Meniscal replacement surgery


Mr Ian McDermott
Consultant Knee Surgeon
London Sports Orthopaedics

Meniscal tears

The menisci (meniscal cartilages) of the knee are two crescent-shaped wedges of elastic cartilage that sit inside the knee between the bones of the femur (the thigh bone) and the tibia (the shin bone), and that act as load sharers and shock absorbers in the knee.

Meniscal tears are very common. In younger people the menisci only tend to tear with specific trauma, such as twisting on a bent knee (football, skiing etc). In older people the menisci tend to become degenerate, and they tend to lose their elasticity and strength, and they become weaker and more liable to tear; and 50% of degenerate meniscal tears in older (40+) patients can occur spontaneously, without any specific trauma.

Meniscal tears tend to cause any potential combination of the following symptoms:

– Pain (tends to be a sudden sharp intermittent pain, particularly with any kind of twisting through the joint)
– Painful clicking / catching sensations
– Giving way
– Locking
– Swelling
– Pain and difficulty with deep flexion (particularly with pain at the back of the knee with forced deep flexion, such as trying to sit back on one’s heels when kneeling on the floor)

If a meniscal tear is symptomatic enough and if the symptoms are not improving with time, then an arthroscopy (keyhole surgery) may be required. This is a relatively simply day-case procedure under a quick anaesthetic with very low risks.

When a meniscal tear is found arthroscopically, at the time of surgery, it is inspected and probed. The tear is then either trimmed (with any torn/unstable tissue being removed) or repaired (stitched back together), depending on whatever looks most appropriate and feasible at the time of the operation. The success rate for meniscal repairs healing is about 90%. However, unfortunately only about 15% to 30% of meniscal tears are actually repairable (depending on the average age of the patient cohort and on the skill-set of the particular surgeon). The most important thing that any younger patient with a meniscal tear can do is to ensure that they see an orthopaedic surgeon ASAP, and that the person they go to see is specifically a knee specialist (not a generalist) and that their surgeon can and regularly does actually perform meniscal repairs. Perhaps surprisingly, and certainly very worryingly, there are still significant numbers of orthopaedic surgeons out there who are performing knee arthroscopies but who never (because they can’t!) repair a meniscus – if you’re unlucky (or silly) enough to see one of them then your torn meniscus will simply be removed, even if it was repairable! (So do your homework and do your research on your surgeon!)

If a meniscal tear is trimmed then this should cure whatever symptoms might have been coming from the torn meniscus. However, this will not restore the function back to the damaged meniscus. The bigger the tear and the more tissue ends up being defunctioned/lost, the less of a shock absorber there will be in the knee, and hence the greater the forces will be on the articular cartilage layers covering the surfaces of the bones in that part of the knee. Increased forces on the articular cartilage leads to increased wear and tear, which eventually leads to degenerative changes in the joint, with thinning and eventual loss of the articular cartilage. Ultimately, if the articular cartilage wears away completely then this will leave bare bone exposed in the joint, which = arthritis.

If an entire meniscus is lost, the the future risk of arthritis in that knee increases by approximately a factor of 15 by a point 20 years later (i.e. a 1500% increased risk!). Losing the lateral meniscus has a greater negative effect than losing the medial meniscus (although medial meniscal tears are more common), and the younger someone is when they lose their meniscus the worse the longer-term consequences, particularly in young active sporty people.

If a patient starts to develop premature degenerative changes in one compartment (side) of their knee as a result of previous loss of a meniscus, then it is sometimes appropriate to consider meniscal replacement surgery.

Meniscal scaffolds

If enough of a meniscus is lost to be significant and to cause problems, but if not the whole meniscus is missing and if the peripheral rim is still fully intact, all the way from the front of the meniscus to the back, then it is possible to replace the missing meniscal tissue with a meniscal scaffold.  The two main types currently available are the Menaflex implant and the Actifit implant. The Menaflex is made from bovine (cow) tendon and is made of collagen, whereas the Actifit is a synthetic scaffold made from polyurethane. With these scaffolds, the scaffold is cut to size to fit the size of the defect in the meniscus, and the scaffold is surgically fixed in place by stitching the scaffold to the native meniscal remnant. New meniscal-like tissue then grows into the scaffold (i.e. not actually normal meniscal tissue).

