ACL and knee ligament injuries. What they are and how to absolutely ace your rehab.

Updated: Mar 10

The anterior cruciate ligament, ( ACL), is probably the most infamous ligament in the knee when it comes to sports or activity related injuries. We are probably most aware of these injuries in professional footballers, netball players or basketball players who undergo knee reconstruction after an injury on the field of play.

Unfortunately in Australia we lead the way in ACL injuries sustained in both adults and children. This is a reflection on the popular sports we play and surfaces we play on.

What is the ACL and what does it do ?

The ACL is a major internal ligament that crosses from the front of the tibia to the back of the femur. It has a partner called the posterior cruciate that goes from the front of the femur to the back of the tibia.

The ACL performs the following functions in the knee:

  • Prevents forward movement/ anterior translation of the tibia on the femur.

  • Prevents external rotation of the tibia on the femur.

  • Helps with joint position sense of the knee, thus improving our movement patterns and balance.

How do we injure the ACL ?

Usually the ACL is injured through;

  • Collision with another player or individual

  • Changing direction / cutting suddenly when running.

  • Landing badly on one leg from a jump.

  • Having the foot fixed on the ground as the body twists over the top of it.

Mechanically the common mechanism is the knee goes into valgus with increased external rotation at the tibia.

Here is a clever little animation that shows us nicely what occurs in a cutting type movement and is made worse with an external collision force.

What happens when we injure our ACL.

When you injure your ACL, you may hear a “pop” at the time of injury coupled with buckling of the knee. There is usually immediate pain and swelling.

The pain may resolve, but the knee may remain unstable and there is sometimes a loss of motion. This may due to the knee being angry and swollen as well as a mechanical block caused by the stumps of the torn ACL.

It is not uncommon that there may be other tissues injured alongside the ACL. Probably the most common that co exist are meniscus tears , bony bruising and medial collateral ligament issues.

What should i do if i have just suffered an ACL injury ?


The first things you need to do are apply the rice principles to the acute injury and seek assessment to ascertain the extent of the injury.

There are certain tests we can do that can identify if the ACL is potentially ruptured. If they come up positive then an MRI is the best way to get confirmation of the diagnosis.

In the MRI the red arrow points to a thick black band which is a healthy intact ACL.

The knee on the right has less defined irregular mass where the ACL should be. That is what a torn ACL often looks like on a scan.


The initial goal is to get the knee back to its "happy place". By that we want to reduce the swelling and pain , restore movement and keep the knee functioning as well as possible.

This usually involves a combination of the RICE/ PEACE & LOVE principles as well as the introduction of basic quads and hamstring exercises such as those in the video below.

Do i need surgery after an ACL rupture ?

Here's where its getting interesting as there is some debate as to whether you go for surgery or not. I think it's a good idea to look at both options but also get a constructive opinion from an orthopedic surgeon:

Surgery for the ACL.

The following are considerations for the surgical option;

1.Does your knee gives way or feel unstable when supporting your weight?

If it does and continues to do so after a period of rehabilitation, you may be more likely to benefit from surgery.

2. Consider the type of sports and activities you want to do. Surgery is more commonly recommended if you want to return to sports that involve cutting and twisting motions such as AFL, rugby league, netball, skiing and touch football, etc.

3. Have you also injured your meniscus or other structures ? The more structures that are injured along with an ACL injury may indicate that surgery is a preferred option for you.

Here's a good video demonstrating a hamstring graft for ACL reconstruction.

The hamstring graft is the most common technique we see but other sites can be used such as;

  • Patellar tendon

  • Peroneal tendon.

  • Artificial grafts such as the LARS.

Non surgical approach.

There is mounting evidence that we can do really well with a focused and intensive rehab approach and not require surgical intervention. However the success behind this approach may depend on a the following factors:

  • Are you a good "coper" ?

Some individuals seem to cope with an ACL deficient knee better than others.

There is was a piece of research done in 2008 that has tried to identify those people that may cope with an ACL deficient knee.

The screening test consisted of :

  • the KOS-ADLs, questionaire.

  • Global Rating of Knee Scale (GRS) questionaire.

  • 6m timed hop test

  • Number of instances of instability or knee giving way the patient had since injury.

A “potential coper” must have passed ALL of the following criteria:

  • >80% KOS-ADLs

  • >60% GRS

  • >80% limb symmetry index 6m timed hop test

  • <1 instability episode

Failing on 1 criterion classified the patient as a “non-coper” and they were referred to orthopaedic surgeon.

  • Have you "aced" your prehab ?

Evidence is showing that a period of 5 week intensive rehabilitation should be done prior to the decision of what path you decide to take.

  • What are you looking to achieve following injury ?

Your long term goals and previous injury history will play a role in your decision.

Some ACL injuries can heal without surgery, it is likely that the ones that heal probably were incomplete ruptures so they had a framework to repair and build around .

For complete tears of the ACL, conservative treatment,meaning no surgery, can potentially be successful in patients who do not intend to return to high level activities that involve cutting, pivoting, jumping or contact sports.

I would always advise that you seek surgical opinion regarding ACL reconstruction as everybody's situation is unique to them.

The 5 week rule and ACL injuries.

Research has shown that a 5 week period of intense prehab (rehab before surgery) gives you better knee strength and outcomes, both before and after surgery? These effects are still relevant even 2 years.

It has also been suggested that after completing 5 week sof prehab you will get a better idea on how you will cope with an ACL deficient knee and if you require surgical intervention.

In our next blog we will have a look at how to ace your pre-hab and rehab.



If you need help with your ACL or knee injury rehab you can book in to see one of the team and get the best rehab program for you. Book here

Eitzen, I., Moksnes, H., Snyder-Mackler, L., & Risberg, M. A. (2010). A progressive 5-week exercise therapy program leads to significant improvement in knee function early after anterior cruciate ligament injury. J Orthop Sports Phys Ther, 40(11), 705-721. doi:10.2519/jospt.2010.3345

Hurd, W. J., Axe, M. J., & Snyder-Mackler, L. (2008). A 10-year prospective trial of a patient management algorithm and screening examination for highly active individuals with anterior cruciate ligament injury: Part 1, outcomes. Am J Sports Med, 36(1), 40-47. doi:10.1177/0363546507308190

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