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Introduction: Early femoral implant stability is essential to long-term success in total hip replacement (THR). Radiostereometric analysis (RSA) provides highly precise measurements of stem micromotion relative to the femur that are otherwise not detectable by routine radiographs. This study characterized micromotion of a tapered, cementless femoral stem using RSA up to 5 years following THR. Methods: This IRB-approved, prospective, randomized, blinded study, involved 46 patients with a mean age of 58 and BMI of 30. All patients received a cementless, porous-coated titanium double tapered stem (M/L Taper, Zimmer) manufactured with 3 tantalum RSA beads and underwent primary THR by a single surgeon (DCA). RSA examinations, Harris Hip, UCLA, WOMAC, SF-36 scores were obtained at 10 days, 6 months, and annually through 5 years. Results: Thirty-four patients have RSA analyses at five years. The y-axis stem subsidence was greatest in the first 6 months (0.09 mm/yr), and stabilized thereafter with minimal further micromotion. The median stem subsidence was 0.01 ± 0.06 mm (standard error, SE) at 5 years. There was a statistically significant difference in subsidence between the 6-month interval and the 5-year interval (p = 0.027). Two outlying patients had significantly higher stem subsidence values at 6 months (0.7 mm and 1.0mm). One stem stabilized without further subsidence after 6 months (0.7mm), and the other stem continued to subside throughout the postoperative period. Neither patient has clinical evidence of loosening. All patients had a statistically significant improvement in pain and function measures following THA (p Conclusion: This cementless, double-tapered femoral stem shows excellent stability in young THR patients through 5 years, with no clinical or radiologic episodes of failure. The small amount of micromotion is less than that previously reported for similar tapered, cementless stems and approaches the accuracy of RSA (0.05 mm).

Introduction: In the active THR (total hip replacement) population, acetabular component stability is crucial for preventing implant failure. Titanium fiber metal coating is the most common material used in cementless THR. Trabecular metal, composed of porous tantalum, is designed to improve tissue infiltration and limit migration. It is unknown if tantalum offers an advantage over titanium in the biologic fixation of porous-coated acetabular shells. Radiostereometric analysis (RSA) provides highly precise measurements of micromotion that are otherwise not detectable by routine radiographs. Methods: In this IRB approved, prospective, randomized, blinded study, 46 patients received a primary THR by a single surgeon. Each patient was randomized to receive a titanium (23) or tantalum (23) uncemented cup. Tantalum RSA markers were implanted around the polyethylene liner and into the patient’s femur and periacetabular bone. Also, patients received either a highly cross-linked (n=25) or a conventional liner (n=21). RSA examinations, Harris Hip, UCLA, WOMAC, SF-12 scores were obtained at 10 days, 6 months, and annually through 5 years. Results: The randomized groups had comparable mean age, preoperative activity, and average BMI. The tantalum shells demonstrated less median translation than the titanium shells at each time-point, but there was no statistical difference between the two shells. At 6 months median translation of tantalum and titanium was -0.01mm and 0.04mm and remained stable with median translation of -0.02mm and 0.04mm at four years. Mean UCLA, WOMAC, Harris Hip, and SF-12 PCS and MCS scores improved similarly in both groups. Conclusions: After THR, both patient cohorts had excellent clinical outcomes with statistically significant improvements in function and pain relief. Although tantalum porous-coated acetabular shells demonstrated less y-translation and y-rotation at all time points, there was no statistically significant difference in shell migration and both shells demonstrated excellent stability with minimal micromotion at four years.