Abaloparatide Increases Bone Mineral Density in Regions Corresponding to Gruen Zones 1, 2, 6, and 7 in Postmenopausal Women With Osteoporosis

Purpose/Aims

We hypothesized that local improvements in bone mineral density (BMD) would be observed following 6 and 18 mo of abaloparatide versus placebo in hip regions corresponding to femoral Gruen zones that influence the fixation and stability of femoral stems in hip arthroplasty.

Rationale/Background

Low BMD at the time of total hip arthroplasty (THA) increases the risk of compromised implant stability and delayed osseointegration (1). Abaloparatide, a synthetic analog to PTHrP(1-34), is FDA approved for the treatment of men and postmenopausal women with osteoporosis. Abaloparatide increases spine and hip BMD and reduces the risk of vertebral and nonvertebral fractures (2).

Methods

A subset of 500 postmenopausal women with osteoporosis from the ACTIVE trial (2) who received abaloparatide or placebo (n=250/group) were randomly selected. Hip DXA scans obtained after 6 and 18 mo of treatment underwent 3D modeling via 3D-Shaper software (3), and a virtual Stryker (Mahwah, NJ) Accolade II hip stem was optimally sized and positioned within each 3D-DXA scan. Periprosthetic regions corresponding to Gruen zones 1, 2, 6, and 7 were assessed for volumetric BMD (vBMD) (integral, cortical, trabecular) and cortical thickness (zones 3, 4, and 5 were beyond the DXA region of interest). Treatment comparisons were made with P values derived from a mixed-effect model for repeated measures.

Results

Abaloparatide significantly increased integral vBMD compared with placebo in Gruen zones 1, 2, 6, and 7 at 6 and 18 mo (P< 0.01 for all) (Table 1). The largest percent increases were in zones 1 and 7. Abaloparatide increased cortical vBMD at 18 mo in all 4 analyzed zones (P< 0.01), increased trabecular vBMD at 6 and 18 mo in zones 1 and 7 (P< 0.0001), and increased cortical thickness at 6 months in zones 1, 6, and 7 (P< 0.01) and in all zones at 18 months (P< 0.001). Color maps of cross-sectional group mean change in vBMD demonstrates more robust BMD accrual with abaloparatide (Figure 1).

Implications

Abaloparatide significantly increased vBMD and cortical thickness in virtual Gruen zones 1, 2, 6, and 7 compared with placebo. Abaloparatide may represent an effective agent for bone health optimization prior to THA by inducing orthopedically important localized gains in BMD. Additional research into preoperative augmentation and postoperative treatment is warranted. References: 1. Aro HT et al. Acta Orthop 2012;83;107-14; 2. Miller PD et al. JAMA 2017;317:442; 3. Winzenrieth R et al. Osteoporos Int 2021;32:575–83.