• Eduardo Martinez Del Campo, Samuel Kalb, Hector Soriano Baron, Jay D Turner, Matthew Neal, Timothy David Uschold, and Nicholas Theodore.
• Neurosurgery. 2015 Aug 1;62 Suppl 1:226.

IntroductionOur goal was to identify and compare the normal occipital-condyle-C1 interval (CCI) in healthy adults with the CCI in adults with atlanto-occipital dislocation (AOD) and establish a highly sensitive and specific cutoff value to diagnose AOD radiographically.MethodsEighty-one patients (59 non-AOD, 22 AOD) were included. Measurements obtained from thin-cut computed tomography scans of the craniovertebral joint to assess atlanto-occipital dislocation included: CCI, condylar sum, and standard diagnostic tools.ResultsNon-AOD patients were 50.8% (n = 30) male and 49.2% (n = 29) female, mean age was 42.4 ± 16 years (range 19-87 years). AOD patients were 45.5% (n = 10) male and 54.5% (n = 12) female with a mean age of 38.2 ± 9.7 years (range 20-56 years). Interrater reliabilities were all above 0.98 (95% CI) for CCI measurements. A total of 1296 measurements were made of the CCI in 81 patients. The mean CCI for non-AOD patients was 0.89 ± 0.12 mm, the single largest CCI measurement was 1.4 mm, and the largest mean for either right or left CCI was 1.2 mm. The mean condylar sum was 1.8 ± 0.2 mm, and the largest condylar sum value was 2.2 mm. Linear regression with age predicted an increase in CCI of 0.001 mm/y (P < .05). The mean CCI in AOD patients was 3.35 ± 1.8 mm (range 1.5-6.4 mm). A cutoff value for AOD was determined at 1.5 mm for the CCI and 3.0 mm for the condylar sum, both with a sensitivity of 1 and false-negative rate of 0. Sensitivity for Powers, Wholey, Harris, Sun, Wackenheim, and Lee tests were determined to be 0.55, 0.46, 0.27, 0.23, 0.41, and 0.41, respectively.ConclusionThe revised CCI (1.5 mm) and condylar sum (3.0 mm) cutoff values have the highest sensitivity and specificity for the diagnosis of AOD in the adult population.

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