Strategies for enhancing spine fusion in osteoporotic spine

Abstract

Osteoporosis is a degenerative disease with worldwide occurrence. Recently, surgical indications for elderly patients with osteoporosis have been increasing. De novo bone formation and remodeling takes place on the fusion bed in spine. Osteoporosis induces negative bone remodeling that can delay bone fusion. It is thus essential for spine surgeons who treat patients with osteoporosis to understand the differences between the osteoporotic and non-osteoporotic spinal fusion. However, only few strategies are available for osteoporotic patients who need spinal fusion. We described 3 fold strategies to increase vertebral fusion of osteoporotic spine including antiosteoporotic therapies, bone substitutes on the fusion bed and, augmented implants based on our published or unpublished research results and review articles. Of the common antiosteoporotic drugs, bisphosphonates (BPs) did not decrease the fusion rate. However, BPs inhibit the maturation of fusion mass. Selective estrogen receptor modulator (SERM) can accelerate bone remodeling in an osteoporotic rat spine fusion model

and furthermore, bone fusion and formation can be enhanced by SERM treatment. Parathyroid hormone, an anabolic agent, may offer an advantage over agents such as BPs and SERM. The osteoinductive recombinant human bone morphogenetic protein (rhBMP) 2 enhances spinal fusion in ovariectomized rats during early bone formation. The rhBMP-2 might potentially improve the outcome of spinal fusion in the osteoporotic patient. Instrumentation and techniques with increased pullout strength may increase fusion rate through rigid fixation. Perioperative strategies in osteoporotic patients may affect the radiological and clinical outcomes. Therefore, surgeons should consider appropriate osteoporosis medication, instrumentation and technique before osteoporotic spine surgery.