Symptoms of a severe and sudden (acute)
anterior cruciate ligament (ACL) injury
- Feeling or hearing a "pop" in the knee at the
time of injury.
- Sudden instability in the knee (the knee feels
wobbly, buckles or gives out) after a jump or change in direction or after a
direct blow to the side of the knee.
- Pain on the outside and back
of the knee.
- Knee swelling within the first few hours of the
injury. This may be a sign of bleeding inside the joint (hemarthrosis). Swelling that occurs suddenly is
usually a sign of a serious knee injury.
- Limited knee movement
because of swelling and/or pain.
After an acute injury, you will almost always have to stop
the activity you are engaged in but may be able to walk.
symptom of chronic (long-lasting and recurrent)
ACL deficiency is an unstable knee joint. The knee buckles or gives out,
sometimes with pain and swelling. This happens more often over time. But not
everyone with an ACL injury develops a chronic ACL deficiency.
Other conditions with symptoms similar to ACL knee pain include injuries
to other knee structures, such as:
- An injury to the cartilage lining the knee
- An injury to the knee cushions (menisci). About
70% of people with an ACL injury also have a
- An injury to the knee ligaments that connect the
upper leg bone to the lower leg bone along the inner side of the knee joint
(medial collateral ligament) and the outer side of the knee joint (lateral collateral ligament).
- A break (fracture) in the bones of the
For more information on knee injuries, see the topics
Knee Problems and Injuries and
Patellar Tracking Disorder.
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