Meniscal Cartilage Injuries
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Each knee has two menisci. They are commonly called “the cartilages”, although this is not strictly accurate. There is one on the medial (inner) side of the knee and one on the lateral (outer) side of the knee. They are C or crescent-shaped and serve to cup the femur as it sits on the tibia to improve the congruity of the joint. The main role of the meniscus is to spread the load being put through the two joint surfaces, thereby protecting the joint surface cartilage. In some ways they act as shock absorbers of the knee. They are made up of a tough gristly material called fibrocartilage.
The menisci are important. A torn meniscus does not function properly, and early wear in the joint may occur. However, depending on age and other factors, this may be more or less important.
The commonest problem which arises with a meniscus is a tear- a “torn cartilage”.
The symptoms from a torn cartilage can range from pain, to clicking and catching sensations, through to complete locking of the knee. A locked knee arises when a large fragment of cartilage jams in the knee, resulting in an inability to fully straighten the knee. Other associated features of a cartilage tear may be swelling or even a sensation of giving way (though this is usually a sign of ligament damage).
The diagnosis of a meniscal tear is often made on the history of injury.
In the younger adult patient or adolescent there may be a very definite story of a twisting or jarring injury followed by swelling and clunking or locking of the knee. If the swelling occurs rapidly it suggests that there has been some bleeding into the knee joint.
These symptoms are often very well localised and the patient may be able to put their finger on one side of the knee or the other according to which cartilage is torn.
Sometimes cartilage tears are associated with other injuries such as ligament ruptures.
A tear of the meniscal cartilage in a young adult usually occurs with a greater force than in a middle aged or elderly person. The reason for this is that the strength of the cartilage reduces as you grow older. With the natural aging process, the meniscus cartilage goes from being tough and resilient to quite fragile and brittle. Therefore the cartilage tears or splits more easily.
In a middle aged or elderly patient a cartilage tear may occur with a relatively minor injury. Rising from a chair, crouching down, standing from kneeling are all classic causes. Indeed sometimes it is difficult for the patient to recall the exact moment at which the cartilage tear occurred, but recent vigorous activity may be relevant e.g. going on a long walk, moving furniture. It may be that a sharp pain is felt during a run or other sport.
In this age group the swelling and pain is often less dramatic- it may not be noticed until the next few days.
The examination of the knee along with the history is a very useful aid to diagnosis.
An x-ray will usually be undertaken even though a cartilage will not show up. This is because it is a simple investigation which can exclude other problems such as arthritis, an injury to the bone, or loose bodies (fragments of bone) in the knee; any of which can mimic the symptoms of a cartilage tear.
Sometimes an MRI scan will be performed to confirm a cartilage tear if there are any doubts. An MRI scan is not always used and will depend on the clinical diagnosis and problems that the patient is having. Even MRI can miss small tears.
Once the diagnosis of a torn meniscus is made you may well require surgery to treat it, as it is uncommon for these tears to heal. This is because in order for something to heal, it requires a blood supply and the meniscus itself has a poor blood supply.
Symptoms from small tears can settle down, however, over about 6 weeks. If symptoms last longer than this, surgery is often necessary. Larger tears usually require surgical treatment.
Surgery will nearly always take the form of an arthroscopic (keyhole) procedure, called an arthroscopy.
Depending on the nature of the cartilage tear, it will either have to be repaired, or trimmed to a smooth edge (a partial meniscectomy).
A small proportion of meniscal tears are suitable for repair. If a tear is treated soon after it occurs and the tear itself lies in the outer part of the meniscus, where there are tiny blood vessels, it may be suitable for repair with special sutures or anchors.
In general this is only considered in the relatively younger age group for a number of technical reasons. Over the age of 30, we know that the chance of a meniscus tear healing is reduced.
In some injuries the point where the meniscus is attached to the tibia (the meniscal root) can be pulled off. This is called a “root” avulsion, and is important because if it happens, the function of the meniscus is completely lost. They may be suitable for repair, depending on a number of factors which your surgeon may discuss with you.
More commonly the torn part has to be removed, a partial meniscectomy. This is done using special small punches and cutters via one of the portals (keyhole incisions) at arthroscopy. The amount of cartilage removed depends on the size of the tear. As little as possible will usually be taken out, trying to leave a smooth stable edge of cartilage. The aim of this is to alleviate the meniscal symptoms.
Sometimes, a cleavage tear (a type of splitting tear within the substance of the cartilage usually found in degenerate cartilages) can be associated with a meniscal cyst. This can be painful in itself and may present as a small lump on the outside of the knee. They are not dangerous. Cysts on the outer (lateral) side of the knee are more common than those on the inner (medial) aspect of the knee. Usually these cysts can be drained into the knee at the time of meniscectomy. Rarely, they may require removal with a bigger cut through the skin directly over the swelling.
With the realisation of the importance of the meniscus cartilage in young patients, for protecting the joint surface against premature wear (arthritis), there have been developments in treatment of meniscus deficiency. However, these techniques are still quite experimental, in that we do not know whether they are effective in the long term.
Where a large part of the meniscus has had to be removed, it is now possible to replace it with artificial or “donor” material.
Devices can be stitched in to replace a missing piece of cartilage. This is a relatively new surgical technique, and the results are not completely clear. The aim is to protect the joint surface from overloading.
It is not known how effective these devices will be in the long term, but there are some encouraging reports, and the technology is evolving.
Where there is little or none of the meniscus left behind, meniscal augmentation will not work. This is because a rim of the normal meniscus is required to stitch it to.
In such cases meniscal transplant may be undertaken. This involves the transplant of donated tissue, given by organ donors. The whole meniscus is stitched into place using a combination of keyhole surgery and small incisions.
A donor meniscus into a knee does not have the same problem of tissue matching that you might have heard of , for example, with kidney transplants, but there are other risks. However, in certain cases, particularly young patients who have lost the whole lateral meniscus, meniscal transplant is becoming a recognised option of treatment to address pain. Can meniscal transplant stop or slow down arthritis? At present we simply do not know. Can it improve pain in the shorter term? Yes, there is evidence now that it can be effective in well selected patients.
So, it is important to be aware that meniscal transplant is relatively new, uncommonly performed, the long term benefits are unproven, but it is a promising technique for some cases.