The measurement of knee-heel length in newborn infants using a simple vernier calipers

Acta Paediatr. 1997 May;86(5):512-7. doi: 10.1111/j.1651-2227.1997.tb08922.x.


Objective: To assess the usefulness of a simple vernier calipers for measuring knee-heel length in neonates.

Subjects and methods: Using a simple vernier calipers, knee-heel length was measured five times by 2 observers in 50 babies (29M, 21F; mean birthweight 1597 g; median gestational age at birth 29 weeks) at a median postnatal age of 11 days. A subgroup of 20 babies had knee-heel length measured similarly at weekly intervals for 3 weeks. Corrected gestational age and weight were simultaneously recorded. One observer was experienced in using the vernier calipers. The precision of the calipers was established using 4 steel gauge blocks of varying length (7.62-10.17 cm).

Results: The calipers were very precise when measuring steel gauge blocks. In babies, there was a downward trend across the first 2 measurements for both observers, the measurements stabilizing over the last three. Using the final three measurements per baby (n = 50), the experienced observer had a mean standard deviation of 0.023 cm and mean coefficient of variation 0.23% when measuring an average knee-heel length of 9.99 cm. The inexperienced observer had a mean standard deviation of 0.057 cm and a mean coefficient of variation of 0.56%, when measuring an average knee-heel length of 10.14 cm. The inter-observer reliability, measured by the intra-class correlation coefficient, was 0.99. The agreement between observers was such that one observer measured knee-heel length consistently less (0.15 cm, SD 0.18 cm) than the other. The reliability for knee-heel length velocity was lower (R = 0.85), but agreement between observers was high with an average difference of 0.016 cm/week. Knee-heel length was significantly correlated (p < 0.001) with corrected gestational age (r = 0.85) and with weight (r = 0.96). There was a weaker but significant correlation (r = 0.47, p < 0.001) between knee-heel length velocity and rate of weight gain (g/day), indicating that weight gain may not always be accompanied by an increase in linear growth.

Conclusion: The measurement of knee-heel length by a simple vernier calipers is an accurate, reproducible and non-invasive method of assessing short-term linear growth in neonates. However, it is recommended that measurements of knee-heel length in a individual baby should be made by a single experienced observer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age Factors
  • Anthropometry / instrumentation*
  • Birth Weight
  • Body Height*
  • Gestational Age
  • Humans
  • Infant, Newborn / growth & development*
  • Leg / anatomy & histology*
  • Observer Variation
  • Reproducibility of Results