Cervical Laminectomy Width and Spinal Cord Drift Are Risk Factors for Postoperative C5 Palsy

Background: Cervical laminectomy and fusion (CLF) is a treatment option for multilevel cervical spondylotic myelopathy. Postoperative C5 nerve palsy is a possible complication of CLF. It has been suggested that C5 nerve palsy may be due to posterior drift of the spinal cord related to a wide laminectomy trough. Purpose: To test the hypothesis that excessive spinal cord drift into a wide laminectomy trough is associated with C5 palsy. Study Design: Retrospective case-control study. Patient Sample: Seventeen patients with C5 palsy, 8 patients as control group. Outcome Measures: Spinal cord positional measurements on magnetic resonance imaging (MRI). Methods: All patients who underwent elective CLF for cervical spondylotic myelopathy or ossified posterior longitudinal ligament using posterior instrumentation between 2004 and 2008 were included. Patients who underwent CLF for trauma, infection, or tumors were excluded. Clinical and radiographic outcomes were assessed by chart review (minimum of 1 y follow-up). Patients who developed a new postoperative C5 nerve palsy underwent repeat MRI. The control group also underwent CLF, did not develop a neurological deficit, and received a postoperative MRI for evaluation of possible infection. MRI measurements included the width of the laminectomy trough, the distance from the posterior vertebral body or disk to the anterior spinal cord, the width of the spinal cord herniated into the laminectomy defect, and C2–7 sagittal alignment. Preoperative radiographic measurements included preoperative vertebral body diameter, spinal canal diameter, and sagittal vertical offset. Results: There were seventeen patients with C5 nerve root palsy and 8 patients without C5 nerve root palsy. There were no baseline differences in fusion levels, instrumentation used, patient age, or sex. MRI measurements revealed an increase in mean postoperative cord drift in patients with C5 palsy at C3 (4.2 vs. 2.2 mm, P=0.002), C4 (4.6 vs. 2.8 mm, P=0.056), C5 (5.1 vs. 2.4 mm, P=0.011), and C6 (5.2 vs. 2.4 mm, P=0.003). There was a significant increase in C5 laminectomy trough width among patients with postoperative C5 palsy (17.9 vs. 15.2 mm, P=0.032), but there was no difference in sagittal alignment. Conclusions: A wider laminectomy at C5 was associated with an increased risk of postoperative C5 palsy. Increased preoperative spinal canal diameter is also associated with increased risk of C5 palsy. In addition, patients who experienced C5 nerve palsy had a significantly greater posterior spinal cord drift. Strategies to reduce postoperative laminectomy trough width and spinal cord drift may reduce the risk of postoperative C5 palsy.