WHAT happens when a knee gives out prematurely due to cartilage damage?

Well, in many cases, knee replacement surgery may become necessary where the natural knee is removed and replaced with a metal knob that's held in place by cement.

But for those who are squeamish about having 'foreign objects' inside their bodies, or who think it a waste to lose the entire knee when only the cartilage is damaged, here's the good news: they can now opt for cartilage transplant.

'The concept is relatively simple - you take undamaged cartilage from your own body, grow it, then inject it back where it's needed,' says Dr Yegappan, a consultant orthopedic surgeon at the Centre for Sports and Shoulder and Elbow Surgery, Mt Elizabeth Medical Centre.

Cartilage is an elastic substance that protects the ends of the bones in your joints from grinding against each other and causing pain. It is found in many other places in the body including the rib cage, the ear and the nose.

Under ideal conditions, cartilage should last a lifetime. However, it can become damaged prematurely through injury, intense wear and tear, and disease. When this happens, external medical help will have to be sought.

'Articular cartilage, which is found in the knee joint, is responsible for much of the compressive resistance and load-bearing qualities of the knee joint and, without it, walking is painful; almost impossible,' says Dr Yegappan.

The problem with cartilage, however, is its limited self-repair capabilities.

'Cartilage cannot rejuvenate itself, because it does not have a blood supply,' explains Dr Yegappan, who has performed more than a dozen cartilage transplants so far. According to him, this option is most suited to those below the age of 50, who are still relatively healthy and who may have damaged their cartilage but have otherwise good, strong bones.

'These days, a lot of young people engage in extreme sports. They tend to place a lot of stress on their joints in training and this could wear out the cartilage,' he explains.

Those involved in traffic accidents may also benefit from this sort of cartilage repair, which was first reported by Swedish researchers at Sahlgrenska University Hospital in G????teberg more than a decade ago. Then, it was considered 'controversial' and the concept of cartilage transplant was not taken up again till much later in the United States.

Explaining how such a transplant is done, Dr Yegappan says, 'It's a two-step process. First, we will harvest healthy, articular cartilage from the knee of the patient with cartilage defects and use it to grow new cartilage. The culturing will take a few weeks. Once we have enough material, we go back to the patient's knee, and put the cultured cells back in place.'

This form of repair, which is called Autologus Chondrocytes Implantation, has one crucial benefit - there's no issue of 'rejection'.

'Since the transplanted material was grown from your own body, there's no fear at all that your body will reject it,' says Dr Yegappan.

The recovery process, too, is relatively straight-forward. There will be a hospital stay of between two and three days, followed by at least six weeks of physiotherapy.

'The most important thing is that the patient must totally keep weight off the knee for six weeks,' cautions Dr Yegappan.

Full recovery, however, will depend on how diligent and motivated the patient is in his rehabilitative exercises, but generally, a patient will be able to return to his normal sports routine within six to nine months.

'In the old days, when a sportsman busts up a knee, there's nothing much to do except retire early. Stop the sports and change the lifestyle. But this transplant option gives a second chance - the transplanted cartilage is very strong, so going back to sports will not be a problem,' he adds.

There is only one drawback to the entire proceeding - costs.

'Cartilage transplant - as with other forms of transplants - does not come cheap. Growing the cells alone will cost about $15,000, so for the entire operation, we are looking at around $40,000,' admits Dr Yegappan. In comparison, a knee replacement surgery will cost about half that amount, or even less.

At the end of the day, however, usage will determine the treatment option.

'The question, I suppose, is how much you're willing to change your lifestyle. If you can't imagine giving up an active sporting life, then cartilage transplant will make sense,' says Dr Yegappan.

This article was first published in The Business Times Weekend on May 31, 2008.