Primary uncemented total hip arthroplasty is the fixation of choice for most patients undergoing hip replacement in North America. Initial stem stability will be detected by the fit and fill of the implant to the bone as well as the overall stem geometry as it relates to its mechanical stability. This study aims to determine the geometric and structural parameters of common cementless tapered femoral stems to better understand their early clinical performance with respect to bony fixation. Templates for six proximally coated tapered uncemented femoral stems: Accolade (Stryker), Profemur (Wright), Taperloc (Biomet), M/L Taper (Zimmer), Anthology (Smith-Nephew) and Trilock (Depuy) were scanned and saved as images on a PC. Stem sizes were assigned according to AP plane width measurements taken at the most lateral implant shoulder, and images analyzed using ImageJ (US National Institutes of Health). Measurements were made of stem length, and at various locations, the width and thickness of the stem. Coronal plane stiffness was calculated according to beam theory, assuming an elastic modulus of 114 GPa for the Profemur, Taperloc M/L Taper, Anthology and Trilock stems. The Accolade stem has a modulus of 85.5 GPa. due to TMZF alloy which is 25% more flexible. Stem thickness and taper ratios were calculated as a measure of lateral vs. AP fill of the femur. All measurements were plotted as manufacturer-specific curves relative to stem width.Purpose
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