REPRODUCIBILITY IN THE MEASUREMENT OF ATLANTOOCCIPITAL INSTABILITY INCHILDREN WITH DOWN-SYNDROME

Study Design. This study compared the reproducibility of three techniq ues used to measure translation between the occiput and C1 in children with Down syndrome. Objectives. Intraobserver and interobserver varia bility were computed to determine if there is a reliable way to measur e occiput-C1 instability. Summary of Background Data. No studies have been performed comparing measurement techniques in children with Down syndrome. Methods. Powers ratios, basion-axial intervals, and translat ional anteroposterior motion as described by Wiesel and Rothman were c alculated for 60 pairs of flexion-extension lateral cervical radiograp hs from children with Down syndrome. Calculations were made on two occ asions by four reviewers. Results. Mean differences between measuremen ts for two observers were 0.14 for the Powers ratio, 1.3 mm for the Wi esel technique, and 1.8 mm for the basion-axial interval. The 95th per centiles of the differences between measurements for two observers wer e 0.38 for Powers ratios, 3.5 mm for the Wiesel technique, and 5.3 mm for the basion-axial interval. Conclusions. Measurement of atlanto-occ ipital translation by any of these methods is not reproducible. Althou gh the technique by Wiesel and Rothman is the easiest to apply, confir mation of instability with magnetic resonance imaging should guide man agement.