- The meniscal cartilages are two C-shaped wedges of elastic tissue in the knee, which act as load sharers and shock absorbers.
- The medial meniscus is on the inner side of the knee and the lateral meniscus is on the outer side. The back part of each meniscus extends round to the back of the knee joint.
- Meniscal tears are very common, and they tend to occur from twisting on a loaded knee, e.g. football tackles, slips or ski accidents.
- From the age of 30 onwards, the menisci can begin to become progressively more degenerate, more friable and weaker, and hence more liable to tear. 50% of degenerate meniscal tears occur spontaneously, with no actual history of an specific trauma.
- Meniscal tears can cause pain, swelling, clicking, catching, giving way and/or locking in the knee.
- The best investigation for confirming a suspected meniscal tear is to get an MRI scan.
- If the symptoms from a meniscal tear are only mild and if there is no significant functional impairment, then you might decide to simply leave your knee alone, protect it by avoiding anything that hurts or aggravates the symptoms, and just wait and see how things go.
- If a meniscal tear is causing significant symptoms and/or functional impairment, if the symptoms are not getting better with time and rest and/or physio treatments, or if the symptoms are actually getting worse, then you are likely to need a knee arthroscopy.
- Any patient with meniscal symptoms and a locked knee that won’t straighten out fully should be considered to have a displaced locket bucket handle meniscal tear until proven otherwise. If you’re in this category then you need an MRI scan ASAP, as if there is a displaced bucket handle meniscal tear then this is very likely indeed to need knee arthroscopy surgery. The longer a displaced bucket handle tear is left, the less likely it is that the torn meniscal tissue will actually be reducible back into place and repairable, and the more likely it is that the meniscus will instead simply end up needing to be removed.
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The meniscal cartilages are two crescent-shaped wedges of elastic cartilage sitting in the middle of the knee joint. The medial meniscus lies in the inner side of the knee; the lateral meniscus is in the outer side of the knee. They look like small potato wedges or thick rubber washers, sitting in between the bone surfaces of the end of the femur (thigh bone) and the top of tibia (shin bone). Prior to the 1970s, it was believed that the menisci had no important function in the knee and that they were just the vestigial remnants of a leg muscle in the joint. However, from the mid-70s onwards research began to be published that showed that actually the menisci had a number of important roles inside the joint …
The menisci function as:-
- They are load sharers and shock absorbers in the joint. About 70% of the joint load in the lateral compartment goes through the lateral meniscus and about 50% of the medial joint load goes through the medial meniscus.
- The posterior horn of the medial meniscus is a secondary stabilizer against anterior laxity, which is only really of relevance in the ACL-deficient knee.
- The meniscus nerve fibres in it, particulary around its periphery and in the anterior and posterior insertional ligaments, and it has been shown to contribute to proprioception (reflexes) in the knee.
- The meniscus has been said to act like a windscreen wiper, spreading synovial fluid over the femoral joint surfaces, thus assisting with joint lubrication.
- Finally, in increasing the movement of synovial fluid over the articular cartilage covering the joint surfaces, it has been proposed that the menisci assist with the nutrition of the articular cartilage (articular cartilage has no blood supply, and the cells in the articular cartilage get their oxygen and nutrients from diffusion from the synovial fluid in the knee.
Prior to the late 1970s, if you tore your meniscus and it was causing sufficient symptoms, then you would be likely to have an open meniscectomy, with removal of most or even all of the meniscus. However, the true importance of the menisci is now fully appreciated and we now know that removal of a meniscus (meniscectomy) significantly increases the future risk of arthritis in that area of the knee joint. As an approximate guide, if a meniscus is completely removed then the risk of arthritis in the knee increases by a factor of x15, over the course of the following 20 years. This therefore emphasizes very clearly indeed just how very important it is to take the menisci seriously, to treat meniscal tears properly, to repair the menisci whenever possible rather than just chop them out routinely, and to replace missing menisci (with artificial bioabsorbable scaffolds or by meniscal allograft transplantation) where indicated.
How do the menisci tear?
