Updated

The Washington Capitals acquired defenseman Kevin Shattenkirk in a trade with the St. Louis Blues on Monday night.

Washington sent a 2017 first-round pick, forward Zach Sanford and minor leaguer Brad Malone and conditional draft picks to St. Louis for Shattenkirk and former Capitals goaltending prospect Pheonix Copley.

Shattenkirk, 28, is set to be an unrestricted free agent this summer. He has 42 points on 11 goals and 31 assists this season and has 66 goals and 218 assists in 471 NHL games.

"We felt it was important to acquire another defenseman to strengthen and add depth to our blue line," Capitals general manager Brian MacLellan said in a statement. "Kevin is a skilled, puck-moving defenseman who we think will help our team at even strength and on the power play."

The New Rochelle, New York, native counts $4.25 million against the salary cap this season. The Blues retained 39 percent of his salary as part of the trade.

Shattenkirk is a right-handed-shooting defenseman who adds depth and offense to the Capitals' blue line.

In addition to the 2017 first-round pick, the Blues get a 2019 second-round pick if the Capitals sign Shattenkirk for next season or reach the Eastern Conference final with him playing at least half of their playoff games.

Other conditions protect the Blues in the event Washington trades Shattenkirk prior to July 1, when he could hit the open market.

Sanford, 22, has two goals and an assist in 26 games during his rookie season.

Copley, whom the Capitals acquired from the Blues in the 2015 trade for winger T.J. Oshie, becomes their third goaltender behind Braden Holtby and Phillip Grubauer.