Knee Popping During Injury – 5 Possible Causes

Posted by Orthopaedic Specialists

I was running when I got injured and heard a knee popping sound. What could it be?

If you heard a knee popping sound during injury, there are a number of things it could be. Five possible causes of knee popping including the following:

1. ACL Tear
The ACL is the major ligament in the knee that provides anterior and rotatory stability to the knee. If at the time of injury a pop is heard, swelling occurs within 12 hours and the athlete is unable to finish playing the game there is an 85% chance that the ACL was torn.


2. Patella Dislocation
The patella aka the knee cap can dislocate or slide out of position. When this occurs it may stay dislocated or more commonly it spontaneously locate on its own. The knee cap sliding back into place is what typically causes the knee popping sound and sensation. When the knee cap relocates it may also knock off a piece of cartilage or bone and this may also produce a popping sound

3. Meniscal Tear
There are two shock absorbers in the knee called menisci. They can get torn with a traumatic event such as a plant and twist of the knee. If this occurs at the time of injury the meniscal tear can produce a pop with acute onset of pain. The knee popping may also be associated with the knee locking. Until the tear reduces itself the knee may stay in a locked position. It may require a doctor to unlock the knee.

4. MCL Tear
The MCL also known as the medial collateral ligament is located on the inner side (medial) of the knee. The MCL helps to stabilize the knee from valgus forces. The MCL is typically torn by a traumatic event such as another player clipping another player’s knee. The injury is commonly seen in soccer and football players. At the time of the injury as the MCL is being torn it makes a loud knee popping sound.

5. Osteoarthritis (if preexisting)
Knee osteoarthritis is the breakdown of the articulate cartilage in the knee joint. On occasion a piece of the diseased cartilage will break off with activity and as it does a loud pop is heard.

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