By: 5 July 2017
The future of knee surgery lies in biological reconstruction

Mr Ian McDermott, Consultant Orthopaedic Surgeon specialising in knees and sports injuries, is looking forward to an exciting future in knee surgery through biological reconstruction.

Things have come a long way since arthroscopy was first introduced to the UK back in the 1970s. Surprisingly, there are still some who see arthroscopy as a 10-minute procedure to be done on a rushed conveyor-belt of a list, with just a “washout” and a “quick trim” being the limit of their skillset before they resort straight to artificial knee replacement surgery. This is what those of us in the know refer to as “bipolar knee surgeons”!

The reality is that at the other end of the spectrum there are a number of specialist knee surgeons who are now regularly undertaking major complex reconstructive surgery in people’s knees, with highly encouraging results.

The most common thing that one tends to see as a knee surgeon is meniscal tears. The menisci are “shock absorbers” and load sharers in the knee, and they sit in between the bones like two rubber washers. However, when subjected to the high compressive and shear forces in a knee joint, the menisci can and often do tear, which can cause pain, clicking, catching, giving way, locking and swelling in the knee. If a meniscal tear is symptomatic then it is likely to need surgery, and unfortunately only a minority of meniscal tears are repairable.

The literature suggests that maybe only about 15 per cent of tears are repairable. However, if you see a proper specialist soft tissue knee surgeon with an interest in meniscal repair, then you’re more likely to have your meniscus repaired rather than excised, and in my hands about 33 per cent of the meniscal tears that I see arthroscopically end up with a repair. This still means that a majority of tears cannot actually be repaired, which means that instead they will end up being trimmed.

The more severely a meniscus is damaged, the more meniscal tissue will need to be trimmed if it is not repairable, and the more meniscal tissue will be lost. With this, the less of a shock absorber is then left in the knee, the greater the probability will be that the patient will develop wear and tear and eventually arthritis in that compartment of their knee at some stage in the future.

In the past, patients with meniscal loss who were starting to develop premature degeneration in their knee were simply told to put up with the symptoms for as long as they could, with a view to them eventually ending up having a knee replacement when they were older (normally 50+). Nowadays, however, we do actually have very good potential surgical solutions for these patients, which we are now able to offer. The obvious thing if someone is developing problems in their knee due to loss of a meniscus is simply to replace the meniscus with a new one, and this is exactly what we are doing nowadays with meniscal transplantation.

Meniscal transplantation involves taking a meniscal allograft from a donor. Tissue is taken by specialised retrieval teams from deceased people who have offered their organs for donation. The donors are screened and tested very carefully for potential transmissible diseases, the donors and the donor tissue is tested, and then the donor tissue is sterilised and deep frozen. The risk of disease transmission in a donor meniscus has been estimated at approximately 1 in 1.6 million. Also, there are no living cells in the donor meniscus, and the meniscus itself is made of collagen, and everyone’s collagen is the same. Therefore, there is no rejection (the tissue is referred to as “immunoprivileged”), and so you don’t have to do tissue typing or use steroids or immunosuppressives, and anyone can have anyone else’s meniscus as long as it’s the correct knee (left vs right), the correct side of the knee (medial vs lateral) and the correct size (the donor meniscus is sized carefully to match the patient’s knee size).

The surgical procedure of meniscal transplantation is fairly major and complex, and it is a procedure that is only undertaken by a very small number of specialist knee surgeons in the UK. The number of surgeons doing this surgery regularly, with decent numbers and experience is even smaller, and I believe that there are actually only maybe two or three of us in the UK who have performed more than 50 meniscal transplants each so far. This is something that I myself have been doing since 2008, and to-date I’ve performed more than
80 procedures. The rehab is very slow and restrictive, but the results are highly encouraging, with a success rate in the region of about 85 per cent at five-year follow-up.

Meniscal transplantation is not perfect, and it will not reverse whatever articular cartilage wear and tear the patient might already have in their knee, but it is an awful lot better than leaving the patient with nothing and just telling them to go on suffering until they’re bad enough for a knee replacement.

The other kind of cartilage in a knee joint is the articular cartilage, which is the thin white shiny layer of tissue that covers the joint surfaces and makes the surfaces smooth and low friction, to reduce wear and tear. If a patient loses a patch of articular cartilage in their knee, this will cause pain and swelling, and if there are loose bits then these may cause giving way or locking. Also, leaving patches of damaged articular cartilage in a joint will simply result in progression of the damage, which then becomes more widespread. When there is widespread cartilage loss with bare bone exposed and with bone rubbing on bone, then this is “osteoarthritis”, and if the damage is severe enough then the patient might then be looking at artificial joint replacement surgery.

The problem with knee replacements in younger patients is that younger people do more, and hence the rate of wear and tear on the artificial joint will be faster, which means that it will wear out quicker. Also, the younger someone is when they have a knee replacement the longer they are likely to live. This is a “double-whammy”, and it means that knee replacement in younger people is associated with a significantly higher probability of the prosthesis failing within the patient’s lifetime and needing revision (and a revision knee replacement is an even bigger and more difficult operation than a primary, with a poorer outcome).

