) provides a contemporary framework for patient selection, with scores exceeding 25 predicting superior clinical satisfaction.

Conclusion: Medial UKA is a highly effective treatment for localized osteoarthritis when performed with meticulous technique. Success depends less on strict adherence to historical age or weight limits and more on the surgeon’s proficiency and the relative proportion of UKA procedures within their clinical practice.