High tibial osteotomy vs. unicondylar arthroplasty: clearly not two for the same!

Background: Medial compartment osteoarthritis is the most prevalent form of knee arthropathy. While high tibial osteotomy (HTO) and medial unicondylar knee arthroplasty (UKA) are established treatments, clinical controversy persists regarding their differential indications, comparative outcomes, and the complexities associated with subsequent conversion to total knee arthroplasty.

Objective: This review aims to delineate the specific indication criteria, patient selection parameters, and clinical limitations of HTO and UKA to facilitate evidence-based surgical decision-making for unicompartmental knee disease.

Key Points: HTO is primarily indicated for metaphyseal varus deformities in younger, active patients, focusing on extra-articular realignment to offload the medial compartment. Success depends on precise frontal plane correction, with a medial proximal tibial angle (MPTA) exceeding 94° associated with higher failure rates. Conversely, UKA is indicated for anteromedial osteoarthritis with intact ligamentous structures, regardless of patient BMI. While UKA offers superior early functional recovery and higher patient satisfaction compared to total knee arthroplasty, registry data indicate higher revision rates in patients under 65 years. Complications for HTO include a 30% overall rate, involving lateral hinge fractures and non-union, whereas UKA risks include aseptic loosening and polyethylene dislocation. Conversion of either procedure to total knee arthroplasty is technically demanding, often requiring revision-style implants and resulting in inferior functional outcomes compared to primary arthroplasty.

Conclusion: HTO and UKA are complementary rather than competing procedures. Precise patient selection based on deformity location, ligamentous stability, and joint line orientation is essential to optimize long-term joint preservation and clinical performance.