Periprosthetic Bone Mineral Density Changes After Implantation of a Curved Bone Preserving Hip Stem Compared to a Standard Length Straight Stem: 5-Yr Results of a Prospective, Randomized DXA-Analysis

Abstract

Introduction: The objective of this prospective, randomized study was to evaluate differences in periprosthetic bone mineral density changes in the proximal femur after implantation of a cementless bone preserving stem (Fitmore) compared to a cementless straight stem (CLS Spotorno). Methodology: Periprosthetic bone mineral density was measured in 140 patients (aged 33–74 yr) before surgery, 7 d, 3, 12, and 60 mo postoperatively, using dual energy X-ray absorptiometry. The 1-yr results have already been published. The results of the first postoperative measurement served as the baseline value. Because of the different length of the 2 implants we used adapted Gruen zones to divide the periprosthetic bone in seven regions of interest with comparable length. Clinical results were recorded using the Western Ontario and McMaster Universities Arthritis Index and the Harris hip score. Results: Clinical findings showed comparable results in both groups at all follow-ups (p > 0.05). A total of 5 yr after surgery, the comparison of periprosthetic bone mineral density changes showed significant differences in regions of interests 3 (CLS −3.9% vs Fitmore −0.2%, p < 0.001) and 5 (CLS −3.6% vs Fitmore −1.3%, p = 0.0028) between both implants. Conclusion: Despite the fact that no exclusive proximal load distribution could be observed, proximal periprosthetic bone loss in the proximal femur was less pronounced after implantation of the bone preserving stem than with the straight stem.