Title: Gait-and posture-related factors associated with changes in hip pain and physical function in patients with secondary hip osteoarthritis: a prospective cohort study ABSTRACT Objective: To identify gait-and posture-related factors associated with changes in hip pain and physical function in patients with hip osteoarthritis (OA). Design: Prospective cohort study Setting: Clinical biomechanics laboratory of a university Participants: Consecutive sample of 30 female patients with mild-to-moderate secondary hip OA. Main Outcome Measures: Hip pain (visual analog scale) and physical function (physical component summary of the 36-Item Short Form Health Survey) were measured at baseline and 12 months later. With changes in hip pain and physical function as dependent variables, linear regression analyses were performed with gait-and posture-related factors as independent variables with and without adjustment for age, joint space width, and hip pain or physical function at baseline. Posture-related factors included angle of thoracic kyphosis, lumbar lordosis, sacral inclination, spinal inclination, and spinal mobility. Gait-related factors were gait speed, steps/day, and three-dimensional hip joint angles, external hip joint moment impulses, and daily cumulative hip moments. Results: Multiple linear regression analyses showed that less hip extension (adjusted standardized B coefficient [95% CI]; −0.51 [−0.85 to −0.17]) and less external rotation angle (−0.52 [−0.88 to −0.17]) during gait were associated with worsening of hip pain. A larger thoracic kyphosis (−0.54 [−0.99 to −0.09]), less sacral anterior tilt (0.40 [0.01 to 0.79]), less thoracic spine mobility (0.59 [0.23 to 0.94]), less steps/day (0.53 [0.13 to 0.92]), and slower gait speed (0.45 [0.04 to 0.86]) were associated with deterioration of physical function. Conclusions: Gait-and posture-related factors should be considered when assessing risk and designing preventive interventions for clinical progression of secondary hip OA.