Measurement variability in the assessment of sagittal alignment of the cervical spine: a comparison of the gore and cobb methods

Abstract

Background: Reconstructive procedures of the cervical spine are being performed with increasing frequency. Maintenance of physiologic sagittal alignment is an essential component of reconstructive procedures of the spine. Two methods exist for measuring sagittal alignment in the cervical spine: the Gore and Cobb methods. An experimental study comparing Gore and Cobb measurement techniques for nonspondylotic and spondylotic cervical spines was conducted. The objectives were to assess the intra- and interobserver variability of both the Gore and the Cobb methods of measurement to determine the most reproducible technique for assessing sagittal alignment of the cervical spine.

Methods: With use of C3 and C7 as the end vertebrae, lateral radiographs of 20 nonspondylotic (group 1) and 20 spondylotic (group 2) cervical spines were measured by the Gore and Cobb methods on three different occasions by three orthopaedic surgeons with different levels of experience.

Results: For group 1, there was less intra- and interobserver variability for the Gore method than for the Cobb method (P < 0.05). Group 2 measurements were also less variable for the Gore method, although this was not statistically significant. Pooling all three observers, 95% confidence limits for intra- and inter-observer variability for the Gore method were 3 degrees and 6 degrees for group 1 and 4 degrees and 7 degrees for group 2, respectively. For the Cobb method, corresponding values were 4 degrees and 9 degrees for group 1 and 5 degrees and 9 degrees for group 2. Overall, intraobserver measurements were less variable than interobserver measurements (P < 0.01). There were no significant differences in variability based on experience level.

Conclusion: Measurements of cervical spine sagittal alignment by the Gore method are more reproducible than by the Cobb method.