Large joint line convergence angle is associated with accelerated coronal alignment progression in osteoarthritic knees: A longitudinal analysis of 10,841 knees

PURPOSE: Coronal knee alignment, determined by both joint line orientation and morphology of femur and tibia, alters with osteoarthritic progression, but its rate of change has not been systematically evaluated. This study aimed to categorise limbs according to the rate of hip-knee-ankle angle (HKAA) alteration and identify factors associated with accelerated alignment progression. METHODS: 10,841 limbs from a tertiary hospital were analysed. Alignment parameters and Kellgren-Lawrence (K-L) grades were measured on standing long-leg radiographs. Limbs were grouped by baseline HKAA as varus (HKAA ≤ 177°), neutral (177° < HKAA < 183°), or valgus (HKAA ≥ 183°). Accelerated and mild progression were defined as ≥ 0.50°/year and < 0.50°/year, respectively. Factors associated with accelerated coronal alignment progression were analysed using multivariable logistic regression. RESULTS: Accelerated varus and valgus progression occurred in 34.0% (95% CI: 32.8%-35.1%) of the varus and 25.7% (21.2%-30.7%) of the valgus category, respectively. After adjustment for age, sex, and body mass index, greater baseline varus alignment, medial proximal tibial angle, and joint line convergence angle (JLCA) were associated with increased odds of accelerated varus progression by 4.9% (4.8%-5.0%), 10.8% (10.6%-10.9%), and 12.9% (12.7%-13.1%), respectively, in the varus category (n = 6519; AUC = 0.823). Higher K-L grade was associated with increased risk of accelerated varus progression compared with Grade 0 (I: 44.8% [44.5%-45.0%], II: 88.9% [88.6%-89.2%], III: 391.8% [346.1%-443.5%], and IV: 378.0% [305.0%-468.5%]; all p < 0.001). In the valgus category (n = 343), greater baseline HKAA and medially-opened JLCA increased the risk of accelerated valgus progression by 17.4% (3.6%-33.5%) and 19.4% (9.2%-28.8%), respectively (AUC = 0.756). CONCLUSIONS: Approximately one-third of limbs with baseline HKAA ≤ 177° and about one-quarter of those with HKAA ≥ 183° exhibited ≥0.50° progression toward varus and valgus, respectively. Accelerated alignment change was associated with greater baseline HKAA, JLCA and higher baseline K-L grade, suggesting characteristics of this potential phenotype. LEVEL OF EVIDENCE: Level III.