The Combined Effects of RhBMP-2 and Systemic RANKL Inhibitor in Patients With Bone Density Loss Undergoing Posterior Lumbar Interbody Fusion: A Retrospective Observational Analysis With Propensity Score Matching

Objective: The risks of nonunion and subsidence are high in patients with bone density loss undergoing spinal fusion surgery. The internal application of recombinant human bone morphogenic protein 2 (rhBMP-2) in an interbody cage improves spinal fusion; however, related complications have been reported. Denosumab, a human monoclonal antibody tar-geting the receptor activator of nuclear factor kappa B ligand (RANKL), hinders osteoblast differentiation and function. Therefore, this study aimed to observe the combined effect of the local application of rhBMP-2 in a lumbar cage and systemic RANKL inhibition on postoperative spinal fusion in patients with bone density loss undergoing posterior lumbar in-terbody fusion (PLIF). Methods: This retrospective observational study included 251 consecutive patients with spinal stenosis who underwent PLIF at a single center between 2017 and 2021. Clinical outcomes were assessed, and radiographic evaluations included lumbar flexion, extension, range of motion, and subsidence. Statistical analyses were conducted to identify the combined effect of the treatment and the subsidence and spinal fusion status. Results: One hundred patients were included in the final analysis. Denosumab treatment significantly reduced the rate of osteolysis (p = 0. 013). When denosumab was administered in combination with rhBMP-2, the fusion status remained similar; however, the incidences of postoperative osteolysis and postoperative oozing day decreased. Conclusion: The combined use of rhBMP-2 and RANKL inhibition in patients with bone density loss can enhance bone formation after PLIF with fewer complications than rhBMP-2 alone.