Torn Anterior Cruciate Ligament / ACL Knee Injury
What is an ACL injury?
A torn ACL is an injury or tear to the anterior cruciate ligament (ACL). The ACL is one of the four main stabilising ligaments of the knee, the others being the Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL). The ACL attaches to the knee end of the Femur (thigh bone), at the back of the joint and passes down through the knee joint to the front of the flat upper surface of the Tibia (shin bone).The knee joint showing a torn anterior cruciate ligament. (c)opyright Peter Gardiner
It passes across the knee joint in a diagonal direction and with the PCL passing in the opposite direction, forms a cross shape, hence the name cruciate ligaments. The role of the Anterior Cruciate Ligament is to prevent forward movement of the Tibia from underneath the femur. The Posterior Cruciate Ligament prevents movement of the Tibia in a backwards direction. Together these two ligaments are vitally important to the stability of the knee joint, especially in contact sports and those that involve fast changes in direction and twisting and pivoting movements. Therefore a torn ACL has serious implications for the stability and function of the knee joint.
How does a torn ACL occur?
A torn ACL or acl injury is a relatively common knee injury amongst sports people. A torn ACL usually occurs through a twisting force being applied to the knee whilst the foot is firmly planted on the ground or upon landing. A torn ACL can also result from a direct blow to the knee, usually the outside, as may occur during a football or rugby tackle. This injury is sometimes seen in combination with a medial meniscus tear and MCL injury, which is termed O’Donohue’s triad.Anterior cruciate ligament injuries are more frequent in females with between 2 and 8 times more females suffering a rupture than males, depending on the sport involved and the literature reviewed. The reason for this is as yet unknown, however areas of current research include anatomical differences; the effect of oestrogen on the ACL and differences in muscle balance in males and females.
Symptoms of a torn ACL
- There may be an audible pop or crack at the time of injury
- A feeling of initial instability, may be masked later by extensive swelling.
- A torn ACL is extremely painful, in particular immediately after sustaining the injury.
- Swelling of the knee, usually immediate and extensive, but can be minimal or delayed.
- Restricted movement, especially an inability to fully straighten the leg
- Possible widespread mild tenderness
- Positive signs in the anterior drawer test and Lachman's test (see assessment).
- Tenderness at the medial side of the joint which may indicate cartilage injury.
Treatment for an Anterior Cruciate Rupture
What can the athlete do?- Immediately stop play or competition
- Apply RICE (Rest, Ice, Compression, Elevation) to the knee immediately
- Seek medical attention as soon as possible.
