Adrian Peterson tore the meniscus in his right knee during Sunday night's win over the Packers. That's hardly a good thing, but considering what could have happened — and how hobbled he was coming off the field — the injury might turn out to be relatively good news for the Vikings.

Though head coach Mike Zimmer offered no timetable for Peterson's return in his briefing with the media Monday, Dr. Jeffrey Macalena from the U of M's department of Orthopedic Surgery helped explain the injury in a phone interview this afternoon.

To be clear: Macalena is not treating Peterson, nor does he know the specific nature of the tear. But in general terms:

*What is a meniscus, anyway, and how common is this injury?

"The meniscus is the shock absorbing disc between the femur and tibia in the center of your knee," Macalena said. "There's one inside (medial) and one outside (lateral). Meniscus tears are very common. They just about always happen when you twist your knee on a planted foot — like when you are carrying a football and you plant or get tackled. It gets pinched between bones and tears."

*How do you treat a torn meniscus?

Macalena said plenty of civilians are walking around with a torn meniscus right now — in fact, Zimmer said Monday that he has one, too.

"By no means does the presence of a tear mean you have to do surgery or a procedure. What you're treating is a symptomatic tear. But to play professional football a lot of times means it is symptomatic," Macalena said. "I think in general when you treat a meniscus tear it's one of two ways. We can sew it up with stitches … or we trim it out. I'd say maybe 85-90 percent of them are cases where we trim it out."

*What does that mean, exactly?

"Think of it like a hangnail. You're fine but then it catches and it hurts. We trim it off and then it's smooth and it doesn't bother you," Macalena said.

*So what is the potential timetable for recovery/return with Peterson?

"When I do that surgery (trimming the meniscus) I send people home on the same day and people often only use crutches for a day or two. I think realistically you're pretty much fully recovered by 6 weeks or so. With that said, for a high-level athlete to get back to playing sports, I'd say 2-4 weeks has been done. I've had patients who have come back sooner," Macalena said. "Once you trim it out, there's nothing to heal. It's getting the raw edges to calm down. People can play not much longer after surgery. And if there's no surgery, I'd say he can play as soon as he wants."

*What makes sense for Peterson and the Vikings?

OK, we're done with the doctor here. It's just me speculating. The Vikings have three more games before their bye week. So let's say Peterson needs surgery. He could miss those three games, have the bye week and then get to close to five weeks of recovery time by the time the Vikings play at Philadelphia on Oct. 23 — a little short of what Macalena might describe as full recovery time but beyond the 2-4 weeks that he describes as possible.

But … the Vikings are 2-0 and have three big games coming up before the bye: at Carolina, home vs. Giants, home vs. Houston. If Peterson doesn't need surgery or could delay it, it's possible he could play during some or all of those games.

That said, it would seem the way the schedule falls makes it prudent — if he needs surgery — to have Peterson sit the next three games. The way he was putting no weight on his leg coming off the field and using crutches postgame would seem to indicate the tear is "symptomatic," to use Macalena's word.

But worst-case scenario based on what we know would seem to be that Peterson misses three, maybe four games.