Modified K-Line in Neck Extension Is a Prognostic Indicator of the Surgical Outcome at 5 Years After Cervical Laminoplasty for Cervical Spondylotic Myelopathy

Study Design. A retrospective comparison of the surgical outcome after cervical laminoplasty for cervical spondylotic myelopathy (CSM) using a modified K-line based on lordosis in neck extension as a predictor: in K-line Back CSM (KB group), the K-line crosses the ventral edge of any of the spinous processes, whereas in K-line Front CSM (KF group), the K-line does not. Objective. To investigate the neurological and radiological outcomes 5 years after surgery and the contact between the spinal cord and posterior elements after laminoplasty for CSM using the modified K-line. Summary of Background Data. No indicators on a lateral radiograph can predict the neurological outcome after laminoplasty for CSM. Methods. Patients with CSM were divided into KB (n = 20) and KF groups (n = 13). We compared the postoperative Japanese Orthopedic Association (JOA) score, recovery rate, grip-and-release and foot-tapping test results, alignment, and contact between the spinal cord and posterior elements between the two groups. Results. The postoperative JOA score and its recovery rate were significantly lower in the KB group (12.4 points and 34.1%, respectively) than in the KF group (14.1 points and 59.0%, respectively) at final follow-up (P=0.0415 and 0.0458). The grip-and-release and foot-tapping test results improved significantly in the KF group but not in the KB group. In the KB group, a larger lordotic angle in extension at 1 year postoperatively continued until final follow-up. The rate of recovery of the JOA score in patients with contacts at both C4/5 and C5/6 and any contact in the KB group (-1.5% and 31.9%, respectively) were lower (P=0.0013 and 0.0534, respectively) than those in the KF group (58.6% and 60.7%, respectively). Conclusion. The K-line Back predicts a poor neurological outcome after laminoplasty for CSM. Decompression with fusion may be recommended for these patients.