The meniscal cartilages are two small C-shaped wedges of elastic cartilage inside the knee. The meniscus on the inner (medial) side of the knee is the medial meniscus, and the one on the outer (lateral) side is the lateral meniscus. Each meniscus is attached firmly to the bone at the top of the tibia (the shin bone) at the front and the back, and they are attached around their outer edge to the capsule (the lining) of the joint.
The menisci act primarily as load sharers in the knee, and they protect the articular cartilage layer that covers the surfaces of the inside of the joint. The end of the femur is curved and presses against the top of the tibia, which is relatively flat, and hence there is a tendency towards point loading over a small surface area, which leads to very high peak contact pressures in the joint. The menisci fill the gap between the bones, which increases the contact areas, spreading the load, which reduces the peak contact pressures.
It has also been suggested that the menisci might have roles as shock absorbers and that they improve proprioception (the subconscious sensation of joint position and movement), and that they may also help improve nutrition to the articular cartilage by spreading synovial fluid over the joint surfaces, which may also aid with lubrication. However, the main secondary role of the menisci is probably one of secondary stabilisation of the joint, as the posterior horn of the medial meniscus in particular helps prevent anterior movement of the tibia, which is of particular importance and relevance in the ACL-deficient knee (i.e. if there has been an ACL tear).
The forces that the meniscal cartilages are subjected to are huge. Most of time the menisci can cope, but if excessive load is applied, for example with a sudden forced twisting type injury to the knee (particularly if the knee is being loaded in a bent position), then the menisci can tear.
Meniscal tears can cause some or even potentially all of the following symptoms:
– Sharp sudden pains in the knee –
– Clicking –
– Catching –
– Giving way –
– Locking –
– Reduced flexion (due to pain) –
The pain from a meniscal tear tends to be felt around the inner side of the joint if it’s a medial meniscal tear or the outer side for lateral meniscal tears. If the back part of the meniscus is torn (the posterior horn), then this can cause pain around the back of the knee, especially with deep flexion of the knee (for example when trying to sit back on one’s heels whilst kneeling).
If a knee feels generally wobbly and unstable then this can indicate that there is actually a ligament tear. However, if a knee is giving way intermittently and the giving way is associated with a sudden sharp pain in the knee, then this can indicate that there might actually be a meniscal tear in the knee, with the torn tissue intermittently catching in the joint.
If a knee is ‘locked’, then this means that the knee becomes ‘jammed’ and stuck when you try to straighten it, and the joint won’t extend fully. With intermittent locking one tends to be able to wiggle the knee around or twist it into certain positions, and the locking may resolve with a bit of a clunk, after which the knee can then straighten out fully again. If a knee becomes locked, and stays stuck in a locked position, this actually makes this an urgent problem – a locked knee is due to a locked displaced bucket handle meniscal tear until proven otherwise.
In this situations an urgent MRI scan is needed followed by urgent surgery to try and reduce and repair the meniscus, if possible. This is really important – if a displaced locked bucket handle meniscal tear is caught early (within the first few weeks) then it is often possible to reduce the meniscus back into place and repair the tear, which means that the meniscus is then salvaged. If a displaced locked bucket handle meniscal tear is left too long (and the rough cut-off here generally tends to be about 6 weeks), then the torn tissue becomes scarred and retracted, and it becomes macerated/shredded – and then it is rarely ever reducible or repairable… in which case the displaced tissue simply needs to be excised and removed from the knee. When this happens, more often than not it means removal of most, if not all of the meniscus. Therefore, an acutely locked knee is a surgical emergency and needs to be dealt with urgently.
The meniscal cartilages have a relatively poor blood supply. There is a ‘plexus’ of capillaries around the peripheral edge of the meniscus, within the capsule, and there are tiny blood vessels that pass into the peripheral edge of the meniscal tissue. However, these only provide a blood supply to the outer/peripheral 1/3 of the meniscal tissue (referred to as ‘the red zone’). Here, the tissue has a reasonably decent blood supply, which means that if you have a peripheral meniscal tear and if you repair it (by stitching the tissue back together), then this has a pretty good chance of healing up successfully. If, however, you have a tear in the inner 2/3 of the meniscus then this tissue has no blood supply (referred to as ‘the white zone’), and hence it is extremely unlikely
to heal up, even if you try and stitch it back together.
