Association of cervical sagittal alignment with adjacent segment degeneration and heterotopic ossification following cervical disc replacement with Prestige-LP disc.

Purpose: Cervical sagittal balance plays important roles in transmitting the load of the head and maintaining global spinal balance. This study aimed to identify the association of cervical sagittal alignment with adjacent segment degeneration (ASD) and heterotopic ossification (HO) after Prestige-LP cervical disc replacement (CDR).
Methods: We enrolled 132 patients who underwent one-level Prestige-LP CDR with 2-10 years of follow-up. Cervical sagittal alignment parameters, including the degree of C2-C7 lordosis (CL), functional spinal unit angle (FSUA), sagittal vertical axis (SVA),, and T1 slope (T1s), were measured. ASD and HO were evaluated at the last follow-up. Unpaired t tests and logistic regression analysis were used to identify the associations of cervical sagittal alignment with ASD and HO.
Results: We found that patients who developed ASD showed significantly lower FSUA (2.1° vs. -1.4°, p < 0.001) and T1s values (28.4° vs. 25.5°, p = 0.029) after surgery. Similarly, the postoperative CL was significantly better in patients without ASD or HO (18.0° vs. 14.4°, p = 0.043). The decrease in the T1s at the last follow-up was significantly larger in the patients with ASD (-11.0° vs. -3.2°, p = 0.003), HO (-6.7° vs. -2.7°, p = 0.050), and ASD or HO (-7.0° vs. -0.8°, p < 0.001) than in those without ASD or HO. Multivariate logistic regression analysis showed that both the FSUA and T1s are associated with ASD and that the degree of CL is associated with postoperative complications.
Conclusion: The results imply that maintaining cervical sagittal alignment after Prestige-LP CDR is important.