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Anterior Cruciate Ligament (ACL) Tear


  • Violent over-twisting of the knee
  • Lower leg forced forward
  • Common in skiing
  • Sudden change of direction
  • Audible pop sound at time of the injury
  • Minor tears - slight pain at start, increasing
  • Swelling and stiffness
  • Unnatural movement of knee joint
  • Major tears - leg will not hold weight
  • Combination of rest and physiotherapy
  • Knee brace to correct alignment and promote healing
  • RICE within first 72 hours
  • Strengthning exercises in later recovery
  • Surgery may be required for major tears or ruptures

What is an ACL Tear?

An ACL Tear is a common sporting injury affecting the Anterior Cruciate Ligament of the knee. The ACL Ligament joins the back of the thigh bone (femur) to the front of the shin bone (tibia) giving the knee joint its stability. It prevents over extending the knee (hyperextension) and it stops the knee twisting too far. There are levels of severity of an ACL Tear, from a slight tear in the ligament to a complete rupture. A complete rupture of the ACL will result in significant pain and very little function of the knee joint. Surgery is potentially the only way of treating a complete rupture. The levels of tear are as follows:
  • Grade 1 tear: a small number of fibres are torn resulting in some pain but the joint will function relatively normally.
  • Grade 2 tear: a large number of fibres are torn and the knee joint will lose a lot of functionality.
  • Grade 3 tear: the ACL ligament is completely torn and the knee becomes unstable. There will be very little if no function of the knee. Surgery is most likely required.

What causes an ACL tear?

Stress on the ACL is caused by excessive twisting of the knee joint, hyperextension or excessive force on the back of the lower leg forcing the shin bone (tibia) forward away from the thigh bone. The most common cause is by violently over twisting the joint. It can be caused by repetitive strain but is normally the result of a specific incident. It is a common injury in high speed skiing accidents as the ski attached to the foot can force the lower leg to twist excessively, particularly if landing from a jump, resulting in an ACL tear. It is frequently seen in contact sports, and in sports which require rapid changes in direction such as football, rugby, basketball and skiing.

Signs and Symptoms

Normally, there is an audible pop, snap or tearing sound at the time of the injury but in the case of minor tears the sufferer may be able to continue with the activity with little initial pain. The pain will begin to increase and the area will often swell and become stiff, particularly following a period of rest after the incident. The sufferer will often find it difficult to pinpoint the exact area of pain as it comes from within the knee joint. If the ACL is completely ruptured there will be a moment of intense pain at the time of the incident but the sufferer may find that is subsides quickly. Within a few hours the area will often swell and there may be unnatural movement of the knee joint due to its instability. The knee will likely collapse under any strain or movement and will become bruised and stiff within a few days of the incident.

ACL Tear Diagnosis

A physiotherapist will often be able to diagnose an ACL tear after an external examination of the knee. The diagnosis will normally be confirmed by an x-ray or MRI scan to determine the extent of the tear and to check for further damage to the knee joint.

ACL Tear Treatment and prognosis

For minor grade 1 or grade 2 tears the treatment is often a combination of rest and physiotherapy. In order to fully rest and support the knee joint a knee brace would be very useful. The body cannot heal correctly if there is continuing damage to the ligament so appropriate rest involves keeping any twisting or hyperextension to an absolute minimum. There may only be a little pain but if the problem is not treated in the immediate aftermath of the even then the recovery time will increase and it could become a chronic condition which will increase the chances of future tears and may require surgery. The immediate treatment is Rest, Ice, Compression, Elevation (or RICE). This is more effective within the first 72 hours of the initial injury. Regularly icing the injury and using a compression bandage or a knee brace on a day to day basis will be beneficial. A physiotherapist will often advise pain free stretching and strengthening exercises, particularly of the thigh muscles (quadriceps), bum (gluteus), and hamstrings to improve support on the knee. Combine appropriate rest with good physiotherapy and the sufferer could be back to normal activity levels within 2 – 8 weeks depending on the severity (and the willingness to rest). For a full rupture of the ACL surgery may be required to reconstruct the ligament. Physiotherapy and rehabilitation should still begin immediately after the time of injury to maximise the potential for success of surgery. After surgery, intense rehabilitation is required and the patient will often undergo this for 6 – 12 months before being able to return to normal activities or sports. See our Full Range of Knee Supports and Knee Braces See our Major Instability Level of Knee Braces