Knee-heel length measurements in preterm infants: evaluation of a simple electronically equipped instrument.

ABSTRACT

AIM: To compare and evaluate a mini-knemometer with a simple and inexpensive electronic caliper with regard to precision, handling error (technical error) and estimation of growth velocity. METHODS: Thirty-five prematurely born infants, with a median gestational age of 29 (range 24-33) wk and a median birthweight of 960 (range 480-2,480) g, were measured on 409 different occasions with both instruments. On each occasion, five independent readings were made. RESULTS: There was no significant difference in precision between the two instruments, when measuring growth velocity over a 4 wk period (median 0.41, range 0.10-0.59 mm d(-1)). The handling error in this study, calculated as the mean standard deviation, was 0.36 (SD 0.18, coefficient of variation 0.38%) mm for the simple electronic caliper and 0.59 mm for the mini-knemometer. Short-term growth was detectable within 2 d when growth velocity was normal. CONCLUSION: Longitudinal measurement of lower leg length is a gentle and useful complementary method for assessing growth in preterm infants. An inexpensive electronic caliper is well suited for routine use in clinical practice, with measurements taken once or twice a week.