This study investigated the relationship between muscle tone assessed at the expected due date and developmental outcomes at 18 months of corrected age in preterm low birth weight infants.
This retrospective study included preterm low birth weight infants who received physiotherapy at the NICU of Tottori University Hospital from April 2015 to July 2022. Data on birth length and weight, gestational age, and muscle tone (assessed using the Dubowitz Neurological Assessment at 37–42 weeks of corrected age) were collected from medical records. Muscle tone was assessed using the Modified Ashworth Scale (MAS) for neck motion (flexion, extension, and rotation) and elbow and knee joint motion (flexion and extension) at 39–41 weeks of corrected age. Developmental outcomes were evaluated using the Kyoto Scale of Psychological Development (KSPD) at 18 months of corrected age, covering four domains: postural-motor, cognitive-adaptive, language-social, and overall development. Spearman's rank correlation coefficient explored associations between developmental scores and each variable, with significance set at 5%.
The study included 56 infants (28 boys, and 28 girls) with a median birth length of 35.0 cm (IQR: 31.1–38.0 cm), birth weight of 1147 g (IQR: 844–1,435 g), and gestational age of 30 weeks (IQR: 28 weeks 5 days to 31 weeks 5 days). Significant correlations were detected between KSPD scores and the following variables: postural-motor domain [birth weight (r = 0.267), MAS knee joint (r = -0.480), MAS neck flexion (r = -0.458), and MAS neck extension (r = -0.574)]; cognitive-adaptive domain [MAS knee joint (r = -0.479) and MAS neck extension (r = -0.464)]; language-social domain [birth length (r = 0.329), birth weight (r = 0.371), and MAS knee joint (r = -0.480)]; and overall domain [birth length (r = 0.265), birth weight (r = 0.288), MAS knee joint (r = -0.479), and MAS neck extension (r = -0.492)]. No significant correlations were detected with gestational age or Dubowitz Assessment Tone items.
The findings suggest that increased muscle tone in the neck and lower limbs during the neonatal and infancy periods, along with decreased birth length and weight, are linked to lower developmental scores at 18 months of corrected age in preterm low birth weight infants. Assessing muscle tone in the neck and lower limbs during the neonatal period may help predict outcomes in this population.
Evaluating neck and lower limb muscle tone in preterm low birthweight infants may provide insight into future developmental outcomes. Simplified assessment methods could allow less experienced therapists to perform effective evaluations and adopt developmentally informed approaches, potentially easing family concerns about their child’s development.
Muscle tone
Developmental tests
