According to the Mayo Clinic website, the injury is usually located under the collarbone and can cause discomfort in the shoulder and neck areas and numbness in the fingers.
"They have to remove your first rib," Lessard said. "[Dodgers pitcher Josh] Beckett had it not long ago."
The surgery on Masset will be performed next week at Barnes-Jewish Hospital in St. Louis and it means he will miss the rest of this season. Besides Beckett, Cardinals ace Chris Carpenter and Mets pitcher Shaun Marcum have also undergone the operation.
Masset, 31, has been in Goodyear, Ariz., all season rehabbing from right shoulder surgery, which he had last September. He last pitched for the Reds in 2011, and not at all since he signed a two-year, $5.5 million contract after that season.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.