The anterior cruciate ligament (ACL) is one of the two big ligaments which cross over one another inside the knee.

Page updated November 2023 by Dr Sheila Strover (Clinical Editor)

anterior cruciate ligament


The anterior cruciate ligament tethers the femur to the tibia, attaching to the femur within the notch.

non-contact injury that may tear the ACL


Injury is often non-contact in nature.



What does the anterior cruciate ligament do?

The ACL is a key stabiliser of the knee joint - it prevents the tibia from excessive forward motion relative to the femur, and also prevents too much inwards twisting.

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What are the signs and symptoms of an ACL tear?

At injury there may be a loud 'pop!' followed by immediate pain and rapid swelling and difficulty walking. After the swelling comes down it may be possible to walk in a straight line, but twisting movements will cause feelings of instability.

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Why is an anterior cruciate ligament injury problematic?

Complex fibre arrangementThe ligament is comprised of two functional bundles - the anteromedial and the posterolateral bundle. The illustration shows how the load is distributed differently in flexion and extension. The wide footprint and the complexity of how loading differs in the two bundles have given surgeons a lot of headaches in their attempts over the years to reproduce the anatomy during a reconstruction procedure.

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Forum discussions

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Peer-reviewed papers

  • Quote:

    "...multiple risk factors act in combination to influence the risk of ACL injury...Anatomic features, such as a decrease in femoral notch width, a decrease in the depth of concavity of the medial tibial plateau, and an increase in the posterior-inferior-directed slope of the tibial plateau, act in combination to increase the risk.. common in athletes...Females are at increased risk...there may be some interaction between the footware and playing surface for activities that take place indoors"

    Citation: Smith HC, Vacek P, Johnson RJ, Slauterbeck JR, Hashemi J, Shultz S, Beynnon BD. Risk factors for anterior cruciate ligament injury: a review of the literature-part 2: hormonal, genetic, cognitive function, previous injury, and extrinsic risk factors. Sports Health. 2012 Mar;4(2):155-61. doi: 10.1177/1941738111428282. PMID: 23016083; PMCID: PMC3435909.

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crucial ligament
cruciate ligament

Dr Sheila Strover (Editor)
BSc (Hons), MB BCh, MBA

See biography...