So, if you see significant articular cartilage damage in a knee joint in a younger person then it absolutely makes sense to treat it proactively rather than just wait for the damage to get worse. Rough or unstable areas of partial thickness damage can be smoothed off and stabilised very effectively by radiofrequency chondroplasty (which “melts” the surface of the cartilage and “welds” it down). Small patches of full thickness damage/loss can be treated with microfracture, which involves puncturing the surface of the bone to allow blood, bone marrow and stem cells to promote healing with fibrocartilage (which is half way between normal cartilage and scar tissue). However, microfracture does not give good results with larger areas of damage (>2cm2) plus with time the results of microfracture tend to drop off, especially after the first five years or so.

For larger areas of articular cartilage loss there is now a variety of types of cartilage graft available for replacing the missing tissue. I personally have been using Chondrotissue for the last five years now. This is a bioabsorbable synthetic scaffold of woven polyglycholic acid impregnated with hyaluronic acid. The defect is first microfractured and the Chondrotissue graft is then cut to size and pinned into the defect using bioabsorbable ActivaNail chondral darts. The surface of the graft is then covered over with a layer of Vivostat PRF (platelet-rich fibrin), which is an autologous bioabsorbable bioactive biological glue. This encourages new cartilage tissue to grow into the scaffold and the scaffold just gradually gets absorbed with time.

Again, articular cartilage replacement surgery is complex, and this is specialised surgery that is only offered by a relatively small percentage of knee surgeons. The surgery is difficult and the rehab is slow, but the results are good, with a success rate in the region of about 80 per cent at five-year follow-up.

If you’ve lost a meniscus and you’ve got articular cartilage loss as well, then this is an extremely difficult issue to address. If you replace a missing meniscus but you don’t properly address the issue of the missing articular cartilage, then the exposed bare bone on the joint surface will wreck the meniscal allograft, and the surgery is very likely to fail. Likewise, if you put an articular cartilage graft into a knee where there’s no meniscus to protect the joint surface, then the cartilage graft is very likely to fail. Therefore, if you’ve got both meniscal loss and articular cartilage loss in the knee of a younger person who is too young for joint replacement surgery, then it is possible (and sensible) to replace both the meniscus and the articular cartilage at the same time – and this is what is referred to as a Biological Knee Replacement.

If there is ligament damage as well and the knee is unstable, then a ligament reconstruction can also be undertaken too. If there is deformity and malalignment, then the knee can also be realigned with a tibial or femoral osteotomy. Very occasionally, it might be necessary to perform most or even all of these reconstructive procedures together, all at the same time. This can be extremely complicated and difficult surgery, sometimes lasting as long as four-and-a-half hours; however, doing just part of the job but just ignoring or neglecting other elements will simply condemn the patient to a poorer prognosis and a higher likelihood of failure. Therefore, sometimes it really is a case of “all or nothing”.

Those of us undertaking this kind of “extreme reconstruction” of the knee are constantly striving to achieve better and better results in more and more difficult knees, and the next step in the evolution of this kind of surgery will be the introduction of stem cells; not just loosely into the knee with simple injections, but in combination with grafts and scaffolds, as part of a combined approach of surgical reconstruction, implantation of stem cells and promotion of healing with growth factors. This is not the kind of thing that is currently widely available, and this kind of advanced surgery is something that should very much be the remit of just a small number of specialist centres.

To promote the evolution of this kind of cutting-edge knee surgery, a group of specialist knee surgeons with a passion for complex reconstruction have set up the UK Biological Knee Society as a study group to support the dissemination of best practice (

The BKS was created over three years ago now and has had three major annual meetings, with the last meeting in Cardiff seeing 50 knee surgeons in attendance and presentations from some of the UK’s leading knee surgeons on topics such as: meniscal scaffolds, osteochondral allografts, articular cartilage grafting, focal resurfacing implants and stem cells, and with an excellent debate about the procurement and processing of allografts.

It’s clear that there is a significant body of younger surgeons who don’t believe that a 10-minute “arthroscopic washout” is an appropriate or acceptable thing, and who have evolved way past the attitude of just “chop it out or neglectfully leave it to get worse”.

The future of knee surgery lies in biological reconstruction, with allografts, with 3D printed biological scaffolds, with tissue engineering, growth factors and stem cells. There are still some surgeons out there who are not even doing MRI scans before performing arthroscopies on their patients. Others of us are not just along for the ride, but are pushing the field forward and helping develop the portfolio of techniques that are available. What’s clear is that knee surgery in the future will be a very different thing from what it is currently, and the future is set to be extremely exciting.


Mr McDermott is one of the UK’s leading experts in Biological Knee Reconstruction, combining highly specialised techniques such as meniscal transplantation and articular cartilage grafting. He was the
first surgeon in the UK to use Vivostat PRF autologous bioactive biological glue in knees and he was also the first surgeon in the UK to perform a Conformis G2 iUni custom-made knee replacement. He now trains other surgeons in these techniques and is a designated Centre of Excellence for training. He is also the President of the UK Biological Knee Society.