CINCINNATI -- The Nationals activated right fielder Austin Kearns from the 15-day disabled list and optioned infielder/outfielder Kory Casto to Triple-A Columbus on Thursday.

Kearns missed over a month of action because of loose bodies in his right elbow. He had a rehab assignment recently, where he went 7-for-17 (.412) with a homer and seven RBIs for Columbus and Class A Hagerstown. The return of Kearns means that Elijah Dukes will now be the everyday left fielder, while Wily Mo Pena is on the bench.

Asked what it means to have Kearns back in the lineup, manager Manny Acta said, "He's another high character guy we can add back from the DL. He will play everyday out there for us. That's something we don't have to worry about. He will improve our defense in our outfield."

As for Casto, he hit .180 (9-for-50) with one homer and seven RBIs in 23 games for Washington. He did have two big hits during his time with the Nationals, both of them game-winners.

Casto hit a pinch-hit three-run homer against the Mariners on June 15, and had a run-scoring single against the Orioles last Friday. Acta said Casto did a good job coming off the bench, but the skipper wants Casto to continue to think of himself as an everyday player.

"We let him know that we liked what we did," Acta said. "He cannot settle right now to being a bench guy. That's what I told him. His goal should be to still be an everyday guy. I really like the improvements he made up here on a part-time situation."

Meanwhile, left-hander Matt Chico had left elbow reconstruction surgery on Thursday. Dr. James Andrews performed the operation. Chico, who went 0-6 with a 6.19 ERA for the Nationals, will miss the rest of the season.

Catcher Johnny Estrada has also started his rehab assignment. He played for the Gulf Coast Nationals recently, and went 1-for-2. He will join Class A Potomac on Friday.

Estrada hasn't played in a Major League game since early May due to ulnar neuritis in his right elbow.