Excessive femoral offset does not affect the range of motion after total hip arthroplasty

Implant dislocations are often caused by implant or bone impingement, and less impingement is critical to prevent dislocations. The aim of this study was to clarify the effect of the femoral offset in avoiding component or bony impingement after total hip arthroplasty (THA). Seventy-eight patients underwent THA with a Pinnacle cup and Summit stem (DePuy). Intraoperative kinematic analysis was performed with a navigation system, which was used to obtain intraoperative range of motion (ROM) measurements during trial insertion of stems of two different offset lengths with the same head size. Further, ROM was also measured after actual component insertion. Maximal ROM was independent of the femoral offset of the stem in each patient. However, the range of external rotation was significantly greater in patients with a greater femoral offset. The Summit stem has enough offset length to avoid implant/bone impingement, even when the standard offset stem is used. Nevertheless, selection of the offset stem should be performed carefully to prevent offset complications.