Biological Knee Replacement


  • Tearing of one of the meniscal cartilages is probably the most common reason for a patient ending up having to see a knee surgeon.
  • Only 25% or so of meniscal tears are repairable; 75% are not.
  • If a meniscal tear is not repairable and if it is causing significant symptoms then it is likely to end up needing to be treated with a knee arthroscopy, to trim the torn meniscus smooth.
  • The more meniscal tissue is lost, the less of a shock absorber there is in the knee, and therefore the bigger the potential risk of wear and tear developing and progressing to fully blown arthritis in the joint.
  • If a patient has lost their meniscus and they have gone on to develop degenerative changes, with areas of bare bone exposed in that part of the knee joint, then they are likely to end up needing a knee replacement.
  • Knee replacement is a big operation that should only be undertaken as a last resort, and preferably only in older (>50 at least) patients.
  • Up until recently, those patients suffering degeneration in the knee secondary to meniscus loss had no real options available to them except a tibial osteotomy (which is a big op to cut and realign the shin bone) or else they would simply have to live with their symptoms and just cope, until such time as they felt that they simply had to proceed with a knee replacement.
  • Techniques are now available whereby the joint can be reconstructed ‘biologically’ (i.e. without the need for an artificial knee replacement).
  • A missing meniscus can be replaced by meniscal transplantation.
  • Areas of worn away articular cartilage with bare bone exposed can be treated by covering the bone surfaces with a Chondrotissue articular cartilage graft.
  • These procedures can be combined to give the so-called ‘Biological Knee Replacement’.
  • Mr McDermott was the first surgeon in the UK to undertake this highly specialised technique.
  • The surgery is big and complex, but has a reasonably good success rate for reducing patients’ pain, improving their function and keeping their knee going for longer, thereby delaying the time when a knee replacement might become necessary.
  • There are very specific indications for who might actually be suitable for this kind of surgery, and the ideal patient is young, with a stable joint (if the knee is unstable then missing ligaments can also be reconstructed), and the knee alignment must be reasonably good.



Over the last few years, a gradual succession of technological advances has given knee surgeons new additional options for offering some patients effective treatments, where in the past either no suitable solutions or only suboptimal options might have been available. ‘Biological knee replacement’ for the treatment of severe knee damage in younger patients is a prime example of this.

Osteoarthritis of the knee is a very common problem, and can cause severely debilitating symptoms, with pain, stiffness, swelling and immobility. Primary osteoarthritis is partly genetic and partly due to age-related wear and tear. Secondary arthritis is where premature degeneration develops in a joint after previous trauma/damage. The only current truly effective treatment to cure primary osteoarthritis in a knee joint (when the symptoms get bad enough to justify it) is artificial knee joint replacement.

Knee replacement surgery is highly effective. However, the younger a patient with a knee replacement is, the more they will use the joint and the bigger the forces will be, and therefore the faster the rate of wear and tear. On top of this, younger patients are going to live longer. Therefore, the younger a patient is at the time when an artificial knee joint is put in, the more likely it is that the joint will eventually wear out and fail and need replacing – a revision knee replacement. Revision knee replacements are more difficult than a primary (first time) knee replacement: it is a longer operation with more bone loss, a higher complication risk, lower patient satisfaction scores and functional scores, and they tend not to last as long as a primary joint replacement. Therefore, if revision knee replacement can be avoided, it should be – and the best way to avoid this is to delay the timing of the surgery and try to reserve artificial joints only for older patients. There is no specific age cut-off for old vs young, but to try and quantify the age-related risks: if a knee replacement is put in in a patient in their 70’s, then there is a risk of only 5% of the prosthesis failing within that patient’s lifetime; if a knee replacement is performed in a patient in their 50’s, then there is an approximately 50% probability that the joint will need revising within the patient’s lifetime.

This therefore leaves us with a group of patients who have severe damage in their knee at a younger age that has developed secondary to previous joint damage (meniscal tears and meniscal loss, cruciate ligament ruptures, articular cartilage damage), who are getting severe symptoms, but who are too young for artificial joint replacement surgery. This is the specific patient group for whom we are now able to offer ‘biological knee replacement’ as a viable option.

The term ‘biological knee replacement’ was coined by the Americans (by Dr Kevin Stone, from San Francisco, who is one of the world’s leading surgeons in this field). It refers to the replacement of missing meniscal cartilage tissue by meniscal allograft transplantation, combined with treating articular cartilage defects (grade III to IV lesions) at the same time. It is not designed to restore the knee back to normal, but instead the aim is to decrease patients’ pain levels, increase their function, keep them going for longer and delay the time when they are eventually likely to end up needing a joint replacement anyway.

The major advantage that we have in the UK over some of the techniques being used in the U.S. is that in the U.S. the FDA has failed to approve yet many of the newer treatments for articular cartilage transplantation / grafting that have been approved for use in the E.U., and this includes technologies such as ACI/MACI and Chondrotissue grafting.

Mr McDermott was the first surgeon in the U.K. to combine meniscal allograft transplantation with Chondrotissue articular cartilage grafting.

