Lions have lost both starting offensive tackles as Backus retires
Turning 36 years old in September and having 191 games under his belt, the announcement is not all that surprising. Backus' effectiveness began to decline in 2012, and he may have wanted to retire before becoming a turnstile on the edge. Though he never made a Pro Bowl, his remarkable number of starts tells you all you need to know about how solid and consistent he was.
Now that Backus has retired, the Lions are facing a pretty serious problem. They have already lost starting right tackle Gosder Cherilus to the Colts, which leaves them with neither of their 2012 offensive tackle starters. 2012 first-round pick Riley Reiff has been waiting for a vacancy at tackle to open up, but he didn't show much promise as a rookie and the Lions are seriously considering moving him to guard. If Reiff does move to guard, the Lions will likely have to upgrade at both tackle spots, as they have no experienced linemen who can play the position.
The departure of Backus and Cherilus breaks up an offensive line unit that started all but one game together in 2012 (Backus was the only one to miss a game). Continuity is an underrated factor in an offensive line's success.
Offensive tackle now sits atop the list of needs for the Lions, who will hope to have a shot at a premier tackle prospect with the 5th overall pick in the draft. They have a good shot at taking Eric Fisher out of Central Michigan if they have the opportunity, but many analysts believe Fisher won't will make it past the Eagles, who have the 4th pick. Any tackle aside from Luke Joeckel (the likely first overall pick) or Fisher would be a reach at 5th overall, and I wouldn't be surprised to see the Lions trade out of that spot if the two top prospects are off the board. I could also seeing them trying to trade up to snag one of the top tackle prospects, if the price is right.
Many of the free agent offensive tackles have been swept up already, and the top two remaining - Andre Smith and Sebastian Vollmer - are likely too expensive for the Lions' current salary cap situation. The best tackles remaining on the market that the Lions have a better chance of affording include Winston Justice (best known for being terrorized by Osi Umenyiora in 2007), Max Starks, and Bryant McKinnie.
With the offensive tackle market thinning out, it's hard for me to see the Lions prioritizing any other position in the draft. My guess is that they are praying for Eric Fisher to fall to them at 5th overall.