A meniscus tear, which is a common knee injury, is often caused by a sudden twist or turn, often while the knee is bent and the foot is planted. This often occurs during sports. Also, aging can cause wear-and-tear of the meniscus, making it more prone to tearing.

There are several levels of meniscus tear. A minor tear can cause pain and swelling and usually subsides in several weeks. A moderate tear can cause pain or swelling to the outside of the knee, which may subside with rest, but can recur without proper treatment and healing. A severe tear can result in the edges or pieces of the meniscus moving into the joint space. This may cause pain and swelling and can also result in catching or locking of the knee, and instability or “buckling” of the knee. Surgery may be done to repair the tear.