NFL Injury Series- ACL Tears

NFL Injury Series- ACL Tears

Today’s article begins a series that precludes the start of training camp and will review the most commonly sustained season-ending injuries in the NFL. Objectives of this series are to help educate fellow fans on the severity of each injury and timelines for recovery. Unfortunately, when these injuries occur, Banged Up Bills will have you covered. Nearly all of these injuries are season ending or become chronic if not managed properly. The first post will assess ACL injuries.

The ACL is a ligament that connects the tibia to the femur and runs medial to lateral or inside to outside, acting as a stabilizer in the knee to prevent the femur from shifting too far forward over the tibia during movement; it also assists in preventing hyperextension in the knee. When the knee is loaded during activity such as cutting and sudden stops, the ACL is designed to keeps the knee stable, but in the presence of injury, the ligament is overloaded which either stretches and partially tears or fully tears based on the activity. It is possible to live a normal lifestyle with an ACL deficient knee, but nearly impossible to resume a high level of play post ACL tear without reconstruction as an adult.


Activities that cause the ACL to tear are direct blows such as a low block or a blow to the knee while the foot is planted. Non-contact typically happen when a player doesn’t land properly after jumping in the air, when they perform a sudden change in direction at a high speed, or when they attempt to quickly decelerate. Tears also occur with hyperflexion or hyperextension of the knee. In the event of ACL rupture, the knee buckles and there is usually immediate swelling, tenderness, loss of ROM, and pain. Risk factors include but are not limited to: sex, age, playing surface, level of play, biomechanical variances, previous injuries to the knee, equipment, and environmental conditions. Recent research has also shown that concussions can possibly increase the risk for injuries such as ACL due to slower reaction times.


As with many injuries, players are not able to return to playing and require further evaluation once in the locker room. X-rays are taken to rule out fractures and special tests are performed including but not limited to: Lachman’s test, anterior drawer test, and pivot shift test. All of these tests rule assist in physically identifying that the ACL is damaged. Typically, when performing the Lachman’s or anterior drawer test, there will be increased laxity when moving the tibia in the opposite direction of the femur. There are 4 grades to determine ACL severity which grade out how much the tibia pulls out in relation to the femur. Grade 1 is <5 mm progressing in severity up to Grade 4 which is >15mm.

Another test that may be performed is a posterior drawer test. This is the opposite of anterior in that it tests for a PCL injury. The reason this is performed is due to the possibility of PCL injury instead leading the tibia to sag back which could initially mimic the laxity seen with the anterior drawer test. A pivot shift test mimics the injury mechanism of the ACL tear and will typically illicit pain and possible clunking which would signify a subluxation of the tibia. To confirm the ACL tear, MRI imaging will be performed once swelling is subsided. Otherwise, the excess fluid could occlude the view of the tear and make the imaging inconclusive.

Once the tear is confirmed and swelling has reduced, surgery is scheduled to repair the structural damage. Regrettably, the ligament cannot be repaired through simple means such as sewing it back together. The ligament has to be cleaned out and repaired through use of a graft. These grafts come from commonly the hamstring or the patellar tendon which are known as autografts or through the use of a cadaver also know as allograft. There are other options which include xenografts which come from animals and lastly, synthetic grafts made from carbon materials or Gore-Tex. While medical research has improved drastically, the preferred method still appears to be the autografts as this comes from within the patients body and have lower rates of failure. The surgery is performed by anatomically lining up the graft as the ACL would normally be in and screwed in to allow to heal to the bone.

Recovery from an ACL tear takes anywhere from 9-12 months to return to full, unrestricted activity. However, there may be concurrent damage sustained in the knee which could include meniscus tear, MCL/PCL/LCL tears, or cartilage damage which could lengthen recovery time. Once the surgery is completed, the first 2 weeks is spent allowing swelling and initial tissue healing to begin. Passive range of motion along with light strengthening of the surrounding muscles is performed. After several weeks have passed, range of motion is increased with emphasis placed on full extension or straightening of the knee which will allow the person to be able to walk fluidly through the gait cycle and fully bear weight.

As the range of motion increases, higher level strengthening activities may begin through the saggital plane which involves motion going forward/backward over the next 10 weeks. During this time, strengthening exercises are primarily composed of closed chain exercises. This means that the foot is in contact with the ground or other surface as the knee performs its movements. Open chain involved exercises that allow the lower limb to move freely which if performed too soon, may place excess torque on the repaired ligament which could cause potential failure if pushed excessively.

Once full ROM is re-established, balance exercises are incorporated to regain proprioception which allows a person to sense their joint and body in space. This awareness is crucial as if the athlete has a poor awareness where their body is at during movement, they are at a much greater risk for injury. After 3 months out, they may continue progressing to running exercises going forward, backwards, and slowly begin agility drills once fitted for an ACL brace. These braces are commonly used to prevent future ACL injuries by restricting rotary and hyperextension forces. The recovery timeline is so long due to the purpose of the ligament and its makeup. As stated before, a ligament attaches bone to bone which creates stability for the joint. Add in the stresses that the joint goes through during running, jumping, and cutting motions, proper healing is required so that the ligament can perform effectively. Lastly, ligaments unfortunately have poor blood supplies which slow down healing time unlike muscles or tendons which have a rich blood supply allowing those tissues to heal quicker.


Once a patient has reached the 6 month plateau in recovery, they must meet certain minimum criteria to begin even considering returning to sport. They must:

  • demonstrate quadriceps and hamstring strength at least 80% that of the noninvolved leg
  • full motion
  • no recurring swelling
  • demonstrate stability both with physical testing and mobility
  • completing a running program

In higher level athletes, the running, jumping, agility set them apart from the general population and because of that, these athletes require further training in order to return to their respective sport. Athletes must be re-educated to safely land, cut and change direction, and essentially relearn how to use their reconstructed knee. Overall, 6 months is a considerable amount of time to heal properly which explains why this is a season ending injury. As the NFL season is only 6 months long, even with the best rehab, it wouldn’t be realistic to return.

However, why if a person is able to get to full recovery after 6 months, why are they out longer than that? Research has shown that the risk for re-injury decreases by over half each month up to 9 months before returning to sport. Once a player does return from an ACL repair, they are at a much higher risk to re-injure with rates up to 20-30% for up to two years after injury. These are the reasons why it takes nearly a year to return to full ability prior to the injury. Overall, ACL reconstruction success rates today are between 82-95%, a significant increase from 50/50% success in the 70’s & 80’s.

Many high level players can and do return to full abilities with proper rehab and training. It is terrible to see a player put all that hard work and training into getting ready for a season for it to all end with an injury such as this, but until medical science improves the healing process so much that players can shorten that 6 month window for healing, we are stuck with the current system. As a fan, I am praying that the Bills continue to avoid major injuries such as this as they were fortunate last season.

This wraps up the first article in the sports injury series. Continue to check back at Banged Up Bills on Facebook and on Twitter @BangedUpBills for the latest articles. As always, thank you for reading and GO BILLS!!


Comments are closed