Anterior cruciate ligament (ACL) injuries

A common knee injury in sports such as football, skiing and basketball.

About anterior cruciate ligament (ACL) injuries

The anterior cruciate ligament (ACL) is a band of tissue that runs through the middle of your knee joint. It attaches your thigh bone to your shin bone.

Most ACL injuries happen during sports – especially those that involve sudden changes in direction such as football, basketball or skiing.

An ACL injury can be treated by building up the muscles around the knee. This helps the other ligaments and tendons support stability and movement.

Younger patients, particularly those who do a lot of sports and those who have a physically demanding job, are likely to be recommended surgery.

Causes of an ACL injury

An ACL injury may be caused by:

  • landing awkwardly from a jump
  • twisting movements, particularly when your foot is on the ground
  • quickly changing direction when running or walking
  • slowing down or stopping suddenly when running
  • excessive bending or straightening
  • a direct blow to the knee

Symptoms of an ACL injury

Some people feel or hear a 'pop' in the knee when an ACL injury occurs.

Other symptoms include:

  • severe pain
  • swelling
  • instability – especially when going up and down stairs
  • not having full range of movement – unable to straighten the leg

If you experience any of these symptoms, it's important to see your doctor straight away.

Diagnosis of an ACL injury

Your doctor will assess the symptoms of your knee injury, will carry out a careful examination of your knee and will usually order an MRI scan to assess the damage.

An MRI scan will show whether the ligament has been stretched or has suffered a full or partial tear. It will also show your specialist what other injuries may have occurred inside the knee.

Treatment for ACL injuries


Most minor soft tissue injury can be managed at home with rest and anti-inflammatories such as ibuprofen.


Our physiotherapy team can also help you recover from an ACL injury. Your physiotherapist will give you exercises to help improve your range of motion and to build up muscle around your knee.


Depending on your activity levels and profession, your orthopaedic surgeon may offer an ACL reconstruction.

This operation is usually carried out as keyhole surgery (arthroscopically). The ligament is repaired by grafting a tendon (either from your own leg or from a donor) in place of the ACL ligament. In some instances, the torn ACL can be primarily repaired.

Complete recovery from surgery can take from six to 12 months.

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Published: 14 January 2020 | Review: 14 January 2023

Disclaimer: This information is published by Cromwell Hospital and is based on reputable sources of medical evidence and experience from over 30 years of treating patients. It has been peer reviewed by Cromwell Hospital doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional. If you have any feedback on the content of this patient information document please email or telephone 020 7460 5901.