Quantitative analysis of bony and soft tissue contributions to varus deformity across knee osteoarthritis stages

Purpose: To investigate the relationships among lower limb alignment parameters and quantitatively clarify the stage-dependent contributions of bony morphology and soft tissue laxity to varus deformity across knee osteoarthritis stages. Methods: We analysed 1346 knees of 673 participants in a community-based cohort. Radiographic parameters, including the hip-knee-ankle angle (HKAA), weight-bearing line ratio (WBLR), femorotibial angle (FTA), medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA) and joint line convergence angle, were measured using full-length standing radiographs. Spearman's correlation coefficients and linear regression analyses were performed for the overall cohort and stratified subgroups: early- (Kellgren-Lawrence Grade [KLG] 0-1), progressive- (KLG 2) and end-stage (KLG 3-4). Results: = 0.20 in the early stage). Conclusions: While bony deformity is a consistent factor, the contribution of soft tissue laxity (joint line convergence angle) becomes substantial in end-stage osteoarthritis. In end-stage osteoarthritis, the joint line convergence angle is a key alignment determinant. Surgical planning for joint-preserving procedures, including high tibial osteotomy, must account for this quantitative confirmation of stage-dependent differences to prevent reducible soft tissue component overcorrection. Level of Evidence: Level III.