P71. longitudinal assessment of cephalic index norms in a large population of well children

PURPOSE: Cephalic index (CI), a normative indicator used to derive criteria for orthotic helmeting, has significantly increased compared to prior norms according to a recent cross-sectional study. Furthermore, studies have shown that CI fluctuates within the first two years. This study aims to evaluate CI longitudinally to inform new indications for orthosis criteria. METHODS: Infants aged 0-6 months and 7-48 months are enrolled. Subjects with two or more encounters are included and stratified into three groups. Group 1 includes subjects with two measurements before 6 months; group 2 has one measurement in each age category; and group 3 has two measurements after 6 months. Biparietal and anteroposterior diameters are obtained using a manual caliper. RESULTS: 91 subjects are included. The mean pooled CIs at 0-6 months are 83.1±7.73 for males and 83.7±6.38 for females. Paired t test comparing CI measurements within group 2 (n=50) demonstrated significant decrease in mean CI in the second measurement of 1.98 (p=0.014). Group 3 (n=31) also demonstrated a significantly decreased CI mean of 3.47 (p=0.0003) in the later measurement. No significant differences were found in group 1 (n=20). CONCLUSION: CI does not change significantly before the first 6 months and starts to trend negatively at 6 months. This trend becomes even more significant between 7-48 months, without intervention. This decrease in CI over time is still significantly higher than published norms, and it sheds light on the natural history of CI that could impact criteria for orthotic helmeting.