Relationship Between Proximal Femoral and Acetabular Alignment in Normal Hip Joints Using 3-Dimensional Computed Tomography

Background: The bony architecture of the hip depends upon functional adaptation to mechanical usage via the dynamic interaction between the acetabulum and femoral head. Acetabular retroversion is thought to be a contributing factor of pincer-type femoroacetabular impingement. Studies of pathological hip joints suggest proximal femoral anatomy compensates for acetabular retroversion. Hypothesis/Purpose: The purpose of this study was to determine if a predictable relationship exists between proximal femoral and acetabular angles, age, and gender in normal hip joints. We hypothesized that, through functional adaptation to mechanical loading, a complementary developmental relationship exists between the acetabulum and proximal femur. Study Design: Descriptive laboratory study. Methods: The femoral neck version, femoral neck shaft angle, acetabular version, acetabular inclination, and center edge angle were measured in 230 normal hip joints in 115 adults using 3-dimensional reconstruction software. Correlations between the angles, age, and gender were examined using the methods of stepwise regression and backward elimination. Results: Regarding side-to-side comparison and variability, there was no statistically significant difference between the left and right sides in the average value of each angle measurement. The correlations specifically between angles, age, and gender were similar on the left and right sides for all pairs except femoral version and acetabular inclination. Regarding significant findings of the study, a positive correlation (P<.05) was found between femoral version and acetabular version (0.38 degrees to 1 degrees). A positive correlation was found between femoral neck shaft angle and acetabular version (0.21 degrees to 1 degrees). A negative correlation was found between femoral neck shaft angle and age (-0.17 degrees to 1 degrees). A positive correlation was found between acetabular version and female gender (2.6 degrees to 1 degrees). A positive correlation was found between center edge angle and female gender (2.8 degrees to 1 degrees). A negative correlation was found between femoral version and acetabular inclination (-0.49 degrees to 1 degrees), although this latter relationship was only observed unilaterally (ie, left hip). Conclusion: This study demonstrates that a correlation exists between multiple proximal femoral and acetabular angles in normal hip joints. These findings support the hypothesis that a complementary developmental relationship occurs between the femoral head and acetabulum. Clinical Relevance: The results of this study suggest that, in some patients, what is thought to be pathological acetabular retroversion may actually be normal anatomy with a compensated femoral version. Investigating the relationship between these angles in patients with the signs and symptoms of pincer-type femoroacetabular impingement may alter a surgeon's approach to this patient population.