Offensive, defensive lines a concern for Lions

The Lions addressed a handful of needs in free agency, but now there are holes to fill in the trenches.

Even with hot-shot quarterbacks and game-breaking receivers, it still comes down to the trenches in the NFL. You have to get to their quarterback and you have to protect yours.

Otherwise, you're going nowhere.

The Detroit Lions made headlines during the first few days of free agency. Reggie Bush will restore the big-play potential at running back and safety Glover Quin should help solidify the secondary.

But in a salary-cap era, when you plug one hole, another is often created. The concerns for the Lions have now shifted to the offensive and defensive lines.

Bush, Matthew Stafford and Calvin Johnson are nothing if there's unreliable blocking up front. An improved secondary remains vulnerable in the end if the other team's quarterback has too much time to throw.

Think back to the start of last season. Continuity on the offensive line was a strength. The entire group was returning for its third straight year together. There was also talk that the defensive line had the potential to be one of the best in the NFL.

Now, four months before training camp opens, both of those positions have to be considered serious question marks.

The offensive line must replace three starters -- left tackle Jeff Backus (retired), right guard Stephen Peterman (released) and right tackle Gosder Cherilus (signed with Indianapolis).

None is an All-Pro. All three certainly can be replaced.

But when you're replacing them at the same time, there's reason for concern. Typically, the veteran offensive lines that have been together for a while are the most effective.

If the Lions opened the season today, last year's first-round draft pick Riley Reiff quite likely would start at left tackle, possibly Bill Nagy at right guard, with Corey Hilliard or Jason Fox at the right tackle.

That's three new starters with very little NFL experience:

* Reiff, 24, was credited with eight starts as a rookie, but that's misleading. Most of those came when the Lions opened up in their three-tackle package. Reiff started just once as one of the five offensive linemen, filling in for an injured Backus against Houston.

* Hilliard, 27, started four games in 2010 and one in 2011. But he was inactive every game last season because of the addition of Reiff and the line's general good health.

* Fox, 24, has been hampered by injuries since being drafted in the fourth round three years ago. He was on injured reserve in 2011 and then inactive every game last season.

* Nagy, 25, claimed off waivers from Dallas last August, spent the entire season on injured reserve recovering from a fractured ankle. He started four games for the Cowboys in 2011.

Maybe all four of them are ready to be reliable starters and are more talented than their predecessors.

But until they do it on Sunday, as a group, we really don't know.

There are similar questions defensively up front. The Lions are strong inside with Ndamukong Suh and Nick Fairley at the tackles, but what about on the edges? Who's going to pressure the quarterback?

That was such a weakness last season that the two starting ends won't be back. The Lions released Kyle Vanden Bosch and didn't re-sign free agent Cliff Avril.

Only three defensive ends are currently on the roster:

* Willie Young, a restricted free agent who didn't live up to the preseason hype he generated once the regular season arrived last season.

* Jason Jones, signed last week as an unrestricted free agent from Seattle. Jones has 18 1/2 sacks in 61 NFL games (31 starts) in his five-year career.

* Ronnell Lewis, a disappointment as a rookie after being a fourth-round pick a year ago.

The Lions could still re-sign Lawrence Jackson, one of their unrestricted free agents. Jackson had emerged as the No. 3 defensive end, ahead of Young.

But at this point, barring some more contract restructuring, Detroit realistically doesn't have enough money available under the salary cap to add a top defensive end or offensive lineman in free agency.

But the Lions do get the No. 5 pick in the NFL Draft. They could conceivably take an offensive tackle (Texas A&M's Luke Joeckel, Central Michigan's Eric Fisher or Oklahoma's Lane Johnson?) or a pass rusher (BYU's Ziggy Ansah, Oregon's Dion Jordan, LSU's Barkevious Mingo or Georgia's Jarvis Jones?)

One thing is fairly clear: The big signings last week will be meaningless unless the right decisions are being made to rebuild the offensive and defensive lines, too.