Computed tomography analysis of acetabular anteversion and abduction

Purpose: The purpose of this study is to define the normal range of acetabular abduction and anteversion in relation to pelvic anatomy as depicted on conventional CT scan. Metods: We retrospectively reviewed 100 pelvic CT scans performed on patients presenting for evaluation of non-orthopaedic pathology. The study group consisted of 58 women and 42 men, aged between 18 and 88 years. Standard imaging protocol included an anteroposterior (AP) topogram with contiguous 5-mm thick axial images from the superior margin of the iliac crest to the lesser trochanter of the femur. The acetabular abduction was measured from the AP topogram by obtaining the angle between a line drawn from the acetabular teardrop to the lateral acetabular margin and a horizontal line between the ischial tuberosities. Acetabular anteversion was measured on axial images at the level of the mid-femoral head. Results: We found the mean acetabular abduction to be 39 degrees (standard deviation 4 degrees, range 27 to 51 degrees) and the mean acetabular anteversion to be 23 degrees (standard deviation 5 degrees, range 12 to 39 degrees). Data suggests that acetabular anteversion may average 2.7 degrees lower in males than females and increase slightly with age, while abduction may tend to decrease with age. Ninety percent of patients had acetabular abduction between 31 and 46 degrees; the 90% central range for acetabular anteversion was estimated to be from 14 to 31 degrees. Conclusion: CT scanning is useful in accurately defining the normal range of acetabular abduction and antiversion. Knowledge of this normal anatomy will allow accurate assessment of acetabular component position as delineated on conventional CT scanning.