Lateral atlanto-dens interval variation in a normal South African population using Computed Tomography

Schoombee, Hendrik Bellingan

Lateral atlanto-dens interval variation in a normal South African population using Computed Tomography

Master Thesis

2019

Abstract

Rationale On routine Computed Tomography (CT) scans for suspected trauma of the cervical spine, the lateral atlanto-dens interval (LADI) is routinely observed and can readily be measured. Although values greater than the upper limit of normal may indicate atlanto-axial subluxation or ligament rupture, it is uncertain what the upper limit of normal for this measurement is, and whether this is a reliable indicator of injury to this region. The overall importance of this measurement in the setting of trauma is not well understood, as may be seen by the numerous conflicting previous studies. A step in the direction of resolving this uncertainty is to determine the range of normal measurements and their variability in a population cohort. Method A total of 201 patients were included in this study after meeting the inclusion criteria that the CT head scans were performed for reasons other than trauma and included the upper spine. Exclusion criteria included patients with any history of prior trauma or known congenital or pathological conditions of the upper neck. The lateral atlanto-dens interval (LADI) was measured on these patients and any asymmetry between the left and right sides was calculated. The degree of head rotation on every patient was recorded and plotted against LADI asymmetry. Results The mean LADI asymmetry was calculated at 0.810 mm with a standard deviation of ±0.724 mm. The largest LADI asymmetry that was measured was 4.7 mm. There was no statistical difference between male and female LADI measurements, nor with asymmetry. For the left and right side LADI’s in our group of patients, the Two One-Sided T-test (TOST) returned a p-value of <0.0001, with a 1 mm tolerance (upper and lower equivalence limit) on either side, suggesting that there was no statistical difference between the sides (region of statistical equivalence of 2 mm) within 2 mm measurement. No statistically significant correlation between head rotation and LADI asymmetry could be established, with the Pearson test returning a p-value of 0.063. Discussion It has long been proposed that LADI asymmetry could be used as a marker for possible injury to the cervico-cranial junction, more specifically with burst-type fractures of the atlas with asymmetrical displacement of the lateral masses In our normal study group, no statistically significant difference between the left and right LADI measurements was demonstrable, allowing a region of statistical equivalence of 2 mm. This agrees with the findings of some previous studies. Only 13 (6.5%) of 201 of the patients in our study had LADI asymmetry of more than 2 mm. Numerous factors potentially influencing LADI measurement such as congenital anomalies and head position have been mentioned in previous work. In our study, however, no direct correlation between the patient’s head rotation and LADI asymmetry could be established. Conclusion Findings in our sample of patients supported the use of 2 mm as the upper limit of normal for LADI asymmetry, which is similar to that concluded by previous studies. Rotation of the head and spine did not influence measurements significantly. However, a possible factor that may influence LADI asymmetry measurement and limit its usefulness as a tool in predicting injury is lateral flexion of the cervical spine. This falls outside the scope of this study, but further work on this aspect may be useful.

Keywords

Medicine

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