Agreement Between Hip Joint Center Estimation Methods and Comparisons of Dependent Hip, Thigh, and Knee Angles.

Hip joint center (HJC) location estimation influences dependent angles and clinical interpretations. We examined the agreement between 6 HJC estimation methods; compared hip, thigh, and knee angles; and explored HJC location and thigh angle associations. Pelvis markers were used to estimate HJC location via 6 popular methods using Harrington's method as the reference standard. HJC limits of agreement analysis and inferential angle comparisons during standing revealed that Bell's (HJC bias range = 0-11 mm, hip angle difference range = -0.2° to 0.1°) and Vaughan's (HJC bias range = -5 to 41 mm, hip angle difference range = -0.5° to -5.3°) methods were most and least like Harrington's but varied by dimension. Stepwise regression showed that anterior-posterior, medial-lateral, and anterior-posterior HJC coordinate differences best explained sagittal (R2 range = .95-.99, P < .001), frontal (R2 range = .83-.99, P < .001), and transverse (R2 range = .54-.72, P < .001) thigh angle differences, respectively. Different HJC methods caused several large sagittal but more minor frontal and transverse plane differences. We urge caution when using different HJC methods.