Effective lordosis: analysis of sagittal spinal canal alignment in cervical spondylotic myelopathy

Analysis of cervical sagittal deformity in patients with cervical spondylotic myelopathy (CSM) requires a thorough clinical and radiographic evaluation to select the most appropriate surgical approach. Angular radiographic measurements, which are commonly used to define sagittal deformity, may not be the most appropriate to use for surgical planning. The authors present a simple straight-line method to measure effective spinal canal lordosis and analyze its reliability. Furthermore, comparisons of this measurement to traditional angular measurements of sagittal cervical alignment are made in regards to surgical planning in patients with CSM.

Twenty preoperative lateral cervical digital radiographs of patients with CSM were analyzed by 3 independent observers on 3 separate occasions using a software measurement program. Sagittal measurements included C2-7 angles utilizing the Cobb and posterior tangent methods, as well as a straight-line method to measure effective spinal canal lordosis from the dorsal-caudal aspect of the C2-7 vertebral bodies. Analysis of variance for repeated measures or Cohen 3-way (kappa) correlation coefficient analysis was performed as appropriate to calculate the intra- and interobserver reliability for each parameter. Discrepancies in angular and effective lordosis measurements were analyzed.

Intra- and interobserver reliability was excellent (intraclass coefficient > 0.75, kappa > 0.90) utilizing all 3 techniques. Four discrepancies between angular and effective lordotic measurements occurred in which images with a lordotic angular measurement did not have lordosis within the ventral spinal canal. These discrepancies were caused by either spondylolisthesis or dorsally projecting osteophytes in all cases.

Although they are reliable, traditional methods used to make angular measurements of sagittal cervical spine alignment do not take into account ventral obstructions to the spinal cord. The effective lordosis measurement method provides a simple and reliable means of determining clinically significant lordosis because it accounts for both overall alignment of the cervical spine as well as impinging structures ventral to the spinal cord. This method should be considered for use in the treatment of patients with CSM.