THE MENISCI OF THE KNEE
What are the menisci?
The menisci (cartilages) of the knee are two crescenteric-shaped wedges of cartilage that sit between the two bones (the femur and the tibia) of the knee joint. One sits in the inner (medial) side of the knee; the other sits in the outer (lateral) side.
The menisci are made of elastic fibrocartilage (similar in some ways to the outer part of the ear). They have a number of functions within the knee, probably the most important of which are to act as shock absorbers and load sharers within the knee.
Tears of the knee cartilages are very common, with about 61 people sustaining a meniscal tear per 100,000 population per year. Most meniscal tears occur during sporting injuries that involve a twisting movement while standing on a bent knee. However, in older people, the mensical cartilages become degenerate (worn) and can tear spontaneously, with either little or even no perceptible trauma (such as when getting up from kneeling or squatting so are common in professions like plumbers or electricians)
Arthroscopic view of meniscal tear
When the menisci tear the most common symptoms are:-
pain on the inside or outside of the knee - depending on which meniscus is torn
swelling - the knee tends to swell up several hours after the initial injury
giving way - this is where the knee 'gives out', causing a patient to stumble or fall
locking - this is where the knee gets stuck in one position (so that a patient is unable to fully straighten the knee).
If you have a knee injury and suspect that you may have sustained a meniscal tear, it is essential that you seek advice from an appropriately trained and qualified healthcare practitioner.
If you see a Consultant Orthopaedic Surgeon, then there is an approximately 90% chance of achieving a correct diagnosis from simple taking of the story of injury and clinical examination.
In cases where the diagnosis is not clear or where there is a suspicion of other associated injuries, your Consultant may refer you for an MRI scan. This involves lying on a bed that goes into a large ring-shaped scanner, with the scan taking about 20 minutes. It is important to appreciate that MRI scans, whilst useful, are not 100% reliable; whilst being good at picking up a wide variety of potential problems, they are only about 80 - 90% accurate at diagnosing meniscal tears. Therefore, if a scan says that there is no tear but a patient has a strong history and clear clinical signs, then specific treatment may be recommended regardless of a negative scan result.
Consequences of meniscal tears
If a meniscus is badly torn then its function is likely to be affected. Without a functional meniscus in the knee (ie if the knee's natural shock absorber is lost), there is an increased risk of developing arthritis (wear and tear) within the knee joint. As an approximate guide, without a meniscus, a knee is 15 times more likely to develop arthritis after 20 years (a relative risk of 1500% !). Therefore, modern surgical management aims at trying to preserve as much normal meniscal tissue as possible and to repair meniscal tears when feasible.
Treatment of meniscal tears
If a patient's symptoms are not severe and they seem to be coping, then a trial of conservative (non-operative) treatment may be justified, such as rest followed by physiotherapy. However, the meniscal cartilages have a poor blood supply and tears therefore often fail to heal up on their own.
For those patients with severe symptoms or for those who have failed a trial of non-surgical treatment, arthroscopy (keyhole surgery) of the knee is the normal treatment of choice.
Arthroscopy of the knee is a relatively small operation that is normally performed under a quick (1/2 hour) general anaesthetic as a day-case procedure. It involves making two small (<1cm) incisions at the front of the knee and inserting a telescope plus probes and instruments into the knee joint.
If a meniscal tear is irreparable (for example, if the tear is ragged or the meniscal tissue is worn and degenerate) then the appropriate treatment is normally to trim the meniscal tear back to normal healthy tissue (a partial meniscectomy). If however, a tear is clean & simple, near the outer edge of the meniscal tissue (where the blood supply is better) and the meniscus is not degenerate, then it may be possible to repair the meniscus.
Meniscal repair is not a new technique. However, recent technological advances have enabled meniscal repairs to be performed arthroscopically with tiny suture devices, without the need for large open incisions. Only about 10 - 20% of meniscal tears are actually repairable. However, these tend to be in younger patients, in whom the consequences of loss of a meniscus are that much greater. Therefore, most specialist knee surgeons would now agree that an attempt at meniscal repair should be made whenever appropriate.
Meniscus following repair
The published literature suggests that with modern meniscal repair techniques, there is a success rate of approximately 60-70% in getting the tissue to heal up properly.
Rehabilitation after keyhole surgery for cartilage tears depends very much, on how much damage was found inside the knee and what actual procedures were performed.
If a simple partial meniscectomy is performed then most surgeons allow their patients to walk fully-weight-bearing more or less straight away after their surgery. They may recommend one or two weeks of rest followed by getting back into exercise and sport gradually thereafter.
If a meniscal repair is performed then there is considerable variation in the types of rehab recommended by different surgeons. Some surgeons advise their patients to wear a knee brace and to use crutches for the 1st six weeks post-op, to protect the repair whilst the tissue is healing. This may be followed by 6 weeks of physiotherapy, with patients only being allowed to start running again at 3 months post-op, with return to sport at 6 months post-op.
However, it is important to note that each individual patient's requirements with respect to recovery and post-operative rehab will be tailored to their own individual situation and needs, and advice should always be sought from your treating surgeon.
Inevitably there will be some patients who have previously undergone partial or total menisectomy (removal of the cartilages) who will unfortunately go on to develop wear and tear and arthritis in the knee.
For those patients with an absent meniscus that do develop significant pain but who have not yet developed fully blown arthritis, one potential surgical option is meniscal transplantation.
Meniscal transplantation involves taking donor tissue, known as an allograft, and surgically implanting a new meniscus into the knee. The tissue comes from donors (much in the same way as a lung, heart or kidney donor) and is screened very carefully and decontaminated fully.
The results of meniscal transplantation have shown success rates of approximately 80% for relief of pain and other symptoms. However, the new menisci may not last forever, and it would appear that the success rate probably begins to drop off after 7 or 8 years after transplantation. However, the surgery does remain one potential good option for hopefully delaying the progression of arthritis and the time when a patient may end up needing a knee replacement.
Meniscal transplantation is being performed in significant numbers in various specialist centres in Europe and the USA. It is relatively new to the UK with fairly few UK surgeons currently offering the procedure. There is much ongoing research into the field of meniscal transplantation - further information can be found on the website of the UK Meniscal Study Group - www.meniscalstudygroup.com