Is there a correlation between pelvic incidence and orientation of the acetabulum? An analysis based on a three-dimensional statistical model of the pelvic ring

Abstract

The pelvic ring is a complex anatomical structure building up the connection between the trunk and the legs. Whilst there is a broad discussion in the literature about the dynamic interaction between spine, pelvis and the hip joints, there is still little information about the relation and interaction of the constant pelvic parameters. Based on a three-dimensional (3D) statistical model consisting of 150 uninjured and bony healthy pelves (100 Europeans, 50 Japanese; 81 males, 69 females; average age 74.3 years ± 17.5 years) an evaluation of pelvic incidence (PI) and acetabular orientation in anteversion and inclination was performed and potential correlations of these intraindividual constant parameters were investigated. Pelvic incidence is defined as the angle between the perpendicular to the sacral plate at its midpoint and the line connecting this point to the middle axis of the femoral heads. Acetabular anteversion is defined as the angle between the perpendicular to the best-fit plane on the acetabular rim and the coronal plane measured in strict lateral view. Acetabular inclination is defined as the angle between the perpendicular to the best-fit plane on the acetabular rim and the sagittal plane in strict frontal view. Data were further analysed with regard to different subgroup's age, sex and ethnicity. A positive correlation between PI and acetabular anteversion could be demonstrated. Further, PI and also the acetabular parameters anteversion and inclination were found to be significantly higher in the European individuals than in the Asian. The results of the present study demonstrate a relation between the anatomical configuration of the constant pelvic parameters building up the connection points to the next proximal respectively caudal skeleton section. The findings might lead to more comprehensive treatment strategies in case of trauma or degenerative pathologies of the pelvis in the future.

Keywords: 3D statistical model; acetabular anteversion; acetabular inclination; acetabular orientation; pelvic incidence; pelvic ring.

FIGURE 1

3D statistical model of the pelvic ring. The figure shows the mean model with the perpendicular to the sacral plate at its geographical midpoint (red line), the best‐fit balls inside the acetabular cavity (light blue) and the axis connecting the acetabular centre with the midpoint of the sacral plate as well as the interacetabular axis (blue lines). Based on these lines PI and PI 3D were calculated. 3D, three‐dimensional; PI, pelvic incidence.

FIGURE 2

Coordinate system within the 3D model of two individual pelves established based on the anterior pelvic plane. Anteversion angle is built up by the red lines in strict lateral view and the y‐axis (b, d), inclination angle is built up by the red lines in ap view and the y‐axis (a, c). 3D, three‐dimensional.

FIGURE 3

Frequency analysis of all samples included (n = 150) and comparison between (a) males and females, (b) comparison between Europeans and Japanese and (c) comparison between individuals ≤65 years and >65 years.

FIGURE 4

Correlation between PI and PI 3D; red = female, blue = male, triangle = European, circle = Japanese, filled = ≤65 years, unfilled = >65 years. 3D, three‐dimensional; PI, pelvic incidence.

FIGURE 5

Correlation between anteversion and PI; red = female, blue = male, triangle = European, circle = Japanese, filled = ≤65 years, unfilled = >65 years. PI, pelvic incidence.

FIGURE 6

Correlation between inclination and PI; red = female, blue = male, triangle = European, circle = Japanese, filled = ≤65 years, unfilled = >65 years. PI, pelvic incidence.

FIGURE 7

Correlation between anteversion and PI 3D; red = female, blue = male, triangle = European, circle = Japanese, filled = ≤65 years, unfilled = >65 years. PI, pelvic incidence. 3D, three‐dimensional; PI, pelvic incidence.

FIGURE 8

Correlation between inclination and PI 3D; red = female, blue = male, triangle = European, circle = Japanese, filled = ≤65 years, unfilled = >65 years. PI, pelvic incidence. 3D, three‐dimensional; PI, pelvic incidence.

FIGURE 9

Correlation between anteversion and inclination; red = female, blue = male, triangle = European, circle = Japanese, filled = ≤65 years, unfilled = >65 years.