The anterior cruciate ligament is one of 4 ligaments involved in conferring stability to the knee joint. The medial and lateral ligaments are on either side of the knee joint and limit excessive bending from side to side. The anterior and posterior cruciate ligaments are within the knee joint and limit excessive forwards and backwards movement of the knee joint.  Collateral ligament injuries usually tend to heal on their own and do not require surgery.  Cruciate ligament injuries do not have the ability to heal on their own.  This may allow a degree of instability within the knee joint that requires surgery to be corrected.  The anterior cruciate ligament injury is usually caused by a twisting movement of the knee joint.  This may occur during contact with another competitor during sport, but most often occurs without contact, such as when twisting, stopping or landing after jumping.

Anterior cruciate ligament injury allows for excessive movement of the knee joint forwards and backwards. This gives a feeling of instability in the knee joint and may lead to actual collapse and giving way of the knee joint.  This is usually not a problem with regular day to day activities or walking in a straight line on a flat surface, but becomes more problematic with twisting and turning movements or on uneven ground.  Anterior cruciate ligament injury may occur in conjunction with injuries to other structures within the knee joint such as:

  • The posterior cruciate ligament;
  • The medial or lateral collateral ligaments;
  • Meniscal injuries;
  • Damage to the joint surfaces.

At the time of injury there is sudden onset of pain.  There is swelling almost immediately, which does not allow the patient to continue activity.


At the time of the initial injury, there will be immediate swelling and pain within the knee joint.  You will not be able to continue with the sporting activity.  Crutches may be required for up to a week.  Your orthopaedic surgeon will undertake an initial history and physical examination. These will be supplemented by investigations, usually an X-ray and an MRI scan.  The X-ray excludes any fractures about the knee joint. The MRI scan will not only confirm the diagnosis, but identify any damage to other structures within the knee joint.

Once the diagnosis has been established a treatment plan will be undertaken in consultation with your surgeon.  Those patients who have injuries to other structures in the knee joint may require surgery to correct these problems.  An anterior cruciate ligament reconstruction can be undertaken at this point in time.

For those patients who do not require early surgery the options are either to have a physiotherapy guided rehabilitation program to strengthen the muscles about the knee, which will give a degree of stability, or to have an anterior cruciate ligament reconstruction.  The decision for this depends upon the future demands of the knee.  Those patients with a relatively stable knee and a sedentary lifestyle may opt to have a physiotherapy guided rehabilitation program, which can often avoid surgery.  For those who have unstable knees or wish to return to sports, anterior cruciate ligament reconstruction is favoured.


The role of the anterior cruciate ligament is to stabilise the knee from excessive movement forwards and backwards.  After rupture of this ligament some of the stability can be achieved by strengthening the muscles about the knee joint, the quadriceps and hamstring muscles. Your physiotherapist can organise a program to strengthen these muscle groups, which will improve the stability of your knee.  Even prior to reconstruction surgery physiotherapy guided rehabilitation can improve muscle function and recovery from surgery.  If anterior cruciate ligament reconstruction surgery is undertaken a post-operative physio guided rehabilitation program is required.  Being familiar with this program from pre-operative physiotherapy will aid recovery.

Anterior Cruciate Ligament Reconstruction Surgery

After it has ruptured, the anterior cruciate ligament has no ability to heal. Therefore, it cannot be repaired.  Any surgery to treat this problem is required to replace the damaged ligament with a “new” ligament (ligament graft).  The majority of this surgery is performed by arthroscopy. The new ligament is created by using a tendon from a remote site; this is either taken from the hamstring tendons, or from the patella ligament which runs in front of the knee.  A separate incision is required to harvest these grafts. 

Arthroscopy allows your surgeon to examine the inside of the knee joint for any damage and correct these problems.  The torn anterior cruciate ligament is removed from the knee joint and tunnels are drilled through the tibia (shin bone) and femur (thigh bone) to allow the ligament graft to be passed from outside through the knee joint.  The ligament graft is passed in place of the torn anterior cruciate ligament and secured in the bone. 

After surgery you will undergo an accelerated rehabilitation program. This initially requires crutches for a few days and a brace until the leg is comfortable.  You will be able to fully weight bear from straight after your surgery.  Your physiotherapist will guide your rehabilitation program, initially concentrating on regaining movement in the knee joint and then a coordinated strengthening program.

It takes many months for the ligament graft to attach firmly to the bone and also for the muscle strength about the knee to recover after reconstruction surgery.  Return to competitive sport will be around 9 to 12 months after surgery. 

Post-Operative Function

Most patients recover well after their anterior cruciate ligament reconstruction. Sedentary workers can return to work at about 2 weeks after surgery, light manual workers at about 6 weeks, and 3 months for heavy manual work.  Driving can be commenced once the knee is comfortable and stable. 

Most people complain of an area of numbness at the front of the knee after surgery.  Some will complain of difficulty with kneeling and squatting.  Up to 80% of people will be able to return to sport.

Risks of Surgery

There are a number of risks associated with arthroscopic cruciate ligament reconstruction, these include infection, excessive stiffness, swelling of the knee / bleeding in the knee joint, damage to the blood vessels or nerves, and new injury to the knee causing rupture of the ligament graft, or ongoing instability.  

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