Abstract
<title>Abstract</title> <p> Background Cervical instability at the atlanto-axial and craniocervical junctions is a well- recognized phenomenon in children with Down syndrome (DS), with radiographic prevalences reported in the range of approximately 10% to 30%, yet the incidence of clinically manifest neurologic involvement remains low (around of 1–2%). Historically, routine radiographic screening of asymptomatic children with DS was widely adopted, particularly in the context of sports participation; however, more recent evidence and updated international guidelines have called into question the diagnostic accuracy and clinical utility of standard radiographic metrics. <sup>3,4</sup> Objective This retrospective case–control study aimed to evaluate the reliability of standard radiographic parameters in detecting cervical instability in children with DS and to assess the value of standard and dynamic radiographs. To this end, we used a control cohort of non-syndromic children presenting with atraumatic atlanto-axial subluxation (AAS). Methods Forty children with DS were compared with twenty-five non-syndromic children with traumatic AAS. Although the DS and AAS groups differed in clinical presentation and symptoms, the AAS group was chosen as a model of ligamentous-only instability with preserved bony anatomy. This pilot study was designed to derive insights into the osseous contribution to instability and, possibly, to identify useful cut-off values for cervical instability in non-syndromic pediatric patients. Three blinded observers measured standard radiographic indices, including the atlanto-dental interval (ADI), posterior atlanto-dental interval (PADI), space available for the cord at C1–C4 (SAC), Powers ratio, Harris BAI–BAI, X-line, Lee index, Chamberlain–McGregor lines, and C1 inclination angle. Interobserver reliability (ICC) and cross-index concordance (Fleiss’ κ) were evaluated. Results Individual measurements showed good reproducibility (ICC > 0.70). Cross-index concordance was poor (κ < 0.40), meaning different indices frequently misclassify the same patient. PADI and SAC C1–C4 were significantly lower in DS patients (p < 0.05), consistent with posterior C1 arch hypoplasia and the synergistic effect of osseous anomalies and ligamentous laxity. Conclusions Plain static radiographic screening of asymptomatic children with DS has limited diagnostic accuracy and appears to play a limited role in clinical practice. On the other hand, dynamic radiographs and measurement of SAC at C1–C4, rather than ADI alone, combined with clinical assessment, may provide a more reliable evaluation of cervical instability. </p>