Differences in periprosthetic bone mineral density tendencies with Types 1 and 3C stems in bipolar hemiarthroplasty following hip fracture

The purpose of this study was to compare the periprosthetic bone mineral density (BMD) changes in the patients who underwent bipolar hemiarthroplasty (BPHA) for geriatric femoral neck fracture between two major different types of cementless femoral stems. A total of 93 patients (96 hips) who underwent BPHA for femoral neck fracture were categorized into two groups: Type 1 (42 patients, 44 hips), and Type 3C stem (51 patients, 52 hips). We investigated the annual follow-up trends of periprosthetic BMD at each Gruen zone during minimum postoperative 5-years; moreover, we compared the trends of periprosthetic BMD between both groups. The mean follow-up period was 7.1 years. In both groups, the overall BMD at the last follow-up had decreased compared with the baseline. In those with the Type 1 stem, BMD in the lateral femoral meta-diaphysis significantly decreased at 1-year follow-up after surgery. In those with Type 3C stem, BMD in the lateral femoral metaphysis postoperatively decreased after 3-years, whereas the BMD in the mediolateral femoral diaphysis drastically decreased postoperative 1-year period and plateaued thereafter. Different tendencies according to stem design were observed obviously in the postoperative BMD change of the proximal femur in patients who underwent BPHA for geriatric femoral neck fracture.