Correlation between cervical spine sagittal alignment and clinical outcome after cervical laminoplasty for ossification of the posterior longitudinal ligament

OBJECTIVE: The goal of this study was to determine the relationship between cervical spine sagittal alignment and clinical outcomes after cervical laminoplasty in patients with ossification of the posterior longitudinal ligament (OPLL). METHODS: Fifty consecutive patients who underwent a cervical laminoplasty for OPLL between January 2012 and January 2013 and who were followed up for at least 1 year were analyzed in this study. Standing plain radiographs of the cervical spine, CT (midsagittal view), and MRI (T2-weighted sagittal view) were obtained (anteroposterior, lateral, flexion, and extension) pre- and postoperatively. Cervical spine alignment was assessed with the following 3 parameters: the C2-7 Cobb angle, C2-7 sagittal vertical axis (SVA), and T-1 slope minus C2-7 Cobb angle. The change in cervical sagittal alignment was defined as the difference between the post- and preoperative C2-7 Cobb angles, C2-7 SVAs, and T-1 slope minus C2-7 Cobb angles. Outcome assessments (visual analog scale [VAS], Oswestry Neck Disability Index [NDI], 36-Item Short-Form Health Survey [SF-36], and Japanese Orthopaedic Association [JOA] scores) were obtained in all patients pre- and postoperatively. RESULTS: The average patient age was 56.3 years (range 38-72 years). There were 34 male patients and 16 female patients. Cervical laminoplasty for OPLL helped alleviate radiculomyelopathy. Compared with the preoperative scores, improvement was seen in postoperative VAS and JOA scores. After laminoplasty, 35 patients had kyphotic changes, and 15 had lordotic changes. However, cervical sagittal alignment after laminoplasty was not significantly associated with clinical outcomes in terms of postoperative improvement of the JOA score (C2-7 Cobb angle: p = 0.633; C2-7 SVA: p = 0.817; T-1 slope minus C2-7 lordosis: p = 0.554), the SF-36 score (C2-7 Cobb angle: p = 0.554; C2-7 SVA: p = 0.793; T-1 slope minus C2-7 lordosis: p = 0.829), the VAS neck score (C2-7 Cobb angle: p = 0.263; C2-7 SVA: p = 0.716; T-1 slope minus C2-7 lordosis: p = 0.497), or the NDI score (C2-7 Cobb angle: p = 0.568; C2-7 SVA: p = 0.279; T-1 slope minus C2-7 lordosis: p = 0.966). Similarly, the change in cervical sagittal alignment was not related to the JOA (p = 0.604), SF-36 (p = 0.308), VAS neck (p = 0.832), or NDI (p = 0.608) scores. CONCLUSIONS: Cervical laminoplasty for OPLL improved radiculomyelopathy. Cervical laminoplasty increased the probability of cervical kyphotic alignment. However, cervical sagittal alignment and clinical outcomes were not clearly related.