The latest 3D printing technology is helping correct bow legs without the need for patients to undergo lengthy hospital stays and painful treatment or spend months with large metal frames pinned to their legs. Four Hong Kong patients have so far been treated using the new technique, and Dr Liu King-lok, who led the study at Chinese University, said: "This is a very big trial which has achieved very positive results." In 3D printing, objects are made by layering materials until the desired effect is achieved. In this case, a 3D printer is used to make replicas of a patient's deformed bones, allowing doctors to design specific sets of instruments that fit the bones accurately. The instruments are then used in an operation to fix plates and screws inside the body to correct the bow legs, which can be caused by several factors. "This has profound implications for the technology to be applied in other bone surgery," said Liu, who carried out the study while working as a clinical assistant professor at the university but has since moved into private practice. The traditional procedure for correcting bow legs requires the patient to wear a large external frame which would be pinned to the bone through their skin. The frame had to stay in place for up to a year, and because there was no way for the doctor to accurately pin it directly to the bone, the patient would often have to stay in hospital for months for repeated rounds of pinning and disinfection of the pin wounds. In 2013, Liu decided to try the new approach, making use of 3D printing - a technology more often associated with high-end engineering. The four patients he has treated have all had satisfactory results. Using the new approach, the patients are able to leave hospital and walk normally within days of the surgery. A further operation is required several months later to remove the pins. One of Liu's patients was a 24-year-old woman called Ann, who was born with the condition and was told she needed surgery as her deformity grew worse. "My knees and my heels hurt whenever I walked, which affected many aspects of my life," she said. "The doctor said I needed surgery. But the traditional correction treatment is so terrifying. I didn't want to wear the external frame for a whole year, with all those needles visibly piercing my legs." After being told of the new approach, the postgraduate student decided to give it a go. She was able to walk, with some assistance, days after the surgery. Doctors have shown a growing interest in 3D printing technology. Last month, a British team revealed it was creating models of body parts and tumours to help medics target anti-cancer drugs more accurately. Liu said 3D printing was still rarely used in medical treatment in Hong Kong, but he believed its popularity would increase in the coming years.