IT's a common problem. Older brother of one of my son's teammates got a spiral fracture pitching. Often, the muscle becomes stronger than the soft growth plate where it is attached can withstand. The high stress during a hard throw actually can cause the bone to splinter. He was a very promising pitcher, but ended up unable to pitch again. The constant stress to that maleable bony area created a bend -- a deformity-- in his shoulder and made it impossible to throw without the shoulder moving out of joint. BE CAREFUL!