Do Infant Motor Skills Mediate the Association Between Positional Plagiocephaly/Brachycephaly and Cognition in School-Aged Children?

Objective: Positional plagiocephaly/brachycephaly (PPB) is associated with lower cognitive scores in school-aged children. This study tested the hypothesis that infant motor skills mediate this association.

Methods: Children with a history of PPB (cases, n = 187) and without PPB (controls, n = 149) were followed from infancy through approximately 9 years of age. Infant motor skills were assessed using the Bayley Scales of Infant and Toddler Development, 3rd edition (Bayley-3), and cognition was assessed using the Differential Ability Scales, 2nd edition (DAS-2). The Bayley-3 motor composite was examined as a mediator of the association between PPB and DAS-2 general cognitive ability (GCA) scores. In secondary analyses, mediation models were examined for the DAS-2 verbal ability, nonverbal ability, and working memory scores; models using the Bayley-3 fine versus gross motor scores also were examined.

Results: Cases scored lower than controls on the DAS-GCA (β = -4.6; 95% CI = -7.2 to -2.0), with an indirect (mediated) effect of β = -1.5 (95% CI = -2.6 to -0.4) and direct effect of β = -3.1 (95% CI = -5.7 to -0.5). Infant motor skills accounted for approximately 33% of the case-control difference in DAS-2 GCA scores. Results were similar for other DAS-2 outcomes. Evidence of mediation was greater for Bayley-3 gross motor versus fine motor scores.

Conclusion: Infant motor skills partially mediate the association between PPB and cognition in school-aged children. Monitoring motor development and providing intervention as needed may help offset associated developmental concerns for children with PPB.

Impact: To our knowledge, this study is the first longitudinal investigation of the development of children with and without PPB from infancy through the early school years and the first to examine motor skills as a mediator of cognitive outcomes in this population. The findings highlight the importance of early motor skills for other developmental outcomes.

Lay summary: Infants' motor skills are related to the development of PPB and its association with later cognition. If your child has PPB, physical therapists may have an important role in assessing and providing treatment to promote motor development.