Plain roentgenographic and CT scan morphometric analysis of the anterior atlantodens interval (AADI) and posterior atlantodens interval (PADI) in the Indian population

INTRODUCTION

An anterior atlantodental interval (AADI) of more than 10 mm is clinically significant as it suggests transverse ligament rupture and the normal upper limit of normal in adults is 3 mm.[3] The lower limit of normal value of posterior atlantodental interval (PADI) in adults is 14 mm. Here, we evaluated/compared the baseline ranges for AADI and PADI utilizing X-rays versus computed tomography (CT) scans in an Indian head-trauma population.

MATERIALS AND METHODS

There were 116 patients with head injuries who underwent cervical X-rays and CT scans in this study. Films were independently evaluated by two orthopedic surgeons who similarly measured AADI and PADI on plain radiographs versus CT scans [Figure 1]. All these patients with head injuries had normal cervical anatomy on imaging.

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Figure 1:: Sagittal computed tomography showing atlantodens interval.

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RESULTS

AADI ranged from 1.36 ± 0.45 mm on X-rays to 1.393 ± 0.47 mm on CT scans, while PADI varied from 18.04 ± 2.44 mm on X-rays to 18.07 ± 2.43 mm on CT scans [Figures 2 and 3]. We found 109 (93.96%) subjects with AADI below 2 mm, and 8 (6.8%) subjects with PADI below 14 mm who were clinically asymptomatic [Table 1]. Using the Mann–Whitney test, the difference between the male and female values was statistically significant while the difference between the parameters as measured on X-ray and CT scan was not statistically significant.

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Figure 2:: Values for atlantodens interval on X-ray.

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Figure 3:: Values for atlantodens interval on computed tomography scan.

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Table 1:: Ranges of AADI, PADI in this study.

DISCUSSION

The values of AADI and PADI obtained in the present study differed significantly from the previously published values based on standard plain radiographs. We found that the differences in measurements of AADI and PADI made on X-ray and CT scans were not statistically significant. Therefore, X-rays are reliable for assessing the CVJ anatomy in emergency scenarios, especially where CT scans are not available.

Rojas et al.[5] found that the normal values for the craniocervical relationships on MDCT were significantly different from the accepted ranges of normal on plain radiographs and 95% of patients had a BDI <8.5 mm on MDCT versus 12 mm on data from plain radiographs.

Chen et al. studied the AADI in a normal Chinese population using CT;[2] the AADI was 1.83 ± 0.46 mm (0.9–3.4 mm) in males and 1.63 ± 0.43 mm (0.5–3.2 mm) in females.

Liu et al.[4] studying AADI using MDCT found that AADI was 0.85–3.12 mm in those 18–39 years of age, 0.71–2.55 mm those 40–59-years-old, and 0.00–2.37 mm in those over 60 years of age, that is, MDCT AADI linearly decreased with increasing age.

Boden et al.[1] concluded that the most important predictor of the potential for neurological recovery after the surgery was the preoperative posterior atlanto-odontoid interval.

CONCLUSION

We found the normal upper limit of AADI on sagittal CT scans was 2 mm versus the previously accepted 3 mm. Further, there can be patients with a PADI below 14 mm who have no neurological symptoms.