Hip joint stress distribution changes depending on three-dimensional pelvic orientation: Finite-element analysis.

BACKGROUND: Pelvis experiences changes in its orientation due to the alignment of the hip joint and spine, and its orientation might affect both joints. Pelvic tilt on the sagittal plane has been widely discussed; however, the pelvis is oriented also on the coronal and horizontal planes. This study aimed to examine how stress distribution on intact hip joint changes under the three-dimensional pelvic orientation.

METHODS: Computed tomography data of five patients with unilateral pelvic girdle were analyzed. Thirteen models were evaluated by the MECHANICAL FINDER: neutral position at 0°; 10° and 20° anterior and posterior pelvic tilt; 10° and 20° pelvic hike and drop; 10° and 20° pelvic forward and backward rotation. Stress assessment was performed in four parts of the acetabulum: anterosuperior, posterosuperior, posteroinferior, and central parts.

RESULTS: Compared with the neutral position, the mean value of the equivalent stress and maximum principal stress in the anterosuperior part significantly increased by 1.51 times and 1.57 times at 20° posterior tilt, respectively. The maximum principal stress in the anterosuperior part significantly increased by 1.44 times at 20° hike. A significant increase of 1.45 times was found in the maximum principal stress in the anterosuperior part at 20° forward rotation.

CONCLUSIONS: Local stress accumulated in the anterosuperior acetabulum at the posterior pelvic tilt, pelvic hike, and pelvic forward rotation, which might lead to hip overload. The effect of posterior pelvic tilt appears to be greater for the hip joint than at the pelvic hike or forward rotation.