What are the symptoms of an anterior cruciate ligament (ACL) injury?

An anterior cruciate ligament (ACL) tear is very painful. Usually the knee swells up right away, and you can't walk on it. Often, people will hear or feel a big pop in their knee, which is the ACL actually tearing.

After a few days, it often subsides to where it's more comfortable, and they can walk around on it. They think they might be getting better until they start to try to turn corners when they walk or go back to their sport. Then they realize something isn't right with their knee. If the ACL is torn, the knee won't feel solid or reliable. It's not usually a very subtle thing.

Anybody who has this kind of injury knows right away they've done something wrong to their knee. They may not know it's their ACL that's torn, but it's usually a very painful traumatic event where your knee gives out on you. You may fall to the ground and then feel or hear the pop in your knee. It's usually not possible to walk on it right after that, because the pain is so severe. Then it often swells up right away and feels unstable.

An ACL (anterior cruciate ligament) sprain is characterized by a pop associated with feeling the knee joint slide followed by inability to walk normally, swelling of the knee joint, fluid buildup around the knee, difficulty straightening the knee, pain in the back of the knee, and the knee feeling unstable.

This answer provided for NATA by Loras College.

Dr. Sean McMillan, DO
Orthopedic Surgeon

Symptoms of an anterior cruciate ligament (ACL) injury include:

  • swelling
  • a grinding sensation
  • joint stiffness
  • pain with movement and weight-bearing activities

A person who suffers an ACL injury often describes hearing a loud pop and then developing intense pain in the knee. The pain makes walking and weight-bearing difficult.

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