Positional plagiocephaly is associated with sternocleidomastoid muscle activation in healthy term infants.

Abstract

To explore the relationship between sternocleidomastoid activation and positional plagiocephaly in healthy full term infants. Participants were 82 infants from a regionally based-longitudinal study of infant development. Sternocleidomastoid (SCM) activation was assessed using active head-righting responses of body-on-head with and against gravity and head-on-body against gravity at 3, 6 and 9weeks. Plagiocephaly was assessed using the Modified Cranial Vault Asymmetry Index (mCVAI) at 9weeks. More severe plagiocephaly was associated with more severe asymmetry in active head-righting responses at all ages (p<0.001). Greater right-sided occipital flatness was related to stronger contralateral/left SCM activation at 3 and at 9weeks (p=0.008). Greater left-sided occipital flatness was related to stronger contralateral/right SCM activation at 3weeks (p=0.004). In infants with any right-sided occipital flatness, the mCVAI was greater in infants with asymmetrical gravity assisted body-on-head responses at 3weeks (mCVAI=4.31 (2.01)%, 95% CI 2.87-5.75) compared to those with symmetrical responses (mCVAI=2.64 (1.66)%, 95% CI 2.06-3.22) (p=0.011). Sternocleidomastoid activation asymmetry is a significant contributor to plagiocephaly development by 9weeks of age due to stronger contralateral SCM activation. Active head-righting responses are appropriate to assess sternocleidomastoid activation in infants under 2months of age.