Meniscal tears can broadly be divided into two different (but not mutually exclusive) categories:-
- In younger people (<40) with normal quality meniscal tissue, the menisci normally only tear with specific trauma to the knee. The best (worst!) way to tear a meniscus is to twist the knee whilst you’ve got your weight on it in a bent position, and this often happens with football injuries or skiing falls. The ‘dangerous’ sports for knees, and for meniscal tears in particular, are netball, volleyball, football, squash, tennis and skiing. In most of these there is twisting on the knee combined with impact. With skiing the real risk is falling at low speak, when the bindings fail to release, and then there is a 5 or 6 foot lever arm from the ski, specifically twisting the knee joint.
- In people over about 40 years old (currently, the official definition of ‘old’ is 44 or older … next year it’ll be 45 -- author’s prerogative!!) the menisci slowly begin to degenerate, which means that they begin to lose their elasticity and become more fragile and friable, and more likely to tear with either just minor trauma or sometimes without any actual particular trauma at all. About 50% of degenerate meniscal tears occur spontaneously, with no specific associated episode of notable injury. In the rest, the tear may occur with just fairly innocuous things such as kneeling/squatting to clean the floor or from gardening. Therefore, if a patient has meniscal symptoms/signs but without any specific history of an actual injury it does not mean that they can’t have a meniscal tear!
What are the symptoms of a meniscal tear?
People with a meniscal tear often report a sudden sharp pain initially, sometimes with a ‘pop’ or ‘crack’ felt/heard inside the knee. Unlike a ligament rupture, where initial symptoms are normally very severe and most people are unable to continue doing whatever it was they were doing, often with a meniscal tear people can actually continue to function reasonably well initially. However, the joint often then swells up, often only moderately and often not until a number of hours after the actual injury.
The classic symptoms of a meniscal tear are:-
- Intermittent sharp pains on either the inner (medial) or outer (lateral) side of the knee, depending on which meniscus is actually torn. If the back part of the meniscus (the posterior horn) is torn, then patients often feel pain around the back of the knee, particularly with deep knee flexion (bending) eg squatting. These sharp pains are often aggravated by any twisting on the knee.
- Patients often also complain of a more constant dull aching pain on the affected side of the joint.
- Swelling – this is due to increased joint fluid in the knee (an effusion).
- Clicking – painless clicking is not of any real significance. However, painful clicking and/or clicking associated with feelings of catching, giving way or locking often indicates the presence of a meniscal tear.
- Giving way – Intermittent sudden giving way, particularly when associated with sudden sharp pains and particularly when occurring with twisting on the knee, can be due to unstable flaps of meniscal cartilage catching in the knee.
- Locking is where the knee joint gets stuck in a bent position and you are unable to straighten (extend the knee). The joint may click or clunk back into place by wiggling the joint. Locking of this nature often indicates an unstable meniscal tear.
Investigation of suspected meniscal damage
What’s really quite frustrating and upsetting, as a Knee Surgeon, is how often I hear patients tell the same old story …. that they injured their knee, that they went to their local NHS A&E Department, that they were seen by a (non-specialist) doctor (or even worse, only a nurse), that they were sent for X-rays and that they were told that they simply had a “soft tissue injury”! (which means pretty much nothing!)
If a patient has a suspected meniscal tear then quite simply – they need an MRI scan, simple as that.
MRI scanning involves lying on a bed that goes into a large tunnel, and it takes about 20 minutes to obtain the scan images. A consultant radiologist (X-ray doctor) will provide a report on the results of the scan. However, any decent specialist knee surgeon will review all of the images themselves and will show you the relevant images and talk you through them in detail when you are seen back in clinic afterwards to receive your results.
The good thing about MRI scanning is that it is non-invasive and therefore zero risk (as long as you have no contra-indications to having a magnetic scan, such as having a cardiac pacemaker). The negative is that MRI is about 90+% accurate at diagnosing specific pathologies in the knee (due to limitations of resolution and clarity), and MRI is therefore not infallible. Although MRI is a great screening tool, the results should be considered with some caution, and viewed in light of the patient’s history, their symptoms and their clinical examination signs. If an MRI scan is ‘normal’ it does not mean that there is definitely no damage in the joint, and one should believe the patient not the scan image.
For information about treatment of meniscal tears, CLICK HERE
Written by Mr Ian McDermott
Consultant Knee Surgeon London
Last updated 24-6-15