Johnson joins the Lions after spending the first four seasons of his career in the NFC North with the Minnesota Vikings. He entered the league back in 2008 as a second-round pick and made a total of 27 starts in his four seasons with the Vikings. Most recently, Johnson spent time with the Miami Dolphins. He joined the Dolphins last April and was released in August.
Coleman departs the Lions after starting in seven games this season. He spent most of 2011 on injured reserve, but the Lions decided to bring him back for 2012. Clearly, safety has been an issue for the Lions this season, so the team elected to make a change.
In other roster news, the Lions decided to fill the empty spot on the practice squad with wide receiver Troy Burrell, who spent part of the offseason with the Lions and was on the practice squad for about a week in November.