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Articular Cartilage Injuries

The bearing surface of all synovial joints is made up of a very specialised material called hyaline cartilage. This material has shock absorbing properties, but it is bizarre in that it has absolutely no blood supply and no nerve supply. It is made up of a matrix of collagen and sugar polymers enclosing cartilage cells in layers and is exquisitely designed with perfect mechanical properties to form a bearing surface. The friction is much less than that of ice on ice and lower than anything that man has managed to design. It gets its nutrition from the joint fluid which bathes it because the cartilage cells which produce the bearing surface material have a very low metabolic rate and do not need much "food". This does mean that the body has little or no capacity to repair any damage to the gristle surface of the joint. This is a shame as once you have stopped growing; any damage to the bearing surface of the joint is going to be permanent.

What can we do about it?

There are some things we can do to encourage the healing of articular cartilage defects. We can simply smooth over the edges of the defect to prevent catching. This is more or less like removing the loose bits of tarmac from a pothole in the road. If the pothole is fairly small then drivers will not notice as they drive over it, but once it becomes a big cavity, big enough for a car wheel to fall into it, it is going to cause more trouble and more complaints from the drivers! The typical history that we hear from patients who have articular cartilage defects is that there is a vague dull ache in the joint most of the time, but it is very much exercise-related, so if they have an easy day it is not too bad, if they play a game of football it is going to be much worse the next day, often associated with some swelling for a few days. It will be eased by non steroidal anti inflammatory drugs (such as Brufen, Nurofen or Voltarol), but it often never goes away completely.

There are a number of things that can be done to help this. This is now good evidence that Glucosamine is helpful in joints with early degenerative change, but it needs to be taken at quite a high dose (1500mg daily) for a prolonged period of time (perhaps three months) regularly to feel the benefit. It is reasonable simply to restrict activities so as to avoid experiencing the symptoms, but many people are not happy to do this. There is a relatively small role for braces and splints and really if the symptoms cannot be controlled with simple measures then we are heading towards surgery.

Operations

The easiest and probably one of the most reliable ways of treating the symptoms arising from a defect in the bearing surface of the joint is with a technique called microfracture whereby we use a specially designed awl to penetrate the bone that sits underneath the articular surface and allow small blood vessels to grow out and produce a fibrocartilaginous scar. This fills in the defect very well and gives a reasonably durable bearing surface. It can be compared to the scar you see in the skin after a burn. It is not quite as good as nature intended, but it does the job of keeping the water out quite well. Because we are simply doing an operation to allow blood vessels to grow out and produce this scar there is quite a long period of rehabilitation associated with this. This is very important in that there is a balance between keeping the joint moving and keeping the muscles around the joint in good condition and avoiding stressing the newly formed bearing surface. This rehabilitation is a crucial part of the treatment and cannot be avoided. The defect is like a muddy field and the operation is like re-seeding a lawn onto it. It is obviously important to allow the grass seeds to germinate and produce not only the grass surface, but some decent interlocking roots underneath before starting to play football on it. There are various protocols for rehabilitating patients following microfracture, but the duration of recovery in getting back go full sport following this (day case key hole) procedure is a minimum of four months and often a bit longer.

Should this fail or for any reason be inappropriate then there are other techniques for reproducing a bearing surface. We can take a chunk of bone covered in articular surface from a less important part of the joint and put it into the defect. This can also be done by taking a chunk of bone from a dead donor. This obviously has some problems of its own and we are increasingly using the relatively new technique of tissue engineering to generate a new biological bearing surface.

Tissue Engineering Techniques

As noted above, hyaline cartilage has little or no capacity to regenerate itself, however, if we take a specimen from an unimportant part of the lining of the joint we can send it to our laboratory where they will mince it up and encourage the cartilage cells to multiply in a test tube. We can then go back around three weeks later and inject the cells under a membrane stitched over the defect and they will quite reliably continue to produce articular cartilage and over a period of time regenerate the true hyaline cartilage surface of the joint. This is a technique which has been done in Sweden for around twenty years & is now approved by NICE for use only in a recognised centre as part of a research study.

Since the cultured cells are in a liquid injected under a membrane this is effectively a blister in the lining of the joint and will obviously, like the microfracture procedure, take quite a long time to rehabilitate from. It is certainly at least a year before there is any kind of decent cartilage surface there and it is probably most appropriate for people looking towards the long term rather than sportsmen who are looking to get back on the field as soon as possible. It is, however, the only way we have of producing a large and integrated hyaline cartilage surface like the one nature intended. The published results of this procedure in ideal cases are extremely good with approaching 90% good and excellent outcomes, but it does involve two operations and prolonged rehabilitation after them.

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