Effects of Abaloparatide on Bone Mineral Density in Proximal Femoral Regions Corresponding to Arthroplasty Gruen Zones

Abstract

Background: Low hip bone mineral density (BMD) in patients who undergo total hip arthroplasty (THA) increases the risk of periprosthetic fractures, implant instability, and other complications. Recently, emphasis has been placed on bone health optimization: treating low BMD prior to a planned orthopaedic implant procedure in an effort to normalize BMD and reduce the potential risk of future complications. Abaloparatide is a U.S. Food and Drug Administration-approved osteoanabolic agent for men and postmenopausal women with osteoporosis and a candidate drug for bone health optimization that, in addition to benefits at the spine, increases hip BMD and reduces nonvertebral fracture risk. We hypothesized that abaloparatide would improve BMD in proximal femoral regions surrounding a virtual THA stem. Methods: This post hoc analysis obtained dual x-ray absorptiometry (DXA) hip scans from 500 randomly selected postmenopausal women with osteoporosis from the Phase-3 Abaloparatide Comparator Trial in Vertebral Endpoints (ACTIVE, NCT01343004) study after 0, 6, and 18 months of abaloparatide (250 patients) or placebo (250 patients). Hip DXA scans underwent 3-dimensional (3D) modeling via 3D-Shaper, followed by virtual resection of the proximal femur and simulated placement of a tapered, flat-wedge hip stem that guided delineation of the Gruen zones that were fully (zones 1 and 7) or largely (zones 2 and 6) captured in the scanning region. Integral, cortical, and trabecular volumetric BMD, cortical thickness, and cortical surface BMD (the product of cortical volumetric BMD and cortical thickness) were determined for each zone. Results: Compared with placebo, the abaloparatide group showed greater increases in integral volumetric BMD in all zones at months 6 and 18; cortical surface BMD in zones 1, 6, and 7 at month 6; cortical thickness, cortical volumetric BMD, and cortical surface BMD in all zones at month 18; and trabecular volumetric BMD in zones 1 and 7 at months 6 and 18. Conclusions: Abaloparatide increases BMD in proximal femoral regions that interact with and support femoral stems, suggesting that abaloparatide may have value for preoperative or potentially perioperative bone health optimization in patients with osteoporosis undergoing THA. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.