Here's the Pitch: Elbows Widen with the Wind-Up

In baseball, many pitchers and outfielders are known to have elbow problems. Researchers are studying the effects of repeated throwing on the elbow joint. By understanding the mechanics of throwing, researchers may be able to suggest ways to prevent elbow injuries.

Ultrasound (also called ultrasonography) has been used to see inside the elbow. Ultrasonography uses sound waves at a very high frequency to make images of the joint and ligaments. Ultrasonography was used in a study of 30 college baseball players. Images of one elbow were compared to the other elbow for each player. Sound waves were directed to the medial side of the elbow. This is the side along the inside edge of the elbow. The throwing motion puts stress on this side of the joint. 

With ultrasound, researchers saw an increased space in the elbow joint of the throwing arm. Near the end of the wind-up, the elbow bends, and the forearm angles out to gather speed. The forces across the inside edge of the joint can cause the forearm bone (the ulna) to slide outward slightly. This shifting motion, called lateral shift, leaves a gap on the inside edge of the elbow joint. The ligament that crosses this part of the elbow (the ulnar collateral ligament) gets stretched as this gap widens. 

Repetitive pitching and throwing cause intense stress on the medial side of the elbow. This stress leads the ulna bone to shift, putting a stretch on the ulnar collateral ligament. Ultrasound can show widening in the joint and tears in the ligament. Information from studies like this one may help researchers find new ways to prevent elbow injuries in baseball players.

References: Junya Sasaki, MD, et al. Ultrasonographic Assessment of the Ulnar Collateral Ligament and Medial Elbow Laxity in College Baseball Players. In The Journal of Bone and Joint Surgery. April 2002. Vol. 84-A. No. 4. Pp. 525-531.