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| |  No Increased Risk of Atypical Femoral Shaft Fractures With Zoledronic Acid: Presented at AAOS By Sophie Bainbridge NEW ORLEANS -- March 15, 2010 -- Three years of zoledronic acid therapy does not increase the risk of subtrochanteric femoral shaft fractures, according to the results of a study presented here at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS). In the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly-Pivotal Fracture Trial (HORIZON-PFT), 3 women on zoledronic acid had fractures that met criteria for subtrochanteric femoral shaft fracture, compared with 2 women who were on placebo (hazard ratio = 1.5; 95% confidence interval, 0.25-9.0). However, “the wide confidence intervals in the trial, which go from a 9-fold increase in risk to a 75% reduction in risk, highlight the difficulty in examining a rare outcome in a single randomised trial of relatively short duration,” said lead investigator Dennis M. Black, PhD, University of California, San Francisco, San Francisco, California, during a poster presentation here on March 11. Long-term use of bisphosphonates may increase the risk of low-trauma, subtrochanteric femoral shaft fractures that are characterised by a transverse fracture pattern and cortical thickening with or without beaking at the point of fracture. The double-blind HORIZON-PFT trial was undertaken to examine the effect of once-yearly zoledronic acid 5 mg on fracture risk in women with postmenopausal osteoporosis (n = 7,736). The study demonstrated that zoledronic acid significantly reduced the risk of vertebral, hip, and other fractures by 41% over 3 years compared with placebo (P < .01). Dr. Black explained that prolonged inhibition of osteoclast mediated bone turnover leads to increased bone mineralisation, which may increase the brittleness of bone. The subtrochanteric or diaphyseal cortical bone is most susceptible to inhibition of bone remodelling and accumulation of microdamage. In this analysis, the investigators sought to evaluate the occurrence of subtrochanteric femoral shaft fractures in women (aged 64-89 y) from HORIZON-PFT who were randomised to either a single 15-minute IV infusion of zoledronic acid 5 mg or placebo at baseline, 12, and 24 months. The women had a femoral neck T score <=2.5 or a T score of <1.5 with radiological evidence of at least 2 mild or 1 moderate vertebral fracture. Overall results showed that zoledronic acid significantly reduced the risk of hip fracture by 41% compared with placebo (P < .01). During the trial, all reported fractures were blindly reviewed and confirmed by x-rays, surgical reports, and radiographs, which were specifically not designed to identify and classify subtrochanteric femoral shaft fractures. In addition, all hip and femur fractures (other than femoral neck and subcapital fractures) were re-reviewed from x-ray or surgical reports and radiographs, when these were available, by a radiologist masked to treatment specifically evaluating fracture location. Periprosthetic and severe trauma fractures were excluded, leaving 83 hip and femur fractures for review. Of these, 5 women had fractures that met criteria for subtrochanteric femoral shaft fractures (3 on zoledronic acid and 2 on placebo). A radiograph was available for only 1 patient on zoledronic acid that showed a transverse fracture with cortical thickening but no beaking, Dr. Black reported. “Important limitations of our analysis were that the classification relied mostly on x-ray and in some cases, surgical reports, and not radiographs; availability of small number of fractures, indicating that subtrochanteric femoral shaft fracture is rare; and a relatively short study duration of only 3 years,” he said. “Optimal studies will need to be done in population studies [probably not randomised] in which radiographs are available so that morphology is evaluable,” he added. Funding for this study was provided by Novartis Pharma AG. [Presentation title: Does ZOL Increase Risk of Atypical Subtrochanteric Femoral Shaft Fractures? Results of HORIZON-PFT. Abstract P532]
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