Lehtivuori was only five years old when he first wore the jersey of Ilves in his hometown Tampere, and he hasn’t changed teams since. The Ilves of his age group is particularly strong and Lehtivuori was there to win both Jr C gold in 2004 and Jr B gold in 2006. The rising of his stock has happened more lately with very strong national team performances in 2005-06, from junior Euro Hockey Tour to the Viking Cup and the U18 WC, from which Lehtivuori returned with a silver medal.
2006-07: Lehtivuori competed in his first full season in SM-liiga in 2006-07, appearing in 40 games for Ilves Tampere. He did not record a point in what was, at times, largely spot duty, but did a fine job taking care of his own end, registering a plus-3 rating. He is expected to take on a larger role with the team this year. Though Finland finished a very disappointing sixth at the WJC, Lehtivuori was a true bright spot for the team. He did not register a point and finished with a minus-4 rating and four PIMs in six games, but continued to display the smooth-skating, puck-handling abilities that have some predicting an NHL career in his future.
2007-08: Although Lehtivuori was not quite the offensive force that he was expected to be for Team Finland at the World Junior championships, he adapted well to a full-time role in his second SM-Liiga season with Ilves.
2008-09: Playing with Ilves, Joonas managed 12 points in 44 games.
2009-10: In his first season on North American ice, Joonas adjusted his game to the smaller ice and more physical play, able to register five goals and 18 assists.