The effect of pelvic tilt on three-dimensional coverage of the femoral head: A computational simulation study using patient-specific anatomy.

Improved understanding of how three-dimensional (3D) femoral head coverage changes as the pelvic sagittal inclination (PSI) is altered would advance clinical diagnosis of hip pathoanatomy. Herein, we applied computer modeling of 3D computed tomography reconstructions of the pelvis and proximal femur to quantify relationships between the PSI and regional 3D femoral head coverage. Eleven healthy, young adult participants with typically developed hip anatomy were analyzed. The orientation of the pelvis was altered to define a PSI of -30° to 30° at 1° increments. Hip adduction and rotation were fixed in a standing position, which was measured by direct in vivo imaging of the pelvis and femur bones using dual fluoroscopy. Femoral head coverage was quantified in the anterior, superior, posterior, and inferior regions for each PSI position. Change in coverage was largest in the anterior region (29.8%) and smallest in the superior region (6.5%). Coverage increased linearly in the anterior region as the PSI increased, while a linear decrease was found in the posterior region and the inferior region (all p < .001). The slopes of the regression line for these regions were 0.513, -0.316, and -0.255, respectively. For the superior region, coverage increased when the PSI was altered from -30° to 5° and decreased when the PSI was larger than 5°. Overall, a 1° increase in PSI resulted in an increase of 0.5% in anterior coverage and a decrease of 0.3% in posterior coverage. Our findings provide baseline data that improve understanding of the effect of PSI on femoral coverage.