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.