Bionic bones may sound like science fiction, but they have already transformed one teenager's life, writes CHARLIE HARRIS

Bio-engineers and surgeons at the Royal National Orthopaedic Hospital (RNOH) in Stanmore have achieved a revolution in the treatment of children with bone cancer, literally.

In November, orthopaedic surgeons Steve Cannon and Tim Briggs fitted the world's first bionic bone into the thigh of 13-year-old Kat Reid.

The extendable prosthesis, to give it its proper name, is a major breakthrough because it allows Kat's left leg to grow in pace with her right, without her having to undergo further surgery.

Instead of needing a surgeon to cut into the flesh to allow a key to be inserted and turned to extend the prosthesis, as is the procedure with traditional designs, the bionic bone can be made to grow by the application of a magnetic field.

As Kat, who lives in Wimbledon with her parents and younger brother, grows, her leg with the prosthesis need only be put through a hole in a box containing a revolving magnetic coil.

The spinning magnetic field activates a tiny gearbox built into the bionic bone. The magnet inside the gearbox is about the size of a 1p coin and spins at 3,000 revolutions a minute, turning a screw: for every 13,000 revolutions, the bionic bone grows one millimetre.

The treatment takes about 15 minutes, and while it is going on Kat feels no pain or unpleasant sensation in her leg at all, although a faint hum from her thigh can be heard through a stethoscope. It does not have to be done in an operating theatre, and afterwards Kat can get off the trolley and walk away, her mobility improved.

Since the operation seven months ago, she has had her bionic bone extended twice.

Mr Briggs said: "Kat came to the RNOH to have the prosthesis extended for the second time. She got up, walked out of the room and went off to X-ray completely unaided. It was amazing."

Under the old procedure, Kat would have to have been admitted to hospital and undergone invasive surgery. After the prosthesis had been lengthened, she would have needed to stay in hospital for five days, taking drugs to relieve the pain and then undergoing physiotherapy. The bionic bone makes that unnecessary, as well as removing the risk of infection.

Mr Briggs said: "This new prosthesis will greatly improve the quality of life for these already poorly patients. Young people like Kat already have to undergo a range of treatments for their condition: saving them from having to go to theatre and spend long periods in hospital can only be good news.

"I pay tribute to Kat. Her determination and spirit has certainly helped. It has been inspirational."

Kat's father Ian said: "Kat has regained a lot of movement in her leg. She is a keen swimmer and looking forward to getting back in the pool as soon as possible.

"We are delighted with what the hospital has been able to do and we hope that this new bionic implant will be able to help many other young people."

Kat said she was pleased to be the first person in the world to have been fitted with the bionic bone, rather than the last person to have received the old design.

The bionic bone has taken 11 years to develop, and each one is custom-made for the patient at a cost of about £9,000, compared to £4,000 for a mechanical prosthesis. But the higher cost is offset by major savings in the costs of surgery and aftercare.

It was designed by the Centre for Biomedical Engineering, which is based at the hospital in Brockley Hill but is part of University College London.

Technical manager Jay Meswania said that, in its present form, the bionic bone could be used in an arm or leg. He also said it could be adapted to help treat other conditions, such as curvature of the spine.

"The next phase is to reduce the size of the gearbox to half its present diameter," he said. "That is the real challenge."

He added that the principle behind the bionic bone could be used in the aerospace and other industries.

Kat has her own ambitions: she said that her experiences at the RNOH had made her interested in becoming a doctor.