A new method for measurement of occipitocervical angle by occiput-C3 angle

The description of the measurement technique of the posterior occiput-third cervical spine (OC3) angle-before performing occipitocervical fusion is still controversial. Setting an appropriate alignment in occipitocervical instrumentation is important for successful fixation surgery. Several methods were used for quantifying occipitocervical alignment on the lateral radiograph. This study was performed to describe a measurement technique of OC3 angle and comparing reliability and reproducibility in the measurement of occipitocervical angle with previous method. The purpose of this study was to determine the best technique for assessing this angle.

Three hundred and twenty-six lateral cervical spine radiographs from volunteers without spinal disorder were taken in neutral position and collected from June 2011 to December 2012. Analysis consisted of measurement of the OC3 angle and posterior occipitocervical angle. Inter- and intra-observer reliabilities were assessed using limit agreement test.

The mean OC3 angle measurements were approximately 107 (94-120) degrees. Intra- and inter-observer error assessed by 95% limit agreement was approximately ±5.5 and ±7.5, while the POCA measurements were approximately 108 (94-120) degrees. Intra- and inter-observer error assessed by 95% limit agreement was approximately ±13.3 and ±18.2.

The OC3 angle measurement is a simple method, good inter- and intra-observer reliabilities to measure of the occipitocervical angle. That can be useful to setting the patient's position and facilitate confirmation of the occipitocervical neutral position during occipitocervical fusion.