ACL tear

What is the anterior cruciate ligament (ACL)?

The anterior cruciate ligament (or ACL) is one of the knee’s internal ligaments. It works to provide stability to the knee joint particularly during twisting manoeuvres. The ACL acts a bit like a guy rope inside the knee, holding together the lower end of the thigh bone (femur) and the top of the shin bone (tibia).


What causes an ACL tear?

ACL tears often occur as a result of your body load twisting on a fixed/planted foot. This is commonly seen in football when a player goes to turn on a planted foot (described as a ‘pivoting non-contact’ injury). The injured knee tends to swell up straight away and it is often not possible to play on. Skiing is an example of another sport which is often associated with ACL tears.

After an ACL tear it can take several days for the swelling and pain to settle down.

What are the symptoms of an ACL deficient knee?

1. Giving way – Individuals with ACL tears may feel that their knee gives way (or buckles) underneath them. In some people this may only occur when they carry out a twisting action during sport, in others this may occur with relatively minor force during more day to day activities.

2. Knee swelling – It is common for the injured knee to swell up following each episode of true giving way.

How is an ACL tear diagnosed?
By examining the injured knee it is possible to feel whether the ACL is intact or torn. This will then be confirmed by carrying out an MRI scan (magnetic resonance image) of the knee which is also used to look for associated injures such as a meniscal tear or bone bruising.


How is an ACL tear treated?

The recommended treatment of a torn ACL varies between individuals. If you have an unstable feeling in your knee and if you are an active individual you may decide to have the ACL reconstructed. The young sportsperson involved in twisting / turning sports is most likely to require surgical reconstruction.

Some of the factors to consider include:

How unstable is your knee?
What is your occupation?
How often do you play sport?
How is your general health?
Can you commit time to the rehabilitation programme?
Are there any associated knee injuries?

– ACL reconstruction may more likely to be recommended if there are associated injuries such as a large meniscus tear.



The torn ACL doesn’t ever heal. However, some people may have no on-going symptoms from their ACL tear, or they may not be very active and wish to avoid surgery.

Physiotherapy is helpful to strengthen the knee following injury. Strengthen the leg muscles (particularly the quadriceps and hamstring muscles of the thigh) can help to support the knee and give it a feeling of stability.

An ACL specific knee brace can be worn when carrying out certain activities, such as skiing or climbing and provide the knee with some additional support.


The aim of ACL reconstructive surgery is to stabilise the knee and therefore prevent further knee injury, such meniscal tears.

ACL reconstruction is a keyhole (arthroscopic) procedure in which a tissue graft (most often hamstrings tendon graft) is used to replace the torn ACL.


For more information on the surgery please see the procedures section under the heading ‘ACL reconstruction’.

Post-operative ACL rehabilitation

Good post-operative rehabilitation is vital to a achieving a good outcome following surgery. You will be required to work hard with the physiotherapists and on your own with specific exercises following your surgery.

In the initial phase the aim of the rehabilitation is to regain a good range of motion in the knee and get the leg muscles working well.

You will then work on a knee-strengthening regime, protecting the new ACL graft, gradually increasing the stress across the ligament.

Finally the rehabilitation will be tailored towards getting you back to your sport of choice.