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.
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