OBJECTIVE: The atlantodental interval (ADI) is used in assessing atlantoaxial stability. This measurement may potentially be affected by several features encountered during patient examination. This study examined the influence of 3 features: age, sex, and posture, on the measurement of ADI in a normal population. METHODS: The ADI was measured sequentially on 269 lateral cervical radiographs of adults with no demonstrated bony injury. Images were stratified by age and sex with equal representation in each age group. A further 25 asymptomatic adults were assessed for posture using craniovertebral angle measured from digital lateral photographs. The ADI was then measured from a lateral radiograph. The data were examined for correlation between age, craniovertebral angle, and ADI using Spearman rank correlation. The ADI of age groups was compared by Kruskal-Wallis test. The relationship between ADI and sex was examined using Wilcoxon rank sum test. Interaction between age and sex was explored using an interaction term in regression analysis. RESULTS: The ADI decreased with age, median measurements reducing from 2.07 to 0.85 mm across age groups (P < .01). No significant relationship was demonstrated between ADI and sex. No significant interaction was demonstrated between age and sex. Measurements of craniovertebral angle did not correlate with ADI (ρ = 0.03, P = .90). CONCLUSION: The magnitude of ADI decreases with advancing age. Age should be considered a modifying factor when interpreting measurement of ADI, particularly in consideration of potential minor instabilities. Patient sex does not appear to influence ADI, either independently or in interaction with age. Craniocervical posture variation does not influence ADI in an asymptomatic adult population.
OBJECTIVE: The atlantodental interval (ADI) is used in assessing atlantoaxial stability. This measurement may potentially be affected by several features encountered during patient examination. This study examined the influence of 3 features: age, sex, and posture, on the measurement of ADI in a normal population. METHODS: The ADI was measured sequentially on 269 lateral cervical radiographs of adults with no demonstrated bony injury. Images were stratified by age and sex with equal representation in each age group. A further 25 asymptomatic adults were assessed for posture using craniovertebral angle measured from digital lateral photographs. The ADI was then measured from a lateral radiograph. The data were examined for correlation between age, craniovertebral angle, and ADI using Spearman rank correlation. The ADI of age groups was compared by Kruskal-Wallis test. The relationship between ADI and sex was examined using Wilcoxon rank sum test. Interaction between age and sex was explored using an interaction term in regression analysis. RESULTS: The ADI decreased with age, median measurements reducing from 2.07 to 0.85 mm across age groups (P < .01). No significant relationship was demonstrated between ADI and sex. No significant interaction was demonstrated between age and sex. Measurements of craniovertebral angle did not correlate with ADI (ρ = 0.03, P = .90). CONCLUSION: The magnitude of ADI decreases with advancing age. Age should be considered a modifying factor when interpreting measurement of ADI, particularly in consideration of potential minor instabilities. Patient sex does not appear to influence ADI, either independently or in interaction with age. Craniocervical posture variation does not influence ADI in an asymptomatic adult population.