Articular Cartilage Transplant

When people hear the phrase “torn cartilage”, they tend to think of the common “shock-absorber” type of cartilage, called fibrocartilage. There is another type of cartilage however, called articular cartilage. Articular cartilage is the “smooth Teflon lining” of the knee joint that coats all the gliding surfaces and makes the knee joint slippery and smooth. This articular cartilage has a coefficient of friction that is better than any man-made product. This remarkable structure is extremely smooth and slippery. In its best state, it functions very efficiently for the mechanics of the knee joint. Unfortunately, articular cartilage can be damaged, and tends to be much more difficult to repair than common fibrocartilage.

History

Up until recent years, the treatment of articular cartilage defects has been remarkably poor. Very little could be done to replace the defect in the smooth surface of the cartilage. The most that could be done was to shave the cartilage down with mechanical instruments, in an attempt to smooth it over.

Occasionally, the damaged area would be drilled with a wire to try and promote bleeding which was hoped would form a fibrous clot that would smooth over to scar tissue. This is a poor healing technique, but is often better than nothing. The concept is that you would pierce the bone plate just underneath the cartilage, and allow cell migration by bleeding into the affected area. In its more modern form, this is referred to as the “microfracture” technique. Improvement in daily activities can be expected in about 2/3 of patients when performed at its best.

Abrasion chondroplasty is a fairly straight-forward technique. A high-speed burr is used on the roughened area, particularly if hardened bone has formed. Once again, this high-speed burr is hoped to help promote the formation of scar tissues but cannot be expected to form normal articular cartilage.

Autologous Chondrocyte Implantation

Originally developed in Sweden, this is an advanced technique where the goal of the surgery is to actually transplant cells into the affected area to form normal hyaline (articular) cartilage. Hyaline cartilage is the specific type of cartilage that articular cartilage is made up off. With this technique, a biopsy is taken during the first arthroscopic surgery, during which a small piece of cartilage removed from a non-critical area of the knee joint. This piece is then sent to a laboratory where the tissue is cultured to produce many more chondrocytes (cartilage cells), until there is enough to transplant back into the knee joint.

The patient is then taken back into surgery, where a bigger operation is performed through an open incision. A piece of tissue from one of the bones of the leg is used to cover the defect in the joint surface, and then the lab-grown cartilage is placed by syringe underneath this “patch”. The patch is then sealed over completely. Patients remain non-weight bearing for an extended period of time, until the knee is safe to support weight and the cartilage transplant has taken hold.

This technique is usually reserved for lesions that are at least 2 square centimeters is size, and for patients who are usually less than 50-55 years old. It is not a good operation for lesions on the patella (kneecap), but it is good for lesions of the femoral chondroid. Any instability of the knees has to be corrected first, and any mal-alignment deformities such as genu varum (bow-legged) must also be corrected first.

This operation is contraindicated in diseases such as rheumatoid arthritis and severe osteoarthritis. If the patient is markedly obese or has other medical contraindications, then he or she is not a good candidate. With this operation, reports have shown up to 85% improvement at 12 months. Interestingly with time, patients can see even better results because the transplant tends to improve as time goes on. It should be understood that it is the patient’s own cartilage cells that are transplanted back into the knee joint, they are simply grown and cultured in the laboratory to multiply.

Osteochondral Autograft Transplantation

The Osteochondral Autograft Transplantation (OATS) procedure, also called “mosaicplasty”, is usually used on smaller lesions between 1-2 square centimeters.  Again, the goal of this procedure is to achieve normal articular hyaline cartilage.

With this particular technique, special instruments are used to harvest an area of hyaline cartilage from a non-critical area of the knee. This cartilage is then immediately transplanted into the area of the damaged cartilage, without any intervening growth period in a laboratory. This means that the size of the transplant is limited by the amount of cartilage that you are able to remove from the non-critical area of the knee. This is why it cannot be done for lesions much more than 2 square centimeters in size.

The advantage with the OATS procedure is that it is all done in one operation, and can usually be done arthroscopically. Grafts are harvested by hollow tubes that are used to drill over the area used as a donor site. Then, the damaged area is drilled out and the tube of bone and cartilage is transplanted. This operation has the advantage of a much shorter recovery period, and removes the necessity for two operations.

Postoperative Course

Depending on the type of surgery, the post-op course is quite different. With the microfracture technique, the patient may be required to be non-weight bearing for a relatively brief period of time but recovers relatively quickly.

With the OATS procedure where the cartilage is transplanted all in one setting, the patient again is going to be non weight bearing for a period of about 6 weeks, but afterwards recovers quickly.

Unfortunately, the recovery period for the autologous chondrocyte implantation technique, where the cartilage is grown in a lab, is much longer. However, it also tends to be used in much more difficult situations and for bigger lesions. It also has to be done through a relatively large, open-incision.

Summary

Damage to the surface of the articular cartilage of the knee joint is one of the most difficult problems to treat in the knee. Up until very recently, there was little that could be done. Now there are some options available to patients. These options & their risks have to be understood before deciding which course is best for you. While certainly not guaranteed, these procedures offer patients a chance at a more healthy knee joint, so they can get back to doing what they love.

If you have any questions about any of these techniques, please do not hesitate to speak with one of our orthopedic surgeons.

One of the most famous orthopedic surgeons in the world is Dr Henry Mankin. He has done a great deal of research into cartilage and has a famous quote in regards to its problems. He said:

“… it should be clear that cartilage does not yield its secrets easily and that inducing it to heal is not simple. The tissue is difficult to work with, injuries to joints are a risk – whether traumatic or degenerative – are unforgiving, and the progression to osteoarthritis is sometimes so slow that we delude ourselves into thinking that we are doing better than we are. It is important, however, to keep trying.”