Comparative Evaluation of Measurement Methods for Positional Skull Deformities in Infants: A Prospective Analysis

The incidence of positional skull deformities in infants has increased following campaigns promoting supine sleeping to reduce SIDS. Although various measurement methods exist to quantify cranial asymmetries, discrepancies between direct anthropometry, 3-dimensional photogrammetry, and plagiocephalometry may lead to differing severity classifications and treatment indications. Comparison of the available measurement protocols is crucial to harmonize assessment of these deformities.

To prospectively compare 3 measurement techniques-caliper-based (spreading caliper and measuring tape), 3D photogrammetry, and plagiocephalometry-for evaluating cranial deformity in early infancy, to assess their reproducibility and their individual impact on clinical decision-making.

In a prospective study, 51 infants aged 3 to 12 months were examined during an outpatient "helmet consultation." Each infant underwent measurements using: (1) standardized direct anthropometry (caliper and tape measurement), (2) 3D photogrammetry with a multicamera system and subsequent semiautomated analysis via the Software Cranioform Analytics 4.0, and (3) plagiocephalometry (PCM) using a thermoplastic strip technique and indirect measurement. Key indices-the cephalic index (CI) and cranial vault asymmetry index (CVAI) (or ODDI for plagiocephalometry)-were calculated. For PCM, a variance component analysis was performed to assess inter- and intraobserver variability. Bland-Altman analyses were used to compare CI and CVAI/ODDI values among the methods, treatment cutoffs were evaluated.

Since reproducibility for caliper measurements was already tested for inter- and intraobserver variability, this method was defined "gold standard" at our center. The treatment threshold for this analytical method was a CVA ≥ 1.0 cm. 3D photogrammetry-with a treatment cutoff at values above the 97th percentile of normative values-demonstrated excellent reproducibility with minimal bias (systematic error in CI of -0.77), whereas plagiocephalometry-with predefined cutoffs-exhibited a slightly higher bias in CI (-1.35). Cranial vault asymmetry index values varied-also due to differing calculation methods described in the available literature. Variance component analysis of plagiocephalometry indicated interobserver and intraobserver contributions below 3%. Discrepancies in measurement planes, angles, and index calculation furthermore led to differences in treatment indications: caliper screening identified more infants with an indication for orthotic treatment for deformational plagiocephaly than did the other 2 methods.

While all 3 techniques provide valuable information, caliper measurement remains a rapid, cost-effective, and fast screening tool. Subsequent evaluation with 3D photogrammetry is recommended for treatment planning. Plagiocephalometry-although provided with high intra- and interrater reliablity-offers no significant advantages in daily practice. Standardization of measurement landmarks and definition of index calculation is needed to internationally standardize and harmonize clinical decision-making.