Contralateral Knee Alignment Parameters Have Limited Influence on Coronal Alignment Progression Compared With Ipsilateral Parameters in Patients With Knee Osteoarthritis

Objective To compare alignment parameters in bilateral lower extremities and evaluate the effect of contralateral limb on hip-knee-ankle angle (HKAA) longitudinally. Methods Native bilateral lower extremities of 3,045 Korean patients with long-leg radiographs were followed for progression of knee osteoarthritis. Concordance rates of Functional Knee Phenotypes (FKPs) and Coronal Plane Alignment of the Knee (CPAK), the proportion of patients with identical bilateral subtypes, were assessed. Varus, neutral, and valgus alignments were defined as baseline HKAA ≤177°, 177°< HKAA <183°, and HKAA ≥183°, respectively. Multivariable linear regressions for follow-up HKAA were conducted. Results Concordance rates for FKPs and CPAK were 41.6% (95% confidence interval: 39.9-43.4%) and 53.5% (51.7-55.2%), respectively, at baseline and 35.5% (33.8-37.2%) and 55.4% (53.7-57.2%) at a mean 4.0-year follow-up. Contralateral parameters, Kellgren-Lawrence grade ( P = 0.005) in bilateral varus group, medial proximal tibial angle (MPTA) ( P = 0.046) in ipsilateral varus-contralateral neutral group, MPTA, and mechanical lateral distal femoral angle in bilateral neutral ( P < 0.001; P = 0.012, respectively) and valgus ( P = 0.003; P = 0.004) groups, were associated with follow-up HKAA. However, their standardized β values were smaller than ipsilateral values. Conclusion Concordance rates of FKPs and CPAK between bilateral limbs were 41.6% and 53.5% at baseline, respectively. Contralateral parameters have limited influence on coronal alignment progression compared with ipsilateral parameters.