Angels' Garrett Richards opts for stem-cell therapy instead of surgery

Angels ace Garrett Richards, who suffered a high-grade tear of his ulnar collateral ligament in early May, has opted to forgo ligament-replacement surgery — for now — in favor of stem-cell therapy in hopes of pitching again this season.

Richards underwent the procedure, in which stem cells are derived from bone or fat and injected into the injury site in hopes of repairing and regenerating the damaged ligament, on Monday. There is no guarantee the procedure will be successful, but doctors should know in six to eight weeks if it is.

"Garrett weighed all the evidence that was given to him through MRI exams, he researched the process, talked to people who have gone through the procedure and people who have not and came to this decision," Angels General Manager Billy Eppler said. "We support him."

Richards, who went 1-3 with a 2.34 earned-run average in six starts, had all but resigned himself to Tommy John surgery, which would have sidelined the hard-throwing right-hander for the rest of this season and most, if not all, of 2017.

If stem-cell therapy, which Eppler termed a "conservative care route," doesn't work, Richards, 27, could have surgery in July and be ready for 2018.

"He got input from numerous sources, both players and doctors, and felt this was the best course of action … to heal and get healthy," Manager Mike Scioscia said. "I don't think you want to jump into any kind of surgery, let alone one the magnitude of Tommy John surgery.

"That puts you out for this season and most of next season. Garrett has a few months to evaluate where his elbow is. He really isn't having many symptoms at all, so I know he's confident with this course of action."

Eppler said there are pitchers "who have had this procedure and are pitching well in the big leagues," but he declined to name any.

New York Mets right-hander Bartolo Colon underwent stem-cell therapy in March of 2010 to help repair ligament damage in his elbow and a torn rotator cuff. Colon, now 43, missed all of 2010 but returned in 2011 and has gone 68-53 with a 3.67 ERA in 155 games since his stem-cell treatment.

If the treatment is successful, Richards could resume throwing by mid-July and return sometime in August. Fellow pitcher Andrew Heaney also opted to forgo elbow surgery in favor of a platelet-rich plasma injection in April.

Short hops

Angels left fielder Daniel Nava left Monday night's game in the fifth inning because of a left groin strain and will undergo an MRI test Tuesday. Nava spent three weeks on the disabled list in April and early May because of patella tendinitis in his left knee. …

C.J. Wilson, sidelined since the start of spring training because of shoulder inflammation, threw a 40-pitch simulated game Monday. The left-hander hopes to return by mid-June. "He looked good for a first workout against some hitters," Scioscia said. "It's encouraging, but it's still a long process." …

Tyler Skaggs, out for three weeks because of biceps tendinitis, was cleared to resume throwing after passing a strength test Monday. …

Closer Huston Street (left-oblique strain) has extended his long-toss program to 140 feet and hopes to throw off a mound Wednesday. … Reliever Javy Guerra cleared waivers Monday and was outrighted to triple-A Salt Lake.

mike.digiovanna@latimes.com

Twitter: @MikeDiGiovanna

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