Are lefty pitchers more injury-prone?

NEW YORK (Reuters Health) - There appear to be differences in the throwing motions of lefty and righty baseball pitchers that could impact their susceptibility to injury.

In a study of college pitchers, researchers found that the mechanics of a lefty's motion resulted in more stress on the bone that runs from the shoulder to the elbow called the humerus. The study is published online in The American Journal of Sports Medicine.

"It's kind of remarkable to me," Dr. Sherry Werner, the lead researcher on the study and the Director of the Center for Sport & Motion Analysis at Texas Metroplex Institute for Sports Performance in Arlington, told Reuters Health. "I never would have expected significant differences."

Werner and her colleagues analyzed the pitching motions of 84 collegiate baseball players, looking at the rotation of their pitching and non-pitching arms, the angles of their elbows and shoulders during the pitching motion, and their arm speed. Then, they took the 28 lefties in the study and matched them up with 28 righties of similar age, height, weight, and throwing speed to examine these details of their motions.

By comparing angle and speed measurements, the researchers found that left-handed pitchers put more stress on their humerus than right-handed pitchers.

"Their range of motion is different to begin with," Werner said, explaining that these mechanical differences could impact the stress on the arm bones. But in terms of significant differences, "the number one thing was torque on the humerus," she said.

This stress is highest, she explained, at the point in the pitching motion where the pitcher has the ball behind him with his arm extended, before the arm accelerates toward the plate. Too much stress on this bone, and it can fracture.

In the history of Major League Baseball, only four pitchers have had this specific type of injury - all lefties, Werner said. But humerus fractures happen to younger players as well, perhaps most notably to Phillies ace (and lefty) Cole Hamels during a game in high school.

There are still questions about whether lefties get injured more than righties in general. When Werner and her colleagues went back through 10 years of information on who has been on the disabled list in the major leagues, they didn't see any differences. But the DL is missing a lot of information, said Dr. Brandon Bushnell, which makes a detailed comparison difficult.

Bushnell, an orthopedist at Harbin Clinic Orthopaedics in Rome, Georgia who has worked with major league baseball clubs, called the study an interesting "step one."

"As far as I know, it's one of the first studies, if not the first one, that really shows that there is a difference in righties versus lefties," said Bushnell, who was not involved in the study. "The question that that raises is -- are those random differences or do those really mean anything?"

Dr. Glenn Fleisig, Research Director at the American Sports Medicine Institute in Birmingham, Alabama who was also not involved with the study, said that his research has not shown any differences in the biomechanics of lefty and righty pitchers. "I don't know why lefties and righties would inherently be physically different," he told Reuters Health. But, he said, "it's certainly worth further investigation."

It's possible, Bushnell said, that lefties may not be more injury prone, or may actually be less injury prone, because they have an inherent advantage that means they don't have to throw as hard as righties.

"Coming from the opposite side of the pitching mound, that alone makes a left-hander valuable," he said. In college, "a left-hander that can throw 90 miles an hour may often be more valuable than a right-hander that can throw 95 miles an hour. They're harder to hit off of."

"I think the number one thing you have to think about as a pitching coach or any sports medicine provider is, we may have to treat the lefties a little different than the righties," Werner said.

She hopes that the current study will spur larger, more in-depth studies of pitching injuries. "We need to understand the differences and know that if we're looking at a lefty, we're not expecting them to look like a right-hander," she said.

SOURCE: link.reuters.com/bat24m The American Journal of Sports Medicine, online June 11, 2010.