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Anterior cruciate ligament (ACL)

The anterior cruciate ligament (ACL) is one of the major stabilising ligaments in the knee. It is a strong rope like structure located in the centre of the knee running from the femur to the tibia.

The anterior cruciate ligament prevents the femur moving forward and rotating abnormally on the tibia. The ACL is required for normal function of the knee. One of the main functions of the ACL is to provide stability during rotational movements such as turning, twisting and sidestepping.

When it ruptures it does not heal itself and the knee often becomes unstable or gives way. Repeated giving way can lead to damage to other structures of the knee and eventually arthritis. Since the knee 'dislocates' when the ligament ruptures there is often damage to other structures in the knee such as bone, cartilage or meniscus. These injuries may also need to be addressed at the time of surgery.

History Of Injury

Usually there is a significant injury involving a twisting force to the knee. It can also occur after landing from a jump, stopping rapidly or direct contact such as in a tackle. It is particularly common in sports such as football, soccer, basketball, netball and skiing but can occur in many other activities.

When the ACL ruptures the patient often feels something giving way in the knee or hear a popping sound. Most people cannot continue with their activity and the knee generally swells up within hours.

Initial Management

The knee should be treated with ice, elevation and a compressive bandage .Crutches and analgesics usually are required. An X-ray is necessary to exclude an associated fracture. Physiotherapy is helpful to reduce swelling and regain motion.

Most patients will be referred to an orthopaedic surgeon for diagnosis and assessment of the injury. Careful clinical examination is required to detect damage to the ACL, other ligaments and structures in the knee such as the meniscus or articular cartilage. It is quite common to damage some of these other structures.


This can usually be made on history and clinical examination. An MRI scan which is a special imaging test is often ordered to confirm the diagnosis in patients where the examination is not conclusive. It also demonstrates damage to other structures such as the menisci or articular cartilage. The diagnosis can also be made with an arthroscopy.


Treatment Recommendations

Most patients who tear their ACL during sport will elect to have it surgically reconstructed, to enable them to return to full activities with a stable knee. Other patients choose to modify their activities and give up sport to avoid further episodes of instability.

In general, the younger and more active you are then the stronger the recommendation for reconstruction. It is generally recommended to have surgery if you wish to get back to sports which involve twisting and pivoting. Many patients who do not have surgery find that their knee becomes more loose over time. This can lead to a knee that gives way during ordinary activities of daily living. These patients should strongly consider surgery to stabilise the knee.

Repeated instability or abnormal movement in the knee can cause ongoing damage leading to stretching of other structures around the knee, meniscal tears or arthritis in the long term. If you do not elect to have surgery it is strongly advised that you give up sports that involve pivoting, sidestepping or rotation.

It is also recommend that people with dangerous occupations such as policemen, firemen, roof tilers and scaffolders have surgery. This is a safety issue to prevent instability in 'at risk' situations.

There is no urgency in performing this operation and in fact it is sometimes better to allow the knee to settle down and regain close to full motion prior to surgery. Your surgeon will advise you on the timing in your particular case.
The Santa Monica Orthopaedic and Sports Medicine foundation has designed an ACL prevention exercise programme which may be of interest in prevention of ACL injury.

ACL Graft Selection

Once the ACL is ruptured, surgical treatment requires reconstructing, not repairing, the ligament. Previous studies have shown that attempts to repair the torn ligament by sewing it back together were unsuccessful. Therefore, current surgical techniques involve taking a tissue from somewhere else and creating a new ACL; this is called reconstructing the ACL. This tissue, called a graft, can be taken from somewhere else in your own body, in which case it is termed an autograft, or it can be taken from a cadaveric donor, in which case it is termed an allograft. Frequent sources of autograft tissue include the middle-third of the patellar ligament and the hamstring tendons.

Patellar Tendon(BTB) Graft

Hamstrings Graft

There are pros and cons of both autograft and allograft tissue.
The ADVANTAGES of ALLOGRAFT tissue include the following:

  1. Surgical incisions are smaller because no tissue is harvested from your knee. This leads to improved cosmetic appearance.
  2. Typically less pain is experienced in the first 3 months following surgery because no tissue is harvested from your knee.
  3. There is a decreased risk of developing stiffness after surgery.
  4. The risks associated with harvesting the graft from your knee (see below) are avoided.
  5. Because no tissue is harvested from your knee, surgical times are typically shorter when allograft tissue is used.

The DISADVANTAGES of ALLOGRAFT tissue include the following:

  1. Because the graft is coming from another person, there is a theoretical risk that your body could reject this graft. Although this risk is theoretical, this has never been reported to occur in the setting of ACL reconstruction.
  2. Because the graft is coming from another person, there is a theoretical risk of a disease, such as a virus, being transmitted from the graft to your body. Examples of viruses that may be transmitted include HIV and hepatitis. The estimated risk of viral transmission is approximately 1 in 1.6 million but no cases of viral transmission have been reported since 1991 when tissue banks have improved their screening processes for potential donors and updated their “sterilization” processes of the grafts.
  3. Animal studies suggest that allograft tissue takes longer to “incorporate” in your knee and become a new ACL. This may have implications for patients attempting to return to competitive sports in a timely fashion.
  4. Some studies have suggested that there may be a tendency for increased laxity in the long-term when allograft tissue is used for ACL reconstruction.

