The
meniscus is a half moon shaped piece of cartilage that lies between the weight bearing
joint surfaces of the femur and the tibia. It is triangular in cross section and is attached to the lining of the
knee joint along its periphery. There are two
menisci in a normal knee; the outside one is called the lateral meniscus, the inner one the medial meniscus.
The menisci play an important role in absorbing about a third of the impact load that the joint cartilage surface sees. It''s been shown that complete removal of a meniscus can result in progressive arthritis in the joint within a decade or so in a younger patient, sooner in patients who are older with pre-existing "wear-and-tear" osteoarthritis. The menisci also cup the joint surfaces of the femur and therefore provide some degree of stabilization to the knee.
The meniscus itself is for the most part avascular that is it doesn''t bleed if cut and doesn''t have blood vessels inside. The exception to this is at the periphery where it joins to the vascular knee lining providing the outermost 20% of the meniscus with a blood supply. As a result of this avascularity a torn meniscus doesn''t have the ability to heal itself unless there is just a small tear confined to the peripheral vascular zone. Similarly the nerve supply providing pain and sensation to the meniscus is for the most part limited to the zone where the blood vessels are located.
In terms of descriptive terminology orthopaedic surgeons divide the meniscus into thirds with three geographical zones; the front third is referred to as the anterior horn, the back third the posterior horn, and the middle third the body.
Some people think that only athletes can tear a meniscus. This is not true. Even people who do not consider themselves "athletes" can tear a meniscus. Some menisci (plural) tear during activities of daily living such as getting in and out of a car or squatting. Menisci also tear during participation in recreational activities such as skiing , dancing, or racquetball.
There are two different mechanisms for tearing a meniscus.
Traumatic tears result from a sudden load being applied to the
meniscal tissue which is severe enough to cause the meniscal cartilage to fail and let go. These usually occur from a twisting injury or a blow to the side of the knee that causes the meniscus to be levered against and compressed.
Degenerative meniscal tears are best thought of as a failure of the meniscus over time. There is a natural drying-out of the inner centre of the meniscus that can begin in the late 20''s and progresses with age. The meniscus becomes less elastic and compliant and as a result may fail with only minimal trauma (such as just getting down into a squat). Sometimes there are no memorable injuries or violent events which can be blamed as the cause of the tear. The association of these tears with aging makes degenerative tears in a teenager almost unheard of.
There are many techniques for meniscal repair and these will depend on the location of the tear. The techniques include an open procedure (following arthroscopic examination of the joint) or the arthroscopic ''inside-out'', ''outside-in'' and ''all-inside'' procedures. The open technique has been advocated for vertical tears of the posterior horn of the lateral and medial menisci within 1-2 mm of the meniscosynovial junction, where visualisation with the arthroscopy is difficult. In all cases the torn surfaces of the meniscus are derided of scar tissue and fibrin clot can be placed in situ before the sutures are tied to enhance healing.
Repaired meniscal tears heal if there is adequate blood supply and tissue stability. A stable knee is therefore important and increased healing rates have been seen with repairs done at same time as ACL reconstruction - possibly as other factors are liberated at the time of the operation.
Post-operative protocols vary but the will be asked to follow a strict physiotherapy regime and avoid contact sports for six months, as opposed to partial meniscectomy when patients can resume normal activities after two weeks.
Conclusions The meniscus is a shock-absorbing cartilage in the middle of your knee. There are two menisci: one on the inside ("medial") and another on the outside of the knee ("lateral").
Pain with meniscus tears is often a sharp pain, usually on the inside or outside of the knee. Many patients will have swelling in the knee with the meniscus tear. Often there is a clicking in the knee when the meniscus is torn. Twisting or squatting can cause increased pain. Sometimes, if there is a large meniscus tear, a patient can complain that their knee locks, that is, it gets stuck in a certain position then needs to be "wiggled" to get it back into place.
Meniscal tears are common and can be traumatic or degenerative. Traumatic tears occur classically during twisting forces on the knee in young active people, are often vertical longitudinal tears and can be associated with ligamentous injuries. Degenerative tears occur as part of progressive wear in the whole joint, most frequently in the over 40''s. They can cause symptoms that affect the function of the joint and require surgical intervention. The majority of symptomatic tears require arthroscopic partial meniscectomy but in a few select cases the tear may be amenable to repair done as an open or arthroscopic procedure.
More abstracts about the Meniscus of Knee