The Female Pelvis Is Associated with a Lateralized Ischium and a Reduced Ischiofemoral Space.

BACKGROUND: Pelvi-femoral conflicts are increasingly recognized for their explanatory role in the pathology of extra-articular hip impingement. Ischiofemoral impingement (IFI) is a type of impingement between the femur and the ischium that causes high femoral antetorsion and valgus femoral neck orientation. It is unknown whether obstetric adaptation of the female pelvis renders the female hip at a higher risk of sustaining IFI. The aim of this study was to determine the influence of the pelvic morphology on the ischiofemoral space (IFS). METHODS: Plain radiographs of healthy individuals with no symptomatic hip disease were obtained in a functional standing position in a standardized manner and utilized for measurement of the interischial and ischiofemoral widths, subpubic angle, and centrum collum diaphyseal (CCD) angle. Linear regression was performed to determine the influence of morphometric measures on the ischiofemoral space. RESULTS: Sixty-five radiographs (34 females and 31 males) were included. The cohort was stratified according to gender. Significant gender-related differences were noted regarding the ischiofemoral distance (31% increase in males, p < 0.001), pubic-arc angle (30% increased in females, p < 0.001), and the interischial space (7% increase in females, p < 0.001). CCD did not significantly differ between genders (p = 0.2). Factors influencing the IFS include the pubic-arc angle (ß = -0.01 (CI -0.02--0.00), p = 0.003), interischial distance (ß = -0.11 (CI -0.23--0.00), p = 0.049) and CCD (ß = -0.06 (CI -0.09--0.04), p < 0.001). CONCLUSIONS: Obstetric adaptation is associated with an increased subpubic angle that shifts the ischia laterally and away from the symphysis. The resultant reduction in the ischiofemoral space renders the female pelvis at a higher risk for a pelvi-femoral conflict, or more precisely, an ischiofemoral conflict, due to the reduced ischiofemoral space of the hip. The CCD angle of the femur was shown not to be gender specific. However, the CCD angle demonstrates an influence on the ischiofemoral space, rendering the proximal femur a target for corresponding osteotomies.