Tehran University of Medical Sciences Journal of Orthopedic and Spine Trauma 2538-2330 10 4 2024 12 30 155 9 Ahmadreza Mirbolook 1. Associate Professor of orthopedic surgery, Department of Orthopedic, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Masoomeh Raoufi 2. Assistant Professor of Radiology, Department of Radiology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Yeganeh Yousefifar 3. Department of Radiology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Mobin Forghan 4. Department of orthopedic surgery, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mohammad Fakhari Student Research Committee, Arak University of Medical Sciences, Arak, Iran Mohammadreza Bozorgmanesh Tehran University of Medical Sciences 2023 08 20 2024 12 21 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. https://jost.tums.ac.ir/index.php/jost/article/view/527 https://jost.tums.ac.ir/index.php/jost/article/download/527/389