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The Anterior Cruciate Ligament

by Jane Hodgson 12 January 2009


It is one of the main stabilising ligaments of the knee and injury to the anterior cruciate ligament will lead to feelings of instability in the knee. Symptoms can be helped with strengthening and exercises

Diagram of the ACL

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Diagram of the ACL

What is the anterior cruciate?

The anterior cruciate ligament is one of the four major stabilising ligaments of the knee. The cruciate ligaments together act as guy ropes preventing the femur and tibia from sliding backwards and forwards on each other.

The ACL starts from the front of the tibial plateau (the flat top of the shin bone) and joins this to the femur (thigh bone). The ACL crosses the posterior cruciate ligament hence the cruciate name. Diagram of the ACL.

The two other major stability ligaments of the knee are the medial collateral ligament which joins the tibia to the femur on the inside of the knee, and the lateral collateral ligament which forms the same function on the outside of the knee.

How is it injured?

The ACL is most usually sprained or ruptured when the body is rotated around a fixed foot. Examples of when ACL injuries occur include

  • Skiing – someone skis across the back of your skis, your lower legs stop moving abruptly, but the upper body continues.
  • Football - A tackle blocks the foot, the body rotates over it
  • Rugby and American football - A direct blow to the knee usually from the outside

What are the symptoms of an ACL injury?

  • Immediate pain and swelling of the knee
  • A feeling of instability of the knee – in other words it feels as if the knee is going to give way under you

Does the ACL repair itself?

No, if the ACL has been ruptured it will not repair itself.

What is the treatment?

ACL injuries can either be surgically repaired or treated conservatively

Surgical repair

The ACL is replaced using either an artificial ligament (very unusual nowadays) a piece of your own tendon (autograft), or a piece of donor tendon (allograft).

Termed an autograft, using a piece of your own tendon to replace the ACL is currently the most common technique. A piece of your patella tendon (the tendon that attaches the kneecap to the shinbone) or some of the hamstring tendon (the large tendon either side of the thigh at the back of the knee) is taken and put in place of the ACL.

An allograft is where tissue is taken form a donor, this may be done for instance in top class skiers where using an autograft would weaken the donor site too much.

Whichever surgical method is used, once the surgery has taken place, it is imperative to undergo intensive physio treatment to regain maximum function from the knee.

Disadvantages of surgery include the general risks of surgery and anaesthetic, infection, and the possibility of pain from the donor site.

Conservative management

Depending on sporting and occupational needs,some people can function adequately without an intact ACL.

Physiotherapy to strengthen the knee joint muscles, using closed kinetic chain exercises and improve the proprioception (balance) of the joint helps enormously.

Disadvantages of conservative treatment – if, even following physiotherapy, there is still some give in the joint, the risk of further damage to the joint such as meniscus (cartilage) tears or arthritis increases.

Disclaimer: The information on this page is written to help you understand your injury. There are many possible causes for knee pain and should you have any concerns you should always seek advice from a qualified health professional such as a Chartered Physiotherapist or your GP.

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About the author

Jane Hodgson - Chartered Physiotherapist Jane Hodgson Jane specialises in lower body injuries and has raced competitively in running, orienteering and adventure racing.

Did you know

The ACL is most commonly injured when the body is rotated on a fixed foot.

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