Source: Raiola's deal worth $20 million

Detroit Lions center Dominic Raiola signed a four-year extension Thursday that will keep him under contract through the 2013 season.

Raiola, 29, is entering his ninth season and, as their starting center since 2002, is one of the Lions' most tenured players.

According to a source, Raiola became the fifth-highest-paid center in the NFL by agreeing to a four-year, $20 million deal, of which $9 million is guaranteed. With the new contract, Raiola will make $13 million this year.

Detroit sent Raiola a strong vote of confidence with this deal. Raiola was entering the final year of his contract and would have been a free agent next season. He was scheduled to make $4 million. Despite an 0-16 season and some questions about the team's offensive line blocking, the Lions stepped up to give him a new contract and job security.

"He's everything that's right about the NFL," Lions coach Jim Schwartz said. "He's a guy that embraces the city he lives in. He lives here year-round. He is as hard a working guy as you're going to imagine."

Raiola was a second-round choice of the Lions in 2001. He didn't start as a rookie but became a fulltime starter after his rookie season.

"If you talk about the great centers, probably in the history of the National Football League," Schwartz said, "I think they'd all have in common: leverage, feet, balance, quickness. Dom has all of those."

John Clayton is a senior writer for ESPN.com. NFC North blogger Kevin Seifert contributed to this story. Information from the Associated Press was used in this report.