Quantitative prediction of spinal cord drift after cervical laminectomy and arthrodesis

Study Design. Retrospective review of radiographic parameters. Objectives. To identify preoperative radiographic parameters that may be quantitatively predictive of postoperative spinal cord drift after cervical laminectomy and arthrodesis. Summary of Background Data. Cervical laminectomy and arthrodesis can be an effective method to treat anterior compressions of the spinal cord if there is a sufficient posterior spinal cord drift after surgery. Preoperative cervical alignment has shown some correlations to the degree of spinal cord shift, but whether this and other preoperative radiographic parameters can be used to quantitatively predict the amount of spinal cord drift is unclear. Materials and Methods. Preoperative and postoperative radiographs (radiographs, MRIs, and CT) of patients who had cervical laminectomy and arthrodesis were reviewed retrospectively. Various radiographic parameters, including sagittal alignment, longitudinal distance index, space available for the spinal cord at cephalad or caudad levels, and distance from apex of the lordosis to the C2-C7 vertical line were measured. In the first cohort of patients, these parameters were correlated with mean postoperative spinal cord shift to identify any relationships. In the second cohort of patients, the identified association was used on preoperative imaging studies to attempt quantitative prediction of the postoperative spinal cord shift. Results. Space available for the spinal cord at the level immediately cephalad to the laminectomized segments had high correlations (R-2 = 0.94) to the postoperative spinal cord shift. This association was used to quantitatively predict postoperative spinal cord shift within 11% +/- 6% of the measured value. If 4 mm of mean postoperative spinal cord shift is desired, the ratio to the available space and anterior posterior diameter of the spinal cord should be approximately 2.0. Conclusion. Relative stenosis at the level directly cephalad to the laminectomized level can affect the degree of postoperative spinal cord shift. Preoperative axial imaging studies should be closely scrutinized to ensure that adequate space is available at the cephalad adjacent level to allow sufficient cord shift after decompressive laminectomy and arthrodesis.