Impact of leg length discrepancy on gait kinematics and biomechanics.

BACKGROUND

Leg length discrepancy (LLD) alters gait biomechanics and dynamic stability; however, the relationship between LLD magnitude and specific gait deviations remains incompletely understood.

RESEARCH QUESTION: This study investigated biomechanical compensatory mechanisms associated with anatomical LLD and examined how these strategies evolve as discrepancy magnitude increases.

METHODS

This retrospective cohort study included 74 patients with anatomical LLD who underwent three-dimensional gait analysis at a single institution. LLD was defined as the absolute difference in total leg length between the longer and shorter limbs. Pearson correlation analysis assessed associations between LLD magnitude and gait parameters, and segmented linear regression was used to identify non-linear thresholds in compensatory adaptations.

RESULTS

Increasing LLD was significantly correlated with mean pelvic obliquity, mean hip adduction, and mean ankle dorsiflexion (r = -0.697, -0.424, and 0.802, respectively; all p < 0.001). In gait kinetics, LLD magnitude was significantly associated with ankle plantarflexion power generation during stance (r = 0.513, p < 0.001). Segmented linear regression revealed non-linear compensatory patterns, with an early threshold for pelvic obliquity at approximately 18 mm and hip adduction at 24 mm, beyond which these compensatory mechanisms saturated. A later threshold was identified for distal ankle compensatory plantarflexion (vaulting), which increased markedly beyond 31 mm.

SIGNIFICANCE: Gait compensation in LLD follows a staged, non-linear progression characterized by distinct biomechanical thresholds. These findings provide objective biomechanical support for clinical decision-making and suggest that corrective interventions should be considered before complex compensatory mechanisms become established.