Analyzing Indianapolis Colts WR Darrius Heyward-Bey's Knee Injury

Knee injuries continue to plague NFL training camps, and according to The Associated Press (via SI.com), Indianapolis Colts wide receiver Darrius Heyward-Bey joined a long list of injured stars over the weekend.

Per Mike Chappell of the Indianapolis Star, doctors diagnosed Heyward-Bey with a grade-one sprain of his left medial collateral ligament (MCL).

In the grand scheme of things, especially when compared to the gamut of season-ending injuries so far this summer, the sprain is fairly minor. However, that is not to say it isn't worth keeping an eye on.

UPDATE: Tuesday, August 6, 1:33 pm ET

According to Mike Wells of ESPN.com, an MRI of Heyward-Bey's left knee is "negative," and the wide receiver is listed as day to day. It isn't entirely clear what that implies. Perhaps the MRI shows no signs on injury—the true definition of a "negative" MRI. It could also mean radiologists could not see an obvious ligament tear, but the ligament is still injured—known as a grade-one sprain (see below).

Regardless of specifics, the new report allows for even more optimism than was already present.

--End of update--

UPDATE 2: Tuesday, August 6, 4:47 pm ET

According to Mike Chappell, Heyward-Bey is dressed in full pads for Tuesday night's practice. The development suggests the injury is, in fact, an extremely minor sprain—if anything at all. So goes the inherent uncertainty in medicine, reporting and reporting on medicine.

It is still worth monitoring his progress, but as of now, it seems the Colts wideout avoided any serious damage.

--End of update--

As one of the knee's four main ligaments, the MCL plays a vital role in stabilizing the knee and coordinating motions such as walking, running and cutting. Specifically, it connects the inside of the femur—the thigh bone—to the inside of the tibia, or shin bone. By doing so, it prevents the knee from buckling inward towards the center of the body.

For a real-life example, imagine a tackler hitting the outside of a running back's planted leg. The hit forces the knee inward, and it is the MCL's job to absorb the blow. However, if the tackle is forceful enough, it can overwhelm the MCL, stretch it beyond its normal length and cause injury.

Ligament injuries are called "sprains" and are classified as grade-one, grade-two or grade-three.

A grade-one sprain is a mere overstretch of the ligament without visible tear on MRI, and symptoms include only pain and swelling.

Grade-two sprains are partial tears of a ligament. MRI shows not only signs of inflammation but also a visible tear to the ligament itself. In addition to the aforementioned pain and swelling, the injury can lead to significant joint weakness or instability.

A grade-three sprain—the worst type of sprain—is a complete rupture of the ligament in question. An MRI will show two free ends of ligament tissue—or sometimes even no tissue at all. Without an intact ligament, the joint becomes very unstable, and in the case of a completely torn MCL, there is no support to prevent a knee from collapsing inward.

Fortunately, Heyward-Bey's injury is of the grade-one variety. Still, according to Rotoworld's Jason Silva, ESPN's Chris Mortensen is not quite as optimistic.

It's possible Heyward-Bey's injury is of the grade-one "plus" variety, an unofficial way of communicating a more serious-appearing grade-one sprain—one with more extensive inflammation on MRI, for example.

Either way, treatment is the same.

With rest, icing and physical therapy, Heyward-Bey should recover nicely.

Run-of-the-mill grade-one sprains usually require one or two weeks of rehab time—recall that Robert Griffin III's 2012 grade-one lateral collateral ligament (LCL) sprain cost him just one week.

With that said, don't be surprised if the Colts hold out their new offensive weapon a bit longer in an effort to ensure he is completely healthy by Week 1. Since injured ligaments are weaker ligaments—and thus more prone to further injury—it would make little sense to rush him back during the preseason.

Unfortunately, that means he will have to miss out on valuable chemistry-building time with quarterback Andrew Luck, but such is the cost of a proper recovery.

If there are any setbacks, or if the injury is actually more serious than a true grade-one sprain, Heyward-Bey could miss more time. For reference, a grade-two injury usually requires around three to six weeks of rehab.

So, what is the take-home message?

The smart money says Heyward-Bey will be back on the field within a month.

Yet, the way this offseason has been going around the league, Colts fans will remain understandably nervous until then.

Dave Siebert is a resident physician at the University of Washington with plans to pursue fellowship training in Primary Care (non-operative) Sports Medicine. Medical information discussed above is based on his own knowledge.

Follow @DaveMSiebert