Effect of implant composition on periprosthetic bone mineral density after total hip arthroplasty

Background The severity of bone mineral density (BMD) loss after total hip arthroplasty (THA) depends on both implant- and patient-related factors. While implant fixation type is an important factor, but few studies have considered the effect of material composition on the same implant fixation type. In particular, differences in mechanical stiffness due to material composition are of great interest. Here, we compared changes in periprosthetic BMD after THA using proximal fixation concept stems comprising different titanium alloys, i.e., beta titanium alloys stem and alpha + beta titanium alloys stem. Methods This retrospective cohort included 122 patients (beta titanium alloys stem, 61 cases; alpha + beta titanium alloys stem, 61 cases) who underwent primary THA between January 2009 and December 2019. The primary outcome was the change in periprosthetic BMD from base line. Age, body mass index, diagnosis, stem size, canal flare index, surgical approach, pre-operative lumbar BMD, and pre-operative activity scores were reviewed and changes in periprosthetic BMD between the two groups were compared using analysis of covariance. The secondary outcome was radiographic response after THA. Results There was significant difference in periprosthetic BMD in zone 6 and 7 at 2 years (p < 0.05) between the two groups. There was no significant difference in other zones. A significant difference in radiographic response was noted only for the Engh classification. Conclusion alpha + beta titanium alloys stem resulted in a significantly higher rate of BMD loss in zones 6 and 7 compared with the beta titanium alloys stem. These results may be due to differences in mechanical stiffness due to the different titanium alloy composition of the prosthetics.