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FOXBORO - It's a fact of life in the NFL that some players make it through a 16-game season to get to the playoffs, and some don't.

The New England Patriots are no different than any other team in that respect.

As they await Sunday's AFC Championship Game against the San Diego Chargers, (3 p.m.; Ch. 4, 12), the Patriots' defensive unit will be missing one key player who played in last year's title game against the Colts, but it will have another back in the fray who missed that contest.

A healthy Rodney Harrison will go to battle at safety against the Chargers while linebacker Rosevelt Colvin, who suffered a broken foot on Nov. 25 against Philadelphia and went on injured reserve a few days later will be watching the game on television. They bring different things to the table, but according to linebackers Mike Vrabel and Tedy Bruschi, the Patriots must soldier on and concentrate upon the Chargers.

"We missed Rosie," Vrabel said during Friday's question-and-answer sessions at Gillette Stadium, televised live over the NFL Network. "We miss all our players. When you show up and Bill (Belichick) and Scott (Pioli) form a team and you end up with 53 guys, you know that you're not going to play the whole season with those same 53 guys. "So with that in mind, you understand that there's going to be some changes," he said. "You're going to go through the season and you're going to lose guys to injury or to whatever."

Colvin finished his injury-shortened season with 28 tackles (17 solo hits), four sacks and one interception. It wasn't the greatest statistical season for the ninth-year veteran from Purdue - who, ironically, lost most of his 2003 season to a hip injury suffered against the Eagles - but as Bruschi said, his absence had a ripple effect throughout the linebacking corps.

"We were five guys in there rotating and everybody doing different things and everybody had their roles," the 12th-year veteran said. "And when you lose a cog, you have to adjust. And of course, Rosey was making big plays for us the sacks, the interceptions, the forced fumbles, and you minus that from an equation, of course other guys are going to have to do different things and we have to adjust defensively especially as linebackers."

Colvin's presence was also missed inside the locker room, Vrabel said.

"We've missed his attitude in the locker room, and just the way that he carried himself and kind of kept everybody light," the 10th-year pro out of Ohio State said. "So we see him, and we certainly miss him on the field but we also miss him in the locker room as well."

"One thing you miss is his production out on the field and his presence in the locker room," Bruschi added. "He's one of the favorite guys we love to joke around with and makes the 'backerhood a lot of fun."

As much as the Patriots will miss Colvin, it can be said that they are doubly fortunate to have Harrison back on the field and wreaking havoc with the opposition for the first time in their last two playoff runs.

A knee injury suffered in the 2006 season finale at Tennessee took Harrison out of the mix for last year's playoff run, and as Vrabel said, the ex-Chargers' fiery style of play brings an edge to the defense that the Patriots will need Sunday.

"It's just emotion," Vrabel said. "You see him making a huge play to end the game last week (his interception of Jacksonville's David Garrard in the fourth quarter), and he's always played very, very well in playoff games that he's been healthy for that I can remember.

"You know, in the Super Bowl (against Philadelphia in Jacksonville), with the pick, a touchdown against (Ben) Roethlisberger and I'm sure I'll forget some sacks," he said, "but the best players, they have got to play great in the big games. So I don't expect anything less from Rodney. Certainly he's done that in the past and shown that he can do it when he's out there." Bruschi said that he can count on Harrison to set an aggressive tone for the Patriots in any game.

"To me, Rodney is our tone setter probably the most physical and violent teammate I've ever been a part of, and his aggression he uses to his advantage," he said. "He'll be the first to tell you that sometimes he's a little too aggressive, but for us to have him is a big plus.

"He can do so much," Bruschi said. "He can be a linebacker, he can be a safety, a defensive back and cover one of the best tight ends in the league. I think he can do everything that this coaching staff has ever asked."

MARK FARINELLA may be reached at 508-236-0315 or via e-mail at mfarinel@thesunchronicle.com