Repeatable procedure for evaluating taper damage on femoral stems with modular necks

Abstract

Understanding the performance of dual-taper modular femoral stems necessitates detailed quantitative assessment. This study reports a repeatable procedure to identify and measure damage on modular taper surfaces and determines whether damage area is a useful parameter for discerning modular femoral stem performance during in vitro corrosion and endurance tests. Twenty-four dual-taper modular necks representing a range of functional conditions were evaluated, including 15 necks previously subjected to in vitro testing and 9 necks explanted during revision hip arthroplasty. Objective identification of six surface features, including four unique damage modes, was accomplished using defined criteria combined with a standardized photogrammetric method for accurate and repeatable measurement of damage area and location. Damage area was a useful parameter for discerning the performance of modular femoral stems subjected to different in vitro tests. The sum of burnished smooth and textured damage areas was linearly correlated with the magnitude of material removed (weight loss) during in vitro testing, predicting ∼ 1.0 mg additional weight loss for every 10% increase in those combined damage areas. Modular necks tested with higher load magnitudes and those coupled with larger, stiffer femoral stems were readily distinguished and showed significantly larger areas of burnished smooth and textured damage.