Purpose: Hip osteoarthritis (OA) is a chronic disease; however, the mechanical risk factor during gait for hip OA progression has not been identified. The purpose of this study was to evaluate the association between mechanical load during gait at baseline and subsequent radiographic progression of hip OA over 12 months. Methods: Fifty patients with secondary hip OA except for end-stage hip OA participated in this prospective cohort study. To assess the change in joint space width (JSW), films at baseline and approximately 12 months later were paired by patients but blinded as to patient and sequence to the reader to avoid bias. Radiographic progression of hip OA was defined as reduction of more than 0.5 mm per year in JSW. Intrarater reliability [ICC (1,1)] of the JSW measurement was 0.99, and minimum detectable change of the JSW was 0.39. With radiographic progression of hip OA as dependent variable (yes/no), univariate and multivariate logistic regression analyses were performed. Independent variables were age, body weight, hip pain (visual analog scale), radiographic variables (CE angle, Sharp angle, acetabular head index, and acetabular roof obliquity), hip impairments (range of motion and muscle strength), and gait-related variables. Gait-related variables were recorded using an 8-camera Vicon motion system at a sampling rate of 200 Hz, and using force plates at a sampling rate of 1,000 Hz. A total of 20 reflective markers were placed by a single experienced examiner. At least 3 successful trials for each patient were recorded for analysis. Gait-related variables included steps per day, gait speed, peak hip joint moment, hip joint moment impulse, and daily cumulative hip load in 3 planes. The number of steps was recorded by a pedometer for 7 consecutive typical days within a month from the day of gait analysis. Daily cumulative hip load was calculated as a product of the non-normalized hip moment impulse in each of 3 planes and the mean number of steps per day for the affected limb (number of steps/day divided by 2). The criterion for inclusion in multivariate analysis was P < 0.1 in univariate logistic regression analysis. Since age and body weight at baseline can be potential confounders, those 2 variables were included in the multivariate model. A P value < 0.05 was considered statistical significant. Results: Of the 50 patients, 21 (42.0%) were classified into the progression group. Change in JSW in the progression group was 1.3 ± 0.8 mm. In univariate logistic regression analysis, increased daily cumulative hip load in the frontal plane at baseline was significantly associated with progression of hip OA (p = 0.038). On average, the cumulative hip load in the frontal plane in the progression group was approximately 1.4 times higher than that in the no progression group (Fig. 1). Minimum JSW (p = 0.066) and steps per day (p = 0.062) were also potential variables for multivariate logistic regression analysis (Fig. 1). The correlation coefficient (ρ = 0.74) between steps per day and daily cumulative hip load in the frontal plane was over the threshold for multicollinearity. Therefore, minimum JSW and daily cumulative hip load in the frontal plane were entered into multivariate logistic regression analysis. In multivariate analysis, reduced minimum JSW and increased daily cumulative hip load in the frontal plane at baseline were associated with radiographic hip OA progression independently. Even after adjustment for age and body weight, minimum JSW and daily cumulative hip load in the frontal plane were remained in the model (Table 1). Conclusions: This study provides evidence that higher daily cumulative hip load at baseline, particularly in the frontal plane, is associated with radiographic progression of hip OA defined by a > 0.5-mm cartilage thickness loss in 12 months. Our findings will help identify patients with higher risk of hip OA progression and clarify the target of intervention to slow hip OA progression.Table 1Multivariate logistic regression predicting the progression of hip osteoarthritisOR (95% CI)P-valueOR (95% CI) adjusted for age and body weightP-valueMinimum JSW at baseline (mm)0.63 (0.40–0.99)0.0460.49 (0.25–0.94)0.031Daily cumulative hip load in frontal plane (kNm seconds)1.02 (1.00–1.04)0.0301.03 (1.01–1.05)0.013 Open table in a new tab