Advanced radiographic osteoarthritis is associated with 5-year coronal varus progression in alignment and bone morphology in a community-based cohort of older adults

Abstract

Purpose: This study aimed to quantify 5-year changes in coronal lower limb alignment and evaluate their associations with baseline osteoarthritis severity. Methods: In the Nagahama cohort, adults ≥60 years underwent weight-bearing knee radiographs at baseline and 5 years later. Alignment parameters included the anatomical lateral distal femoral angle (aLDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA) and femorotibial angle (FTA). Changes were tested using paired t tests, and associations were modelled using Gaussian generalized linear models adjusted for age, sex, body mass index and baseline Kellgren–Lawrence (K–L) grade. Group differences among K–L ≤ 1, 2 and ≥3 were tested by one-way analysis of variance with Tukey's Honestly Significant Difference, and within-group correlations were assessed using Pearson's coefficient. Results: A total of 2974 knees were analysed. Baseline K–L grades were: 0: 164 (5.5%), 1: 1975 (66.4%), 2: 694 (23.3%), 3: 135 (4.5%) and 4: 6 (0.2%). Over 5 years, FTA increased by 0.3° (p < 0.001). aLDFA also shifted 0.3° toward the varus (p < 0.001), whereas MPTA and JLCA remained stable. A higher baseline K–L grade was independently associated with varus progression, particularly when driven by decreased MPTA and increased JLCA. Consistent with the multivariable analysis, the K–L ≥ 3 group exhibited a significant MPTA decrease and a 2.6° varus shift in FTA. By contrast, K–L ≤ 2 groups showed no significant change in MPTA, whereas FTA showed a slight varus shift with a modest JLCA increase. In all subgroups, FTA change correlated with changes in aLDFA (r = 0.48–0.54), MPTA (r = −0.55 to −0.46) and JLCA (r = 0.21–0.48), with all p < 0.001. Conclusions: Coronal alignment shifted slightly toward varus over 5 years. In advanced OA, progression reflected a decreased MPTA and increased JLCA, with a modest aLDFA increase. Level of Evidence: Level I, prognostic studies—high-quality prospective cohort study.