Segmental Assessment of Trunk Control in infants from 4 to 9 months of age- a psychometric study

Background: Efficient trunk control is crucial in infant motor development when infants first learn how to move against gravity. Traditional assessments of trunk control commonly treat the trunk as one unit but the Segmental Assessment of Trunk Control (SATCo) assesses trunk control segment by segment. Good reliability and validity of the SATCo have been proved in children with neuro-disability but not yet validated in young infants. The present study was to examine if the SATCo was reliable, valid and responsive for infants aged 4 to 9 months. Methods: Infants born at full-term and at less than 30 weeks of gestation were recruited and assessed using the SATCo monthly from 4 to 9 months of age (corrected for prematurity). Intra-class correlation coefficients (ICC) were used to examine intra- and inter-rater reliability between 2 raters. The ability of the SATCo to demonstrate differences between the full-term and preterm infants was examined using the Mann Whitney U test. The responsiveness of the SATCo on the full-term infants was tested using the Friedman test. Results: Twenty full-term (mean gestation = 38.7 weeks; birthweight = 3019.9 g) and 20 preterm infants (mean gestation = 27.2 weeks; birthweight = 989.6 g) were recruited. The intra and inter-rater reliability of the SATCo levels on full-term infants was good (all ICC > 0.75), except inter-rater reliability at 6 months. The preterm infants scored significantly lower in reactive trunk control at 8 months (Mann Whitney U = 102.0, p = 0.016) but this was the only difference noted. A significant developmental trend was shown in the static, active and reactive trunk control of the full-term infants (Chi-square = 81.4, 75.6 and 79.5 respectively, all p < 0.001. Conclusions: The SATCo was reliable and responsive in assessing trunk control in young infants aged from 4 to 9 months. Care should be exercised when testing infants aged 5 to 6 months, who are more likely to use subtle hand support, and for those who have already achieved independent sitting. The SATCo could differentiate the reactive trunk control between the full-term and preterm infants at 8 months but not earlier. Psychometric properties of the SATCo in infants with motor disorders requires further investigation.