I am a fairly new journalist now assigned to a small town newspaper sports column. My first assignment is to research shoulder dislocations in throwing athletes. Parents of our local little league players are worried about their kids ending up with one dislocation after another. I'm looking for some background information and maybe a new angle from what's already been reported. Can you help me out?
The shoulder joint called the glenohumeral joint is made up of two main parts. On one side is the humerus (the upper arm bone). At the top of the humerus is a round ball-shaped bone that fits into a shallow socket of the scapula (shoulder blade). This shallow socket is called the glenoid fossa or just glenoid. Movement of the head of the humerus in the glenoid is what gives us our shoulder movements of flexion, extension, abduction (arm away from the body), and rotation (internal and external).
Most of the attention on shoulder dislocations is focused on the head of the humerus and surrounding tissues. But the glenoid (socket) side is just as important. Any damage to the already very shallow glenoid can contribute to shoulder instability. Defects in the rim around the glenoid and bone loss within the socket are two ways the glenohumeral contact can be affected, adding to the problem of chronic dislocations.
Sometimes these defects occur because the shoulder dislocates in a traumatic event. Bone is actually fractured and a fragment of the rim breaks off. In other cases, the bone just wears away from constant contact and compression. Remember, these are athletes who are practice and perform overhead throwing motions sometimes 100s of times each season.
Other athletes such as football, volleyball, or soccer players may suffer a traumatic injury with damage to the ligaments attached to the glenoid rim. Without that little rim of fibrocartilage around the joint, it's much easier for the shoulder to pop out of the socket and dislocate again and again. Even a small instability can change the biomechanics of the shoulder complex enough that over time, the bone wears away unevenly. In either case, rim defects get larger over time. The result is a worsening of the instability.
And so the vicious cycle gets set up and continues. Changes in the joint structure cause biomechanical alterations (i.e., the way the shoulder moves in the socket). Changes in the arc of shoulder motion wear the joint surface unevenly. This, in turn, alters forces within the glenohumeral joint, wearing the glenoid bone unevenly, and the cycle continues. This is how even a small defect can ultimately lead to chronic instability.
Athletes must be taught how to throw properly and keep a log of number of pitches thrown per practice and per game. Players must be trained from early on to report symptoms of pain, shoulder clicking or popping, and dislocation. When a minor injury isn't treated and the player continues to throw, problems are inevitable. Everyone (players, parents, coaches) can work together to ensure safe training techniques and injury prevention.
Dana P. Piasecki, MD, et al. Glenoid Bone Deficiency in Recurrent Anterior Shoulder Instability: Diagnosis and Management. In Journal of the American Academy of Orthopaedic Surgeons. August 2009. Vol. 17. No. 8. Pp.482-493.
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