Interventions for osteoporosis in patients with degenerative scoliosis

Osteoporosis is a disorder of bone metabolism primarily affecting elderly individuals in the United States. Structurally, there is a decrease in the quantity of bone which can lead to fracture and degenerative changes in the spine. These changes lead to altered mechanics, deformity, and diminished quality of life. According to estimates, the aging population will further intensify the burden of disease in the upcoming decades and rates of spine surgery are increasing in this population. Osteoporosis presents a unique set of challenges for instrumentation and correction of spinal deformity. Several medical therapies are available to improve bone quality. These include calcium and vitamin D supplementation to increase the raw materials for bone formation in deficient individuals. Additionally, medications like bisphosphonates, denosumab, and recombinant PTH (teriparatide) directly alter the biochemical process regulating resorportion and bone formation. While initial studies have generally shown positive effects of these therapies on bone quantity, their effectiveness in spine surgery and in improving fusion rates is inconsistent. As a result, there is no consensus on preoperative and postoperative protocols. Intraoperative interventions aim at improving the durability of fixation in osteoporotic bone and preventing catastrophic complications. Prime methods of attaining durable fixation are by increasing the amount of points of fixation often by creating longer constructs and extending to the pelvis. Additionally, augmenting pedicle screw fixation with sublaminar wires and hooks has shown improved fixation. Regarding individual pedicle screws, techniques like cementing pedicle screws, increasing insertional torque, and attaining bicortical fixation have significantly improved the pullout strength. Methods of preventing proximal junctional kyphosis include adding hooks at the most proximal level and limiting construct stiffness proximally. Osteoporotic bone presents many challenges when trying to manage deformity. Adequate preoperative planning includes assessing risk factors, taking measures to improve BMD with or without the addition of medical therapies. Intraoperatively, technical considerations aim to improve bone/implant interface as well as increase the number of fixation points.