The ACL Explained

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As you may have seen from the accompanying video, the anterior cruciate ligament, shortened to ACL, is one of the most important ligaments on the knee. Here we’ll just flesh this out in a little more detail. This will be useful for you if you have a client with an ACL injury, if you have one, or indeed if you just have an interest


Why is the ACL Important?

It stops abnormal movement of the lower leg (tibia) sliding forward and importantly twisting relative to the upper leg (femur).

ACL Injury

People who’ve ruptured their ACL know how just how important it is, twisting and turning becomes virtually impossible, particularly at speed and you don’t have to be playing sports to see the symptoms. A person may twist at the bottom of the stairs and suddenly collapse to the ground.

Symptoms of ACL Injury

The major symptom of ACL injury is instability. Sure, it hurts when you injure it, but if the knee is left to settle and there’s no other injury inside the knee, pain isn’t usually a problem.  The injured person, however, becomes very aware of rotational movements and will avoid them at all costs on the injured leg as they just won’t be able to stay upright!

A Common Injury

It’s such a common injury, especially in females. Did you know females are 2-5 times more likely to rupture their ACL compared to male counterparts? Shocking isn’t it? What’s more shocking is that we’ve known about this for over 20 years and still we’re trying to find out the reasons why. Indeed some of my own research has tried to address some of the issues.

ACL injuries are a frequent occurrence in sport and commonly occur in activities such as football, basketball, handball, skiing, rugby, motorcross.  I injured mine playing basketball.

Mechanisms of ACL Injury

The classic mechanisms include:

  • Weight-bearing (foot planted on the ground during landing, running etc)
  • Sudden twist/rotation
  • Sudden deceleration
  • Non-contact
Always liked this image – but never understood why she’s wearing shoes..?!

The majority of ACL injuries happen without contact. The knee appears to collapse from under the person – A very strange thing to watch, and experience!.  If you’re not too queasy about these things and want to see an ACL injury happening, here’s a typical video clip. and another of Mary Pierce, the tennis player.

What Happens Next?

A combination of the following things:

  • Person falls to the floor
  • People nearby may hear a loud ‘POP’
  • Massive swelling develops in the knee almost immediately
  • Person goes to Accident & Emergency
  • Blood is drawn off the knee
  • An X-ray is taken and person is discharged told there’s nothing wrong

Sorry, the last one is a bit of a joke. So many injuries like this used to be missed because people didn’t know about them, I’d see it regularly during my clinical training in the early 2000s. Thankfully it’s not so common now.


Treatment of ACL Injury

Treatment will vary depending on the severity of the injury and what the person wants to do afterwards, for example, if they’re willing to give up or reduce ‘unpredictable’ sporting activities. The clinician will do several tests (Lachman, pivot shift, anterior draw) to judge how badly the ACL is injured, a decision that may be supplemented with a scan.

Whilst conservative treatment is possible – which involves lots of muscle rehabilitation focussing especially on the hamstrings(!) this will very much depend on:

  • the patient’s goals (if they want to return to competitive sport),
  • the extent of damage to the ACL (partial or compete tear) and
  • the degree of instability in the knee

If surgery is advocated, there are several choices of graft that can be used. These typically involve either using patient’s own tissue (hamstrings graft; bone-patella tendon-bone graft) or a synthetic replacement. The graft selection, again, will depend on several factors, including whether or not the patient has already had reconstructive surgery in the same knee, tissue quality, surgeon preference, the patient’s occupation and sporting demands etc. Usually, however, ACL reconstruction is a very successful procedure
it is the rehabilitation afterwards that often determines whether or not an individual can Get Back To Sport!.  I’ll cover ACL rehabilitation in the next post, where we’ll look at rehabilitating muscle strength, endurance and power; explosive muscle conditioning and the importance components of end-stage rehabilitation that will determine a successful and safe return to sport.

Are you a fitness professional with an ACL-injured client?  Do you have an ACL injury?  If you have any questions, get in touch and, or, ping us an e-mail, we love to help!


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