Failed age-dependent maturation of the occipital condyle in patients with congenital occipitoatlantal instability and Down syndrome: a preliminary analysis

Object. Normative morphological data pertaining to the development of the occipital condyle have not been reported. The first goal of this study was to establish normative data characterizing the shape of the occipital condyle in healthy children. The second objective of the study was to compare these data with measurements collected in patients with congenital occipitoatlantal instability (COI) or Down syndrome (DS). The effectiveness of CT and plain radiography data was also compared. Methods. The authors retrospectively reviewed data obtained in 39 patients (14 with DS/COI and 25 age-matched controls). Patients underwent plain lateral radiography and CT scanning of the cervical spine. Normalized measurements of the occipital condyle were obtained for both groups using plain radiography and CT imaging techniques. Results. The curvature of the occipital condyle in healthy children increased by 60% from infancy to adolescence. Comparison of condylar morphology on plain lateral radiographs and CT scans in patients with DS/COI and in age-matched controls demonstrated a significant difference in mean normalized depth/length ratios. Comparison of curvature data obtained using plain lateral cervical radiography with measurements obtained using cervical CT scanning demonstrated a correlation coefficient of 0.63. However, intra- and interobserver reliability for plain radiographic analysis of the occipital condyle was poor (r(2) = 0.40 and 0.44, respectively). Conclusions. Patient with DS/COI who have occipitoatlantal instability fail to develop the Curved architecture in the occipital condyle that occurs in age-matched controls over time. Sagittal 2D CT reconstructions accurately determine the precise structure of the occipital condyle, although the indications for CT scanning are limited. Because of the poor intra- and interrater reliability on static plain radiographs, dynamic flexion/extension cervical spine radiographs remain the study of choice by which to directly evaluate occipitocervical motion. (DOI: 10.3171/PED.2008.2.11.359)