Increased knee flexion excursion during early stance is associated with reduced knee adduction moment in asymptomatic varus lower extremities: a cross-sectional study of 937 limbs.

Abstract

The aim of the study was (1) to identify gait parameters associated with knee adduction moment (KAM) and (2) to investigate the associations among early-stance knee flexion excursion, peak knee extension moment (KEM), and KAM. For 937 asymptomatic limbs, radiographic parameters including mechanical tibiofemoral angle (mTFA) were measured from long-leg radiographs, and gait analysis was conducted. Limbs were categorized into varus (mTFA ≥ 3°) (n = 221), neutral (-3°< mTFA < 3°) (n = 676), and valgus (mTFA ≤ -3°) (n = 40). Multivariable regressions using linear mixed models (LMMs) for positive KAM-time integral and maximum KAM, accounting for age, sex, and body mass index, were performed including radiographic and gait parameters. Associations among knee flexion excursion (θ), peak KEM, and KAM variables were analyzed using LMMs. Positive KAM-time integral and maximum KAM were associated with gait parameters (marginal R² = 0.510 and R² = 0.375, respectively), such as knee varus angle. Among gait parameters associated with reduced KAM, increased external rotation (ER) of tibia (17.3° vs. 12.7°, P = 0.031) and foot progression angle (FPA) (11.2° vs. 7.9°, P = 0.011) were greater in varus compared to valgus group. θ was greater in varus (15.1°) than neutral (14.2°, P = 0.011) or valgus (12.6°, P = 0.032) limbs. θ was associated with early-stance peak KEM (β=+10.542; 95% confidence interval, 9.006-12.079), positive KAM-time integral (β = -6.300, -10.791 to -1.808), but not with maximum KAM (β = -1.226, -3.260-0.808). Varus limbs displayed increased ER of tibia and FPA, which may be gait adaptations to reduce KAM. Increased early-stance knee flexion excursion in varus limbs was associated with increased peak KEM and reduced positive KAM-time integral.