The anterior cruciate ligament (ACL) is an important stabilising structure inside the knee. It runs between the two bones of the knee (femur and tibia) and maintains their relative position with each other during normal knee motion.
It can be damaged by twisting or hyperextension injuries to the knee joint. It is a tough structure so it requires considerable force to break it.
When it is ruptured, it results in a painful swollen (blood filled) knee. Initially, mobility is restricted by pain and swelling but over time this slowly settles. Sometimes, with a partial injury, it can settle with the help of physiotherapy but if the ligament is completely ruptured it leads to either acute or chronic instability. This causes a sense of the knee giving way with twisting motion such as turning around or simply changing direction.
An ACL rupture is often clearly present on clinical examination but diagnosis is confirmed with an MRI scan.
In the immediate post-injury period, rest, ice, compression and elevation are indicated and as the acute pain settles, physiotherapy is commenced to restore normal mobility to the knee and allow other soft tissue components of the injury to settle as well. When the knee is chronically unstable, a reconstruction will be required.