Knemometry, a new tool for the investigation of growth. A review

Cross-sectional and longitudinal studies of human growth have revealed almost every detail of the typical human growth pattern. Yet, the description of this pattern is still limited to the traditional vocabulary of "growth rates", i.e. height or length differences divided by certain time intervals such as months or years. Almost no information is yet available on finer details of this pattern. This review concerns the existing experimental and clinical data collected by a novel and non-invasive technique of accurate lower leg length measurement named "knemometry" that has been used for the study of short-term growth. This technique estimates the distance between heel and knee of the sitting child with an accuracy (technical error) of 0.09-0.16 mm. Several authors have presented evidence that lower leg growth is non-linear. There is not only a marked day-to-day variation of the lower leg length which far exceeds the error of the measurement itself, but there is also a characteristic up-and-down pattern of lower leg growth consisting of sharp growth spurts ("mini-growth-spurts") alternating with periods of decreased growth velocity every 30-55 days in 45 out of 73 healthy children. This pattern can be visualized by the calculation of "mean daily lower leg growth velocities", an approach that gives information on the kinetic properties of the growth process. In spite of much initial criticism, knemometry has opened a fascinating new dimension of the physiology of human growth and provided finer details of growth than hitherto obtainable by conventional techniques of growth measurement.