On top of this, as you get older, the blood supply to the meniscus tends to diminish and the meniscal tissue tends to become more degenerate, and hence weaker, less elastic, more friable and more likely to tear. Degenerate meniscal tears are common in people over the age of 40, and about 50% of degenerate meniscal tears occur spontaneously, with no history of any specific trauma/injury. The other 50% tend to occur from just minor relatively innocuous things such as kneeling down, squatting, gardening etc.
There are many different ways of trying to describe meniscal tears, and people tend to use the following terms:
• Radial tears
• Horizontal (cleavage) tears
• Vertical tears
• Circumferential tears
• Flap tears
• Parrot beak tears
• Complex tears
• Degenerate tears
• Bucket handle tears
An MRI scan is fairly good at picking up the presence of a meniscal tear in a knee… but not perfect. The accuracy of MRI for diagnosing meniscal tears is probably in the region of 90% (particularly if your scan is done on a high-res 3T scanner, but this figure is probably lower when lower-res 1.5T scanners are used).
CLICK HERE to read about the importance of 3T MRI scanners for diagnosing meniscal tears.
What an MRI is not very good at is determining exactly what type of tear a meniscal tear might be, how extensive it might be, the quality of the tissue (healthy or soft, ragged and degenerate) or, importantly, the potential repairability of the tear. In order to determine the type of meniscal tear and condition of the meniscus, knee arthroscopy (keyhole surgery) is key – as the meniscus can then be visualised and inspected directly, and, importantly, probed (a bit like a dentist using a dental probe to check for cavities in a tooth). It’s only intra-operatively, during the actual keyhole surgery, that a surgeon discovers for sure what the specific nature of an individual meniscal tear actually is, which determines whether it’s repairable or not, and if not then how much tissue might actually need to be trimmed.
It’s far better to repair a torn meniscus, if possible, rather than trim it. However, only a minority of meniscal tears are actually repairable.
The scientific literature is not very clear about this, and it’s difficult to know the exact figures. However, it is generally agreed that probably somewhere in the region of only 15% of meniscal tears are actually repairable. This is not a particularly meaningful figure, however. Meniscal repair is ‘fiddly’ and technically demanding. If you go and see an orthopaedic surgeon who doesn’t do many meniscal repairs then their threshold against doing a meniscal repair will be high, and you’ll be that much more likely to end up having your meniscus trimmed (even if in someone else’s hands it might actually have been repairable).
It is concerning that some orthopaedic surgeons, claiming to be ‘specialist knee surgeons’, do not attempt meniscal repairs – most probably because they can’t! Unfortunately, in these cases, the surgeon simply trims the meniscus regardless of what it looks like. If you’re young and if you’re active and you have a meniscal tear, then it’s extremely important that your tear is actually repaired,
if possible, not just ‘chopped out’ regardless. It is therefore very important that you do your homework and check out in advance the credentials of whichever Orthopaedic Surgeon you might potentially go and see about your knee injury, to ensure that they do actually specialise specifically in knees and that they do have a specialist interest in (i.e. can actually do) meniscal repair. Even better, the most difficult and technically challenging type of meniscal surgery is meniscal transplantation. If your surgeon can do meniscal transplantation then you can be confident that they’re at the top of their game and that if a meniscal tear is potentially repairable then they’ll be capable of repairing it and doing the best possible job.
Mr McDermott regularly audits his work, and even with his particular specialist interest in meniscal repair and meniscal replacement surgery, still only about 33% of the meniscal tears that he sees end up being repaired, at most. This means that even in the very best of hands, a majority of meniscal tears will end up being trimmed, not removed.
CLICK HERE to read more about meniscal repair.
Bizarrely, it’s sometimes said by some (ill-informed) people that ‘arthroscopy causes arthritis’. That’s a bit like saying that ‘pens cause war’, or ‘electricity causes electrocutions, so electricity is bad’! ‘Arthroscopy’ simply means looking (‘scopy’) into a joint (‘arthro’), it doesn’t tell you anything about who’s doing it, what their skillset is, what’s actually found inside the knee or, most importantly, what’s actually done. Any tool in the wrong hands is a potential weapon!
If you chop out a normal meniscus, then yes – that’s not just bad, that’s crazy and that’s actually criminal, because it’s probably assault! However, with most meniscal tears the damage to the meniscal tissue defunctions that part of the meniscus. This means that the damage has already been done. Therefore, the decision as to whether or not to go ahead with an arthroscopy should be based on the level of the individual patient’s potential symptoms.
