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Everyone has heard of a torn cartilage and they tend to think of that as the much more common problem where the shock absorber type of cartilage is damaged in the knee. This confuses people because they don’t understand the difference between that type of cartilage and 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 remarkable structure is extremely smooth and slippery. In its best state, it functions very efficiently for the mechanics of the knee joint. Unfortunately, it can be damaged, and when this smooth articular cartilage is damaged, it can be a much bigger problem than when the U-shaped shock absorber or menicus is torn.
Up until recent years the treatment of articular cartilage defects has been remarkably poor. The most that could be done was to shave it down with mechanical instruments in an attempt to smooth it but we could do very little to replace the defect in the smooth surface.
Occasionally the whole, or damaged area, would be drilled with a wire to try and promote bleeding which we hoped would form a fibrous clot that would smooth over to scar tissue which would be better than having a defect in the cartilage. This is a very poor healing technique but it is better than nothing. The concept is that you would violate so that you would pierce the bone plate just underneath the cartilage and allow cell migration by bleeding into the area. In its more modern form this is referred to as "microfracture" technique. Improvement in daily activities can be expected in about 2/3 of patients when performed at its best.
Abrasion chondoplasty is an easy to understand technique. A high-speed burr is used on the roughened area, particularly if hardened bone is 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 area which can be expected to form normal hyaline cartilage. Hyaline cartilage is the specific type of cartilage that is usually present in normal articular cartilage. With this technique, a biopsy is taken during the first arthroscopic surgery which is simply a small piece of cartilage removed from a non-critical area of the knee joint. This piece is 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 an operation is performed through an open incision. A liquid form of the cartilage, which has been grown in the lab, is placed by syringe underneath a patch. The patch is then sealed over completely and the patient remains non-weightbearing for an extended period of time until knee is safe to weight bear on and the cartilage transplant has taken.
This technique is usually reserved for lesions that are at least 2 square centimeters in size and in 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 chondro. Any ligament instability of the knees has to be corrected first and any mal-alignment deformities such as genovarigm (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 they can get even better results because the patients tend to improve as time goes on. It should be understood that it’s 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.
Osteochrondro Autograft Transplantation
This procedure is also known as an OATS Procedure. It has also been called mosaicplasty. This procedure is usually used on smaller lesions between 1-2 square centimeters Again, the goal is to achieve normal articular hyaline cartilage with this operation.
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 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 we can’t do it for lesions much more than 2 square centimeters in size.
The advantage is that it is all done in one operation and can usually be done arthroscopically. The grafts are harvested by hollow tubes that are used to drill over the area that we use as a donor site. And then again, the damaged area is drilled out and the tube of bone and cartilage is transplanted into the damaged area. This operation has the advantage of a much shorter recovery period and it removes the necessity for two operations.
Depending on the type of surgery, the post-op course is quite different. With the micro-fracture 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 type of 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 quite quickly.
Unfortunately, the recovery period for the autologous chondrocyte implantation technique, where the cartilage is grown in a lab, is much longer but we must remember that it is used in much more difficult situations and bigger lesions. It also has to be done through a relatively large open incision when compared to the other two operations.
Articular damage to the surface 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. But now there are some options available to patients. These have to be understood and the limitations of these operations, as well as the risks, have to be understood. While certainly not guaranteed, they do offer patients at least a chance at getting more normal knee joint and participating in the activities and work that they want to.
If you have any questions about any of these techniques, please do not hesitate to speak with one of our orthopaedic surgeons.
One of the most famous orthopaedic 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 has 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."