Prevalences of bowing and knock knee, measured at a standard stance, have been obtained on Negro, Coloured, Indian and Caucasian schoolchildren aged 7, 12, and 16-17 years. These two abnormalities were unexpectedly common, affecting about one-fifth and one-third of all children respectively. Ranges of prevalences of chest abnormalities were—Harrison's sulcus, 0-5%, and pigeon chest, 0-2%. Prevalence of bowing increased with age. That of knock knee was little affected by age, but increased markedly with body mass. There was no age trend with prevalences of chest abnormalities.
Prevalences appeared unrelated to vitamin D intake. As to sunshine, the annual mean for the Transvaal is 8·4 hr daily. Results from radiological, skin pigmentation, and biochemical studies were non-contributory. Since a primary deficiency of vitamin D is evidently not the causal factor, one explanation is that a secondary deficiency is involved, arising from an impairment in metabolic availability. Further, a proportion of leg abnormalities may be physiological variants; moreover, it cannot be excluded that unknown factors may bear, or share, in responsibility.
Elucidation may be forthcoming by investigating the interrelationship between vitamin D status and frequency of leg abnormalities during and after puberty; in addition, results of serial studies of prevalences of abnormalities from birth to post-adolescence would be illuminating.