In addition, the Blues assigned defenseman Jake Walman to the Rampage.
Mikkola, 23, has appeared in 30 games with the Rampage this season, tallying 11 points (two goals, nine assists) and 14 penalty minutes. The 6-foot-4, 205-pound native of Kiiminki, Finland, Mikkola was originally drafted by the Blues in the fifth round (No. 127 overall) of the 2015 NHL Draft.
Walman, 23, made his NHL debut on Jan. 4 in Vegas. The 6-foot-1, 202-pound defenseman has also dressed in 32 games with the Rampage this season, recording 18 points (four goals, 14 assists) and 24 penalty minutes. The Toronto, Ontario, native was originally drafted by the Blues in the third round (No. 82 overall) of the 2014 NHL Draft.