title: Positional plagiocephaly is associated with sternocleidomastoid muscle activation in healthy term infants.
abstract: OBJECTIVE
  To explore the relationship between sternocleidomastoid activation and positional plagiocephaly in healthy full term infants.
  
  
  METHODS
  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 9 weeks. Plagiocephaly was assessed using the Modified Cranial Vault Asymmetry Index (mCVAI) at 9 weeks.
  
  
  RESULTS
  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 9 weeks (p = 0.008). Greater left-sided occipital flatness was related to stronger contralateral/right SCM activation at 3 weeks (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 3 weeks (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).
  
  
  CONCLUSIONS
  Sternocleidomastoid activation asymmetry is a significant contributor to plagiocephaly development by 9 weeks of age due to stronger contralateral SCM activation. Active head-righting responses are appropriate to assess sternocleidomastoid activation in infants under 2 months of age.
authors.affiliation: School of Health & Rehabilitation Sciences, The University of Queensland, St Lucia, Q4072, Australia. yuen.leung@uqconnect.edu.au.
authors.forename: Amy
authors.initials: A
authors.lastname: Leung
authors.affiliation: School of Health & Rehabilitation Sciences, The University of Queensland, St Lucia, Q4072, Australia.
authors.forename: Allison
authors.initials: A
authors.lastname: Mandrusiak
authors.affiliation: School of Health & Rehabilitation Sciences, The University of Queensland, St Lucia, Q4072, Australia.
authors.forename: Pauline
authors.initials: P
authors.lastname: Watter
authors.affiliation: Ipswich Hospital, Ipswich, Q4305, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Gavranich
authors.affiliation: School of Health & Rehabilitation Sciences, The University of Queensland, St Lucia, Q4072, Australia.
authors.forename: Leanne
authors.initials: L
authors.lastname: Johnston
mesh_terms: D005260:Female; D007839:Functional Laterality; D006257:Head / Q000503:physiopathology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D009334:Neck Muscles / Q000502:physiology*; D009989:Orthotic Devices; D026741:Physical Therapy Modalities; D059041:Plagiocephaly / Q000534:rehabilitation*; D016059:Range of Motion, Articular / Q000502:physiology; D016683:Supine Position; D013997:Time Factors
keywords: Head-righting response; Infant; Modified cranial vault asymmetry index; Positional plagiocephaly; Sternocleidomastoid