Study design: Retrospective study.
Objective: To investigate whether loss of cervical lordosis (LCL) after laminoplasty can be predicted from specific preoperative dynamic radiograph measurements.
Summary of background data: Recent studies have focused on the correlation between LCL after laminoplasty and T1 slope. These studies explain this correlation through the injury of the posterior neck muscular-ligament complex (PMLC); however, this muscle injury model could not explain the less kyphotic change in high T1s patients, as reported in some studies as controversy. We have focused on the PMLC constriction reservoir which was represented by extension function (EF).
Methods: We retrospectively analyzed 50 consecutive patients who underwent open-door laminoplasty (>1-year follow-up). EF is defined as extension C2-7 Cobb angle (CA) minus neutral C2-7 CA (Ext CA - CA). LCL is defined as follow-up CA minus preoperative CA (CA [FU] - CA [PRE]), and significant kyphotic change was defined as LCL smaller than -10°.
Results: The distribution of LCL was -3.70 ± 7.98 and the significant kyphotic change occurred in 20% of the patients (10/50). EF, C2-7 sagittal vertical axis (PRE), and C2 slope (PRE) were found to be risk factors for LCL by multiple linear regression analysis. The receiver operating characteristic curve analysis revealed that EF could predict the significant kyphotic change well than previously known risk factors. The cutoff value of EF was 14°. No significant kyphotic change occurred at EF greater than or equal to 14°. Upon limiting the number of patients with preoperative straight curvature (n = 28), there is also no significant kyphotic change occurred in any patient whose EF was greater than or equal to 14°.
Conclusion: In our study sample, we found that there is no relation between T1 slope and LCL. We have identified a new factor, EF, that could predict LCL after laminoplasty. No significant kyphotic changes after laminoplasty occurred particularly when the EF was greater than or equal to 14°.
Level of evidence: 3.