Tuesday, 7 September 2010

Knee injury: ACL (Part I)

My sister-in-law recently ruptured her ACL playing touch footy and will be undergoing surgery in a month. Hence it prompted me to write about the ACL - what it is, what happens with an ACL injury, and provide an overview of surgery and rehabilitation from a physiotherapist's perspective.

What is the ACL?
The Anterior Cruciate Ligament (ACL) is one of the four major stabilising ligaments of the knee.

The other three are: Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL).

The term 'cruciate' is used as the ACL crosses the PCL in a crucifix position.

Where does the ACL attach? 
(NB. Femur = thigh bone, tibia = shin bone)

Origin: Medial aspect of the lateral femoral condyle in the intercondylar notch (distal end of the femur)

Insertion: In front of the intercondyloid eminence of the tibia plateau (parts blended with the anterior horn of the lateral meniscus)

The ACL is made up of two bundles, named according to where each bundle inserts into the tibia.
1. Anteromedial bundle: smaller, tight in flexion, more prone to injury with the knee in flexion (bent)
2. Posterolateral bundle: larger,  tight in extension
In Extension (knee straight):
- Both bundles are in parallel to each other.

In Flexion (knee bent):
- Both bundles are crossed
- Femoral insertion of the posterolateral bundle moves anteriorly
- Anteromedial bundle tightens and posterolateral bundle loosens

Functional Anatomy
The main role of the ACL is to prevent anterior translation (forward movement) of the tibia from underneath the femur.
1. The anterolateral bundle limits anterior translation of the tibia from the femur with the knee in flexion.
2. The posterolateral bundle limits anterior translation, hyperextension and rotation of the tibia.

What happens in an ACL injury?
ACL strains, tears and ruptures are usually a result of sports which involve fast changes in direction and twisting/pivoting movements. A typical description would be that a twisting/pivoting force was applied to the knee whilst the foot was firmly fixed to the ground. Another cause could be a direct blow to the knee joint (usually a valgus force, ie. from the outside) such as in soccer or rugby tackle. This particular cause is sometimes associated with injuries to the MCL and lateral meniscus, aka the 'unhappy triad'. 

ACL injuries occur more commonly in women than men (2-8:1), with possible rationale being differences in anatomy, hormone effects and muscle balance, however the cause is still unknown.

Signs and Symptoms of a torn ACL
  • Audible pop or crack
  • Instability of the knee upon weightbearing
  • Pain
  • Swelling of the knee
  • Reduced movement of the knee joint, esp. inability to fully extend (straighten) the knee
  • Positive signs in Anterior Drawer Test, Lachman's Test, Pivot Shift Test
  • Tenderness around and inside the joint (indicating other ligament injuries or meniscal tears)

What to do following an ACL injury
  • Immediately stop play
  • Apply RICE (Rest, Ice, Compression, Elevation)
  • Seek medical attention asap from a sports trainer, physiotherapist or Doctor who can assess your knee joint and determine the severity of injury (MRI Scan may be required to confirm diagnosis)
  • If MRI confirms a torn ACL, you may be referred to a Orthopaedic Specialist to discuss the surgical treatment option if required.
  • If surgery is required, you should commence a pre-operative rehabilitation program under the guidance of a physiotherapist to reduce swelling, regain range of motion and strengthen the knee. This will facilitate best results post-op.

Will I need surgery?
There are two treatment options post ACL tear: (1) Conservative or (2) Surgery.

This decision will depend on a variety of factors, such as age, lifestyle, sport, occupation, severity of injury and instability, and other associated injuries.

For example, an individual with a less active lifestyle, older in age and low-contact sporting involvements may not necessarily require surgical management. With some lifestyle changes, it is actually possible for such individuals to manage with a deficient ACL. However it is important and strongly advised that these individuals see a physiotherapist and undergo a rehabilitation program to strengthen their knee and retrain the stability of the joint.

On the other hand, a younger fit person with a very active lifestyle and regular sporting involvements will more likely require surgery and a strict rehabilitation program post-op. This will maximise their ability to return to pre-injury levels of fitness and strength, and more importantly, return to sport in due time.

When can I return to sport?
Depending on your Orthopaedic Specialist and Physiotherapist, most rehabilitation programs require between 6 to 9 months (to work on range of motion, strength, agility and fitness) before a gradual return to sport.

In my next post, I will discuss about Surgery and ACL Rehabilitation Program.


  1. woohoo! I made it on your website! =) if only it were for something else eh?

    thanks for the post berty!

  2. nice summary!
    had one of these last week at the rugby!!
    it's actually an interesting operation to watch cos each surgeon does it a little differently.
    the latest fad in ACL recon is the LARS... not much research though but all the professional footy players are going for it.
    - Mel