Metrology for Dual Taper Total Hip Arthroplasty

Recent hip implant designs have included modular necks to offer surgeons the ability to optimally suit each patient's unique anatomy. Certain designs have experienced high rates of adverse local tissue reactions secondary to suspected corrosion at the additional modular taper of the stem-neck interface. This study used a coordinate measuring machine to determine the volumetric material loss at this interface in a single such design. Because of the unique geometry of this dual-taper design, a computational approach was developed to reverse engineer the as-manufactured geometry and report the amount of material released into the patient's joint space. Approximately 90 % of the total volume loss in the taper interface can be attributed to the male component. Volumetric cobalt-chromium-molybdenum loss rates are estimated to exceed 2.3 mm(3)/year (95 % confidence interval [C.I.]: 1.67-2.96 mm(3)/year) and are of similar magnitude to rates identified for material loss in metal-on-metal hips. The average rate of material loss in vivo is thus of clinical relevance in the context of the observed adverse outcomes.