Normal Development and Measurements of the Occipital Condyle-C1 Interval in Children and Young Adults

Abstract

Background and purpose: Widening of the occipital condyle-C1 interval is the most specific and sensitive means of detecting atlanto-occipital dislocation. Recent studies attempting to define normal measurements of the condyle-C1 interval in children have varied substantially. This study was performed to test the null hypothesis that condyle-C1 interval morphology and joint measurements do not change as a function of age.

Materials and methods: Imaging review of subjects undergoing CT of the upper cervical spine for reasons unrelated to trauma or developmental abnormality was performed. Four equidistant measurements were obtained for each bilateral condyle-C1 interval on sagittal and coronal images. The cohort was divided into 7 age groups to calculate the mean, SD, and 95% CIs for the average condyle-C1 interval in both planes. The prevalence of a medial occipital condyle notch was calculated.

Results: Two hundred forty-eight joints were measured in 124 subjects with an age range of 2 days to 22 years. The condyle-C1 interval varies substantially by age. Average coronal measurements are larger and more variable than sagittal measurements. The medial occipital condyle notch is most prevalent from 1 to 12 years and is uncommon in older adolescents and young adults.

Conclusions: The condyle-C1 interval increases during the first several years of life, is largest in the 2- to 4-year age range, and then decreases through late childhood and adolescence. A single threshold value to detect atlanto-occipital dissociation may not be sensitive and specific for all age groups. Application of this normative data to documented cases of atlanto-occipital injury is needed to determine clinical utility.

Fig 1.

Method used to make sagittal (A) and coronal (B) CCI measurements in an 8-year-old boy. Note the use of localizer lines (solid black lines midjoint) to avoid the notch when selecting the appropriate coronal image from which to obtain measurements. On sagittal images (A), the anteriormost measurement is taken beginning at the anterior margin of the C1 joint (solid white line) and the posteriormost measurement is taken beginning at the posterior margin of the C1 joint (dashed line). On coronal images, the medialmost measurement is taken beginning at the margin of the foramen magnum (dashed white line) and the lateralmost measurement is taken where the superior aspect of the C1 lateral mass goes from a rounded contour to a flat articular plane (dotted line).

Fig 2.

Scatterplots representing each of the 248 joint spaces in the coronal (A) and sagittal (B) planes.

Fig 3.

Average CCI by age group in the coronal (A) and sagittal (B) planes. The gray box represents ±1 SD, and the bars represent ±2 SDs from the mean.

Fig 4.

Coronal (left) and sagittal (right) images of the CCI in subjects of the following ages: 3 months (A), 1.5 years (B), 4 years (C), 9 years (D), 17 years (E), and 22 years (F).

Fig 5.

Sagittal CT (A) demonstrates the medial occipital condyle notch (white arrow) in an 8-year-old boy. A 3D surface-rendered reconstruction image (B) with a medial-to-lateral perspective demonstrates the 3D contour of the occipital condyle notch (black arrow). For orientation, the anterior arch of C1 (white hollow arrow) is to the right and the posterior arch of C1 (white block arrow) is to the left. The internal auditory canal is shown by a hollow black arrow. Note how the notch is wider at its medial aspect compared with the lateral aspect. Ant indicates anterior; post, posterior.

Fig 6.

Prevalence of the medial occipital condyle notch by age group.