[headline style=”1″ align=”center” headline_tag=”h2″]Introduction to ACL Tears


The ACL is the most commonly injured ligament of the knee. Roughly fifty percent of all knee injuries are a result of an ACL tear according to some studies.

As clinicians with direct access we need to discern ACL tears in acute and chronic situations and refer out if needed, especially as sport and orthopedic PT’s.

Over the past few weeks I have personally seen many patients with acute knee injuries with potential ACL tears.

For this reason, I have included some of the latest research to help clinicians rule in and rule out tears of the ACL, the function of the ACL , why it is frequently torn, the best examinations tests, and some concluding remarks.


[headline style=”1″ align=”center” headline_tag=”h2″]Why Is the ACL Frequently Torn?


There is no one reason for the predisposition of ACL tears.

Some authors suggest lower and upper extremity biomechanics while others suggest narrow notch width, genetics, hormonal levels, decreased proprioception, tibial plateau slope, weakness of hip rotators, excessive pronation, etc.

A few studies did find that females are more prone due to decrease size of their ACL’s, knee abduction angles, and reduce knee flexion during change of direction.

Therefore, at this current time nothing points directly in regards to research, but rather a multimodal approach is needed.

I personally argue that more of it is biomechanics in nature in addition to poor strength and conditioning programming but ….

I could be wrong about this assumption and that some may be genetically predisposed to ACL tears.

[headline style=”1″ align=”center” headline_tag=”h2″]The Anatomy of the ACL


[images style=”0″ image=”http%3A%2F%2Fwww.scottgraypt.com%2Fwp-content%2Fuploads%2F2017%2F03%2FGreys-anatomy-ACL-2.jpg” width=”200″ align=”center” top_margin=”0″ full_width=”Y”]

The ACL attaches distally at the anterior intercondylar fossa of the tibia. It runs at an angle posterior and laterally to the intercondylar fossa adjacent to the lateral femoral condyle.

It has both anterior and medial fibers in addition to posterior lateral fibers.

[headline style=”1″ align=”center” headline_tag=”h2″]The Biomechanics & Function of the ACL


According to Kaeding and et al, the ACL functions to limit internal rotation, anterior tibial translation, and knee abduction.  These motions are created bottom up through gravity and ground reaction forces or momentum.

 These forces can become excessive with abnormal mechanics, weakness, fatigue, altered proprioception, and trauma.

The ACL will usually tear when too much knee flexion (anterior translation), excessive tibial IR, or valgus of the knee.


[headline style=”1″ align=”center” headline_tag=”h2″] The ACL Can Be Torn With Extension Too…



Have you ever wondered why some athletes tear their ACL with knee extension or femoral external rotation?

Me too.

In fact, I thought about this for years.

I thought the ACL prevented knee abduction, tibial IR, and anterior translation as described above.


That is what I was taught in school and what it shows in the research.


What they didn’t tell you the functional biomechanics and relative joint motion.

You see, many athletes are getting tibial IR, knee abduction, and anterior translation of the tibia top down when the femur is moving faster.

This is something I learned from Gary Gray and David Tiberio.

Relative motion rules.

The eye sees knee extension or femoral external rotation but it doesn’t see the relative motion.

For instance, if the femur is rotating faster into external rotation than the tibia, the joint feels relative knee internal rotation. This can cause tension to the ACL.

Similarly, the knee can feel a relative anterior translation of the knee with posterior translation of the femur. Again, this occurs if the femur is moving faster than the tibia.

Lastly, knee abduction can increase tension on the ACL with top down motion as well, too. This occurs when the femur goes into adduction which places relative abduction at the knee joint.

I struggled with this for years wondering how ACL’s were being torn with external rotation and extension.

But the biomechanics explain why….

It is still anterior translation, knee internal rotation, and knee abduction but created top down rather than bottom up.

[headline style=”1″ align=”center” headline_tag=”h2″]ACL Tests


When evaluating an ACL tear, your physical examination really depends on what stage of condition the knee is in.

For instance, in an acute setting, the majority of tests have poor sensitivity and specificity. Meanwhile, they do better when swelling and muscle guarding has subsided.

However, it was interesting that one pilot study did find the lever sign test to 100% sensitivity and specificity but huge bias was done on this study. Rarely, if ever, will their be a test that is 100% sensitive and specific.

No orthopedic test is the gold standard. Several tests need to be performed in conjunction with a solid history.

According to Benjamin and Et al, they concluded the following is highly likely to discern an ACL Tear:

  1. Popping during MOI
  2. Positive Lateral Pivot Shift
  3. Positive Lachmans
  4. Positive Anterior Drawer

Although these tests are great and have their place, I look at function rather than an array of tests.

At the end of the day we are after function, right?

Wouldn’t it make sense to test that ACL by seeing if the athlete can run, jump, hop, and twist?

Simply put, can the ACL handle the forces that make it taught and stretched?

For example, I just got done treating a patient of mine at the Mountain Dew Tour who twisted his knee. Instead of doing an array of tests that can give you false positives, I had him do the above.

Sure, he had some pain, but he was able to drive his knee into abduction and internal rotation without his knee giving away.

I felt pretty confident letting him return to skating without further damage.

Although our tests have some merit both on table and functionally, the MRI is still the gold standard to rule in or rule out an ACL tear. So if your still reserved and not sure, get an MRI.

Below are some sample videos the most common ACL tests that should be performed clinically.






[headline style=”1″ align=”center” headline_tag=”h2″]Concluding Remarks On The ACL…


Although ACL tests are important to perform, they are not the end-all be-all. Be sure to piece everything together from a sound history, special tests, and functional exercises testing (if appropriate).

If you’re still not sure if the athlete tore their ACL, don’t be afraid to rest the athlete and refer out for an MRI.

Abnormal biomechanics are part of the equation in injury prevention of ACL tears but genetics and anatomy may also play a role in this equation.

The ACL can be torn with knee extension and femoral external rotation secondary to relative joint motion.

[headline style=”1″ align=”center” headline_tag=”h2″]References


Benjaminse A, Gokeler A, van der Schans CP. Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis. J Orthop Sports Phys Ther 2006;36: 267–88.

Kaeding, Christopher C., Benjamin Léger-St-Jean, and Robert A. Magnussen. “Epidemiology and Diagnosis of Anterior Cruciate Ligament Injuries.” Clinics in Sports Medicine 36.1 (2017): 1-8. Web. 2017.

Lelli A, Di Turi RP, Spenciner DB, et al. The “lever sign”: a new clinical test for the diagnosis of anterior cruciate ligament rupture. Knee Surg Sports Traumatol Arthrosc 2016;24:2794–7.