Comparison of Direct and Digital Measures of Cranial Vault Asymmetry for Assessment of Plagiocephaly

Measurement of cranial vault asymmetry (CVA) is a common feature in the treatment of patients with deformational plagiocephaly (DP). In many cases, this measure is the primary marker of improvement. CVA is typically measured with calipers and is subject to interrater variability. There is little research comparing results of calipers with those of three-dimensional (3D) photogrammetry.Fifty nine visits were made by 51 children previously diagnosed with DP. Thirty eight were male and 13 were female. Thirty one of the visits included a 3D photograph. Direct measures were obtained by 2 experienced anthropometrists and included head length, width, circumference, and CVA. Their results were compared to digital measures including measures unobtainable with calipers, asymmetry of head circumference and global asymmetry.The interrater reliability of all caliper measures was excellent (intraclass correlation coefficients>0.94). Caliper and digital measures of length, width, cephalic index, and circumference were strongly correlated (R-2>0.90). There was a consistent bias, caliper measures being 1 to 4mm shorter than their digital analogues. Caliper measured CVA was highly correlated (R-2>0.90) with the directly corresponding digital measures. It was poorly correlated with measures of overall hemispheric asymmetry (R-2<0.10).The cranial measurements of children with DP taken independently by 2 experienced anthropometrists showed excellent interrater reliability. Caliper measures are consistently smaller than the digital measures, presumably due to pressure of the calipers and/or the use of skullcaps during photography. Like circumference and other assessments, cranial vault asymmetry measures correlate well with their analogous digital measurements.