Analysis of digital measures of cranial vault asymmetry for assessment of plagiocephaly

BACKGROUND: Deformational plagiocephaly (DP) is an asymmetry of the skull caused by extrinsic compression. With the advent of the Back to Sleep campaign, DP is of increased interest to parents and healthcare providers. Traditionally, this asymmetry has been assessed by caliper measurements. However, little consensus exists as to which caliper measures (linear) give the most accurate representation of DP. The purposes of this study are to examine different measures and to determine which have the greatest validity in the assessment of skull asymmetry. METHODS: Six linear measures were assessed using 31 three-dimensional photographs of 26 children diagnosed with DP. These measurements were compared with more encompassing measures: a head perimeter measurement, a global three-dimensional measure of hemispheric asymmetry, and the radial symmetry index. These 3 broader measures were used to determine which linear, caliper-style measurements most accurately reflect overall DP. RESULTS: Intrarater reliability of the measurements varied widely (intraclass correlation coefficients from 0.42 to 0.99). Correlations between the measures also varied widely (0.10 < r < 0.95). The linear measure that best correlated with the inclusive measures of asymmetry was FZ-EU, the distance from the frontozygomaticus to the contralateral eurion (r ≤0.90). CONCLUSIONS: These data introduce 2 digital measures that might serve as standards against which linear measures of asymmetry may be tested: Global asymmetry and head perimeter measures were strongly correlated to each other. When these 2 parameters were compared against linear measures, FZ-EU was noted to be the best linear measure of asymmetry based on these benchmarks.