The cross-sectional area of the cervical spinal canal in patients with cervical spondylotic myelopathy - Correlation of preoperative and postoperative area with clinical symptoms

Study Design. Retrospective analysis of routine computed tomography investigations. Objective. To investigate whether the extent of clinical symptoms in patients undergoing surgery for cervical spinal myelopathy depends on the transsectional area of the cervical spinal canal. Methods. Forty-five patients underwent surgery using different techniques to enlarge the width of the spinal canal. For clinical evaluation before and after surgery. a modified score of the Japanese Orthopedic Association was used (mean follow-up period, 19.6 +/- 9.1 months). The cross-sectional area of the spinal canal in computed tomography scans (C4-C6) was quantified 1 day before and 1 week after surgery using pixel-dependent area calculation software for three different density ranges given in Hounsfield units. Results. After surgery, a significant enlargement of the cervical spinal canal of 78.2 +/- 55.9% could be achieved. The Japanese Orthopedic Association score increased significantly by 3.7 +/- 2.2 points from a median preoperative score of 10 to a score of 14 after surgery. Patients with a preoperative Japanese Orthopedic Association score greater than or equal to 10 achieved a significantly better outcome after surgery. Conversely, no patient with a postoperative area larger than 1.6 cm(2) achieved a score of less than 12 Japanese Orthopedic Association-points. No significant linear correlation, however, was found between the postoperative transsectional area and the postoperative Japanese Orthopedic Association score of all patients. Conclusion. The preoperative clinical presentation of the patient was found to be the only prognostic hint for improvement after surgery. Preoperative area measurements of the spinal canal cannot be used as a prognostic tool for surgical outcome. Further, the postoperative measurements do not correlate with the clinical outcome. These data, however, which refer to C4 to C6, provide evidence that every surgical procedure to enlarge the cervical spinal canal should result in an area of 1.6 cm(2) or more.