Relationship between knee and hindfoot coronal alignment in community-dwelling Japanese adults: Cross-sectional analysis of 1000 hip-to-calcaneus radiographs.

Abstract

Hindfoot compensation for coronal knee deformity is recognized in end-stage osteoarthritis (OA), but evidence in non-surgical populations is limited. This study aimed to clarify the independent association between knee and hindfoot coronal alignment and to identify factors related to hindfoot compensation in community-dwelling adults. In this cross-sectional study, adults aged ≥40 years underwent bilateral hip-to-calcaneus radiography. Knee varus angle, hindfoot valgus angle, medial distal tibial angle, and talar tilt angle were measured. Knee OA was defined as Kellgren-Lawrence grade ≥2. Simple linear regression evaluated univariate associations between the hindfoot valgus angle and the knee varus angle. Generalized linear mixed models assessed independent associations, adjusting for other radiographic parameters and participant characteristics. We analyzed 1006 legs from 509 participants (66% female; median age, 71 years). Median knee varus and hindfoot valgus were 2.3° and 1.3°, respectively. Knee OA was observed in 526 (52%) legs. Knee varus angle was positively associated with hindfoot valgus angle in both univariate (β = 0.26, P < 0.001) and multivariate analyses (β = 0.19, P < 0.001). Varus knee OA (β = 1.03, P < 0.001) was also independently associated with increased hindfoot valgus angle. Approximately 30% of varus knee OA cases exhibited varus hindfoot, indicating absent compensation. In community-dwelling older adults, hindfoot valgus increased with increasing knee varus, supporting the physiological coronal-plane compensation, although substantial individual variability was observed. Knee OA was independently associated with hindfoot valgus. These findings provide data for clinical assessment in patients with knee OA.