Reference ranges for atlantodental interval in adults and its variation with age and gender in a large series of subjects on multidetector computed tomography.

The atlanto-dental interval measurement in the cervical spine in young adults has been reported on multidetector computed tomography (MDCT), but has not been systematically assessed in all ages.To evaluate the reference ranges for the atlanto-dental interval (ADI) in a large sample of adult patients on MDCT and to analyze the relationships of these measurements with gender and age of the patients as well as inter-observer performance.First, a consecutive series of 700 Chinese patients aged over 18 years undergoing an upper cervical MDCT scan were divided equally into seven age groups. Second, the mid-sagittal image of the atlanto-dental joint was chosen for measurement and ADI was defined as the distance intercepted from the segment line linking the center of anterior atlas tubercle with that of posterior tubercle. Third, the correlation of ADI with age and gender was analyzed using linear regression analysis. Finally, the inter-observer performance was assessed using Bland and Altman's limits of agreement.The ADI was 1.77 ± 0.39 mm, 1.61 ± 0.37 mm, 1.58 ± 0.36 mm, 1.41 ± 0.29 mm, 1.31 ± 0.29 mm, 1.34 ± 0.28 mm, and 1.06 ± 0.47 mm in the age groups 18-24 years, 25-29 years, 30-39 years, 40-49 years, 50-59 years, 60-69 years, and older than 70 years, respectively. The range of ADI was 0.85-3.12 mm in the age group 18-39 years, 0.71-2.55 mm in the age group 40-59 years, and 0.00-2.37 mm in the age group older than 60 years. There was no difference between gender and ADI (r = 0.00, P = 1.000). ADI decreased linearly with age (r = -0.511, P = 0.000). The inter-observer performance was reliable.ADI measurements on MDCT linearly decrease with increasing age, and these are not affected by gender in adult patients. Different reference values might be used at different ages when diagnosing atlantoaxial anterior dislocation or subluxation.