The knee is the largest joint in the body. It is a specialised hinge joint made up of four main things: bone, cartilage, ligaments and tendons. The main movement that occurs in the knee joint is flexion and extension. It does however allow for a small amount of rotation and gliding on the surfaces.
The anterior cruciate ligament (ACL) is a rope-like ligament located in the centre of knee joint that attaches to the femur and the tibia to prevent the femur and tibia from sliding backwards and forwards over each other or rotating sideways.
Injury to the anterior cruciate ligament may range in severity. A grading system is used to guide how severe an injury is and what treatment may be required. Grade 1injuries reflect mild stretching or spraining of the ligament, however the ligament is still able to perform its normal function. Grade 2 injuries are moderate stretching of the ligament that results loosening of the ligament or partial tearing. Grade 3 injuries are complete tearing of the ligament and can result in instability of the knee joint.
The most common cause of damage to anterior cruciate ligaments is sporting injuries. Sports or activities that involve the following motions are most likely to cause injury to the anterior cruciate ligament:
- Suddenly stopping
- Slowing down whilst running
- Rapid change in direction or sidestepping
- Twisting or turning
- Direct contact such as a during a tackle or a collision with another player
A popping sound is often heard when ACL injuries occur. This is often followed by the knee giving way and feeling unstable to walk on. As the anterior cruciate ligament does not heal itself ongoing instability can lead to damage to other structures in the knee that also require treatment.
Other symptoms include:
- Swelling – the knee will begin to swell within 24 hours of the injury
- Limited range of movement
- Localised tenderness
- Discomfort on weight bearing
Your doctor will ask you questions about the injury and your symptoms.
Your doctor will do a clinical examination of your knee to assess the structures in your knee joint.
Your doctor may refer you for an X-ray or MRI (magnetic resonance imaging) scan to assess your knee. The diagnosis of an ACL injury can generally be made after taking a history of the injury and examining the knee alone. These investigations, however, can help to determine if other injuries of the bones (fracture), menisci or other ligaments have occurred.
Immediate treatment of an injury to the ACL includes:
- Apply ice – ice packs should be applied to the knee in 20-minute intervals. Ice should not be applied directly to the skin.
- Compression – apply a supportive bandage to help with the swelling
- Elevate the affected leg
- A brace may be required to immobilise the knee and crutches may be needed to limit weight bearing
An ACL tear will not heal itself. Surgical treatment may not be required where the knee is stable and your activity level is low. In this instance, physiotherapy and bracing are effective non-surgical options. Returning to sporting activities or a physically active lifestyle will generally require surgical treatment.
Complete tearing of the ACL requires ACL reconstruction surgery (link to ACL reconstruction surgery page). ACL reconstruction is generally performed through a minimally invasive surgical procedure called arthroscopy. The procedure involves removing the torn segments of ligament and replacing them with graft tissue. The graft is usually made from a tendon around the knee joint. During the procedure, other structures in the knee that were damaged in the injury can also be treated.
Following an ACL reconstruction, it is important to follow your surgeon’s post-operative instructions. It is usually six months or more before you will be able to return to sport and other highly physical activities.
As with any surgery there are potential risks to undergoing an arthroscopy.
General complications of any surgery include:
- Allergic reactions to medications
- Blood loss requiring transfusion
- Complication from nerve blocks such as infection or nerve damage
The complications specific to ACL reconstruction include:
- Nerve damage or numbness
- Deep vein thrombosis (blood clot)
- Excessive bleeding and bruising
- Failure to relieve pain
- Loosening of the new ligament
- The tendon graft not attaching to the bone
- Joint stiffness
- Pain or swelling at the donor tendon site
Arthroscopic ACL reconstruction is often a day only procedure or an overnight hospital stay. You will require crutches to aid mobilisation although you will usually be able to weight bear almost immediately following surgery. Your knee may need to a brace for additional support.
For the first week you will need to apply ice to the knee for 20 minutes at a time as often as possible to help reduce the swelling and may need medication to help with any pain.
Physiotherapy is an integral part of recovery for ACL reconstruction. This will be commenced as soon after surgery as possible. Adherence to a strict exercise program including cycling and swimming will increase the success of your procedure.