Studies have shown that implanting a meniscal scaffold can reduce a patient’s post-meniscectomy knee symptoms, but it is important to appreciate that this does not give the patient a perfect new normal meniscus.

The results of meniscal scaffold surgery have been variable, at best, with a significant percentage of failures having been reported. Whilst the future may well lie with the field of 3D-printed patient-specific scaffolds and tissue engineering with stem cells and growth factors, unfortunately the current technology falls way behind this, and at present the use of meniscal scaffolds has not really gained much popularity with UK surgeons, due to the concerns regarding poor outcomes.

Meniscal transplantation

The current gold-standard for replacing a missing meniscus is to simply replace the missing meniscus with a proper new meniscus – from a donor, which is called an allograft. Meniscal allografts come from people who sadly have died and who have donated their organs. The donors are screened carefully, and if they are in any high risk categories or if they have suffered any specific infections then the tissue is not used. The donor’s blood is also tested for bacteria, viruses and fungi, including hepatitis and HIV – any positives, and the tissue is simply not used. The donor tissue itself is also tested – any positives, and it’s not used. Assuming the donor tissue passes all of the above, then the tissue itself is sterilised and deep frozen. The risk of having a contaminated graft and of disease transmission has been estimated to be in the region of about 1 in 1.6 million (i.e. you’re probably more likely to get run over by a bus on your way home from hospital than receive a contaminated graft!).

There are no living cells in a donor meniscus, and any cellular material that is present is locked within a dense cartilage matrix so that the recipient’s immune system does not identify or attack them, and the structure and make-up of cartilage is the same in everyone. Therefore, anyone can have anyone else’s meniscus without the need for tissue typing/matching and without the need for steroids or immunosuppressives, and donor meniscal tissue is not rejected – hence it is referred to as ‘immunoprivileged tissue’. One simply has to match right vs left and medial vs lateral, and one also has to correctly match the size of the donor meniscus to the required size for the patient’s knee (which is normally done from X-rays with size-markers).

Meniscal transplantation is a fairly major complex operation, which should only be undertaken by experienced specialist knee surgeons with the appropriate training, and there is a significant learning curve involved. In the appropriate hands, the surgery tends to take about 2 to 2½ hours, and it is normally performed under a general anaesthetic with a 1-night post-op hospital stay. There are potential risks (as with any operation), such as infection, nerve or blood vessel damage, or blood clots – and these should be discussed in detail directly with your surgeon.

The rehab required after meniscal transplantation is slow, restrictive and lengthy. Patients are normally kept on crutches for the first 6-week period, with the knee in a hinged brace locked at 0 to 90 degrees flexion. By the end of this period the knee will be stiff, the muscles will inevitably be wasted and the patient will have lost their strength, their reflexes and their fitness. After this first 6-week period, an extensive period of regular physiotherapy rehab treatments will be required, and it normally takes most people about 6 to 9 months to feel that they have fully got over the surgery.


Biomechanical studies have shown that implanting a new meniscus into a meniscus-deficient knee increases the contact surface area in the joint and decreases the peak contact pressures on the articular cartilage. Clinically, meniscal transplantation has been demonstrated to reduce patients’ pain, to improve their function and to help them keep their knees going for longer, delaying the time when artificial joint replacement surgery might become necessary.

It is very difficult to put specific figures on the outcomes after meniscal transplantation surgery, because the surgery tends to be performed on such a widely disparate cohort of patients who often have multiple things wrong with their knee, and the meniscal transplantation surgery is frequently combined with other concomitant procedures.

However, as a general rule of thumb, about 85% of cases are still deemed ‘successful’ when looked at 5-years post-op, about 70% are still deemed a success after 10 years, and maybe 25% or so by 25 years post-op (meniscal transplantation is not, in most people, a long-term solution). Importantly, the more ‘other things’ are wrong in the joint and, in particular, the worse the damage is to the articular cartilage, then the worse the outcome from meniscal transplantation is likely to be.

Importantly, a meniscal allograft is better than having no meniscus, but it is never as good as the patient’s own native original meniscus. Also, meniscal transplantation does not reverse the articular cartilage damage that is already present in a knee. Therefore, one really should consider meniscal transplantation as just ‘salvage’ surgery, and not ‘restorative’.

Should you go back to sport after meniscal transplantation?

