External Validity of the Novel Surrogate Measures for Occipitocervical Alignment

Background: Occipitocervical fusion (OCF) is a rare and often challenging surgical procedure. Several methods have been introduced to obtain the best measures for occipitocervical alignment. The mandible-C2 angle was first introduced in 2020. In this study, we aimed to evaluate the out-of-sample validity of these measures. Methods: We retrospectively studied 274 lateral cervical radiographs of patients aged 1 to 87 years with no cervical pathology evident on X-ray. A board-certified radiologist and a second-year radiology resident performed the measurements on five specific angles as suggested by Bellabarba. The five angles measured consisted of: 1) anterior C2 body/anterior mandible angle (AB/AM), 2) anterior C2 body/posterior mandible angle (AB/PM), 3) posterior C2 body/anterior mandible angle (PB/AM), 4) posterior C2 body/posterior mandible angle (PB/PM), and 5) occipito-C2 angle (OC2A). Results: Inter-rater correlation data were calculated for single and average measures. The inter-rater agreement for individual angle measures of O-C2A, AB/AM, AB/PM, PB/AM, and PB/PM were 0.49, 0.11, 0.25, 0.33, and 0.49, respectively. The intraclass correlation coefficient (ICC) for average measures of O-C2A, AB/AM, AB/PM, PB/AM, and PB/PM were 0.66, 0.20, 0.40, 0.50, and 0.66, respectively. Conclusion: Our study did not find statistically significant evidence to confirm that these angles were dependable indicators of occipitocervical alignment, except for the PB/PM angle, which showed a validity comparable to our reference angle