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The Golden State Warriors were less than a minute into the first quarter against the Wizards when Kevin Durant took the sort of body hit that makes everyone watching shudder. Washington center Marcin Gortat shoved the Warriors’ Zaza Pachulia aside, causing Pachulia to stumble and fall onto Durant’s left leg.

The news could have been worse, but it wasn’t good: an MRI Tuesday night showed the power forward had suffered a Grade 2 Medial Collateral Ligament (MCL) sprain and a tibial bone bruise. The Warriors said he’d be out of action indefinitely and will be re-evaluated in four weeks. But hopes were high that he return in time for the playoffs, which start in six weeks.

We asked Dr. Nick Grosso, a sports medicine surgeon and president of The Centers for Advanced Orthopaedics in Maryland, to walk us through the injury and help us sort things out:

So how bad is it?

Of the two injuries, the bone bruise is the more serious.

Let’s start with the MCL. What’s it do?

There are four major ligaments in the knees – the anterior cruciate, posterior cruciate, medial collateral and lateral collateral. And the medial keeps the knee from going back and forth like windshield wipers. The medial is the only ligament with remedial capabilities of its own, meaning that 90 percent of the time it can heal itself if it’s treated carefully. It’s the same injury Steph Curry had last year.

What exactly is a sprain?

Ligaments are like cables containing parallel fibers that run from A to B. Ligaments attach bone to bone; they have a set length, so if you change that length by stretching it you damage the fibers inside that cable.

And what does the sprain’s “grade” mean?

The strain varies by the degree to which the ligament has been stretched, and they’re graded from one to four. One is not stretching it at all, just inflammation. You grade them by examining how loose the knee is, so it’s very subjective; you have ten surgeons look at an MCL and some may grade it a two while others may grade it a three. With an MRI scan, you look for swelling around the tendons. You can’t see down to the fiber level, but you can see if they’ve been disrupted. If the MCL is torn, the fibers, instead of being straight will look wavy.

Can all four grades heal themselves?

A grade four, which is completely torn, can heal itself, but we often have to go in and fix it. The other three grades will usually heal on their own. But a two is not bad; we brace the knee and in two or three weeks it could be back to normal.

So what about the bone bruise?

It’s funny, but we didn’t know they existed until the MRI was invented back in the mid-90s. You can’t see them on an xray, but with an MRI you can actually see the swelling of the bone. It’s amazing. These bruises are part of the stress spectrum which goes all the way to fractures. It’s trauma to the bone, and a bruise can take a while to heal and it can be very painful. You don’t want to put any stress on a compromised bone because it can get worse and keep coming back and eventually turn into a real fracture.

What’s the timing here?

A bone bruise can take four to six weeks to heal, with some rehab after that.

What’s the treatment for Durant’s injuries?

The hardwood has no give whatsoever, so KD’s joints took tremendous stress. I’d be leery of getting him back during the regular season, but with six weeks left, there’s a good chance he’ll be back for the playoffs. He’ll have a hinge brace on 24-7 for maybe a month, which will allow him to bend his knee but it’ll prevent that side-to-side movement, even in his sleep. Rolling over in bed can put enough strain on the MCL that it won’t heal.

And the bone bruise?

For the bone bruise he might have to continue to wear the brace during playoffs. A bone bruise just has to heal itself, but it can take up to six weeks. Even saying four or five weeks may be a bit too optimistic.

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