This is a golden but highly contentious question!

Some surgeons state that 70%+ of their patients get back to sport after meniscal transplantation. However, one should remember that a new meniscus is never as good as the patient’s own original meniscus, plus meniscal transplantation does not reverse the damage that is already present in a joint, and it simply slows down the progression of the articular cartilage wear and tear. The best way to ensure that a meniscal transplant succeeds and that the longer-term outcomes are good is to protect the knee, which means not pounding the joint with heavy weights, loaded twisting/pivoting and impact – which means not going back to running and not returning to sport.

This concept generates quite a lot of stress and upset with patients. Some surgeons espouse the virtues of sport, emphasising the health, social and psychological benefits. My personal opinion, however, is that they are perhaps taking the easier option in the short-term by simply telling the patient what they want to hear (rather than what they need to hear), and perhaps pandering to the patient’s desires and aspirations rather than emphasising to them the true harsh realities. My personal approach is very clear and very specific:

– Meniscal transplantation is salvage surgery, designed to reduce symptoms, to allow people to do regular non-impact cardio fitness exercise (in order to stay fit and healthy) and to keep people’s knees going for longer, delaying the probable eventual need for knee replacement surgery in the future anyway.
– A meniscal allograft is never as good as the patient’s own original meniscus.
– Meniscal allograft transplantation only partial restores the normal biomechanics back to a joint, but not fully.
– Meniscal transplantation does not reverse whatever wear and tear / degeneration there might already be in a knee joint.
– If you go through all the pain, risk and hassle of meniscal replacement surgery then the only sensible way forward is to protect your knee and to protect the graft, to give yourself the best possible chance of hopefully achieving a better long-term outcome.
– You shouldn’t subject your knee to heavy weights, loaded twisting/pivoting or impact after meniscal transplantation.
– Therefore, you should not return to running or sport after meniscal transplantation surgery.

When to have a meniscal transplant

The perfect patient for meniscal transplantation surgery fulfils all of the following criteria:

– The patient has lost most or all of their meniscus, or there is a significant segmental defect that extends to the peripheral meniscal rim (i.e. the meniscus has been de-functioned).
– The patient is beginning to develop early premature degenerative changes in that compartment of the knee from where the meniscus was lost.
– The patient is suffering significant symptoms from that compartment of the knee, with pain and functional impairment.
– Any articular cartilage damage is only partial thickness.
– The knee is stable.
– The joint alignment is good.
– The patient is too young for artificial knee joint replacement surgery to be an appropriate option.
– The patient is able to cope with the rehab that will be required after the surgery, they have realistic expectations about likely outcomes and they understand that they should protect the knee for good after their surgery and not return to impact/pivoting exercise or sport.

It is difficult to advocate meniscal transplantation surgery in a patient who has lost their meniscus but who is actually asymptomatic. If a patient has symptoms, and in particular if the symptoms feel like they are getting worse with time, and especially if imaging shows that there are early degenerative changes beginning to develop in that compartment of the patient’s knee, then it is often easy to justify the pain, the hassle and the potential risks of meniscal replacement surgery. The one situation where this does not necessarily apply is in children, adolescents and young adults…. The younger someone is then the longer they are likely to live and the more years of loading and hence wear and tear their knee is likely to be subjected to. The consequences of meniscal loss are significantly greater in younger more active people. Therefore, there is actually a reasonably strong argument for advocating early prophylactic meniscal replacement in a younger person who has lost a meniscus (and particularly so for the lateral meniscus), in order to protect and preserve the articular cartilage on the joint services instead of just waiting for the damage to develop and only then replacing the meniscus, once the damage has already developed.

Other concomitant procedures

Meniscal transplantation is contraindicated in unstable knees or knees with malalignment.

Ligament instability / reconstruction:

If the knee is unstable (for example, with an ACL tear) then a ligament reconstruction should be performed to stabilise the joint either prior to the meniscal replacement surgery or else at the same time.

Likewise, if there has already been an ACL reconstruction in the knee but if the ACL graft is suboptimal and slack, then this might need to be revised prior to or at the same time as the meniscal transplant surgery.

