Introduction

There are two menisci in each knee. The meniscus on the inside of the knee is medial meniscus and the outside of the knee is called lateral meniscus. The meniscal cartilages are shaped like crescent moons and sit between the two bones that form the knee, the femur (thigh bone) and tibia (shin bone). The menisci function primarily as shock absorbers and secondarily as stabilizers in the knee. The medial meniscus absorbs 30% of the load in the medial compartment and the lateral meniscus absorbs 50% of the load in the lateral compartment.

Meniscal Tears

The menisci commonly tear when they are caught between the moving bones of the femur and tibia. The menisci have blood supply only to the outer 1/3 peripheral zone, and therefore have a limited ability to heal if torn. Most tears occur in the inner zones of the meniscus because this is the part of the meniscus that gets caught between the moving bones. These inner tears and many of the complex outer zone tears cannot heal.

Symptoms

Pain is the most common symptom of a meniscal tear. The pain is usually located on the sides or behind the knee. Catching and occasionally locking also can occur. Swelling always means there is something wrong inside the knee and is commonly associated with meniscal tears.

Treatment of Meniscal Tears

When the meniscus tears, the torn piece no longer has the capability to cushion the bone surfaces. If left alone the torn meniscal piece continues to tear into previously normal cartilage. As a result more meniscus is subsequently lost. In addition, in those meniscal tears that are repairable (longitudinal tears in the outer third) the tears will become unrepairable because of additional damage to the meniscus. MRI scans are usually diagnostic of meniscal tears with an accuracy of ~90%.

Arthroscopy of the knee is the recommended treatment for meniscal tears. Arthroscopy is a relatively simple surgical procedure that takes approximately 15 minutes. The procedure is done in a surgical center as an outpatient procedure. It can be done under local anesthesia through 2 portals or skin incisions 6mm wide (1/4 inch). After the procedure Band-aids are used to close the skin. Crutches usually are not necessary unless a repair of some other procedure is performed.

1. The first image shows a perfect / untorn meniscus sitting between the thigh (femur) bone and shin (tibia) bone.	2. The next image shows a torn meniscus.
3. This image shows the torn portion of the meniscus after it is removed.	4. This image shows a 'bucket handle tear' of the meniscus where a portion of the meniscus has been torn and flipped forward.
5. Here in this image it shows what it looks like after the bucket handle tear is removed.

Future Prognosis

Following a partial menisectomy most patients are able to resume to normal non-sporting activities comfortably in a few days. Generally light sports such as biking and swimming are well tolerated in 1-2 weeks. Heavy sports such as running, basketball and tennis usually take longer.

The long-term prognosis depends on how much meniscus was lost from the tear. Naturally occurring (aging) arthritis is accelerated depending on the amount of meniscus lost. There are new techniques designed to repair those menisci that are repairable and replace that portion of the meniscus which is lost. Entire menisci can be replaced using cadaver transplants.
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