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Anterior Cruciate Ligament (ACL) Tear


Knee ligament tears are commonly caused by sports injuries. They can vary in severity, and treatment depends on the specific ligament that has been ruptured and its likely consequence for the patient.

The anterior cruciate ligament (ACL) rupture is the most common injury requiring specialist treatment. The ACL helps stabilise the knee in antero-posterior and twisting movements and is usually ruptured during pivoting sports such as football or skiing. Initial treatment is with rest, anti-inflammatory measures and a graduated return to activity under the care of the physiotherapists. If symptomatic instability results, then surgical reconstruction may be required. This is usually done using an arthroscopic (keyhole) technique. Results are good, with the majority of patients regaining normal knee function.


The patient will typically have had a pivoting injury, whilst turning on a flexed and loaded knee. The patient will classically have been aware of a pop or snap, will not have been able to play on, and will have had rapid swelling of the knee.

Long-term symptoms are those of instability and giving way, often followed by a period of reduced mobility and swelling. They are often not able to return to sports.


Special tests are generally required to diagnose ACL deficiency. Lachmann and pivot shift tests are the most sensitive and specific. Pivot shift can be limited in the outpatient setting by patient apprehension.

Special Investigations

MRI of an Anterior Cruciate Ligament (ACL) TearMRI is the usual diagnostic tool especially in the acute phase.

Natural History

Once ruptured, the ACL tends not to heal. In many cases it results in instability especially during twisting movements, but in some patients this may not be the case. There is debate as to whether ACL deficiency increases the long-term risk of arthritis of the knee. It does seem to result in an increase risk of damage to the medial meniscus.

Conservative Treatment

Conservative treatment is with physiotherapy aimed at strengthening the dynamic constraints of the knee. The physiotherapist will work specifically on propriocetion and joint position sense. It may be necessary to use a brace for certain activities.

Operative Treatment

Surgical reconstruction requires the use of a graft. Direct repair of the torn ends tends not to be possible, especially in the chronic injury. Graft choices include autograft hamstring and patellar tendon, allograft and artificial ligament. The most popular choice of graft is the hamstring autograft, which has low donor site morbidity compared to a patellar tendon graft, and better biomechanical properties compared to allograft.

The technique is performed arthroscopically and is done as a day case or with one overnight stay.

Post-operative physiotherapy is vital and the patient is advised to refrain from sports until 6-12 months following surgery.

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