Is bone mineral density a risk factor for femoral stem subsidence in primary cementless total hip arthroplasty: a prospective study

The success of primary total hip arthroplasty (THA) in patiens with primary osteoarthritis (OA) of the hip is significantly influenced by stem osseointegration, migration and implantation. Additionally, the bone mineral density (BMD) of the proximal femur, the femoral morphology and stem design play important roles in these outcomes. This study aimed to evaluate the effect of BMD on subsidence who underwent primary cementless THA with a fit-and-fill stem design for primary OA of the hip, assuming that subsidence is not influenced by BMD. This prospective study included 72 hips from 67 patients who underwent primary cementless THA for OA between May 2019 and March 2022. Two patients were excluded due to intraoperative complications, and the final analysis was conducted on 70 hips. Patients were grouped according to preoperative BMD and proximal femur anatomy based on Dorr classification. Harris Hip Score (HHS), radiological subsidence and Engh score values ​​were used for postoperative clinical evaluation. The mean age was 65.99 ± 8.10 years (range 52 to 83 years). The mean follow-up was 24.6 ± 5.8 months (range, 12 to 34 months). Amongst 70 OA of the hip cases, 22 (31.43%) were Dorr type A, 44 (62.86%) type B, and 4 (5.71%) type C. Forty-three patients (61.43%) had normal BMD, while 27 patients (38.57%) were osteopenic or osteoporotic. The mean axial migration at the latest follow-up was 1.04 ± 0.69 mm (range 0 to 3.1 mm). Total Engh score was 22.89 ± 3.28 (range 14 to 27), and in terms of stabilization bone ingrowth was seen in all of the femoral stems. There was no statistically significant effect of femoral T-score levels (p = 0.853) or femoral morphologies (p = 0.763) on femoral stem subsidence. No statistically significant differences were observed in clinical or radiological outcomes between patients with normal and low BMD. These findings suggest that early stem migration and osseointegration are more closely related to initial mechanical stability than to BMD. Cementless femoral stems can therefore be considered reliable across different bone qualities, offering an innovative perspective that challenges the conventional emphasis on bone density in implant selection.