The ACL is normally damaged following a twisted knee injury during sports or a fall. You can also damage it just by stretching your knee too far. Normally you’ll hear or feel a pop in the knee and the joint will then give way. You’ll feel a sudden pain and the knee will usually begin to swell in a few hours.
You might not be able to bear weight on the affected leg, and could feel unstable either when playing sport or, if the injury is more serious, during normal day-to-day activities.
After you’ve twisted your knee, it might feel like you have dislocated it. However, ACL is actually a tear in the ligament of the knee. During the injury you may also have torn the meniscus, which is cartilage tissue that acts like a shock absorber in the knee, or injured the Medial Collateral Ligament (MCL). Your knee specialist will carry out tests on your knee to find out how much damage has been done.
It may take a few weeks for the swelling to go down, but once it has done your knee should feel more stable. You can strengthen the knee with specific exercises, but you might also need surgery. A knee arthroscopy, which is a small incision 'keyhole' operation, is sometimes used to mend a tear in the meniscus or reconstruct the ruptured ligament.