Purpose: The purpose of this study was to evaluate whether the bone morphology of the hip affects the range of motion (ROM) in total hip arthroplasty (THA).
Methods: Using the CT data of 63 patients who underwent THA, we calculated the ROM of flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) using 3D dynamic analysis software. We measured the distance between the anterior surface of the stem and anterior aspect of the greater trochanter (GTa length) at the cutting point and between the tip of the antero-inferior iliac spine (AIIS) and coronal plane of both femoral heads (AIIS length), as a parameter of the femur and pelvis, respectively. The relationship between the ROM, bone anatomy and impingement site was evaluated.
Results: We found a significant decrease in the ROM of Flex and the Int-R to be inversely proportional to the GTa and AIIS length. In Flex and Int-R, the anterior intertrochanteric region often impinges on the AIIS in patients with larger bone anatomy.
Conclusions: We demonstrated that the bone morphology of the hip substantially affects the ROM of Flex and Int-R, especially in patients with large bone anatomy. For these patients we should consider bony impingement in THA.