Malalignment / realignment osteotomy:

If there is malaligment in the leg then this can also be a significant issue. If there is loss of cartilage from the medial compartment and if there is medial joint space narrowing, then the knee may develop a varus deformity (bow-legged), which simply further overloads the medial compartment. Likewise, if there is cartilage loss in the lateral compartment and lateral joint space narrowing then the knee may develop a valgus deformity (knock-knees), which will overload the lateral compartment. If you put a meniscal allograft into an overloaded compartment then the graft is far more likely to fail.

It is therefore important to carefully assess the lower limb alignment prior to meniscal replacement surgery, and any relevant / significant deformity should be corrected with a realignment osteotomy. This can sometimes be done at the same time as the meniscal transplantation surgery; however, realignment osteotomy is a major procedure and it would normally tend to be performed separately, ahead of any meniscal replacement. Importantly, if a patient gets good symptomatic relief from offloading the damaged compartment in their knee through realignment surgery, then they might actually choose not to bother proceeding with the meniscal replacement surgery if their knee then feels ‘good enough’, which is another good reason for performing any potential realignment surgery as a separate operation, ahead of any potential meniscal replacement.

Articular cartilage loss / replacement:

It is very important to assess the state of the articular cartilage in a knee prior to committing to meniscal replacement surgery.

The worse the damage is to the articular cartilage in that compartment of the knee, the lower the probability of a good long-term outcome from meniscal transplantation surgery. In particular, if there is full thickness articular cartilage loss with bare bone exposed then this will macerate and tear the meniscal allograft, and there is little point in proceeding with the meniscal replacement surgery unless something is also done about the articular cartilage loss.

If there is just partial thickness articular cartilage damage (which is very common, as this is one of the main indications that justifies proceeding with meniscal replacement surgery), then this can be smoothed off and stabilised by radiofrequency chondroplasty at the time of the meniscal transplantation surgery.

Small (<2cm2) patches of full thickness cartilage loss can be treated quite effectively with microfracture.

However, if there are larger areas of full thickness cartilage loss with bare bone exposed then microfracture is unlikely to work well, and in this instance it is normally better to proceed with articular cartilage grafting.

There are a number of different techniques for articular cartilage grafting. However, the technique that I personally use is Chondrotissue grafting.

Importantly, articular cartilage grafting will fail if it is performed in a compartment of a knee where there is no meniscus to protect the articular cartilage graft. Likewise, meniscal transplantation will fail if there is full thickness articular cartilage damage in that compartment of the knee, with bare bone exposed. Therefore, if both the articular cartilage and the meniscus are missing in a compartment of a knee then both need to be replaced simultaneously for the patient to have any hope of achieving a successful outcome.

Even though it is not generally recommended (because of the associated poorer outcomes), it is actually possible to replace the articular cartilage on both sides – the femur (upper) and the tibia (lower) – of a compartment at the same time as performing a meniscal transplantation. However, this is an ‘extreme’ reconstruction, and if this is to be performed then it is important that the patient fully understands the magnitude of the surgery and the increased risks of potential failure compared to a simpler less complex reconstruction.

Is my knee suitable for meniscal transplantation?

The decision as to whether to reconstruct a knee, and if so then exactly how, is a difficult and complex thing, and not something that be decided upon simply from reading a website or reading some papers. It is also not something that can or should be done remotely, just via e-mail. What’s required is a full detailed face-to-face assessment, including your surgeon taking your full past history, performing a detailed clinical examination, and reviewing a full set of up-to-date imaging.

The imaging that is normally required (as a minimum) is:

– Weight-bearing X-rays with size markers
– Long-leg alignment X-rays of both lower limbs if there is even the slightest suspicion of possible malalignment
– A high-res high quality (preferably 3-Tesla) MRI scan

Then, you and your surgeon will need a full detailed discussion about exactly what surgery might actually be indicated, along with a full discussion about the potential risks, the rehab that will be required and the anticipated success rates that might be anticipated.

Hopefully, you should be able to appreciate from this, this is not something that can or should be rushed, and it required care, time and attention (and not a ‘conveyor belt surgeon’!)

Importantly, only a small number of surgeons in the UK actually have any proper experience with meniscal transplantation surgery, and even fewer have proper experience with combining meniscal replacement with other concomitant reconstructive procedures such as simultaneous articular cartilage grafting. Therefore, you need to do your homework and you need to ensure that you see the right surgeon for the right job – all surgeons are most definitely not the same!



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