BBC Science Correspondent James Wilkinson reports

The first step in the new technique involves growing bone cells in the laboratory.

The coral is shaped to look like a thumb

The cells are cultures from the patient's own bone tissue.

The new bone is then grafted on to coral sculpted into the shape of the old thumb.

If it works, the patient will be the first person in the world to have part of his thumb made out of coral.

Scaffolding

Coral is porous and doctors hope it will act as a scaffolding that the patients own bone cells can colonise.

Dr Charles Vacanti: Looking to bigger things

"We shaped it [the coral] to precisely the shape of the bone that was missing. At that point we took a needle and placed it into the coral and injected cells that we had obtained several weeks ago from the individual," said Dr Charles Vacanti from the University of Massachusetts.

The doctors say it will take several weeks for the patient's bone cells to grow properly.

They are very hopeful because it similar techniques have worked in the past.

Mouse ear

Already an ear has been grown on the back of a mouse. The ear was made of cartilage which had grown over a scaffolding made of fibres.

The mouse ear sparked protest

It had been placed under the skin of the mouse for a few weeks simply to make sure the technique was safe and had a good chance of working.

Dr Vacanti hopes his methods may eventually work for larger pieces of bone.

"It's a very complex problem to replace an entire limb, but I believe -if this is successful - this is the first step in humans to accomplishing such a goal," he said.