Anterior Cruciate Ligament


The anterior cruciate ligament (ACL) is one of the four major ligaments in the knee. These ligaments, along with the muscles around the knee provide the joints stability. The ACL is found deep inside the knee joint and prevents the femur (thigh bone) to move forward during weight bearing as well as preventing rotation of the job.

Causes of Injury

Rupture or tear of the ACL is a relatively common injury, particularly in certain sports. Women are two to five times more likely to sustain an ACL injury than men. ACL injuries occur most often when an athlete is pivoting, decelerating suddenly or landing from a jump (particularly if the knee is hyperextended forcefully). This injury could also be caused by another player falling across the knee or in direct contact sporting incidents. Factors that may increase a person’s risk of ACL injury include:

  • Participation in high risk sports, such as netball, football, soccer, basketball, volleyball and skiing, involving sudden start-stop movements.
  • Previous ACL injury
  • Females Males


Ligament stability tests such as the ‘anterior drawer’ or ‘Lachman’s’ tests place stress on the ligament and can detect a torn ligament. An MRI may also be used to determine if the ligament is torn, and also to determine whether any associated injuries are present.

ACL injuries can be graded on a severity scale:
Grade 1: Mild injury to the ligament- stability maintained.
Grade 2: Partial tear of the ligament- some degree of instability of the knee.

Grade 3: Complete tear or rupture of the ligament- the knee joint is unstable.


  • Sudden “pop” or “snap” sensation/sound.
  • Immediate pain, usually severe
  • .
    Large degree of swelling within 1-2 hours after the injury.
  • Often the knee will feel unstable initially but this may be masked by swelling later. This may be described as giving way or buckling of the knee.
  • Restriction of joint movement, in particular with fully straightening the knee
  • .
    Difficulty weight bearing.

Treatment/ Management

ACL-RuptureInitially, the aim of treatment is to reduce pain and inflammation associated with the injury. Treatment and management options include:

  • Rest- restriction of all activity with crutches to enable non-weight bearing walking.
  • Reduce inflammation through rest, ice, compression, elevation and physiotherapy. Anti-inflammatory medication as recommended by a doctor or pharmacist may also assist in the healing process.
  • Knee brace if required.
  • Physiotherapy to assist in reducing pain and swelling and for maintenance of knee range of movement and strength.

Further Treatment

Surgical reconstruction is a very common method used to repair a completely torn ACL. Surgery will likely be recommended to active individuals and generally involves replacing the damaged ligament (often using part of a tendon from somewhere else in the body) and stabilising the knee. Following surgery, physiotherapy will assist in reducing pain and swelling whilst commencing and progressing the rehabilitation program as indicated.

Return to Activity/Sport

A comprehensive rehabilitation program is essential to ensure optimal function is achieved after recovery from the injury. The program is progressed gradually in stages so that the knee is not put under too much stress whilst healing. A physiotherapist will advise the individual on the appropriate range of movement, strengthening, stretching and balance exercises as well as supervising progression to a return to full activity.

It is recommended that athletes with reconstructed ACL injuries return to sport with the approval of their orthopaedic surgeon. This is usually when strength, range of movement and co-ordination/proprioception are close to full capacity. This usually takes nine to twelve months. A small number of surgically repaired ligaments do not achieve optimal stability of the knee.