Purpose of review
Excessive femoral component stiffness contributes to stress shielding and thigh pain. A more flexible stem that provides enduring biologic fixation, reduces stress shielding, and minimizes thigh pain would therefore be of significant clinical benefit.
Recent findings indicate success in attaining these goals using the Epoch composite stem (Zimmer, Warsaw, Indiana, USA). Mechanical testing demonstrates reduced stiffness without compromise of strength and fatigue properties. Canine and human radiographs and postmortem retrievals show reliable and extensive bone ingrowth. Prospective trials indicate outstanding clinical results. Plain film and dual-energy X-ray absorptiometry studies, including series of bilateral total hip arthroplasty with an Epoch on one side and an alternative design on the other, show reduced stress shielding with the Epoch.
The favorable results observed with the Epoch stem have significant clinical implications. Larger, stiffer solid metal stems, even if made of titanium alloy, are associated with higher incidences of stress shielding and thigh pain. The use of a composite femoral stem may circumvent these problems.