From birth through early adolescence, epiphysial ossification centers sequentially appear.   In the mid-shaft of the pitching armís long bones, i. e., the humerus, radius and ulna bones, diaphysial centers appear early in childhood.   The proximal humerus has two epiphysial centers and the distal humerus has four.   The proximal and distal ends of the ulna and radius bones have only one epiphysial center each.         a.   Appearance Sequence
Critical pitching epiphysis remain non-united through adolescence.   Consequently, they are susceptible to irreversible injury.   The following is a listing of the order in which the critical baseball pitching epiphyses appear.01.   The humeral head epiphysis appears at two months.
The epiphysial centers of the humerus, ulna and radius also unite with their diaphysial centers in a specific sequence.   To determine the age at which pitching is safe, we need to learn when these critical baseball pitching epiphysial and diaphysial centers unite.01.   The capitulum epiphysis unites at thirteen years.
This information shows that young baseball pitchers have incomplete critical skeletal maturation until nineteen years old.   However, the most critical growth plate with which baseball pitchers need to have concern is the medial epicondyle.   Five powerful baseball pitching muscles arise from the medial epicondyle.   They exert tremendous force during all types of baseball pitches.   Therefore, after the growth plate of the medial epicondyle completely ossifies, the danger of irreparable damage to the baseball pitching arm significantly decreases.   Nevertheless, baseball pitching coaches must always be alert to complaints of discomfort located deep in the bone at the distal ulnar epiphysis, the greater tuberosity epiphysis of the humerus, the distal radial epiphysis and the humeral head epiphysis in pitchers up to twenty years of age.