If you’ve got a meniscal tear in your knee but it’s causing you little or even no actual symptoms, then you’re probably just going to simply leave it alone. If it just hurts a bit with certain movements or activities, and if you can happily enough just simply avoid those particular things, then Option 1 is always to just leave things alone, avoid surgery, wait and watch, and just see how things go. If, however, you’ve got a meniscal tear that’s symptomatic, and if the symptoms are painful / annoying / intrusive enough and if the symptoms are causing functional limitations and preventing you from doing the things that you want / need to do, then you’d be entirely justified in going ahead with a knee arthroscopy to sort things out.
If, at the time of a knee arthroscopy, you find that a meniscal is not repairable, and if you do end up having to perform a meniscal trim (a meniscectomy), then any decent surgeon will only remove as much (as little!) meniscal tissue as necessary in order to get rid of the torn tissue, get the remaining tissue smooth and stable, and eliminate the patient’s symptoms. However, at the same time, you also try to preserve as much meniscal tissue as possible.
A partial trim of a torn meniscus is called a partial meniscectomy. If the whole meniscus has to be removed, then this is called a total meniscectomy.
The more meniscal tissue is damaged and the more your surgeon has to trim away, the more meniscus is lost … and the more meniscus is lost, the less of a load sharer there will then be in that compartment of the knee, and hence the faster the rate of wear and tear, and bigger the potential risk of arthritis in that side of the knee in the future.
The important thing to note here is that it’s not the arthroscopy or the meniscal trim/excision that causes the increased risk of arthritis – if only the torn defunctioned meniscal tissue is removed, then the damage was actually done at the time that the meniscus tore. Hence, it’s not the partial meniscectomy nor the arthroscopy that “causes arthritis”, it’s the fact that the meniscus has actually torn.
When meniscal tissue is trimmed, this reduces the volume of functional meniscus left in the knee. The more meniscus is lost, the less of a load sharer will be left in the knee. This means that there are increased pressures on the articular cartilage surfaces. Again, it is difficult to quantify this accurately, but if a meniscus is removed then the peak contact pressures on the articular cartilage can increase by as much as 235%! The increased pressures on the articular cartilage cause the articular cartilage to fail prematurely, with accelerated ‘wear and tear’. If the cartilage wears away fully, with full-thickness loss, then this will leave bare bone surfaces exposed in the joint, and if the patient ends up with bare bone rubbing on bare bone, then this is what is referred to as osteoarthritis.
It’s difficult to quantify the exact increase in the risk of osteoarthritis that results from loss of a meniscus, because there are so many factors that affect this.
As a ball-park figure, if the whole meniscus is lost then the risk of the patient subsequently developing arthritis in that compartment of the knee increases by a factor of about x 15 (i.e. a 1500% increase!) within the following 20 years.
Nowadays, it’s thankfully not very common that an entire meniscus ends up having to be removed. Prior to the 1980s this was, however, all too common a practice. (It’s only in the 1970s that research began to show that the menisci actually had a function in the knee, and prior to this is was thought that the menisci were just the vestigial remnants of a muscle in the knee that had no actual function. Hence, it was common practice to remove an entire meniscus with the smallest of excuses.) Now that we fully appreciate the true importance of the meniscal cartilages, the aim is to try and preserve as much meniscal tissue as possible. Therefore, partial meniscectomy is far more common than total meniscectomy. If a meniscal tear is not repairable, then we remove as much meniscal tissue as is necessary in order to get the remaining tissue smooth and stable, but leaving behind as much meniscal tissue as possible. Once more, this is a judgement call that can only be made intra-operatively, at the time of the actual knee arthroscopy surgery.
Some tears are more damaging than others. Tears in the inner free margin of the white zone of the meniscus might need just a small trim that might result in just a minor reduction in the function of the meniscus. Full thickness radial tears tend to cut through the circumferential collagen fibres of the meniscus and tend to defunction the meniscus significantly (and unfortunately, it’s rarely ever possible to repair these particular tears). Tears or avulsions of the insertional ligament of a meniscus (usually the posterior insertional ligament) can also completely defunction a meniscus (if these are caught early, then these can sometimes be repaired).
