The prevalence, natural history, and determinants of non-synostotic plagiocephaly and brachycephaly in infants

Abstract

A dramatic increase in referrals of infants with non-synostotic positional plagiocephaly and brachycephaly has occurred since the adoption of supine sleep position recommendations to prevent sudden infant death syndrome (SIDS). Repeated positioning of the soft infant skull on firm surfaces is postulated to cause flattening of infant heads. There are concerns that parents who are worried about their infants' head shapes may reject SIDS prevention guidelines. This thesis was undertaken to provide greater understanding of the determinants, prevalence and natural history of non-synostotic aberrant head shapes. It includes a literature review that summarises the historical background, anatomy and skull growth of the infant cranium, clinical characteristics of non-synostotic plagiocephaly and brachycephaly, cephalometry methods, prevalence, risk factors, prevention, treatment and outcomes. Three studies were conducted. Firstly, a case control study was undertaken to investigate a range of possible risk factors. One hundred cases from plagiocephaly clinics and 94 community controls were administered a questionnaire covering obstetric, sociodemographic, infant, and infant care factors. Infants with plagiocephaly were significantly more likely to be male, firstborn, premature, supine sleeping, less active, to have a preferential head orientation at 6 weeks, to have a developmental delay, and to have a less educated mother. They were likely not to have had the head position varied when being put down to sleep in the first 6 weeks, and to have had less than 5 minutes a day of prone play time in the first 6 weeks. Next, a study of a new digital photographic technique that was developed to measure infant head shape used 31 plagiocephaly cases and 29 controls. The method, named HeadsUpTM, used an elastic band to define the head shape in the fronto-occipital plane. A digital camera recorded the head shape, and custom-written software quantified measurements from the photos. Compared with the conventional flexicurve measuring method, the HeadsUpTM method was more acceptable to both mothers and infants and less variable on measures of plagiocephaly and brachycephaly. Although it is recognised that head shape is a continuum from perfectly symmetrical to severely asymmetrical, thresholds were calculated to allow dichotomisation between "normal" and abnormal. The cut-off for cephalic index [(head width/head length) * l00] was identified as 93%, while the cut-off for the oblique cranial length ratio (the ratio of the longer cross-diagonal length to the shorter cross-diagonal length) was identified to be 106%. Beyond these points, brachycephaly and plagiocephaly, respectively, are deemed to exist. Finally, a prospective cohort study of 200 newborn infants combined the methods from both previous studies to further enlarge on determinants, prevalence and natural history of the condition. Ninety-one percent of the children were followed to two years of age. Using the cut-off points determined in the photo study, it was seen that 29.5% of the cohort developed plagiocephaly or brachycephaly at some time during the first 8 months, after which there were no new cases. Prevalence of plagiocephaly at 6 weeks was 16.0%, increasing to 19.7% at 4 months, then reducing to 9.2%, 6.8% and 3.3% at 8, 12, and 24 months respectively. Risk factor analysis was conducted on the 6-week and 4-month cases and controls. Significant determinants identified were: male gender, a limitation of head rotation, supine sleep position, more than 21 hours of supine-lying time a day at 6 weeks, head position when put down to sleep not varied in first 6 weeks, maternal reporting of low activity level at 4 months, and average-to-difficult temperament at 4 months. Although the cohort study showed that nearly all infants improved over time, there were a few persistent cases. Heads in the cohort were wider and shorter than those measured in infants during earlier decades when prone and side sleeping positions were the norm, highlighting a need for further research to provide age-specific norms for cephalic index in supine-sleeping infants. The photo study cases, recruited from plagiocephaly clinics, were in general of greater severity than the cohort cases. Further research is needed to allow early identification of infants who do not improve over time. Although supine sleeping is a risk factor for the development of plagiocephaly, this position is highly protective against SIDS and should be maintained. However, varying the head position at sleep, providing tummy time, limiting supine-lying time when awake, and awareness and treatment of head rotation problems may help to prevent the condition. These practices need to be confirmed in future studies of primary prevention.