Site-specific differential effects of once-yearly zoledronic acid on the hip assessed with quantitative computed tomography: results from the HORIZON Pivotal Fracture Trial.

UNLABELLED: We used new approaches to the analysis of diagnostic scans to detect changes in bone density in different regions of the hip after 3 years of treatment with the zoledronic acid. We showed that the drug significantly increases hip bone density compared to placebo at regions where hip fractures usually occur.

INTRODUCTION: This study aims to identify whether treatment with zoledronic acid exerts site-specific differential effects on volumetric bone mineral density (vBMD) at the hip.

METHODS: We analysed quantitative computed tomography scans of the hip obtained at baseline and 36 months in 179 women participating in the HORIZON Pivotal Fracture Trial. Cortical, trabecular and integral BMDs were determined at three main regions of interest-the femoral neck (FN), trochanter (TR) and total hip (TH)-and several sub-regions of interest, namely the proximal, middle, distal, anterior, posterior, inferomedial and superolateral FN, and the middle and distal TR.

RESULTS: Volumetric BMD increased significantly (p < 0.05) from baseline with zoledronic acid compared to placebo. Trabecular vBMD increased as follows: FN, 5.4 %; FN sub-regions, 6.0 % (proximal), 4.4 % (middle), 5.6 % (distal), 7.5 % (anterior), 7.0 % (superolateral) and 5.4 % (posterior); TR, 6.5 % and TH, 5.7 %. Cortical vBMD increased as follows: FN sub-regions, 5.0 % (proximal FN) and 2.3 % (anterior); TR, 4.6 %; middle TR, 2.7 % and TH, 3.8 %.

CONCLUSIONS: The effects on vBMD of annual infusion of 5 mg of zoledronic acid are site-specific and dominated by trabecular changes.