Thorburn, 35, will remain with the Blues through the playoffs.
Thorburn played in 50 games for St. Louis last season (his first with the Blues), but only one this season, on Oct. 13, when he got 1:52 of ice time over three shifts against Chicago. He played 40 games with the Rampage, posting seven points (two goals, five assists) and 45 penalty minutes.
Thorburn entered the league with Buffalo in 2005 and has played in 801 NHL regular-season games, making him one of just eight players with more than 800 games played and 950 penalty minutes during that time. He has 134 points (53 goals, 81 assists) and 968 penalty minutes in his career.