Ovariectomy-Induced Osteoporosis Does Not Impact Fusion Rates in a Recombinant Human Bone Morphogenetic Protein-2–Dependent Rat Posterolateral Arthrodesis Model

摘要

>Study Design Randomized, controlled animal study. >Objective Recombinant human bone morphogenetic protein-2 (rhBMP-2) is frequently utilized as a bone graft substitute in spinal fusions to overcome the difficult healing environment in patients with osteoporosis. However, the effects of estrogen deficiency and poor bone quality on rhBMP-2 efficacy are unknown. This study sought to determine whether rhBMP-2-induced healing is affected by estrogen deficiency and poor bone quality in a stringent osteoporotic posterolateral spinal fusion model. >Methods Aged female Sprague-Dawley rats underwent an ovariectomy (OVX group) or a sham procedure, and the OVX animals were fed a low-calcium, low-phytoestrogen diet. After 12 weeks, the animals underwent a posterolateral spinal fusion with 1 μg rhBMP-2 on an absorbable collagen sponge. Representative animals were sacrificed at 1 week postoperative for alkaline phosphatase (ALP) and osteocalcin serum analyses. The remaining animals underwent radiographs 2 and 4 weeks after surgery and were subsequently euthanized for fusion analysis by manual palpation, micro–computed tomography (CT) imaging, and histologic analysis. >Results The ALP and osteocalcin levels were similar between the control and OVX groups. Manual palpation revealed no significant differences in the fusion scores between the control (1.42 ± 0.50) and OVX groups (1.83 ± 0.36; p = 0.07). Fusion rates were 100% in both groups. Micro-CT imaging revealed no significant difference in the quantity of new bone formation, and histologic analysis demonstrated bridging bone across the transverse processes in fused animals from both groups. >Conclusions This study demonstrates that estrogen deficiency and compromised bone quality do not negatively influence spinal fusion when utilizing rhBMP-2, and the osteoinductive capacity of the growth factor is not functionally reduced under osteoporotic conditions in the rat. Although osteoporosis is a risk factor for pseudarthrosisonunion, rhBMP-2-induced healing was not inhibited in osteoporotic rats.