Unicompartmental Knee Arthroplasty in Spontaneous Osteonecrosis of the Knee: A Narrative Review of Indications, Techniques, and Outcomes.

Spontaneous osteonecrosis of the knee (SONK) is a painful condition characterized by localized subchondral bone necrosis, predominantly affecting the medial femoral condyle in older adults. While total knee arthroplasty (TKA) is a definitive solution, unicompartmental knee arthroplasty (UKA) has emerged as a bone and ligament preserving alternative for this typically unicompartmental disease. This narrative review synthesizes current evidence on the indications, techniques, and outcomes of UKA for SONK. In well-selected patients, those with isolated condylar involvement, intact ligaments, correctable deformity, and a lesion size <50% of the condyle, UKA demonstrates excellent outcomes, including significant improvements in knee scores, high patient satisfaction (91-97%), and favorable 10-year survivorship (89-97%). Advantages over TKA include faster recovery, lower morbidity, and preservation of native kinematics. However, success is contingent upon strict adherence to these selection criteria, as UKA is contraindicated in inflammatory arthritis, metaphyseal extension, or significant patellofemoral arthritis. Technical execution must address challenges like bone defects and precise component alignment to mitigate risks of bearing dislocation or subsidence. Ultimately, UKA represents a successful joint-preserving strategy for appropriate candidates with SONK, although future work is needed to establish long-term data and refined guidelines.