ACL Injury

ACL Injury

It’s probably the most dreaded knee injury of them all. I’ll explain what happens during an ACL injury and how to manage it.

What is it?: The ACL refers to the Anterior Cruciate Ligament which is deep in your knee and its main role is to prevent anterior translation of the tibia on the femur (or basically the bottom of your leg sliding forward too far) and helps control the knee during twisting movements. It is torn when it fails to cope with an excessive load and can be damaged by 3 main causes.

The cause:

  1. Non-contact (which is most common)- For example when changing direction rapidly, in particular a cutting action
  2. Contact- When someone or something hits your knee with force usually from the outside of your knee (lateral contact causing valgus stress)
  3. Indirect contact- For example being bumped while in the air which causes your planned movement or landing position to shift and land awkwardly


Signs & symptoms: You may hear a pop or a crack sound, usually with immediate pain and are typically unable to continue your sport or activity. Swelling usually starts within 2 hours and your knee may feel unstable to walk on.

Confirm diagnosis: A physio can perform a couple of tests that indicate a high likeness of ACL tear, but to confirm the diagnosis an MRI is usually warranted. Often the ACL is damaged in conjunction with the MCL (medial collateral ligament) and the medial meniscus. It can also involve bone bruising or a cartilage defect, which is why an MRI is important to confirm the correct diagnosis.

How to treat it: You can choose a surgical or conservative approach which should be discussed with a physiotherapist and orthopaedic specialist, as the decision will ultimately depend on individual factors including age, sport and lifestyle.

If you have opted for surgery (which is a common choice) it is recommended you undertake at least 5 weeks of pre-operative strengthening under the guidance of a physio. This is highly recommended as it can result in significantly better outcomes post-op than if you do nothing beforehand.

Post-op physio should start straight away with the first aims being to get your knee bending and straightening, your knee muscles ‘firing’ and reduce any swelling. As you progress further into rehabilitation your physio should begin to work more in conjunction with a strength and conditioning coach or exercise physiologist who can tailor your program toward to your goals/specific activity.

Longer term, injury prevention programs (better described as neuromuscular training) have been shown to decrease the injury risk or recurrence and also improve athlete performance. There common programs available, such as the Netball KNEE program, which are easily accessible and recommended to be incorporated into training and game day warm up.

Products: Wearing a knee brace on return to sport isn’t often recommended, but there may be times where your physio might recommend it and hence should be discussed directly with your physio.

Recovery time: In regard to returning to sport post-op current research suggests (at a minimum) 9 months for an elite athlete, 12 months non-elite person and closer to 18 months-2 years for someone under the age of 18. However, there has been a shift more toward criteria driven protocols over time-based protocols for rehab. These are guided by your physio and strength & conditioning coach and involve you achieving certain milestones prior to moving through to next phase of rehab. For example, prior to running, you should be able to single leg press 1.5 x your body weight and balance for 45 seconds on the single leg with your eyes open and 10 seconds with them closed.

Although they are common, ACL’s still require an individualised physio approach as I mentioned, so to find a physio in your area of Australia or New Zealand click here and remember to sign up to my mailing list or follow me on Facebook or Instagram for regular physio tips.

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