CONDITION - Knee Locking
If your knee is locked in a specific position and you are unable to move the knee you should seek medical treatment immediately.
Locking is the sensation that your knee is stuck in one position and you are physically unable to move the knee. Sometimes people with locking say that they have to "wiggle the knee" back into position for it to unlock.
This is usually due to either a large tear of your cartilage rings called a meniscus tear. Again, this is usually associated with a previous injury to your knee. Locking may also be due to a loose body or even a patellar dislocation.