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04/11/09 9:26 PM ET

Webb expands on bursitis in shoulder

D-backs ace talks about ailment, will play catch Sunday

PHOENIX -- On Saturday, D-backs starter Brandon Webb reiterated that bursitis in his right shoulder caused the stiffness that led him to miss his start against the Dodgers, but he expects to play catch Sunday and make his next scheduled start Friday against the Giants.

According to the Web site WebMD, bursitis is the inflammation or irritation of the bursa -- a sac filled with lubricating fluid located between tissues such as bone, muscle, tendons and skin -- which decrease rubbing, friction and irritation. The condition is most often caused by repetitive, minor impact on the area, or from a sudden, more serious injury. Age and overuse can also play a role in the condition.

"You have these bursa sacs, and when they fill with fluid it's like having fluid in your knee, and you can't bend it all the way," Webb said. "That's basically what was going on with my shoulder. I've had that before, so that's nothing uncommon at all."

According to reports, the MRI on Webb's shoulder Friday showed no unusual structural damage. On Opening Day, Webb (0-0, 13.50 ERA) allowed six runs on six hits in four innings against Colorado. He was scheduled to pitch against Los Angeles in the second game of the three-game series Saturday, but Yusmeiro Petit started in his spot instead.

"I've just been doing a lot of manual stuff and concentrating on getting my shoulder stronger," Webb said. "The MRI came out really well yesterday, so that was good. It's just a matter of having bursitis and getting that fluid out of there. That's basically what was causing the tightness."

Jesse Sanchez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.