Dynamic patterns of varus deformity among osteoarthritic knees during computer-navigation assisted total knee arthroplasty and their surgical implications

Aims: The aims of this study were to (a) identify the dynamic patterns of varus deformity among osteoarthritic knees, (b) describe their surgical implications, and (c) compare post-operative lower limb alignment, clinical outcomes and satisfaction among patients with different deformity patterns managed intra-operatively based on deductions drawn from the same. Methods: Patients with primary osteoarthritis of the knee with an intra-articular varus deformity, undergoing computer-navigation assisted total knee arthroplasty using a sub-vastus approach and the "femur-first" measured resection technique between October 2019 and June 2020 were recruited. Following surgical exposure, the coronal knee deformity was assessed during full extension and 15°, 30°, 45°, 60°, 75°, and 90° of flexion. The levels of bony and/or soft-tissue pathology were identified based on the deformity pattern noted. Mechanical bone resection and indicated soft-tissue releases were performed. Post-operative alignment and outcomes were compared among knees with different deformity patterns. Results: In all, 127 patients (59.1 % women) with a mean age of 62.4 years were available for follow-up. The mean duration of follow-up was 24.7 months. Five patterns of varus deformity emerged, each indicating different levels of pathology: (i) pattern-1: the deformity increased on flexion, (ii) pattern-2: the deformity decreased on flexion, (iii) pattern-3: the deformity remained constant throughout flexion, (iv) pattern-4: the deformity increased initially, then decreased on flexion, and (v) pattern-5: the deformity decreased initially, then increased on flexion. Individualized soft-tissue release helped restore alignment within 3° of the mechanical axis in all knees. At the two years' follow-up, the clinical outcomes and patient satisfaction were comparable among patients with all deformity patterns. Conclusions: Knees with primary varus osteoarthritis demonstrate simple dynamic patterns of coronal deformity. An understanding of these patterns permits identification of the levels of pathology and helps in their optimal management, resulting in uniformly satisfactory outcomes.