A portable knemometer: a technique for assessment of short-term growth.

Knemometry is the technique of choice for short-term growth studies, as it is the only anthropometric technique available that allows sufficiently accurate measurement of the lower leg (in anatomical terms, the leg) to enable changes in leg length to be detected over as short an interval as a week or less. The portable knemometer, like the Valk knemometer, essentially consists of two main parts: a rigid metal frame holding the footplate, measuring ruler and plateau and a moveable chair that moves on frictionless rollers on a track on the base of the frame. Unlike the Valk knemometer there is a standardized seat position for all subjects, making it easier and quicker to use. Assessment of technical error was done using mean coefficient of variation (CV) of lower leg length measurements done on the portable knemometer. Comparison of measurements made by two different observers was made by using percentage reliability. A small PR implies consistency between the two methods or observers being compared. Measurements from 164 visits were used to calculate the machine precision. Mean CV using all four measurements was 0.13% and using only three, having discarded the first, was 0.11%. Given a mean lower leg length of 246.3 mm for the children studied this translates to a machine precision of 0.32 mm if all four measurements are used and 0.27 mm if the last three measurements in the set are used. The mean difference in lower leg length between observers was 0.11 mm. Percentage reliability between the two observers for the portable knemometer was 0.03%. For comparison, PR for standing height and sitting height are 0.37% and 0.86% respectively. PR between the Valk and the portable knemometer was 0.04%.