In comparison with alendronate, romosozumab substantially improves bone strength and mass at the lumbar spine in postmenopausal women with osteoporosis, says a study published in The Journal of Bone and Mineral Research. The findings of the phase III ARCH study indicated that romosozumab for one year followed by alendronate resulted in larger areal bone mineral density (aBMD) gains and a higher decline in fracture risk than alendronate alone.

aBMD is related to bone strength; however, it does not capture all the determinants of bone strength that may be differentially influenced by anti-osteoporosis drugs. Researchers thus investigated the alterations in bone strength, lumbar spine volumetric BMD (vBMD), bone mineral content (BMC), and bone volume with romosozumab compared to alendronate in a subset of ARCH participants. For assessment, quantitative computed tomography (QCT) and finite element analysis (FEA) were utilized.

In ARCH, 4093 postmenopausal females having severe osteoporosis and a prevalent fragility fracture were given monthly subcutaneous romosozumab 210 mg (n=2046) or weekly oral alendronate 70 mg (n=2047) for 12 months. This was followed by an open-label weekly oral administration of 70 mg alendronate for ≥12 months. Overall, 90 (41 alendronate, 49 romosozumab) were recruited in QCT/FEA imaging substudy.

For determining alterations in integral (total), cortical, and trabecular lumbar spine vBMD, the QCT scans were examined at baseline and months six, 12, and 24. The corresponding bone strength was assessed via FEA. Also, alterations in aBMD, bone volume, and BMC were investigated. In comparison with alendronate, romosozumab led to higher gains in lumbar spine cortical, trabecular, and integral BMC and vBMD at months 12 and six, with the higher gains maintained upon transition to alendronate through the 24 months.

These improvements were followed by remarkable improvements in FEA-estimated bone strength. The majority of the newly-formed bone was found to accumulate in cortical compartment, with romosozumab demonstrating better absolute gains in BMC. The findings showed consistency with higher vertebral fracture risk decline noted with romosozumab than alendronate in ARCH and offered insights into structural determinants of this differential therapy effect.