Dynamic Evaluation of the Spinal Cord in Patients With Cervical Spondylotic Myelopathy Using a Kinematic Magnetic Resonance Imaging Technique

Abstract

STUDY DESIGN: This prospective study analyzed preoperative and postoperative dynamic changes of the spinal cord in patients with cervical spondylotic myelopathy. OBJECTIVE: (1) To study preoperative kinematic characteristics of the spinal cord in patients with cervical spondylotic myelopathy and compare results with healthy individuals, (2) to understand the dynamic changes of the spinal cord after posterior decompression, and (3) to discover whether the degree of posterior shifting is correlated with surgical outcomes using kinematic magnetic resonance imaging (MRI). SUMMARY OF BACKGROUND DATA: Laminoplasty for cervical myelopathy increases the space occupied by the spinal cord leading to a decompressive effect on the cord. However, no consecutive studies have reported the kinematic characteristics of the cervical spine in patients with cervical spondylotic myelopathy both preoperatively and postoperatively. Additionally, there have been no reports investigating the effects of posterior cord shifting in the neutral and maximum flexion and extension positions on surgical outcomes after cervical laminoplasty. METHODS: Twenty cervical spondylotic myelopathy patients who underwent extensive laminoplasty and 20 healthy individuals were examined. Preoperative and postoperative MRI records were available in all cases. The cervical spines of the subjects were examined in the neutral and maximum flexion and extension positions using an MRI scanner. Sagittal T1-weighted images were obtained at 12 different angles. Images were analyzed for the distance between the dorsal edge of the vertebral column and the center of the cord at each disc level using NIH image software. RESULTS: Average cord distances (L value) in the neutral position and maximum extension position at C4/5 was significantly smaller than those at the other disc levels. The spinal cords of the patients after laminoplasty moved dorsally in the enlarged spinal canal in the neutral position, and in the maximum flexion and extension position. However, the degree of posterior spinal cord shifting was not correlated with surgical outcomes. CONCLUSIONS: Cord distances are relatively smaller at C4/5 and C5/6 levels, resulting in a narrowing of the posterior subarachnoid space with posterior cord compression in patients with cervical spondylotic myelopathy. The outcome of surgery was not correlated with the magnitude of postoperative backward shifting of the spinal cord, although the spinal cord of patients after posterior decompression moved significantly dorsally at any of the flexed, neutral, or extended spinal positions. Thus numerous factors might affect the postoperative outcomes.