ASSESSMENT OF THE USEFULNESS OF WEEKLY KNEMOMETRIC MEASUREMENTS IN GROWTH STUDIES

Abstract

Knemometry is an accurate technique of measuring lower leg length (1.1.1.) but the variability might limit its usefulness for growth studies. This was investigated by performing 12 consecutive weekly knemometric sessions (each consisting of 6 measurements) and 4-weekly stadiometry on 31 healthy children of 6-12.5 years of age. The average SD of 6 measurements was 0.12 mm. A regression (linear and 4 orthogonal polynomials) was computed of 1.1.1. on time. The residual mean square was much higher than the variance within 6 measurements. The linear regression was significant at 0.05 level in 29 children. Average (±SD) 1.1.1. growth velocity was 0.36±0.14 mm/week, and height 1.27±0.54 mm/week (ratio 3.9±2.0). The 2nd, 3rd, and 4th polynomials were significant more often than expected if higher order effects would be absent. When growth velocities were calculated over the first 6 weeks (v₁) and last 6 weeks (v₂), v₁ and v₂ were different from zero in 23 and 19 children. Mean ± SD of tne 31 v₁ values were 0.39 and 0.15 mm/week. v₂-v₁ was significantly different from zero in 5 children. Mean ± SD of the 31 v₂-v₁ values were -0.051±0.23 mm/week. If a one-side test is used, a difference v₂-v₁ greater than 0.37 mm/week is significant. This corresponds with a statural growth response of 7.5 cm/year. In conclusion, observation periods of 6 weeks are too short for a reliable comparison of 1.1.1. growth velocities.

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