Use of Knee Height as a Surrogate Measure of Height in Older South Africans

ABSTRACT

The study aimed to determine whether knee height would be a more appropriate surrogate measurement than armspan in determining height and body mass index (BMI) in a group of South African older people (.. 60 years). A random sample of adults (older than 18 years) who attended selected clinics or who lived in selected old-age homes in the Western Cape volunteered to participate in the study. Subjects were divided into a study group of older people (.. 60 years of age; N = 1 233) and a comparative group of younger adults (18 - 59 years; N = 1 038).Armspan; knee height; standing height and weight were measured using standardised techniques. The standing height measurements were significantly different between the two groups (p = 0.0001); with a mean for adults of 1.61 m (standard deviation (SD) 0.09) compared with that of older peole (1.57 m (SD 0.09)). Mean standing height decreased with age. Knee-height measurements were not significantly different between the two groups; but when used to calculate height; the adults were significantly taller (p = 0.0001); with a mean height of 1.67 m (SD 0.06) compared with that of the older people (1.59 m (SD 0.08)). Mean armspan also decreased with age; and derived standing height was significantly different (p = 0.0001) between the two groups; with adults being taller (1.67 m (SD 0.11)) than the older people (1.63 m (SD 0.11)). In this study group; the knee-height measurements were more closely related to the standing height than the armspan. The BMI calculated from armspan-derived height tended to classify the older people towards underweight. Knee-height measurement would appear to be a more accurate and appropriate method to determine height in older people in South Africa