Preoperative Decreased Hounsfield Unit Values of Cervical Vertebrae and the Relative Cross-Sectional Area of Flexion/Extension Paraspinal Muscles Are Novel Risk Factors for the Loss of Cervical Lordosis after Open-Door Laminoplasty

Abstract

Open-door laminoplasty is widely used for patients with cervical spondylotic myelopathy (CSM). However, the loss of cervical lordosis (LCL) seems to be unavoidable in the long-term follow-up after surgery, which may affect the clinical outcomes. The risk factors for this complication are still unclear. In this study, patients who underwent open-door laminoplasty between April 2016 and June 2021 were enrolled. Cervical X-rays were obtained to measure the C2–7 Cobb angle, C2–7 sagittal vertical axis (SVA), T1 slope (T1S) and ranges of motion (ROM). Cervical computed tomography (CT) scans and magnetic resonance imaging (MRI) were collected to evaluate the cervical Hounsfield unit values (HU) and the relative cross-sectional area (RCSA) of paraspinal muscles, respectively. A total of 42 patients were included and the average follow-up period was 24.9 months. Among the patients, 24 cases (57.1%) had a LCL of more than 5° at a 1-year follow-up and were labeled as members of the LCL group. The follow-up JOA scores were significantly lower in the LCL group (13.9 ± 0.6 vs. 14.4 ± 0.8, p = 0.021) and the mean JOA recovery rate was negatively correlated with LCL (r = −0.409, p = 0.007). In addition, LCL was positively correlated to the preoperative T1S, flexion ROM, flexion/extension ROM and the RCSA of flexion/extension muscles, while it was negatively correlated to extension ROM and the HU value of cervical vertebrae. Furthermore, multiple linear regression showed that preoperative T1S, mean HU value of cervical vertebrae, flexion/extension ROM and the flexion/extension RCSA were independent risk factors for LCL. Spine surgeons should consider these parameters before performing open-door laminoplasty.