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Anterior Cruciate Ligament Injury

ACL injuryAnterior cruciate ligament injury or ACL tear is a sprain of anterior cruciate ligament in the middle of the knee joint. We explain the symptoms, causes and treatment options including surgery available.


At the time of injury the athlete will experience extreme pain in the knee. The knee is likely to swell up quickly from bleeding within the joint which will feel warm to the touch. There may be an audible pop or crack at the time of injury and a feeling of instability.

Often an athlete will seek professional advice at a clinic the next day or two after injury. By that time there will be considerable swelling making it very difficult to diagnose exactly what is wrong with the knee. After a few days when the swelling has gone down it will be easier to examine the knee joint. Symptoms will also include restricted range or movement with particular difficulty straightening the leg. It will be tender all around the knee joint. Specific tests a professional will use to help diagnose an ACL injury include the anterior drawer test and Lachman's test which both aim to stress the ligament to reproduce pain or instability.

See ACL injury assessment for more detailed information.

What is an anterior cruciate ligament sprain?

There are four main stabilizing ligaments in the knee.The ACL passes from the front of the tibia or shin bone to the back of the femur or thigh bone and prevents the tibia moving forward. It passes across the knee joint in a diagonal direction and with the posterior cruciate ligament passing in the opposite direction forming a cross shape, hence the name cruciate ligaments.

The role of the ligament is to prevent the tibia bone from moving forwards of the knee. The posterior cruciate ligament does the reverse preventing the shin bone moving backwards. Together these two ligaments are vitally important for the stability of the knee joint, especially in contact sports and those that involve fast changes in direction.

Cruciate ligaments of the kneeA torn ACL usually occurs through a twisting force being applied to the knee whilst the foot is firmly planted on the ground or upon landing. It can also be caused from a direct blow to the knee, usually the outside, such as that occuring during a football or rugby tackle. This injury is often seen in combination with a medial meniscus tear, articular cartilage injury or medial ligament sprain.

Immediate treatment for ACL injuries

Coldone knee wrapIf a knee joint sprain of any kind is suspected then stop play or competition immediately, assuming you have a choice! Apply the PRICE principles of protection, rest, ice, compression and elevation. Applying ice and compression will help limit pain and stop bleeding and swelling. Some professional therapists at pitch side will immediately apply a compression wrap fairly tightly to prevent the knee swelling up however this should only be left on for 10 minutes at a time to avoid stopping blood flow completely and causing further injury. Seek medical attention as soon as possible.

Ice can be applied for 10 to 15 minutes every hour for the first 24 to 48 hours although not directly against the skin. There are a number of commercially available cold wraps which are excellent for knee joint injuries as they provide compression as well as cold at the same time. Elevating the limb will also help swelling and tissue fluids drain away from the site of injury.

What can a Professional do?

ACL assessmentA Doctor or sports injury professional is not likely to be able to do much the day after an injury. The joint is likely to be too tender and swollen to properly assess. Once the swelling has died down then a more accurate assessment and diagnosis can be done. An MRI scan can confirm the diagnosis and an X-ray eliminate an avulsion fracture where the ligament pulls a piece of bone away.

It is likely the doctor will refer for surgery if required as well as advice on a pre-surgery rehabilitation program in order to strengthen the knee and reduce the swelling in preparation for surgery. This will help produce the best results following surgery.

Do I need surgery?

SurgeonsThe decision whether or when to operate to reconstruct a torn anterior cruciate ligament is a controversial one. Surgery can be performed shortly after injury, a few weeks or even months after injury or not at all.

The decision of whether to operate is based on a number of factors, including the athletes age; lifestyle; sporting involvement; occupation; degree of knee instability and any other associated injuries. Older people who are less active and perhaps injured their ACL following a fall as opposed to during sport may be unlikely to undergo surgery.

A younger, fit person who regularly plays sport or needs to be active for work and would be more likely to adhere to a complex rehabilitation program is more likely to be offered surgery. Other factors include whether a meniscus repair is required or any other joint injury and the degree of instability in the knee.

See expert interview for more detailed information.

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