Variations in the retroversion of the humeral head.

It is generally accepted that the humeral head in adults is retroverted between 25 degrees and 35 degrees. To assess the validity of this belief, 336 dry bone specimens of humeral heads were measured. The specimens were taken from various ethnic groups: white Americans, black Americans, New Mexican Indians, northern Chinese, Alaskan Eskimos, and Negev Desert bedouins. There was significant variation in retroversion angle between specimens from different ethnic groups and even wider variation between specimens within particular groups--a finding contrary to popular belief. Retroversion angle in the specimens ranged from -8 degrees to +74 degrees. In addition, 50 fetal skeletons of white and black Americans were studied. The mean humeral head retroversion angle in the fetal skeletons was 78 degrees, much greater than that in adults. It was evident that the large retroversion angle in the very young decreases with growth and that it does so to a varying extent among different ethnic groups and individuals. It is of clinical importance to understand the variations in humeral head retroversion among individuals undergoing operation and the ways in which this parameter might be manipulated to surgical advantage.