The ADVANTAGES of AUTOGRAFT tissue include the following:

  1. Because the graft is coming from your body, there is no risk of graft rejection or viral disease transmission.
  2. Animal studies suggest that autograft tissue “incorporates” into your knee quicker. This may have implications for patients attempting to return to competitive sports in a timely fashion.

The DISADVANTAGES of AUTOGRAFT tissue include the following:

  1. Because the graft must first be harvested from your knee before it can be reimplanted into the location of the new ACL, larger surgical incisions are required and longer operative times are needed when autograft tissue is used.
  2. Because the graft must first be harvested before it can be reimplanted, patients typically have greater amounts of pain for the first 3 months following surgery when compared to patients who undergo ACL reconstruction with allograft tissue.
  3. There are potential complications or consequences associated to harvesting the graft from your knee.
  • When the patellar ligament is harvested as the autograft, there is a risk of fracture of the patella, disruption of the patellar tendon after surgery, injury to one of the nerves under the skin in the area of the incision that may cause numbness on the outside aspect of the leg, or pain in the front of the knee that is worse with kneeling and squatting activities.
  • When the hamstring tendons are harvested as the autograft, there is a risk of weakness of hamstring muscle function, especially with deep knee flexion activities.

Pre-Op Instructions

  • Cease aspirin and anti-inflammatory medications (e.g., voltaren, feldene) 10 days prior to surgery as they can cause bleeding.
  • Cease any naturopathic or herbal medications 10 days before surgery as these can also cause bleeding.
  • Continue with all other medications unless otherwise specified.
  • Notify your surgeon if you have any abrasions or pimples around the knee.
  • Please bring any X-rays, MRI scans or other investigations you have had done which may be relevant to your surgery.
  • Bring a list of medications with you to give to the anaesthetist.

You are advised to stop smoking for as long as possible prior to surgery.

The hamstring tendons are harvested through a small incision just below the knee and are fashioned into a new graft which takes the place of your old cruciate ligament. Tunnels (holes) are then drilled in the tibia and femur (the two bones making up the knee joint) and the graft is passed trough this tunnel. The graft is then fixed with various devices at each end to stabilise it and allow it to heal to the bone. The fixation devices vary and are surgeon specific.

This surgery is mainly done using an arthroscope using small incisions approximately 1cm each. The inside of the knee is thoroughly visualised and any other problems such as meniscal tears or damage to the joint lining (articular) cartilage are treated at the same time.

After Surgery
During surgery local anaesthetic is injected into the knee to reduce the amount of pain you will feel. Pain relieving medication will be provided for you both in hospital and at home.
There may be a drain in your knee which will be removed prior to discharge. You will have a dressing on your wound and a compressive wrap.

Most patients go home the day following surgery but some may go home the same day.

You will be seen by a physiotherapist prior to discharge who will teach you how to use crutches and show you some simple exercises to do at home. Your dressing should be left intact until your first postoperative visit.

Ice packs should be used regularly to reduce swelling.
Your graft is strong enough to put all your weight on your operated leg. You can walk around but rest as much as possible for the first week and elevate your leg when sitting. Most patients require crutches for a week or so.
Pain is variable and prescription pain killers may be required for a week or two.

You may shower but not bath or swim prior to your review. It is normal to have blood under the dressing. If there is excessive ooze the dressings can be changed by someone experienced in wound care. If concerned please contact your surgeon.

You will be followed up in the rooms about 10 days after your operation when the dressings will be removed and the wounds inspected. The surgery and any other findings will be explained to you.

If there is any redness, increased swelling or you have temperatures you should contact the rooms or the hospital where the surgery was performed so they can contact your surgeon.

Time off work depends on your work requirements and is very variable. Office workers usually require 2 weeks off work and manual labourers 2 to 3 months or longer.


Physiotherapy is an integral part of the treatment and is recommended to start as early as possible. Preoperative physiotherapy is helpful to better prepare the knee for surgery. The early aim is to regain range of motion, reduce swelling and achieve full weight bearing.

The remaining rehabilitation will be supervised by a physiotherapist and will involve activities such as exercise bike riding, swimming, proprioceptive exercises and muscle strengthening. Cycling can begin at 4 weeks, jogging can generally begin at around 3 months. The graft is strong enough to allow sport at around 6 months however other factors come into play such as confidence, fitness and adequate fitness and training.

Professional sportsmen often return at 6 months but recreational athletes may take 10 -12 months depending on motivation and time put into rehabilitation.

The rehabilitation and overall success of the procedure can be affected by associated injuries to the knee such as damage to meniscus, articular cartilage or other ligaments.


Despite advances in surgical technique and the utmost care being taken during surgery, complications can still occur. It is very important for patients undergoing this operation to understand the reasons for the procedure and to have a major role in making an informed choice to proceed with surgery rather than non surgical treatment.


In general this procedure is very successful but complications can occur with any surgical procedure. Other rare or unexpected complications can occur. This is an elective procedure and as the patient you need to make an informed decision on whether or not to proceed with surgery.