Study of the human pelvis using CAT-scan: gender differences and anatomy of the ramus ossis ischii

In a descriptive study we present the CAT-scan norm data of pelvic sizes in Caucasian men and women. The study was performed to investigate possible differences in pelvic sizes between men and women and the inter-individual range of pelvic sizes. The data may be useful as a guide in the development of orthoses and prostheses.

Pelvis CAT-scans of 40 subjects, 20 males (23-66 years) and 20 females (20-72 years) were investigated. The research was approved by the regional ethics committee.

The angle of the ramus ossis ischii (ROI) with the line of progression in the transverse plane (angle a) was 38.6 degrees (SD 3.4) in females and 31.8 degrees (SD 4.4) in males. This difference was statistically significant (Student's t-test (p < 0.0001). The ROI angle in the coronal plane (angle b) was negative or zero both in males and females. The horizontal distance between the medial border of the ROI and the lateral border of the femur (RF distance) was slightly smaller in females (95 mm) compared to males (107 mm), but this difference was not statistically significant. The distance between the midfemoral line and the anterior surface of the leg was also slightly smaller in females (89 mm) than in males (106 mm) but the difference was not statistically significant. We found a linear relation between the total AP soft tissue distance and the soft tissue circumference of the proximal leg at the level of the ROI.

There are significant gender differences in pelvic size and shape. The medial plane of the ROI is not in a slight angle of inclination towards the midline but appears to be zero. The medial contour of the ROI in the AP direction is slightly curved.