SUN-385 Differential Effects of Abaloparatide and Teriparatide on Hip Cortical Volumetric BMD by DXA-Based 3d Modeling

The osteoanabolic agent abaloparatide (ABL) has been shown to significantly increase total hip BMD over an 18-month period in postmenopausal women with osteoporosis. However, it remains unknown if these gains predominantly occur in the cortical or trabecular compartments of the proximal femur, and how they may differ from the effects of teriparatide (TPTD). Therefore, a 3D modeling approach was applied to DXA images from patients in the ACTIVE trial to estimate cortical and trabecular changes in the proximal femur over 18 months of treatment with placebo (PBO), ABL, or TPTD. A subset of 750 patients, 250 from each of the treatment groups in ACTIVE (PBO, ABL, TPTD) with non-missing BMD data were randomly selected with data stratified by study site and patient race/ethnicity. Hip DXA scans at baseline and months 6 and 18 were subjected to DXA-based 3D modeling to evaluate volumetric BMD (vBMD) in the cortical and trabecular compartments, as well as cortical thickness and cortical surface BMD (sBMD) (3D-SHAPER v2.10.1, Galgo Medical, Spain). Pairwise group comparisons were made for percentage change from baseline data using P-values derived from contrast tests based on an MMRM model adjusting for BMI, age, value at baseline, and DXA scanner. At 18 months, total hip areal BMD was significantly increased in both the ABL and TPTD groups (P<0.001 vs PBO), with gains from baseline significantly greater with ABL versus TPTD (4.2% vs 3.3%; P<0.05). Similar increases from baseline were observed with ABL and TPTD for both trabecular vBMD (9%) and cortical thickness (1.5%) at month 18 (both P<0.001 vs PBO). In contrast, cortical vBMD was significantly increased from baseline with ABL (1.3%) compared with PBO (-0.2%) and TPTD (0.4%) at month 18 (both P<0.05 vs ABL). Cortical sBMD, the product of cortical thickness and vBMD, was also increased with ABL (+2.8%) versus both PBO (-0.2%) and TPTD (+1.8%) at month 18 (both P<0.05). Although ABL and TPTD increased trabecular vBMD and cortical thickness similarly at the hip by DXA-based 3D modeling after 18 months, ABL significantly increased cortical vBMD and sBMD to a greater extent than TPTD. Additionally, ABL appears to increase cortical density relative to TPTD in clinically important regions of the proximal femur. Further studies may be warranted to investigate these differences and how they may impact hip strength.