The normal ischiofemoral distance and its variations.

The aim of this study is to measure the ischiofemoral distance (IFD) in the normal hip with healthy surrounding soft tissues and describe its variations caused by gender, age and proximal femoral anatomy so that this could serve as a reference for future studies on this subject. This is a retrospective study in which we reviewed the CT scans of 149 patients (298 hips) who had a CT of their pelvis for non-orthopaedic (abdomino-pelvic) pathology. The images were reviewed by two independent observers and the IFD (the smallest distance between the lateral cortex of the ischial tuberosity and the posteromedial cortex of the lesser trochanter), offset (the perpendicular distance from the centre of the femoral head to a line running down the middle of the shaft of the femur) and the neck-shaft angle (the angle between the lines in the middle of the neck to the line forming the axis of the femoral shaft) were measured. The CT scans belonged to 71 males and 78 females (M: 48%, F: 52%), with an average age of 51  ± 19 years (range 18-92). The mean IFD was 18.6  ±  8 mm in the females and 23  ± 7 mm in the males and this difference was statistically significant (P <  0.001). The IFD increased by 1.06 mm for each 1 mm of offset and dropped by 0.09 mm with each year of age. However, the neck-shaft angle did not show any significant correlation with the IFD.