The concussion Casey FitzSimmons suffered on Dec. 6, the last of several in his career, forced the long-time Lions tight end into retirement. He made the announcement through his agent on Wednesday. He is just 29.

“This has been a very difficult decision. I feel like 2009 was one of the best seasons of my career, because I was so consistent and was able to contribute in a variety of ways. If it wasn’t for the concussions, I would not be retiring,’’ he said in a statement.

“It’s frustrating because the rest of my body is still capable of playing at a high level in the NFL. However, given the seriousness of the risk associated with continuing to play, I have to listen to the advice the team has given me.’’

FitzSimmons, who was signed by Detroit as an undrafted free agent out of Carroll College (Mont.) in 2003, played in 99 games over seven seasons for the Lions.