Intradaily variation of the human ulnar length and short term growth--a longitudinal study in eleven boys.

In order to detect the intradaily variation of the clinical ulnar length in eleven boys the right ulnar length was determined using a condylograph at seven set times of each day during a study period of three weeks. The mean standard error of the determinations amounted 0.09 mm. In 86% of the days concerned the ulnar length changed significantly (one way analysis of variance p less than 0.05). As far as the whole group concerned the ulnar length decreased significantly during the time interval from 8.00 h to 12.00 h (Friedman's related samples test, p less than 0.01). The decrement amounted 0.4 mm. During the rest of the day the changes in the ulnar length were not significant. A consistent decrement of the ulnar length during the day in combination with total growth of 0.99 mm during the three week study period suggested that growth in length of the human ulna occurs during the night.