This week, during Detroit's bye, we'll take a look at each position group at the halfway point of the season.

Prior reviews: Quarterbacks.

What has worked: Reggie Bush has been almost exactly what Detroit wanted him to be when the Lions signed him as a free agent this summer. He's the multi-purpose back the Lions have wanted in their offense since Calvin Johnson and Matthew Stafford arrived with the franchise, the player who can take short screen passes and turn them into 77-yard touchdowns like he did in the first week of the season.

Joique Bell has also been a good third-down and change-of-pace back for the Lions, rushing 62 times for 236 yards and four touchdowns while catching 27 passes for 296 yards.

Combined, the duo has given relief to the Lions passing game. It hasn't quite opened up Johnson as much as initially planned, but when Bush is healthy the Lions have a deep-to-short dynamic in the passing game few teams in the league possess.

Bush also said before the season that his goal was to have at least four yards a carry. He is currently surpassing that number, at 4.4 yards a carry and four rushing touchdowns. His combined 853 yards is third in the NFL -- just ahead of his teammate, Johnson, and behind Jamaal Charles and LeSean McCoy.

What has not: For as effective as he has been in becoming a second target for Detroit quarterback Matthew Stafford and a perfect balance for wide receiver Calvin Johnson, Bush has really struggled catching passes. While he hasn't dropped a pass since Week 6, he is dropping 11.6 percent of the passes thrown his way. That's five actual drops this season.

Bush has the fifth-worst drop rate of qualifying players in the NFL. It is compounded by an 8.8 percent drop rate for Bush's complement at the position, Bell. Bell has only three drops on the season, all coming in a Week 2 loss to Arizona.

The other thing that has not worked for Detroit has been former second-round pick Mikel Leshoure. For a guy who started a few games for the Lions last year, he has been invisible for Detroit after losing the backup job to Bell. He has two carries this season for nine yards.

Prognosis: Much of Detroit's success at running back relies on the health of Bush and Bell, both of whom have had injuries this season. Bush injured his knee against Arizona and missed the Lions' Week 3 win over Washington. Bell hurt his ribs at Cleveland and while he didn't miss a game, he was in a lot of pain.

Considering Detroit's other options -- the little-used Leshoure or the rookie Theo Riddick -- the health of the Lions' two main ball carriers is paramount at this point in the season. While Bush is the catalyst for a lot of what Detroit can do since he can turn a small screen into a big touchdown, as long as Johnson and either Bush or Bell is healthy, the Lions have a chance to be a potent offense.

Bush's health is something to pay attention to. He is on pace for 300 touches between rushes (238) and receptions (62). That would be more production and attempts for him than he has had in any season of his career. If he can stay healthy, though, he is on pace for a 1,000-yard rushing season and a 700-yard receiving season. If he can pull that off, it was more than a good investment for the Lions, especially considering Bell is also producing when he gets carries.

Many of the statistics used in this post come from ESPN Stats & Information.