Joe Flacco's Knee Injury: A Closer Look at His MCL Sprain, Knee Bracing

According to NFL.com's Gregg Rosenthal, Baltimore Ravens quarterback Joe Flacco suffered a "mild" MCL injury as a result of a blow to the outside of his left knee on Monday. Fortunately, the Ravens do not expect their franchise quarterback to miss any time.

A screenshot from a GIF of the injury, courtesy of @gifdsports via ESPN's Monday Night Football, shows exactly what happened:

Though mild, playing through an MCL sprain carries its own set of risks. Luckily, medical personnel have tools at their disposal to mitigate them.

For instance, the Associated Press (via Fox Sports) reports Flacco will wear a brace on his injured knee Week 16.

Though certainly not perfect, knee braces serve to restore some of the stability lost after a sprain. By working as an external barrier that assists ligaments in preventing abnormal bending of the knee, they can also help deter further injury.

In the case of the MCL, or medial collateral ligament, a brace helps keep the knee from buckling inward—the exact motion the ligament itself tries to prevent.

However, the MCL can only resist so much inward-directed force, and hits to the outside of the knee—such as in Flacco's case—can overwhelm its protective capabilities. When the knee bends in too far, the MCL—connecting the femur to the tibia—can stretch or tear.

Injury mechanisms like Flacco's can also cause ACL damage as well as meniscal tears—often concurrently with an MCL sprain—but fortunately, the Ravens signal-caller avoided such a fate.

Nevertheless, as mentioned, he did sustain a mild injury—presumably a grade-one sprain.

Grade-one injuries represent minor ligament overstretches with microscopic tearing and are the mildest type of sprain. Grade-twos and grade-threes are partial and complete ligament tears, respectively.

On average, grade-one sprains can lead to anywhere from zero to two weeks of rest and rehab. Grade-twos sometimes need up to or over a month, and grade-threes may need over three. Usually, isolated MCL injuries of any severity do not require surgery.

Luckily, the optimism of media reports suggests Flacco suffered among the mildest of mild MCL sprains.

Yet that does not necessarily mean it can be dismissed.

Rather, as injured ligaments are weaker ligaments, Flacco's MCL cannot withstand insults as it could prior to the injury. Blows similar to the one on Monday night could potentially lead to further, serious damage—possibly worse than would occur on a non-injured knee.

That's where the extra protective support of the brace comes in. It can sometimes successfully absorb softer hits that may have otherwise damaged the MCL even further.

Of course, a hit of a large enough magnitude can overcome even a braced knee, but such is the risk Flacco and his medical team have elected to take.

After all, his playing style may help minimize the threat.

As a pocket passer, the 2012 Super Bowl MVP may be less likely to sustain low blows—when compared to a running back, for example—due to limited rushing attempts. According to NFL.com's official statistics, Flacco rushed for less than 100 yards in four of the past five seasons.

Furthermore, a minor MCL sprain will also affect his throwing mechanics very minimally—if at all.

On the other hand, his mobility within the pocket may suffer, potentially leading to more sacks or hurried throws.

That said, with the Ravens fighting to claim a spot in the playoffs, the benefits of playing on a minor injury certainly outweigh the risks.

For now.

Dr. Dave Siebert is a resident physician at the University of Washington. He plans to pursue fellowship training in Primary Care (non-operative) Sports Medicine.

Follow @DaveMSiebert