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When I watch my son wind up and throw the ball when he's pitching, I can't help but wonder how that extreme motion is going to affect his shoulder joint years from now. Are there any studies to show what happens inside the joint?

There are some long-term effects of throwing in the shoulders of throwing athletes. The glenohumeral (shoulder) joint comes under high joint forces, speed, and stress during this activity.

Extreme positions of motion may actually alter the shape of the joint capsule and surrounding ligaments. Joint stability may even be compromised. Right now all we have are theories. Evidence to prove any of these changes occurs is lacking. Even the idea that the soft tissues "stretch out" after long-term throwing remains unproven.

In a recent study of elite baseball pitchers, physical therapists from the University of Florda offer some insight. They measured the joint motion and stiffness of 34 professional baseball pitchers. They found the same amount of motion on both sides (throwing versus nonthrowing shoulders). What they noticed was that the pitching arm had more external rotation. The nonthrowing arm had more internal rotation.

The front portion (anterior capsule) was stiff in both arms. This stiffness gave the joint greater stability. There was less risk of injury. The risk of arthritis in the adult years with overhead pitching in young children isn't known yet. More long-term studies are needed.

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