Collared Triple Taper Stems Have Superior Biomechanical Characteristics in Compromised Bone

Femoral periprosthetic fractures following total hip arthroplasty are a common cause for early revisions, especially in osteoporotic patients. Despite the protective nature of cemented stems, the widespread use of press-fit stems persists. The following biomechanical study quantifies resistance against subsidence and failure provided by a collar and triple taper stem design in a synthetic osteoporotic femur model.

Twenty-four synthetic osteoporotic femurs were instrumented with 4 uncemented stems (6 per group): single-wedge (blade) stems, triple-taper metaphyseal stems with and without a collar, and fit-and-fill stems. Each femur was subjected to 10,000 cycles of axial and torsional loading to simulate walking while the following outcomes measures were recorded: stem subsidence during axial loading, rotational stiffness, and torque to failure.

The single-wedge stem experienced greater subsidence (1.4 ± 0.2 mm) compared to all other stem designs, while the triple-taper stem with a collar demonstrated the least amount of subsidence (0.53 ± 0.12 mm). The rotational stiffness of the collared triple-taper stem was significantly greater than the 3 other designs, and the maximum torque to failure for both triple-taper stem designs was significantly greater than the single-wedge stem and the fit-and-fill stem.

This study demonstrated superior biomechanical characteristics of collared triple-taper femoral stems compared to single-wedge, collarless triple-taper, and fit-and-fill stems. Clinically, this suggests collared stems should be considered when performing uncemented arthroplasty in patients with compromised bone.