In vivo 3D kinematic changes in the cervical spine after laminoplasty for cervical spondylotic myelopathy

Object. Cervical laminoplasty is an effective procedure for decompressing the spinal cord at multiple levels, but restriction of neck motion is one of the well-known complications of the procedure. Although many authors have reported on cervical range of motion (ROM) after laminoplasty, they have focused mainly on 2D flexion and extension on lateral radiographs, not on 3D motion (including coupled motion) nor on precise intervertebral motion. The purpose of this study was to clarify the 3D kinematic changes in the cervical spine after laminoplasty performed to treat cervical spondylotic myelopathy. Methods. Eleven consecutive patients (6 men and 5 women, mean age 68.1 years, age range 57-79 years) with cervical spondylotic myelopathy who had undergone laminoplasty were included in the study. All patients underwent 3D CT of the cervical spine in 5 positions (neutral, 45 head rotation left and right, maximum head flexion, and maximum head extension) using supporting devices. The scans were performed preoperatively and at 6 months after laminoplasty. Segmental ROM from Oc-C1 to C7-T1 was calculated both in flexion-extension and in rotation, using a voxel-based registration method. Results. Mean C2-7 flexion-extension ROM, equivalent to cervical ROM in all previous studies, was 45.5 degrees +/- 7.1 degrees preoperatively and 35.5 degrees +/- 8.2 degrees postoperatively, which was a statistically significant 33% decrease. However, mean Oc-T1 flexion-extension ROM, which represented total cervical ROM, was 71.5 degrees +/- 8.3 degrees preoperatively and 66.5 degrees +/- 8.3 degrees postoperatively, an insignificant 7.0% decrease. In focusing on each motion segment, the authors observed a statistically significant 22.6% decrease in mean segmental ROM at the operated levels during flexion-extension and a statistically insignificant 10.2% decrease during rotation. The most significant decrease was observed at C2-3. Segmental ROM at C2-3 decreased 24.2% during flexion-extension and 21.8% during rotation. However, a statistically insignificant 37.2% increase was observed at the upper cervical spine (Oc-C2) during flexion-extension. The coupling pattern during rotation did not change significantly after laminoplasty. Conclusions. In this first accurate documentation of 3D segmental kinematic changes after laminoplasty, Oc-T1 ROM, which represented total cervical ROM, did not change significantly during either flexion-extension or rotation by 6 months after laminoplasty despite a significant decrease in C2-7 flexion-extension ROM. This is thought to be partially because of a compensatory increase in segmental ROM at the upper cervical spine (Oc-C2).