Last year, I had an ACL repair on my right knee. Even after going through a complete rehab program, the knee still feels unstable. The doctor and physical therapist assure me that it’s safe to use it normally. What causes this problem?

You’re not alone. Many studies show that some patients continue to report these kinds of sensations. The leg doesn’t give way or fail to hold you up, but you feel as though it could.

Researchers can’t find any problem in the repaired tissue to account for this. The joint is just as strong and stable as before the injury. It may be caused by a loss of proprioception. This is the joint’s sense of its own position.

Proprioception is damaged or lost when the ACL is torn or injured. After surgery, it’s a full six months before the sense of joint position returns. There may be a permanent loss of proprioception if the surgery is delayed too long.

Not much is really known about this problem. Studies are ongoing to find some answers.