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Autologous Chondrocyte Implantation - Joint Repair

Damage to the smooth articular cartilage in our major weight-bearing joints such as the knee can be painful and disabling for sports people and others. A physiotherapist will help diagnose and treat your condition and you may be able to manage your knee pain without surgery.

Autologous chondrocyte implantation, a new cell culture technique, can give function back to a joint of a young person damaged in sport, and may one day put off joint replacements or make them unnecessary.

A quick tour of articular cartilage

Most of us do not give a thought to the way our joints work. Imagine you are walking along the lovely harbour of a sunny holiday island, enjoying the view and the beautiful people. What is really happening? Your joints are effortlessly (more or less) carrying a big heavy animal (yes, you!) around, and it feels little different if you are strolling or going up steps. This is the gift our major joints give us, an almost friction-free movement under load.

The stuff responsible for this ancient wonder of biotechnology is hyaline articular cartilage. It makes a layer up to 5mm thick over the ends of our joints, forming a glassy, translucent covering which allows the almost friction-free movement. It can cope with great loads, up to five to seven times our bodyweight.

Since it has no nerves and blood vessels, it relies for nutrition on the synovial fluid in the joints and on seepage through the underlying bone. Cartilage is produced by chondrocytes, specialised cells which make up only a small amount of the tissue. Cartilage has a very high water content.

What goes wrong

Millions of people all over the world suffer from defects in their cartilage from a variety of causes. The most common causes are direct trauma to the area such as in sport, and a condition called osteochondritis dissecans. Since adult articular cartilage is very limited in its ability to repair itself, the chances of these problems getting better on their own is very small.

In normal healing the body forms a different kind of tissue called fibrocartilage, which is much softer than hyaline cartilage and cannot stand up to the stresses in a joint. If the defect extends down to the bone underneath the cartilage it is unable to heal on its own and will eventually lead to osteoarthritis in that joint.

Arthroscopy and other surgery

Arthroscopy (keyhole surgery) is commonly used to examine and treat defects in cartilage. Various procedures have been tried from tidying up rough edges to washing out the joint to drilling into the exposed bone. It is not clear whether these treatments help the joints but healing is by fibrocartilage again, unsuitable for the stresses the joint must endure.

Another technique is to cover the defect with grafts from the bone or cartilage nearby, but these also do not give a good end result, as they tend to change into bone. Lastly, cores of cartilage can be taken out from one area and inserted into the damaged area. Only small areas can be treated in this fashion and the long-term results are not clear.

Autologous chondrocyte implantation

The idea of this treatment is to replace deep defects in the cartilage with the proper material, hyaline cartilage. It is used to replace defects in the knees at the moment but may be extended to other joints.

Patients are typically from 15 to 55 years of age and with a defect varying between one and ten square centimetres in area, and need to have some healthy cartilage remaining in the joint. The patient’s own cartilage cells are implanted into the defect and the area covered in a membrane made of purified pig collagen.

The process

The surgeon takes a biopsy of healthy articular cartilage during arthroscopy of the knee. In the laboratory the cartilage cells are separated from the rest of the material and cultured for three to four weeks. Once 15 to 20 million cells have grown a special nutrient solution is added and the mixture sent to the operating theatre.

The surgeon will clean up the defect and make sure the sides of it are vertical, stitch the collagen membrane around the outside to make it watertight and inject the solution of the patient’s cells into the defect. Then an adhesive is applied to make the membrane completely watertight. There are other, closely related techniques which are performed differently but this is the basic process.

Rehabilitation

It is important to protect the repair and to stimulate the cartilage cells to produce the right kind of cartilage to fill the defect. A planned rehabilitation programme is necessary, with the knee protected from weight bearing by using crutches for six to twelve weeks. A gradual increase in weight bearing and joint movement is encouraged.

Bicycling may be delayed for six months and sports such as tennis for twelve months, as the cartilage may not mature and harden until the one to two year period.

Results are very encouraging and this technique is spreading to those surgeons who specialise in knee treatment and have the skill to perform the procedures. It all looks very promising so far.


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