Lateralized ankle positioning deficits at initial contact distinguish affected limbs in Hoehn-Yahr stage 1 Parkinson's disease.

OBJECTIVE: Gait impairment emerges early in Parkinson's disease (PD), yet quantitative kinematic characterization at Hoehn-Yahr (H-Y) stage 1 remains limited. This study examined lateralized gait deficits to identify early motor control biomarkers. METHODS: This cross-sectional study enrolled 30H-Y stage 1 participants with PD and 20 age-/sex-/BMI-matched healthy controls (controls). Three-dimensional gait analysis during the medication OFF state assessed spatiotemporal parameters, joint kinematics (hip/knee/ankle angles), and Gait Deviation Index (GDI). Within-PD limb comparisons (affected vs. relatively unaffected) used paired t-tests; between-group comparisons (each PD limb vs. controls) used independent-samples t-tests. RESULTS: The affected limb demonstrated a distinctive plantarflexed ankle position at initial contact (-1.25 ± 5.61°) compared with the relatively unaffected limb (2.50 ± 4.20°; Δ=-3.75°, 95% CI -6.15 to -1.35°, p = 0.003, Cohen's d = 0.580) and controls (2.35 ± 4.24°; Δ = -3.61°, p = 0.003). The relatively unaffected limb did not differ from controls (p = 0.888), confirming deficit specificity to the affected limb. Both PD limbs showed shorter stride length and lower walking velocity than controls (all Bonferroni-adjusted p < 0.020), as well as reduced peak hip extension (all Bonferroni-adjusted p < 0.006). CONCLUSION: H-Y stage 1 PD exhibits a lateralized plantarflexed ankle position at initial contact in the affected limb, alongside bilateral gait abnormalities relative to controls. Quantitative initial-contact analysis may provide a complementary marker of early motor dysfunction.