Jason Shaw’s son Ethan had only been at the trampoline park near where they live in Manchester for 10 minutes before he broke his leg. All he had been doing was bouncing from one trampoline to another. Shaw watched him fall and, when he didn’t get up, went over. When he got nearer, he found Ethan, who was 12, screaming in agony. His left leg had landed on the padding on the edge of the first trampoline, and his right leg had landed on the second trampoline. The momentum carried him forward, but his right leg didn’t move – Shaw blames the non-slip socks every visitor has to wear – and it snapped. He broke his tibia and fibula, the two long bones in his lower leg, and was in a full leg cast for six weeks, followed by another eight weeks wearing a support boot. Nearly a year on, although he can walk and run, it hurts to kick a football. “He’s healing well but it’s a long process and it’s still causing him pain,” says Shaw.

Last week, the BBC obtained figures which showed that in the year to April 2016, 315 ambulances were called out to 30 trampoline parks. The Flip Out park in Stoke called out an ambulance about once a week; its branch in Chester is under investigation after three people reportedly broke their backs in one day after jumping 4m into a foam pit. Usually a warehouse-style building, filled with trampolines linked together, the parks are relatively new to the UK, but the sector is growing rapidly. There are now about 150, with an estimated 10-15m visits a year. In that context, the number of injuries is low, but they can be severe – there have been head injuries, and broken backs and necks.

In the past decade, trampolines have also become an increasingly common – and controversial – garden fixture. The American Academy of Paediatrics has said parents should not buy one for their children because of the risk of injury; the Canadian Paediatric Society says the same.

Amir Qureshi, orthopaedic surgeon at University Hospital Southampton, has been monitoring trampolining injuries for some time, long before the parks became popular in the UK. Last year, one opened near the hospital. Since then, “there has been quite a steady influx of severe injuries,” he says. “We’ve had neck injuries, broken arms, elbows, ankles.” We speak the day before he is to operate on someone who sustained multiple ankle injuries on a trampoline. Younger children, up to about four or five years old, have disproportionately large and heavy heads, with less strength and control over their body’s movements, putting them at more risk when bouncing. “As you get older that proportion gets lower and then you have more muscular control.”

Qureshi is about to publish a report into trampoline-related injuries seen at his hospital. In the six months before the new park opened, there were 14 injuries that resulted in 18 “hospital days” (time spent in hospital being treated). In the six months after, there were 27, resulting in 42 hospital days. “So you can see the impact on the health service,” he says.

Trampolining does carry inherent risks, says David Walker, leisure safety manager at the Royal Society for the Prevention of Accidents (RoSPA). “Equally there are lots of benefits. Is it better to have a PlayStation or a trampoline? My view is it’s probably better to have a trampoline. We would much rather see children be physically active.”

Trampolines at home are safer than they used to be, he says. “They didn’t really have nets, some of the padding on some of the products was questionable.” People would bounce off and hit the ground, or fall between the springs, causing bad lacerations. “A lot of those types of injuries have gone.”

The serious life-changing injuries that occur now, says Walker, tend to happen when two or more people are on the trampoline, particularly an adult and a child where there is a big weight difference. Children can be injured when the bigger person lands on them, or from the bouncing itself. “If you think about two people bouncing in sync, the trampoline is stretching and becoming taut at the same time. But once they come out of sync, if the smaller person lands on it when it’s taut, it’s like hitting the ground or a fixed object.”

RoSPA recommends setting trampolines on grass or wood chips, which will absorb energy, rather than concrete. Walker suggests sinking the trampoline into the ground, “but obviously that’s quite a significant amount of engineering to your back garden – you’re basically creating a big hole. That’s why we pushed for having nets.” But nets can give a false sense of security, he adds, with people more inclined to try somersaults and flips “or starting to use them as wrestling cages”.

RoSPA has worked with the British Standards Institution and the UK International Association of Trampoline Parks to produce a set of guidelines to make parks as safe as they can, which was published this month. “As a parent, it’s still difficult to check whether your park is safe, so you need to go in and be quite inquisitive about how the park is managed. These standards are quite new. It’s about making sure you understand the rules. I would be avoiding the higher jumps [towers from which people jump into pits] – a lot of the parks have taken them out now anyway.”

Qureshi, who has four children, says he would never have a trampoline at home or take them to a trampoline park, although he admits he only gets to see the relatively few people who suffer severe injuries, rather than the thousands who are fine, “but those I do see have serious injuries. I don’t want to sound like a killjoy but these are not innocent injuries.”

Is there any way of using a trampoline safely? “I think trampolining is an attractive, healthy sport,” Qureshi says, “but my personal feeling is it should be in a supervised environment, so you’re in a trampoline club with someone who is trained. You wouldn’t put your child on a horse without training, or put them at the top of the ski slope. Kids need to play outside; I wouldn’t for one second say kids should stay inside and not do anything dangerous. Sport can be dangerous – but it should be in a supervised environment.”