The characteristics of a knemometer designed for accurate lower leg me
asurement in babies were assessed. Repeated measurement of a 100 mm Pe
rspex rod gave a mean length of 99.993 mm and a mean SD of 0.058. When
used to measure leg length, technical error of the measurement techni
que was 0.31 with a mean leg length of 98.49 mm (coefficient of variat
ion 0.31%). Leg lengths measured at birth in 324 babies from 23 to 42
weeks' gestation gave an estimated in utero leg length velocity of 0.4
3 mm/day (95% confidence interval 0.41 to 0.45). Assessment of interob
server variation showed poor agreement in absolute values of leg lengt
h, although similar estimates of leg length velocity could be obtained
. The neonatal knemometer allows measurements to be made in situations
where conventional growth measurements are not possible. It is believ
ed that knemometry has an important role in accurate evaluation of fac
tors that can influence short term bone growth.