Measurement of short-term growth with a new knee height measuring device

Information on short-term growth (growth over periods of 1 month or less) has potential use in the clinic for treatment of children with growth disorders, and knowledge about patterns of short-term growth may also contribute to an understanding of growth control mechanisms. Limitations of measurement reliability for most measurements of linear growth have generally confined us to evaluation of growth over periods 3 month or longer. This report introduces the Knee Height Measuring Device (KHMD) The Knee Height Measuring Device is available from Intersciences Development Associates, 3508 Market St., Philadelphia, PA 19104 (215-662-0700), patent pending. , which can measure changes in size of the lower leg of approximately 0.5 mm and thus assist in evaluation of short-term growth. It is smaller, more portable, and less expensive than the Valk lower leg measuring device (knemometer) and uses a less subjectively biased measurement technique. Preliminary comparisons using a sample of 15 children measured twice at a 28-day interval of the validity and reliability of a prototype KHMD and the Valk knemometer. Yielded an intraobserver error of 0.295 for the KHMD and 0.206 for the knemometer. Agreement of the two instruments on the presence of detectable growth was 90%. Pearson correlation of growth rates detected by the two instruments was 0.73. After additional alterations improving the design and measurement methodology of the KHMD, 103 children 6-10 years old were measured at 28-day intervals from January to June and then at 3-month intervals from June to December of 1988 using the improved KHMD alone. Intraobserver error for these measurements was 0.22 mm. This error was modestly associated with the weight of the child (r=.31) but unrelated to sex, height, or growth in any dimension. Interobserver error for 22 children measured by two observers was 0.33 mm. We analyzed the knee height growth data primarily to test whether monthly growth could be reliably detected by this instrument. Average 28-day knee height growth was 1.76±0.3 mm, which is three times greater than the 0.5 mm growth detectable with the KHMD. Over any given 1-month interval, fewer than 10% of the children had growth less than that which could be detected with the instrument. We conclude that the KHMD can reliably detect growth over a 1-month interval and has potential clinical use for monitoring growth and for evaluating the characteristics and associations of short-term growth.