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The Spine Blog

Friday, June 12, 2020

Post-operative teriparatide or bisphosphonate for osteoporotic fusion patients?

The treatment of spinal deformity in the osteoporotic, elderly patient remains a major challenge. Osteoporosis increases the risk of hardware loosening, nonunion, proximal junctional kyphosis, and fracture. Bone density can frequently be improved with 6-12 months of teriparatide or a  bisphosphonate, though most patients do not wish to postpone surgery for that duration. Prior research has suggested that daily or weekly teriparatide given post-operatively can improve fusion rates in osteoporotic, elderly patients undergoing single level lumbar fusion. Multilevel cases represent a more challenging fusion environment, and Dr. Oba and colleagues from Japan sought to determine if teriparatide or a bisphosphonate improved fusion rates in this setting. They randomized over 100 elderly, osteoporotic patients undergoing multilevel lumbar interbody fusion to either post-operative weekly teriparatide or a once monthly bisphosphonate. They followed them with CT scans immediately following surgery and then at 2, 4, and 6 months after surgery. Fusion in the most caudal interbody space was graded on a 2 (fully fused) to 6 (not fused) point scale, and patient reported outcomes included the JOA Back Pain Questionnaire and the Oswestry Disability Index (ODI). They also classified patients as having bridging bone graft in contact with both endplates on the initial post-op CT scan or not. At 6 months, the teriparatide group had a slightly better fusion score (3.8 vs. 4.2), though this was not statistically significant. The fusion rate was also somewhat higher in the teriparatide group (47% vs. 33%), though this difference was not significant either. There were no differences in patient reported outcomes between the teriparatide and bisphosphonate groups. The presence of bridging bone graft contacting both endplates was a strong predictor of fusion at 6 months, with 47% of the bony contact group and 10% of the non-bony contact group having a solid fusion at 6 months. Overall, 79% of patients had bony contact between the endplates on the immediate post-op CT scan.

This is an RCT to see if teriparatide or bisphosphonate was favored in elderly, osteoporotic patients undergoing multilevel lumbar interbody fusion. In the short term (6 months), there might have been a slight advantage for teriparatide, but this was not statistically significant. While randomizing over 100 patients undergoing multilevel fusion is commendable, this study is still likely underpowered to answer the question of which pharmaceutical agent was associated with a better fusion rate. Also, there was no control group to which no osteoporosis treatment was given, so it is unclear if either teriparatide or bisphosphonate is favored over no treatment for multilevel fusion. Additionally, 6 months is too short of a time-frame to study fusion, and hopefully the authors will publish 12 and 24 month data on this cohort. That time-frame would also allow them to determine if radiographic nonunion was associated with worse outcomes, an issue that has still not been settled. The paper does make it clear that meticulous interbody bone grafting technique is important for fusion, though the authors do not go into detail about their technique. While this was a Level 1 study, this paper may raise more questions than it answers. It remains unclear which, if any, pharmaceutical agent should be given to osteoporotic patients following multilevel lumbar fusion. The role of BMP-2 in this population also remains undefined, though it may provide an advantage for long thoracolumbar fusions. How BMP-2 interacts with teriparatide or bisphosphonate is also unknown. This group has made a significant contribution to the literature with their research on this topic, though we still do not have great treatment options for the osteoporotic, elderly adult deformity patient.

Please read Dr. Oba's paper on this topic in the July 1 issue. Does this paper change your approach to the osteoporotic patient undergoing lumbar fusion?

Adam Pearson, MD, MS

Associate Web Editor