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Anatomy of an ACL Tear

ACL tears are ending athlete's seasons and sometimes their careers, but have they been missing an opportunity to implement an important injury prevention program?

Derick E. Hingle-USA TODAY Sports

In the violent game of football, there are countless injuries players will sustain throughout their careers. Of all those possible injuries, one of the worst words a player never wants to hear are "torn ACL." Even for athletic freaks of nature, like Minnesota Vikings running back Adrian Peterson, a typical return to the field will take at least 9 months following the injury. Some players come back stronger after an ACL tear, but many are never the same again with regard to their overall athleticism.

New Orleans Saints defensive end and "Jack" linebacker, Hau’oli Kikaha tore his ACL for the third time during team OTA’s earlier this month. Even though the Saints have yet to place Kikaha on the injured reserve list, anyone with a brain or even the slightest knowledge of anatomy and biomechanics can be safe in assuming the promising second year player will not be gracing the Dome with his presence any time soon.

After taking an amazing workshop last weekend focusing on injury prevention to the ACL, I realized, how little I actually knew about the ligament, its importance to knee stabilization, and how prevalent its injury is across all sports. According to a study by Placzek & Boyce in 2001, 47% of knee ligamentous injuries affect the ACL. Another 13% affect both the ACL and MCL. 71.2% of all boys’ ACL injuries are sustained while playing football, and 72% of ACL injuries occur without direct contact to the knee itself (Joseph et. AL, 2013).

These numbers indicate an injury epidemic, particularly in the sports of football and women’s soccer. It’s clear the ACL is injured far more than any other knee ligament. It’s particularly interesting to note that a dominant percentage of these injuries occur without a blow to the knee itself. More commonly, the injury occurs while an athlete is landing from a jump, rapidly stopping, cutting and pivoting, or suddenly decelerating while changing direction.

To better understand this injury, we must first review our basic anatomy. ACL stands for Anterior Cruciate Ligament, while MCL stands for Medial Collateral Ligament. LCL stands for Lateral Collateral Ligament. Anterior means towards the front of the body. Medial means towards the mid-line of the body. Lateral means towards the outer-line of the body.

The ACL "attaches to a facet on the anterior part of the intercondylar area of the tibia and ascends posteriorly to attach to a facet at the back of the lateral wall of the intercondylar fossa of the femur" (Drake, et al. 2005). In essence, the ACL prevents anterior translation of the tibia relative to the femur. What the hell does that all mean, you ask? Basically the ACL keeps one’s knee from sliding out of its proper range of motion, specifically keeping the upper leg, or femur, properly resting in the groove above the shin bone, or tibia.

The ACL is pulled most taught in knee extension, which means that when one’s knee is fully extended, the ACL is at its greatest risk for tearing. If hyperextension of the knee occurs while the athlete is cutting, ACL injury risk is even higher. The legs should NEVER cross each other to avoid this pressure on the ACL. My heart hurt for the De La Salle boy’s football team the other day as I watched their coach make them karaoke back and forth across the field. That’s the WORST motion one can possibly do for the ACL.

According to a study by Alentorn-Geli, et al. 2009, common intrinsic risk factors include:

  • generalized and specific knee joint laxity
  • pre-ovulatory phase of menstrual cycle in females not using birth control
  • decreased (relative to quadriceps) hamstring strength and recruitment
  • muscular fatigue
  • decreased "core" strength and proprioception (spacial awareness)
  • low trunk, hip, and knee flexion angles
  • valgus force on knee (knee bowing in towards the mid-line of the body)

Common extrinsic risk factors include:

  • dry weather
  • dry surface
  • artificial surface instead of natural grass

Once the injury occurs, an athlete has several surgical options to consider. During ACL reconstruction, there are two types of grafts used. A graft, in this case, is when part of a tendon is used to build a new ACL surgically. An autograft uses either the athlete’s hamstring or patellar tendon, which rests directly over the knee cap, or patella. An allograft uses cadaver tissue from either the achilles or posterior tibialis tendon. Yep, cadaver means the graft comes from a dead body. That means it’s dead tissue, not live like a graft from one’s own body.

Autograft techniques are preferred for young people and athletes. In my opinion, it is better to use a patellar graft because one, it re-injures less, and two, in using a hamstring graft from the non-affected limb, the surgery is effectively weakening the musculature that was already weak and under-recruited to begin with.

Allograft techniques are suited for older, less active populations, and typically have a 30-36 month lifespan before they simply tear again. I wouldn’t be the least bit surprised if Kikaha had a cadaver graft because the timeline between his ACL tears fits the profile of a cadaver graft lifespan.

Why is this happening to professional athletes who appear to be in peak physical condition? While watching video of the USA women’s soccer team running suicides, our workshop class noticed even these professional athletes were not decelerating properly. Instead of slowing down incrementally and breaking up their foot impact patterns, every girl on the team was simply leaning backwards to slow down. This hyperextension of the lower back represents terrible biomechanics and can indeed lead to knee injuries.

Just because an athlete is performing at a professional level does not mean that athlete is moving with proper technique (biomechanics) at all times. If it seems frustrating that so many pro athletes can’t even get it right, fear not, as there’s hope. Neuromuscular and proprioceptive programs appear to reduce knee injuries by 26.9% and ACL injuries by 50% (Myer, et al. 2008). Just think of the impact these injury prevention programs could have on the overall population, and not just athletes. Future medical costs with regard to this injury, which are already in the billions of dollars annually, could be reduced by half!

First, one must undergo a biomechanics analysis to see how one moves one’s body. Second, one will receive biomechanics instruction through verbal and visual feedback, hopefully by a licensed Physical Therapist and not a coach as they are simply not qualified to adequately analyze the athlete’s biomechanics. Third, one will undergo video analysis of one’s movements. It’s much easier to dissect movement through repeated video rather than from making someone repeat a move (most likely incorrectly and dangerously) over and over.

There are two current programs that stand head and shoulders above the rest today. Sportsmetrics TM was created under the direction of orthopedic sports medicine surgeon, Frank R. Noyes, M.D. It has been proven to reduce the risk of serious knee injury, increase vertical jump height up to 4 inches, improve hamstring to quadriceps strength and symmetry, improve landing mechanics, and reduce side to side movements at the knee. Enhance Performance Training Program (PEP), created by the Santa Monica Orthopedic and Sports Medicine Group is a 15 minute program that includes warming up, stretching, strengthening, plyometrics, agility work, and alternate exercises.

These programs truly go back to basics and teach the athlete how to properly run, cut, pivot, decelerate, jump, and land without injury. Simply completing the doctor’s prescribed physical therapy protocol following surgery will not prepare the athlete to return to the field of play. Learning how to move again, properly and efficiently, will greatly decrease an athlete’s chances for re-injury in the future.

Post ACL reconstruction neuromuscular training should be lifelong or the athlete risks re-injury. Of course, if an athlete hasn’t experienced a ligamentous knee injury yet, programs like the ones above can keep the athlete healthy and active at a much greater rate. As an athlete myself, I’m excited to implement these programs into my workouts, but no matter your activity level, every one can benefit from learning how to move the right way. Let’s hope the Saints training staff are implementing neuromuscular and proprioceptive training programs for every player on the roster.