Published online May 18, 2026. doi: 10.5312/wjo.v17.i5.118547
Revised: January 29, 2026
Accepted: February 27, 2026
Published online: May 18, 2026
Processing time: 133 Days and 13.7 Hours
Coronal plane malalignment of the knee secondary to knee osteoarthritis (OA) is known to influence ankle joint alignment. Although the direction and magnitude of ankle joint realignment are well studied, the knee deformity threshold beyond which the ankle will align outside the accepted neutral coronal plane alignment remains incompletely defined.
To investigate the relationship between knee and ankle joint alignments in the coronal plane in patients with primary knee OA, and to identify knee deformity thresholds beyond which ankle alignment exceeds the accepted neutral range.
This cross-sectional radiographic study included 845 lower limbs from 523 patients with primary knee OA. Coronal alignment was measured on long-leg standing radiographs as the hip to knee to ankle angle (HKAA) to assess knee deformity and the tibiotalar angle (TTA) to assess ankle joint alignment, with neutral alignment defined as 180° ± 2° for HKAA and 88.9° ± 3.0° for TTA. Associations between knee and ankle alignment were assessed using correlation analysis, categorical association testing, and multivariable regression. Direction-specific linear and logistic regression models were used to identify knee deformity thresholds associated with ankle malalignment. Analyses were adjusted for age, sex, and Kellgren-Lawrence grade.
Varus knee alignment was present in 74.8%, while valgus alignment was uncommon (5.0%). A significantly small-to-moderate association was observed between knee and ankle alignment categories (Cramér’s V = 0.19, P < 0.001), where varus ankle alignment was commonly observed with knee varus deformity and vice versa. HKAA and TTA demonstrated a moderate positive correlation (Spearman’s ρ = 0.396, P < 0.001), with an average increase of approximately 0.5° in TTA per 1° increase in HKAA. In multivariable linear regression, HKAA was the strongest independent predictor of TTA (β = 0.49, P < 0.001), while OA severity showed a smaller but significant inde
Coronal knee alignment is the primary predictor of ankle alignment adaptation in knee deformity secondary to primary OA, with varus deformity exerting a stronger and more predictable influence than valgus deformity. Clinically relevant ankle malalignment occurs at about four degrees of varus knee deformity, whereas valgus ankle malalignment requires about eight degrees of valgus deviation.
Core Tip: We investigated 845 lower limbs with primary knee osteoarthritis (OA) and detected an association between knee deformity and ankle joint alignment in the coronal plane. Varus knee alignment was the most commonly occurring and was strongly associated with varus ankle alignment, whereas valgus knees showed heterogeneous ankle adaptation. The hip to knee to ankle angle (HKAA) and the tibiotalar angle were moderately correlated, with knee alignment as the significant determinant of ankle alignment, independent of age and sex. OA severity (Kellgren-Lawrence grades) was associated with progressively greater varus alignment at the knee and ankle. The ankle joint will align beyond the accepted neutral range at specific HKAA thresholds of approximately 175.7° and 189.2° for varus and valgus knee deformity, respectively. These thresholds were consistent across sex and OA severity, underscoring the primacy of coronal knee alignment in driving ankle compensation.