Sex Differences in Hip Morphology: Is Stem Modularity Effective for Total Hip Replacement?

Total joint arthroplasty, one of the most successful orthopaedic procedures, predictably relieves pain and improves function for patients with a painful arthritic hip joint1. This high success rate has increased patient expectations, particularly those regarding hip function, after the surgery. To achieve better function and to reduce the implant dislocation rate, more attention has been given to the role of the restoration of femoral offset and soft-tissue balancing2,3. Surgeons today are committed to restoring the anatomy in each case independent of the patient's age or sex or the pathological condition of the hip. Anatomic studies of hip anatomy, specifically on the femoral side, have shown sex-based anatomic differences4-8. Women tend to have a shorter femoral neck, a thinner femoral shaft, a lower cervicodiaphyseal (CCD) angle, a lower femoral offset, and greater anteversion of the femoral neck (Fig. 1). These differences should be addressed during revision hip surgery in order to restore hip anatomy. In particular, to achieve proper soft-tissue balancing, the femoral offset should be accurately restored. The femoral offset is represented by the perpendicular distance from the center of the femoral head to the long axis of the femur (Fig. 2). McGrory et al.9 found a correlation between a lack of restoration of femoral offset and abductor muscle weakness and limping. These results depend on hip mechanics, with a fulcrum between body weight and the hip abductors (Fig. 3). The length of the lever arm of the hip abductors is smaller than that of body weight. Therefore, the abductors must generate a force that is larger than body weight to maintain a level pelvis. In contrast, an increase in femoral offset increases the lever arm of the abductors, reducing the force required to balance body weight and thereby …