New technology may spare children with bone cancer the need for repeat surgery after they have had their tumours removed. Usually, they have part of the bone replaced with a metal rod, called a prosthesis, but then face regular operations to lengthen the limb as they get older. The technology introduced to Hong Kong last month enables the prosthesis to be extended to the correct length by a magnetic process without the need to operate. It was used for the first time last month on 16-year-old Patrick Yip Chun-kit, by doctors from Chinese University. His affected leg was lengthened 4mm without any pain in the initial adjustment. Bone cancer patients under the age of 16 normally require prostheses to lengthen the affected leg and match the other. Wong Kwok-chuen, honorary clinical assistant professor of the university's department of orthopaedics and traumatology, said the technology allowed gradual and frequent length adjustments to the prostheses, which could allow patients to move more easily. 'With the new method, the patient simply has to put his leg into a magnet-driving device and a suitable length matching the other leg can be adjusted. 'It can be done frequently and conveniently in a clinic.' However, Dr Wong said not every teenage bone cancer patient could benefit from the technology as it depended on the size and location of their tumour. Patrick, a Form Five pupil, had a tumour in his right thigh five years ago and underwent a bone transplant. But last year he discovered the affected leg could not be stretched properly and he was constantly tired after walking for an hour or two. He said the adjustments lasted for about 16 minutes and were painless. 'I could immediately feel that my leg had grown longer. I am very happy because I am very afraid of pain,' Patrick said. He hopes to play badminton again after the whole procedure of length adjustments is completed.