The Effect of Transpedicular Injection of Recombinant Human Bone Morphogenetic Protein-2/Beta‐Tricalcium Phosphate Carrier on the Prevention of Proximal Junctional Kyphosis in Adult Spinal Deformity Surgery: A Pilot Study

BACKGROUND AND OBJECTIVES: Several studies have explored strategies to prevent proximal junctional kyphosis (PJK) which is the unresolved issue in adult spinal deformity (ASD) surgery. This study aimed to investigate the preventive effects of upper instrumented vertebrae (UIV) recombinant human bone morphogenetic protein-2 (rhBMP-2) with beta‐tricalcium phosphate (β-TCP) carrier injection on PJK. METHODS: This study was conducted through a retrospective analysis of data collected both prospectively and retrospectively. In the rhBMP-2 group, consisting of 25 patients with ASD, rhBMP-2 along with β-TCP carrier was administered to the UIV through the pedicle. To minimize time-related bias, control-1 included 66 patients who had undergone ASD surgery by the same surgeon in the year preceding the commencement of the study. Control-2 consisted of 63 patients who had undergone ASD surgery by the same surgeon during the year after the end of the study. The primary outcome is the occurrence of PJK within one year postsurgery, and the secondary outcome is the change in Hounsfield unit of the UIV one year after the surgery. RESULTS: When comparing baseline characteristics with control groups, a significant difference was observed only in body mass index, with control-1 ( P = .006) and control-total (control-1 + control-2, P = .026) having a higher body mass index than the study group. In the rhBMP-2 group, there were 3 cases (PJK rate, 12.0%) of PJK, whereas control-1 and control-2 had 26 cases (PJK rate, 39.4%, P = .012) and 20 cases (PJK rate, 31.7%, P = .057), respectively. In the control-total, there were 46 cases (PJK rate, 35.7%, P = .020) of PJK. The UIV that received rhBMP-2 showed a statistically significant increase in Hounsfield unit measurements compared to preoperative values 1 year after surgery ( P = .001). CONCLUSION: The transpedicular injection of rhBMP-2/β-TCP carrier at the UIV significantly contributed to the prevention of PJK and effectively increased trabecular bone density at the UIV.