Medium-term outcomes of C3-6 laminoplasty for cervical myelopathy: a prospective study with a minimum 5-year follow-up.

C3-6 laminoplasty preserving muscle insertions into the C7 spinous process is reportedly associated with a significantly decreased frequency of postoperative axial neck pain. However, no prospective study has reported medium-term outcomes of C3-6 laminoplasty. The purpose of this study was to elucidate medium-term outcomes after C3-6 laminoplasty. Subjects comprised 31 patients with cervical myelopathy who underwent C3-6 laminoplasty preserving all bilateral muscles attached to the C2 and C7 spinous processes and were followed for ≥5 years. Clinical and radiological data were prospectively collected. Neurological status was assessed using Japanese Orthopaedic Association (JOA) score. Axial neck pain was graded as severe, moderate or mild. Sagittal alignment of the cervical spine and progression of ossification of the posterior longitudinal ligament (OPLL) were assessed by comparing serial lateral radiographs. Mean JOA score improved significantly from 10.6 before surgery to 14.7 at the time of maximum recovery, and slightly declined to 14.3 at final follow-up. In six patients who developed late deterioration, these conditions were unrelated to the cervical spine. As of final follow-up, only one patient (3.2%) had complained of axial neck pain persisting for 5 years. Although progression of OPLL was found in 63.6% of patients, none had experienced neurological deterioration due to this progression. At final follow-up, sagittal alignment of the cervical spine was more lordotic than before surgery. Medium-term outcomes of C3-6 laminoplasty were satisfactory. Frequencies of persistent axial neck pain and loss of cervical lordosis after surgery remained significantly decreased for ≥5 years postoperatively.