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Scarf ratio: A method of measuring the Scarf sign in preterm born infants
Raweewan Lekskulchai1, Joan Cole
1School of Physiotherapy, Curtin University of Technology, Shenton Park, WA, 6008, Australia. plekskulcha@cc.curtin.edu.au
Insights
A novel Scarf ratio method quantifies infant muscle tone. This continuous scale measurement shows increasing resistance to passive arm movement as preterm infants mature, offering an alternative to traditional Scarf sign assessments.
Area of Science:
- Neonatal assessment
- Pediatric neurology
- Developmental pediatrics
Background:
- The Scarf sign is a clinical assessment of upper limb muscle tone in infants.
- Traditional Scarf sign assessment provides categorical data.
- A continuous, quantitative measure could offer more detailed insights into muscle tone development.
Purpose of the Study:
- To introduce and validate a new quantitative method for measuring the Scarf sign, termed the Scarf ratio.
- To analyze longitudinal Scarf ratio data in preterm infants.
- To compare the Scarf ratio with a newly developed categorical scoring system.
Main Methods:
- The Scarf ratio was defined as the distance of the olecranon process across the trunk relative to biacromial width.
- Longitudinal data were collected from 111 Thai preterm infants.
- Data were analyzed across four post-conceptional age ranges (28-31, 32-36, 37-39, and 40 weeks PCA).
Main Results:
- The mean Scarf ratio increased with post-conceptional age, indicating increasing resistance to passive arm movement.
- A categorical scoring system was developed, with scores correlating to age: score 1 (low tone) for 28-31 weeks PCA, score 2 for 32-39 weeks PCA, and score 3 (high tone) for 40 weeks PCA.
- The Scarf ratio demonstrated a continuous scale for muscle tone assessment.
Conclusions:
- The Scarf ratio provides a reliable, continuous quantitative measure of the Scarf sign.
- This method can serve as a valuable alternative for assessing muscle tone, particularly when continuous data are preferred.
- The findings support the use of the Scarf ratio in monitoring the neurodevelopment of preterm infants.
Abstract:
A new method of measuring the Scarf sign called the Scarf ratio is described in which data derived were reported on a continuous scale. The Scarf ratio is the distance of the olecranon process of the arm being tested as it moves across the trunk compared with the infant's own biacromial width. Longitudinal data for the Scarf ratio were measured in a cohort of 111 Thai preterm born infants. The data were collapsed into four age ranges ie 28-31, 32-36, 37-39 and 40 weeks post-conceptional age (PCA) according to the trends from the longitudinal plots. As the means of the Scarf ratio increased with age, it can be described that the resistance to the passive movements of the arm increased when the infants grew up. Data were also converted to a newly developed categorical scoring system. All infants between the age of 28 and 31 weeks PCA recorded a score of 1 (low tone). Most infants aged 32-36 and 37-39 weeks PCA recorded a score of 2 while most infants aged 40 weeks PCA obtained a score of 3 (high tone). Thus, this method can be an alternative when continuous data for the Scarf sign are desirable.
