Apophysitis refers to irritation, inflammation or trauma to an apophysis, or an area where a tendon, muscle and bone connect. The apophysis is the weakest point in this connection, and it can be injured by overuse. Continuous stress on the growth cartilage in this muscle-tendon unit can cause pain and swelling. While some develop apophysitis due to muscle weakness or balance issues, most often it is the result of a repetitive activity, such as running or throwing a ball. It also can be caused by an avulsion fracture, which occurs when a small piece of bone breaks off and becomes lodged in the cartilage. Apophysitis is most common in children and teenagers who play sports. Overuse injuries have become more common in young athletes as training demands have increased.

One of the most common forms of apophysitis is Osgood-Schlatter disease, which manifests in the knee. Other common forms are Sever's disease, which affects the heel, and Little League elbow. It also is seen often in the foot, shoulder and pelvis. Treatment for apophysitis usually begins with rest and anti-inflammatory drugs such as ibuprofen. Physicians may recommend applying ice to the area, and in more pronounced cases, physical therapy may be necessary. Orthopedic aids, such as knee pads, heel cups and ankle braces, may be helpful in some cases.