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

Abstract

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.

Can measurements from an anteroposterior radiograph predict pelvic sagittal inclination?

“…To be retained in the final model, a component had to be statistically significant at the 0.05 level and account for at least 5% of the variance in each parameter. 4 Correlation coefficients (r) >.8 were considered to be very strong. 22 After the regression model was determined for each parameter using the mean of all the participants, the model was applied to each individual to quantify error in the estimation of PSI from each radiographic parameter.…”

“…The horizontal axis of the APP was set as a line connecting bilateral ASIS. PSI was defined as the angle between the APP and the vertical line of the body on the sagittal plane of the pelvis, as described previously 4,8,9 . Anterior rotation of the pelvis was set as a positive PSI whereas a posterior rotation was set as a negative PSI (Figure 1).…”

“…A polynomial regression analysis was employed to fit the data with an appropriate model to clarify the relationship between each parameter and PSI. To be retained in the final model, a component had to be statistically significant at the 0.05 level and account for at least 5% of the variance in each parameter 4 . Correlation coefficients ( r ) >.8 were considered to be very strong 22 .…”

“…PSI was defined as the angle between the APP and the vertical line of the body on the sagittal plane of the pelvis, as described previously. 4,8,9 Anterior rotation of the pelvis was set as a positive PSI whereas a posterior rotation was set as a negative PSI (Figure 1). As the PSI defined herein was computationally determined from the 3D surface models of the pelvis, it was set as the gold-standard and was used to compare with the predictions made by the regression models.…”

“…However, previous studies have reported that the inclination of the pelvis in the sagittal plane (pelvic sagittal inclination [PSI]) changes with patient posture and is altered after hip surgery. Understanding how PSI changes in several postures is important as it affects the measurements of femoral head coverage 1‐4 as well as the functional location of the acetabular cup in the setting of total hip arthroplasty (THA) 5,6 . As abnormal changes in PSI lead to progression of hip osteoarthritis and dislocation of the hip, 7,8 many studies have quantified PSI in different postures, with some of these including a large clinical cohort, 8,9 and a postoperative period of more than 10 years 10 …”