A technique which uses an ultraviolet laser to examine damaged knees could lead to vastly improved operations.

Most people over the age of 30 have some sort of problem with their knees which makes sport or even walking uncomfortable.

This is partly due to the degeneration of cartilage, the "shock-absorber" material made out of protein which cushions the joint.

Thousands have surgery to remove damaged cartilage - but it is often difficult for the surgeon to distinguish between damaged and undamaged cartilage - both look the same to the naked eye.

The new process uses the laser to spot the difference between the two types of cartilage.

Dr Marta Dark, of the Laser Biomedical Research Center in the Massachusetts Institute of Technology, said: "We can measure how far the light travels into the tissue, which indicates how much protein and water are present.

"This shows how healthy the tissue is because, if the cartilage is damaged, protein breaks down and water accumulates.

Keyhole operations

"We can also use the laser to measure the elastic properties and the tensile strength of the tissue."

Dr Dark looked at cartilage which had been removed during operations.

Surgeons believe that during an operation, laser light can be shined onto the cartilage inside the knee using a fibre-optic cable.

This is even possible during keyhole surgery, which is how most operations are carried out.

The surgeon could then decide which bits of the cartilage need to be taken out and leave as much healthy tissue behind as possible.