In children and adolescents the bones are still growing. The growth plates are made of cartilage and are actively producing more bone. The growth plates are the weakest part of the elbow, and the UCL and flexor tendon attach to a bump of bone immediately adjacent to one of the main growth plates on the inner side of the elbow.
In a child or young adolescent the ligament is stronger than the growth plate. If the elbow is over-stressed, instead of the ligament failing, the growth plate will be damaged and may develop a stress fracture through it. This is called “Little League Elbow”. The player will have pain on the inner side of the elbow made worse with throwing. Sometimes the growth plate may actually fracture and the bones pull apart. If this happens surgery is often necessary to avoid a permanent problem with the elbow. It is for this reason that persistent elbow pain in the young athlete must be closely monitored and evaluated by a physician. If it is ignored a permanent problem can develop.
A common problem is that the best youth pitchers usually play on multiple teams and take the mound for each team independent of the others. Of course, the coaches want the most talented pitchers to pitch the most innings for their team. So, the innings add up and the young athlete is vulnerable to overuse injuries of the elbow, in particular, the growth plates around the elbow and shoulder.