If you have a meniscal tear that’s not actually causing any significant symptoms (i.e. there may be some minor intermittent discomfort, but no actual pain per se and no mechanical symptoms, such as catching, giving way or locking, and if there are no significant functional restrictions) then unless there are good reasons to the contrary, it may be difficult to justify going ahead with surgery.
The potential arguments for going ahead with an arthroscopy for a meniscal tear even if the symptoms are relatively minor, are that:
However, there’s a lot of ‘may’s and ‘might’s there in this list! Alternatively, if you leave a minimally symptomatic meniscal tear alone and if you’re sensible and careful with your knee, then even though the tear itself is extremely unlikely to heal, the symptoms can sometimes just gradually resolve with time.
What’s important with surgery of any kind is always to balance the potential benefits against the potential negatives and risks. The negatives of arthroscopy are:
The decision as to whether or not to go ahead with a knee arthroscopy is sometimes very obvious and clear-cut. However, in many instances the decision may not be so easy. This is why it’s terribly important that you have a full and detailed assessment of your knee by a proper specialist and that you’re given a clear, specific, detailed diagnosis of exactly what’s going on in your knee and a clear and full explanation of your options and the associated pros and cons, the risks and the various potential consequences. Crucially, the only true knee specialist is a Consultant Orthopaedic Surgeon who specialises specifically in knees – and even then, there is a huge range of expertise and ability between different consultants; you absolutely can’t assume that all consultants are the same, because they’re most certainly not – so, do yourself a very big favour and do your research properly, and take enormous care in picking the best knee surgeon to go and see, not just ‘the local guy’ because he’s convenient or ‘the cheap guy’ that your insurance company might want you to see, simply to save themselves a small amount of money.
Given all the negative consequences of meniscal loss, the obvious thing with any meniscal tear is to try and repair it if you possibly can.
It’s difficult to know the exact figures, as the data’s just not readily available, but generally most people would tend to agree that only about 15% of meniscal tears are actually repairable. The reason that this figure is not really particularly reliable or meaningful is that the probability of any meniscal tear being repairable depends on a number of specific factors. Therefore, it’s better to give each individual patient a personalised specific opinion rather than just a population-based generalisation.
The main factors here are:
The sooner a meniscal tear is caught, the better the chance that it’ll be repairable. The longer you leave a meniscal tear, the bigger and more ragged the tear is likely to get, the less likely it’ll be that it’ll be repairable, and if it does end up needing to be trimmed then the more tissue is likely to have to be removed.
There’s no specific didactic cut-off here, but the older a person is over 40, the poorer one’s healing potential, plus the more likely it is that the meniscal tear will be degenerate (and hence ragged, with a poor blood supply), and hence the less likely it’ll be that a meniscal tear will be repairable. On top of this, not only are tears in younger people more likely to repairable, but the younger someone is, the more important it is that their meniscus is saved, because the consequences of meniscal loss are that more grave in younger, more active people.
Type of tear:
Ragged complex tears, radial tears and flap (parrot beak) tears are rarely repairable. Degenerate tears are also rarely ever repairable. A majority of horizontal tears are actually degenerate tears; however, some horizontal tears can sometime be repairable (or at least just partly trimmed and partially repaired). Importantly, you can only ever really tell the exact morphology of a meniscal tear and the state of the actual tissue intra-operatively, at the time of an actual arthroscopy. Hence, the decision as to whether to trim the meniscus or whether to repair it is something that is, more often than not, down to the judgement of the surgeon at the time of the actual surgery.
The more one is ‘into’ a specialist subject like ‘knees’, and the more experience one has, then the more likely it will be that as a surgeon one will have the skillset required to be able to perform a good meniscal repair. I audit my work regularly, and in my hands I personally repair somewhere between 25% to 33% of the meniscal tears that I see. That means that even in the hands of a dedicated specialist expert, still only a minority of meniscal tears are actually repairable. What is of most concern is that surprisingly, there are still Orthopaedic Surgeons out there doing knee arthroscopies who cannot, and therefore do not, perform meniscal repair. This means that if you’re unlucky enough to see one of them then your meniscus will definitely be trimmed, even if your tear was actually repairable! It is therefore extremely important that as a patient you do your homework carefully and you ensure that you know as much as possible about the experience and specialist skill-set of whichever surgeon you might end up going to see about your knee.