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Examining the Irish: Injury Report And A Look at ACL & MCL Tears

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The terms ACL, MCL, and meniscus get thrown around a lot in modern sports coverage. We all know they mean bad news, but how do we decipher this anatomical alphabet soup? OFD takes a look at two of the most common injuries in sports and also a brief run-down of the Irish injury situation.

Rich Barnes-USA TODAY Sports

Current Injuries

  • Mike Heuerman - sports hernia
  • Nicky Baratti - shoulder injury
  • Austin Collinsworth - labrum tear, left shoulder
  • Jarrett Grace - tibia/fibula fracture

Other players who have been battling injuries but have played: Amir Carlisle (MCL), Christian Lombard (high ankle sprain), Corey Robinson (hand injury), Nick Martin (hand injury), and Torii Hunter Jr. (groin injury)

All in all, the Irish have been pretty fortunate with injuries (knock on wood), and if it were not for the academic dishonesty situation, I believe everyone would feel pretty good about our depth, particularly on defense.

ACL/MCL Injuries

The human knee was not designed for football.  Nor was it designed for soccer, hockey, baseball, or any other field sport for that matter.  Evolutionarily, humans are designed to be champion long distance walkers, not running backs.  With this in mind, let us examine two of the most common and discussed athletic injuries: the ACL tear and MCL tear.

Some Basic Anatomy

To get a concrete understanding of what is involved with ACL & MCL injuries, let's first define some terms:

  • Connective tissue = fibrous tissues that make up the supporting structures of the body including tendons, ligaments, bones, etc.
  • Tendons = connective tissue responsible for connecting muscle to bone.
  • Ligaments = connective tissue responsible for connecting bone to bone.
  • Meniscus = a connective tissue pad that cushions joints and ensures a tight fit between articulating bones (functionally similar to an O-ring).
  • Valgus stress = in the case of the knee, a force that causes the tibia to swing outward, away from the midline.

The knee joint is made up of two bones: the femur and the tibia.  A third bone, the patella, is surrounded by the quadriceps tendon and provides protection for the joint but is not involved in movement.  While the quadriceps tendon, the hamstring tendons, and the synovial joint capsule provide the knee joint with most of its mass, our focus will be on the ligaments.  These ligaments prevent any exaggerated deformations of the knee outside of its normal range of motion.  To be clear, that range of motion is like a hinge: it can flex and extend in one plane and has no appreciable side-to-side component.

Normal Knee Anatomy

The image above is a drawing of the right knee.  Note the position of the patella; it has been moved superiorly so that we can see the structures behind it.  Normally it would sit right in front of the articulation of the femur and tibia.  The structures labeled in red are the ones on which we want to focus. These are the structures that will be damaged during an ACL or MCL injury.  A few quick points before we get into the injuries themselves:

  • The ACL prevents anterior translation of the tibia.  During anterior translation, the superior aspect of the tibia will move forward in relation to the inferior part of the femur.  The ACL also resists lateral (i.e. valgus) stress.
  • The MCL is an important stabilizer of the knee that resists lateral stress.
  • The medial meniscus ensures a tight fight between the femur and the tibia.
  • Notice that the MCL and the medial meniscus are attached to each other while the LCL and lateral meniscus are not. The implication here is that when the MCL is injured, the medial meniscus is often injured as well.

The take-home message is that the ACL, MCL, and medial meniscus can all be injured when a lateral force is exerted on the knee joint.  In practical terms, this lateral force could be generated by a linebacker lowering his shoulder and making a hit with the point of impact on the knee itself.  Because they are often injured together, the ACL, MCL and medial meniscus are commonly referred to as the "Unhappy Triad."

In the image below, we can see that when a lateral force is applied to the knee, the tibia swings outward (red line), away from the previous axis of the joint (pink line), and the ACL, MCL, and medial meniscus (all highlighted) can be damaged.

Unhappy Triad

ACL injuries

ACL injuries are the most common knee injury.  They occur when the foot is planted and an impact is made to the lateral aspect of the knee.  The likelihood of an ACL tear increases if the impact occurs if the impact occurs when the knee is flexed.  In the image below, we can see that when the leg is flexed (red arrow), the upper part of the tibia translates forward (blue arrow), and the lower part of the tibia moves backward (green arrow). At this moment, the ACL is working to oppose the blue arrow and under stress, making it particularly vulnerable to injury.

Knee flexion

PHOTO CREDIT: Rich Barnes - USA TODAY Sports

Initially, the injury is painful because the joint capsule swells with fluid and blood from ruptured blood vessels.  As the swelling decreases, the pain will also decrease, but the joint will remain highly unstable.

On the field, the most common test for an ACL injury is the anterior drawer test.  In this case, the patient is lying on his back with the affected knee flexed 90°.  The examiner places his weight on the patient's foot for stability and pulls the upper part of the tibia toward himself.  If the ACL is intact, the tibia should not translate anteriorly in relation to the femur.  The test is positive if the tibia does indeed translate, indicating damage to the ACL.

MCL injuries

MCL injuries occur in the same fashion as ACL injuries, except that they can also be caused by abrupt movements of the knee and quick changes in direction without an impact.  As mentioned above, the deepest layer of the MCL is attached to the medial meniscus, thus a serious MCL injury will likely also involve the medial meniscus.

The on-field test for an MCL injury is the valgus stress test.  For this test, the examiner stabilizes knee joint in one hand, and grasps the ankle in the other.  He then moves the ankle away from the midline.  If the MCL is damaged, the examiner will observe greater movement.  A grade scale from 1 to 3  is used to determine the severity of the tear with 1 involving minimal tearing and 3 corresponding to a complete MCL tear.  These numbers correspond to how much movement is produced by the valgus stress test (i.e. increased movement will correspond with a higher grade).

In this clip, you can see the anterior drawer test being performed on an injured Syracuse player during their game against Maryland.  The valgus stress test is not visible, but just as the camera cuts away it looks like the trainer is moving his hands into position to perform it:

Anterior Draw Test 1

As a practical note, an MRI is the gold-standard diagnostic tool for either of these injuries, and these other tests serve primarily as rapid assessments.

Recovery

Depending on the severity of the injury, MCL injuries can take 3-6 weeks to heal.  ACL injuries take significantly longer, often on the scale of months to years.  The disparity in recovery time is related to anatomy and blood flow.  Joint capsules and the structures inside them lack blood vessels, so instead of blood, a special fluid, called synovial fluid, nourishes the cells inside.  Since the ACL is in the middle of the joint capsule, it is primarily nourished by this fluid.  The MCL, on the other hand, is located on the periphery of the joint and has access to blood vessels running around the knee. These blood vessels provide the nutrients and cells that are critical in rapid tissue repair.  Because the ACL lacks this direct blood supply, healing is a much more protracted affair.

Summary

ACL, MCL, and medial meniscus injuries truly are an unhappy triad when it comes to athletic injuries.  Luckily, advances in therapy have made full recovery a more likely scenario, particularly for ACL injuries.  Your feedback is appreciated, and if there are any other injuries you would like me to write about, drop them in the comments and we will take it from there.