The development of humeral head retroversion

Humeral head retroversion is important in a variety of clinical situations, but it is not known when retroversion actually develops to adult values. I n utero and at birth, the humeral head is known to be in marked retroversio n. It derotates sometime thereafter to assume the more standard value with which orthopedic surgeons are familiar. By studying a unique collection of children's bones (180 humeri), I have been able to determine that the great er part of this process takes place, on average, by the age of 8 years (SD +/-2.12 years); from then on, however, the development continues more slowl y until the final adult dimensions are reached, as heralded by the appearan ce of the radial groove at approximately 16 years of age. This process, alo ng with its timing, appears to be similar, but opposite in direction to, th e derotation process that is known to take place in the hip. It has not pre viously been documented in the shoulder.