Abstract 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 In the overall cohort, the HKAA exhibited robust correlations with WBLR ( r = −0.99, p < 0.001) and FTA ( r = 0.86, p < 0.001), validating FTA as a reliable global alignment surrogate. Stage‐dependent analysis revealed a change in the relative associations among determinants of deformity. In the early‐ and progressive‐stage groups, varus alignment was predominantly associated with bony parameters (MPTA and LDFA). Conversely, in the end‐stage group, the correlation between the joint line convergence angle and varus deformity strengthened significantly ( r = 0.61 vs. r = 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.
Ishibashi et al. (Wed,) studied this question.