K-line (-) in the neck-flexed position negatively affects surgical outcome of expansive open-door laminoplasty for cervical spondylotic myelopathy.

Abstract

BACKGROUND\nThe K-line in the neck-flexed position (FK-line) on radiography reflects dynamic factors and cervical alignment. Although the FK-line has been reported to affect the neurological recovery after muscle-preserving selective laminectomy for cervical spondylotic myelopathy (CSM), its influence on surgical outcomes after expansive open-door laminoplasty (ELAP) has not been investigated.\n\n\nMETHODS\nWe reviewed the surgical outcomes in 81 patients with multilevel CSM who underwent C4-C6 ELAP combined with C3 and C7 partial laminectomy using a laminoplasty plate and were followed up for at least 2 years. We defined the K-line (-) as some portion of a bony spur or the vertebral body crossing the FK-line, whereas the FK-line (+) was defined as that never crossing the FK-line. Patients were divided into the FK-line (+) (n\xa0=\xa061) and FK-line (-) groups (n\xa0=\xa020), and the surgical outcomes were compared between the groups. A multivariate analysis was performed to identify the factors that influenced the neurological outcomes.\n\n\nRESULTS\nThe FK-line (-) group had a smaller C2-C7 angle, smaller C7 slope, greater postoperative increase in the C2-C7 sagittal vertical axis, greater kyphosis in cervical flexion and less lordosis in cervical extension, and higher incidence of postoperative residual spinal cord compression. The preoperative-to-postoperative changes in the Japanese Orthopedic Association (JOA) score and JOA score recovery rate (RR) were lower in the FK-line (-) group. The multiple linear regression analysis revealed that the K-line (-) (β\xa0=\xa0-0.327, P\xa0=\xa00.011) and high signal intensity (SI) changes on T2-weighted imaging (WI) combined with the low SI changes on T1-WI in the spinal cord (β\xa0=\xa0-0.320, P\xa0=\xa00.013) negatively affected the JOA score RR.\n\n\nCONCLUSIONS\nThe FK-line can be used for patients with CSM as a simple indicator of neurological outcomes after ELAP.