ESPN's Chris Mortensen says that Patriots LB Brandon Spikes wasn't placed on the injured reserve just because of his knee. He reports that Spikes was late to team meetings on Friday, during the bye week, and that was the final straw for the coaches and front office. Apparently Mort also reported that this wasn't the first incident for Spikes this season. The Patriots placed him on the injured reserve instead of releasing him.
Spikes had been nursing a knee injury for the last portion of the season, but he can't afford to be late to practices on a bye week. Rookie Jamie Collins and sophomore Dont'a Hightower were playing well in Spikes' stead, and veteran Dane Fletcher is another capable body. However, no one can replace the fire that Spikes brings to the defense.
Spikes was late to practice because of the snow and if you click the link, it'll show Spikes' car stuck in some pretty deep snow. While it may seem unfair, it echos the 2009 season where Randy Moss, Gary Guyton, Derrick Burgess, and Adalius Thomas were sent home for being late to practice for a similar snowfall.
The fact that the Patriots were willing to cut Spikes, if not for it being the playoffs and some other team signing him, means that it's very likely the impending free agent is not coming back next season. It makes the most sense as the Patriots can move forward with Collins and Jerod Mayo as the outside linebackers and Hightower as the middle linebacker in the 4-3 fronts.
This is shocking news to come out on game day, and it will be interesting to see how any more news will be released or handled.
Update: Apparently this was a mutual move. Spikes agreed to go on the IR for his tardiness. He remains with the Patriots, gets paid for the playoffs, and gets to use the Patriots training staff to heal up. The Patriots don't have to worry about him signing elsewhere and have a potential compensatory draft pick in play, should Spikes sign for a solid contract.