Preoperative Factors Predicting the Severity of BMD Loss Around the Implant after Total Hip Arthroplasty

Background: Stress shielding after total hip arthroplasty (THA) leads to the loss of bone mineral density (BMD) around the femoral implants, particularly in the proximal area. BMD loss around the implant is likely to occur within 1 year after THA, but its severity depends on patient characteristics. This study evaluated preoperative factors associated with the severity of zone 7 BMD loss after THA.MethodsThis retrospective cohort study included 48 patients who underwent primary THA at our hospital from October 2011 to December 2015. All patients underwent implantation of a Zweymüller-type femoral component without any postoperative osteoporosis medications. The objective variable was change in zone 7 BMD after 1 year. Factors evaluated included age, body mass index (BMI), Japanese Orthopaedic Association (JOA) score, Harris Hip Score (HHS), Canal Flare Index (CFI), and lumbar BMD on the frontal and lateral sides. Factors associated with loss of zone 7 BMD were identified by univariate and multivariate regression analyses.ResultsUnivariate regression analysis showed that CFI (P=0.003) and preoperative lumbar BMD on the frontal (P=0.003) and lateral (P<0.001) sides were significantly correlated with loss of zone 7 BMD. Multivariate regression analysis showed that CFI (P=0.014) and lumbar BMD on the lateral side (P<0.001) were independently correlated with loss of zone 7 BMD.ConclusionLower preoperative lumbar BMD on the lateral side and lower CFI were significantly associated with zone 7 BMD loss after THA. Patients with these characteristics should be carefully monitored for severe BMD loss after THA.