ACL is an abbreviation for 'anterior cruciate ligament'.

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

anterior cruciate ligament


View of ACL from the front of the bended knee. The anterior cruciate ligament is one of the two large ligaments which cross over each other right inside the knee joint notch.

ACL - knee cut in half


View of the ACL from the side, with the knee cut in half.


The ACL and knee stability

Both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are important for knee stability. They tether the tibia to the femur in such a way as to allow bending and straightening while preventing forwards and backward movements of the two bones in relation to one another.

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ACL injury

The ACL can rupture through the body of the ligament during a knee injury, or the ligament can pull off its attachment to the wall of the notch (avulsion). The former is more common in adults, and the latter is more common in children. An ACL injury is very disabling and usually the person is immediately unable to continue with the activity that caused it. It is often acompanied by immediate joint swelling due to bleeding into the joint capsule (haemarthrosis), and the knee generally feels unstable when trying to bear weight.

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Tests of ACL integrity

The most common test of the integrity of the ACL is the anterior drawer test. The examiner will position the patient optimally, and then pull against the tibia, looking for excessive anterior translation.

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Forum discussions

  • Born without ACL's in both knees?!

    A youth soccer coach is astonished to find that some people are born without cruciate ligaments.

  • Born without ACL's

    A more detailed discussion about the problems people face who are born without ACLs.

  • Do I need ACL surgery?

    Discussion involving skiers about the merits or otherwise of initially following a conservative route after ACL injury in the hope that stability can be achieved without surgery.

  • ACL injury - no reconstructive surgery

    Another discussion about making the decision to proceed to reconstructive surgery after ACL injury.

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Peer-reviewed papers

  • Quote:

    "Congenital absence of the cruciate ligament is a rare condition with a prevalence of 0.017 per 1000 live births."

    Citation: Benassi AB, Guerreiro JPF, de Oliveira Queiroz A, Gasparelli RG, Danieli MV. Anterior and posterior cruciate ligament agenesis. J Surg Case Rep. 2018 Aug 15;2018(8):rjy216. doi: 10.1093/jscr/rjy216. PMID: 30151108; PMCID: PMC6101568.

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anterior cruciate ligament
crucial ligament

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

See biography...


Relevant content -

Ms Sue D Barber-Westin2006 - Lower limb strength in preadolescent children - by Ms Sue D Barber-Westin (Clinical Researcher)


eBook - ACL Repair in Children

- written by Professor Adrian Wilson (Knee Surgeon)

An easy-to-read book about a challenging subject as cruciate ligament injuries in children are complicated because any surgery needs to avoid their growth plate as it is still open until after puberty. Free to download.