The Predictable Factors of the Postoperative Kyphotic Change of Sagittal Alignment of the Cervical Spine after the Laminoplasty

STUDY DESIGN Prospective study. OBJECTIVE To identify the impact of laminoplasty on range of motion (ROM) and sagittal alignment of the cervical spine. SUMMARY OF BACKGROUND DATA Cervical laminoplasty is an effective procedure decompressing multilevel spinal cord compression. Preoperative lordosis of the cervical spine is a prerequisite for laminoplasty, and maintaining postoperative lordosis is also important for decompression of the spinal cord. MATERIALS AND METHODS Eighty-five patients who planned open door laminoplasty from C3-C7 were studied. Preoperative diagnosis included myelopathy cases associated with cervical spondylosis in 52, ossification of posterior longitudinal ligament in 29, and multilevel disc herniation in 4 cases. Cervical spine lateral radiography in neutral, flexion, and extension were taken before surgery and at 2-year follow-up. The cervical lordosis or kyphosis was measured by the Cobb's method. Diagnosis, degree of preoperative lordosis in the neutral position, and degree of preoperative sagittal alignment in flexion and extension were studied as risk factors for postoperative kyphosis. RESULTS ROM was decreased 30.5% after laminoplasty. The mean preoperative lordosis in the neutral position was 16.2 degrees and postoperative lordosis was 11.4 degrees. Kyphosis (mean, 12.2 degrees) was observed in 9 patients (10.6%) after surgery. All of them had been diagnosed as myelopathy cases associated with cervical spondylosis. The preoperative lordotic angle was significantly smaller in the kyphotic group than in the lordotic group. In the kyphotic group, preoperative flexion was 10.2 degrees larger and extension was 10.3 degrees smaller than in the lordotic group. The kyphotic group showed 19.3 degrees of kyphosis in flexion and 8.7 degrees of lordosis in extension before surgery. CONCLUSION ROM of the cervical spine decreased by 30.5% after laminoplasty. Kyphosis was developed in 10.6% of the patients. The preoperative factors affecting postoperative kyphosis are diagnosis of myelopathy cases associated with cervical spondylosis, a lordosis angle of <10 degrees, and a kyphotic angle during flexion that is larger than a lordotic angle during extension.