Areal bone mineral density is not associated with femoral stem subsidence in patients younger than 70 years undergoing total hip arthroplasty

INTRODUCTION: Femoral stem subsidence is a known complication after uncemented total hip arthroplasty (THA). The purpose of this study was to determine the frequency of osteoporosis and to investigate the relationship between areal bone mineral density (aBMD) and subsidence in a cohort of patients younger than 70 years.

METHODS: One hundred consecutive patients (age 60 ± 6 years; 52 female, 48 male) undergoing uncemented THA using a collarless press fit femoral stem were retrospectively reviewed. Dual-energy X-ray absorptiometry (DXA) was performed preoperatively at the proximal femur and lumbar spine, and if not feasible at these sites, at the distal radius. DXA results were compared to a cohort of 100 patients ≥ 70 years scheduled for cemented THA. Age, sex, and body mass index (BMI), canal flare index (CFI), and canal fill ratio (CFR) were assessed. Analysis of stem subsidence and migration was performed on standardized, calibrated radiographs obtained postoperatively and at follow-up.

RESULTS: The frequency of osteoporosis was considerably lower in the study cohort compared to patients ≥ 70 years (7% vs. 19%, p = 0.02). Illustrated by the high CFR (mean 96 ± 4%) in the mid-stem region, a sufficient press fit was achieved. After a mean follow-up of 7.4 months, the mean stem subsidence was 0.9 ± 0.9 mm. Only two patients had subsidence greater than 3 mm, one of whom was morbidly obese and the other diagnosed with severe osteoporosis. There were no correlations between any of the parameters (CFI, CFR, age, sex, BMI) and femoral stem subsidence. In addition, aBMD T-scores showed no correlations with subsidence.

CONCLUSION: aBMD by DXA does not appear to be associated with stem subsidence in patients younger than 70 years and with adequate press fit.