Measurement of occipitocervical angle.

STUDY DESIGN: This study compared the reliability of 3 techniques used to measure alignment between the occiput and cervical spine. OBJECTIVES: Intraobserver and interobserver intraclass correlation coefficient were computed to determine the most reliable method to measure occipitocervical angle. SUMMARY OF BACKGROUND DATA: No studies have been performed comparing occipitocervical angle measurement techniques. METHODS: The angles between the inferior endplate of second cervical vertebrae and the occiput line using the Chamberlain line, McRae line, and McGregor line were measured from lateral cervical radiographs of 30 healthy volunteers. Five spine surgeons made measurements. RESULTS: Mean intraobserver variances of the angles using Chamberlain line, McRae line, and McGregor line were 2.0 degrees (ranging from 0 degrees-15 degrees), 4.7 degrees (from 0 degrees-28 degrees), and 1.5 degrees (from 0 degrees-9 degrees), respectively; intraobserver intraclass correlation coefficients of the angles were 0.956, 0.835, and 0.975. Mean interobserver variances of the angles using Chamberlain line, McRae line, and McGregor line were 2.3 degrees (from 0.4 degrees-6.4 degrees), 5.0 degrees (from 1.8 degrees-11.9 degrees), and 1.4 degrees (from 0 degrees-4.5 degrees), respectively; interobserver intraclass correlation coefficients were 0.939, 0.802, and 0.972. The highest reliability indexes were obtained for McGregor line. CONCLUSIONS: The McGregor line is the most reproducible and reliable method for measurement of the occipitocervical angle.