MATERIAL and METHODS: Forty-nine patients were analysed, who underwent surgery for BI, between July 2020 and June 2023. Radiological assessment was done in all the patients using reconstructed midsagittal images on computed tomography scans .

RESULTS: Mean age was 34.82 ± 10.52 years with male preponderance (67.35%) in patients with BI. We also analysed randomly selected 120 control subjects (male: female = 59:61) with mean age 43.5 ± 14.08 years. The mean distance of tip of the odontoid process from PI line in patients with BI was 3.39 ± 3.09 mm. The mean value of KI in the patients with BI was 28.57 ± 1.68 mm. Receiver operating characteristic (ROC)curve was used for analysing the distance of the tip of the odontoid process from PI line in the patients with BI which produced area under curve( AUC) of 0.97 (confidence interval [CI] -0.931 to 0.990, p<0.0001). Cut-off point of 7.5 mm was identified for the distance of tip of odontoid process from PI line with sensitivity of 89.8% and specificity of 97.5% having 95.27% diagnostic accuracy for BI. ROC curve analysis of value of KI for the diagnosis of BI produced AUC of 1( CI: 0.978 to 1.000, p<0.0001). Cut-off value of 33.2 mm for KI was identified for diagnosing BI with 100% accuracy.

CONCLUSION: The distance of tip of the odontoid process from PI line <7.5 mm and value of KI <33.2 mm, both of these parameters can diagnose BI with comparable accuracy to most widely used conventional radiological methods. Keywords : Basilar Invagination, Palato internal occipital protuberance, Klaus? index, Odontoid process, Chamberlain?s line, Diagnosis, Criteria