“This machine helps you grow the leg,” she said in her room in a clinic near Beijing.

Every day for many months Ms Dong endured excruciating pain as she tightened the knobs to stretch her legs. By constantly forcing the broken bones apart before they can heal, new bone grows to fill the gaps.

Ms Dong is now 5ft 3in tall and delighted with the operation, which cost her more than £6,000, although it could be another six months before she can walk without a frame. “It’s definitely worth it,” she said. “There are many prejudices against short people. Some companies won’t hire them, and it’s hard to find a boyfriend.”

Advertisements on television offer stretching machines. Vitamin supplements are in great demand. And thousands undergo the same excruciating operation as Ms Dong.

“I got the surgery because of my job,” she said. “I’m an image ambassador for a cosmetic surgery clinic. You have to look good and give a professional image so people believe in what you say.”

The operation took two hours. Later there were follow-up procedures to remove the pins and extension material. “I’m not allowed to run or walk for about 18 months after the operation,” Ms Dong said. Xia Hetoa has run the clinic for about a year, but he has been helping people to grow taller since 1996.

“The new leg can fulfil all the functions of the original leg,” Professor Xia said. “If you do this operation according to our standards, it’s very safe.” He has treated more than 1,500 patients.

Other Chinese medical practitioners oppose the procedure. Li Qihong, of Chongqing, a medical professor at No 3 Military University in Sichuan province, said: “I’ve only done leg extensions on about ten people who hadn’t suffered from accidents or disabilities, and always under strong pressure from the patients. Of these, one couldn’t stretch her legs out properly after the operation and has one leg slightly longer than the other. Another two suffered from different knee problems.”

Zhang Kefeng, his colleague, was also sceptical. “The operation takes a lot of time and money,” he said. “It causes intense physical and psychological pain. For a healthy person, is it worth it?”

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