Unrestricted Kinematic Alignment Is a Feasible Strategy for Lateral Compartment Osteoarthritis: Short-Term Outcomes of a Contralateral Knee-Referenced Approach

Background/Objectives: Although unrestricted kinematic alignment (uKA) has gained increasing acceptance in total knee arthroplasty (TKA), its application in knees with lateral compartment osteoarthritis (OA) remains a subject of debate due to concerns over postoperative gap imbalance and alignment outliers. The purpose of this study was to evaluate the surgical, radiographic, and clinical outcomes of contralateral non-OA knee–referenced, caliper-verified uKA in lateral compartment OA. Methods: This retrospective study included 40 patients with isolated lateral compartment OA who underwent primary TKA using contralateral non-OA knee–referenced, caliper-verified uKA. Surgical outcomes were assessed by measuring bone resection thicknesses of the distal femur, posterior femur, and proximal tibia, as well as extension and 90° flexion gaps. Radiographic outcomes included mechanical hip–knee–ankle angle, medial proximal tibial angle, lateral distal femoral angle, and Coronal Plane Alignment of the Knee (CPAK) classification. Patient-reported outcomes (PROs), including Pain VAS, EQ-5D, satisfaction, and Forgotten Joint Score, were assessed at a minimum follow-up of 2 years. Results: The resected osteochondral thickness was consistently greater on the medial side than on the lateral side, and all gap balances were well maintained, with a gap difference ≤ 2 mm observed in 95% of knees in full extension. Postoperatively, restoration to the same CPAK category was achieved in approximately 90% of cases. All PROs improved and reached levels comparable to those of the contralateral knee. Conclusions: In patients with lateral compartment OA, caliper-verified uKA may be appropriately applied when guided by a reliable anatomic reference, such as the contralateral non-OA knee. This strategy achieves stable soft-tissue balance, reliable coronal alignment restoration, and favorable clinical outcomes in carefully selected valgus knees undergoing TKA.