Who is suitable?

This kind of surgery is complex and difficult, and there are very specific inclusion and exclusion criteria, as to who might or might not be a suitable and appropriate candidate.

The ideal candidate:-

  • Young (but with no specific cut-off)
  • Active, (but not intending to continue with ‘knee-unfriendly’ high-impact type exercise/sport, such as football, squash etc.)
  • Previous loss of a meniscal cartilage (from having the cartilage surgically removed/trimmed after a previous tear).
  • Signs of damage to the articular cartilage in the joint, in the same compartment (region) of the knee joint as where the meniscal cartilage is missing from.
  • Significant symptoms / functional restriction that is getting progressively worse with time.
  • A stable knee joint with good alignment.

Exclusion criteria:-

  • Old enough to be within the realms of acceptable for joint replacement surgery (50s+, but with no specific cut-off).
  • Widespread damage affecting the whole joint, rather than just 1 damaged compartment.
  • Deficiency of any ligaments in the knee, such as the ACL (i.e. any instability); in which case the knee ligament(s) will need to be reconstructed first (it is sometimes possible to reconstruct any missing ligaments at the same time as meniscal transplantation and articular cartilage grafting, although this is an even more major undertaking).
  • Malalignment of the joint i.e. valgus or varus deformity (knock-kneed or bow legged), in which case the joint may first need to be realigned, e.g. with a tibial or femoral realignment osteotomy (cutting one of the bones on one side of the knee, changing the angle to straighten the joint, and then fixing the bone with a metal plate and screws to allow it to heal straight).

Why do age and severity matter?

Advising against Biological Knee Replacement in older patients is not ageism! … it is simply that the older you are the poorer your healing potential and therefore the lower the likelihood of a positive outcome after this kind of complex biological surgery, which relies very much on the body’s healing and regenerative powers.

Also, if the damage in a knee joint is too severe then this will also significantly decreased the probability of success.

Biological Knee Replacement is a very major undertaking; it is big complex surgery that has significant potential risks, that requires very careful slow rehab, that takes a long time to fully recover from and that does not come with any guarantee of success. Therefore, it is not something to be entered into lightly, and it is essential to pick and choose very carefully those patients who are actually proper appropriate candidates who fulfill all the relevant inclusion and exclusion criteria.

The rehab

The rehabilitation after this kind of major complex soft tissue reconstructive knee surgery is slow. It is important to protect the joint, to allow the meniscal allograft and the chondral graft to heal in properly before getting the knee moving and getting going. Therefore, for the 1st 6 weeks post-op we protect the knee with crutches and a knee brace. Also, it is important to avoid overly stressing the joint whilst the grafted tissues are ‘bedding in’ and maturing. Therefore, heavy weights, loaded twisting and impact are prohibited until at least 9 months post-op.

The rehab after Biological Knee Replacement follows the same protocol that is used for isolated meniscal transplantation.

The results

Probably the best indicator of longer term outcomes from this kind of surgery actually comes from the work of Dr Kevin Stone, in San Francisco. Dr Stone’s published research has shown that the estimated mean survival time after Biological Knee Replacement is about 10 years. In Dr Stone’s series, ‘failure’ was defined as the patient subsequently ending up needing joint replacement surgery. Out of 115 patients studied, 20% with a Biological Knee Replacement had ‘failed’, and in this group the average time from operation to ‘failure’ was 5 years.

When I discuss outcomes with my patients, I explain that at 5-year follow-up, about 85% of meniscal transplantation patients are doing well (i.e. a 15% failure rate). Articular cartilage grafting has a success rate of about 80% at 5-year follow-up. When estimating anticipated success rates, one can in theory just multiply the individual success rates for each separate aspect of the combined procedure:-

Isolated Meniscal Transplantation = 85%

Articular cartilage grafting = 80%

ACL reconstruction = 95%

Meniscal transplantation + 1 Chondrotissue graft (tibia or femur) = 0.85 x  0.8 = 68%

Meniscal transplantation + 2 Chondrotissue grafts (tibia + femur) = 0.85 x 0.8 x 0.8 = 55%

Meniscal transplantation + 2 Chondrotissue grafts (tibia + femur) + ACL reconstruction = 0.85 x 0.8 x 0.8 x 0.95 = 50%.

From this, it can be seen that the more complex a procedure is, and the more different things need to be done inside the joint at the same time, the lower the probability is that the patient will actually achieve a successful final outcome. In addition to this, one must consider the small potential risk of possible complications (such as infection, nerve/blood vessel damage, blood clots) than can potentially occur with any operation. Furthermore, patients potentially considering this kind of surgery must also take into account the slow and careful rehab that has to be followed after the actual surgery …

This is why even though this kind of complex surgery can give truly excellent results, it really should be considered very much as salvage surgery for patients with severely damaged knees with significant symptoms who are too young for artificial joint replacement surgery. It is not a realistic options for patients with severely arthritic knees who are old enough to be appropriate candidates for standard knee replacement.