Meniscus Tears: Overview

Meniscus Tears: Overview

The meniscus is commonly described as a shock absorber for the knee. Each knee contains two C-shaped menisci: the medial meniscus on the inner side of the knee and the lateral meniscus on the outer side. These structures sit between the thigh bone, or femur, and the shinbone, or tibia, helping to cushion the joint and distribute forces during movement.

The meniscus is made mostly of water, along with spongy connective tissue and proteins. In cross-section, the outer edge is thick while the inner edge is very thin, a shape that helps stabilize the knee by allowing the rounded femur to rest on the relatively flat top of the tibia. Without the meniscus, the surface cartilage of the knee would experience significantly more pressure—up to 50 percent more when the knee is straight and as much as 200 percent more when bent—greatly increasing the risk of early arthritis.

Meniscus tears most commonly occur when the knee is compressed, such as during standing or running, while simultaneously twisting. This combination of compression and rotation places stress on the meniscus and can cause it to tear. Meniscus tears vary in size and pattern, with one well-known type being the bucket-handle tear, where a long tear remains attached at both ends and the torn portion can flip back and forth within the joint.

Approximately one-third of meniscus tears occur alongside an anterior cruciate ligament, or ACL, tear. Traumatic meniscus tears are more common in younger, athletic individuals and typically result from injury, while degenerative tears develop gradually over time and are more common later in life. Although meniscus tears cannot always be prevented, maintaining flexibility and strength in the leg muscles may help reduce risk. Some patients may also use a brace if their knee feels unstable or if they are recovering from another knee injury.

Each meniscus is anchored to the top of the shinbone at two points called the anterior root in the front and the posterior root in the back. These attachments sit near the ACL and posterior cruciate ligament, or PCL, in the center of the knee and allow the meniscus to shift slightly as the knee bends and straightens.

Healing potential of the meniscus depends on blood supply, which varies by location. The outer edge, known as the red-red zone, has the greatest blood supply, followed by the red-white zone where blood flow decreases. The inner portion, called the white-white zone, has very little blood supply, meaning tears closer to the inner edge are much less likely to heal on their own than those near the outer edge.

Patients with a meniscus tear commonly report pain along the joint line, clicking or catching sensations during movement, and sometimes a feeling of instability when walking or twisting. Swelling may develop within the joint, although unlike an ACL tear, it may take several days for swelling to appear.

Health care providers use specific physical exam tests designed to reproduce symptoms and help diagnose a meniscus tear. X-rays are obtained to rule out fractures and assess for arthritis, and in some cases full-length leg x-rays are used to evaluate alignment. While ultrasound can provide helpful information, MRI is the best imaging study for evaluating the meniscus and other soft tissues. Once a diagnosis is confirmed, the patient and provider work together to develop a treatment plan aimed at returning the patient to their desired level of activity.