Mechanisms of compensatory for cervical lordosis changes after laminectomy with fusion

BACKGROUND: The compensatory mechanisms for cervical lordosis change after laminectomy with fusion was not clear. The objective of this study was to evaluate the compensatory behaviors for cervical lordosis change after laminectomy with fusion. METHODS: This was a retrospective radiological analysis of 43 patients with cervical spondylotic myelopathy who underwent laminectomy with fusion (LCF). The following cervical parameters were measured: C2-7 Cobb angle (C2-7), occiput-C2 angle (O-C2), the cervical sagittal vertical axis (cSVA), and T1 slope (T1S). The difference was calculated for all angle parameters between the two time points using the following formula: the amount of change (Δ) = (value at the follow-up)—(preoperative value). Non-parametric tests and the t-test were used to compare the difference. The Pearson correlation test was performed, and stepwise multiple regression analysis was performed to determine the best correlation between ∆cSVA and ∆T1S. RESULTS: The mean age of 43 patients was 65.51 ± 9.80 years. All patients were classified into two subgroups based on ΔcSVA: Group M (maintained) and, Group I (increased). The preoperative O-C2, C2-7, T1S, and cSVA were similar between Group M and group I (p = 0.950, p = 0.731, p = 0.372, and p = 0.152, respectively). Postoperative O-C2 and postoperative cSVA were significantly different (p = 0.036 and p = 0.004, respectively). ∆O-C2, ∆T1S and ∆cSVA were significantly different between the two groups (p = 0.006, p = 0.000, and p = 0.000, respectively). ΔcSVA had significant correlations with ΔO-C2 neutral angle (r = 0.377) and ΔT1S (r = 0.582). A linear regression equation was established: ΔcSVA = 0.602 + 0.103 * ΔT1S (R = 0.582, R(2) = 0.339). CONCLUSIONS: The decrease of TIS should be the first and foremost compensation for the loss of lordosis in C2-7 segments after LCF. When the change of T1S alone can not prevent the deterioration of cervical sagittal balance, further increases in the O-C2 segment occur.