Modular Versus Nonmodular Femoral Necks for Primary Total Hip Arthroplasty

In total hip arthroplasty (THA), proximal femoral neck stem modularity (PFNSM) has theoretical advantages over nonmodular stems, including the ability to more closely reconstruct anatomy and improve stability. However, risks of metallosis and breakage at the junction must be considered. In this study, we compared the head centers of a modular neck system with that of its nonmodular counterpart. Of 463 primary THAs with a modular stem, 261 (56%) had a head center equivalent to that of its nonmodular counterpart, and an additional 132 (29%) had a head center within 4 mm in length and 2 mm of offset. Thus, only 70 stems (15%) had a head center that was more than 4 mm in length and more than 2 mm in offset different from the nonmodular stem. Only 12 stems had a verted neck. These findings suggest that, in a majority of primary THAs, use of a modular stem results in head center positions also achievable with a nonmodular stem. Given the risks of modularity, PFNSM should be used with caution. We recommend PFNSM in cases that cannot be reconstructed with the nonmodular option.