Children's sports getting faster and more professional are among the reasons being suggested for a rise in the number of young people needing knee reconstructions.

Key points: Historically, the average age for an ACL was 27

Historically, the average age for an ACL was 27 Children needing ACL reconstructions has more than tripled over 15 years

Children needing ACL reconstructions has more than tripled over 15 years The rise is partly blamed on children's sport becoming professionalised

The ABC has spoken to doctors, physiotherapists and sports injury experts who said they had observed a rise in the number of children having their anterior cruciate ligament (ACL) replaced.

Research physiotherapist Lucy Salmon said Medicare data showed the number of children undergoing ACL reconstructions had more than tripled in the past 15 years.

She said those figures did not take into account children who injured their ACLs but did not undergo surgery, children who were not correctly diagnosed, or that were treated in the public system.

The ACL ligament helps hold the knee together. It can be injured when a person pivots, changes direction quickly or lands awkwardly from a jump.

ACL injuries are commonly associated with elite athletes in sports such as netball, AFL and rugby.

The physiology of female hips and knees means teenage girls are more susceptible to the injury, but since boys are more likely to play some form of football their rates of ACL reconstruction are higher than girls.

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ACL injuries have serious consequences, including expensive treatment, lengthy rehabilitation and recovery times, and putting the patient at greatly increased risk of osteoarthritis.

Lucy Salmon is a physiotherapist at a private clinic in Sydney that is seeing many more children with ACL injuries than it was 10 years ago.

"I'm worried about the number of children we're seeing," she said.

"Historically the average age for this injury in 27 and all of a sudden it seems that we're seeing an awful lot of very, very young children, as young as six sustaining this injury which was nearly unheard of historically."

'I couldn't believe it happened to someone so young'

Kylee Hooker with her son Callum, who has damaged the ACL ligament in both knees. ( ABC News: Meredith Griffiths )

Callum Hooker was 9 years old last year when he injured his ACL playing eagle tag — a form of touch football.

"It was really sore, couldn't really walk at all, so I had to get just carried off," he said.

His mother Kylee Hooker was shocked when she heard the diagnosis.

"I couldn't believe it had happened to someone so young," she said.

Dr Roe, who was their surgeon, used part of Ms Hooker's hamstring to replace her son's ACL.

It took Callum a year to recover — with his mother watching him closely to make sure he did not do anything to jeopardise his recovery.

"It's quite stressful and full on, always keeping an eye on him," she said.

Callum was given the go-ahead to start playing sport again in March this year. But he recently injured his other ACL playing rugby for his school.

Gabi damaged the ACL ligament in her knee playing soccer ( ABC News: Kathryn Ward )

Gabi Cardoso, 14, is only getting back onto the soccer pitch now after tearing her ACL in the finals of her soccer competition last year.

"When I found out I had to have surgery I cried, because I didn't want to have a year off of soccer," she said.

"I was really worried that I wasn't going to be able to play soccer anymore and that it was just like one stupid thing that I had done that would have ruined it forever."

Children in sport being pushed 'more and more'

Many reasons are suggested for the increase, including that doctors have better tools like MRIs that produce more accurate diagnoses.

There also seems to be consensus that the rise maybe because more children are playing more organised sport.

What is an ACL? The anterior cruciate ligament is an important ligament that helps stabilise your knee

The anterior cruciate ligament is an important ligament that helps stabilise your knee Torn ACLs can cause the knee to collapse when trying to twist or turn

Torn ACLs can cause the knee to collapse when trying to twist or turn Repairing torn ACLs typically requires replacement tissue from somewhere else in the body

Repairing torn ACLs typically requires replacement tissue from somewhere else in the body Australian rules football, rugby, soccer and netball are all high-risk sports Source: Better Health Channel

"Certainly the rates of participation in sport at a very young age are increasing, we also know that the amount of time children are spending playing those sports is greater than it has been previously, children are specialising in one particular sport from a much earlier age than they would have done previously," said Dr Salmon.

Experts said junior sport was becoming more "professional" and not played in an ad hoc environment any more.

"I think the games we're playing now are a lot faster, our information about how to play the games is a lot better," leading knee surgeon Justin Roe said.

"The parents, the coaches, the trainers, the strength and conditioning people are pushing the athletes more and more, so we probably are playing in a way that was different to a couple of decades ago."

Others point the finger at changes in playing surfaces, such as more games being played indoors, on synthetic turf or on grasses that are more drought-proof.

New types of shoes may play a role as well.

"Twenty years ago you didn't have a pair of netball shoes, you had one pair of runners that you might have used across a number of sports and now you're getting specialist equipment and specialist surfaces that are not necessarily conducive to reducing the rates of injury," said Dr Salmon.



Push for better prevention programs

Dr Roe said children whose ACLs were reconstructed using part of their parent's hamstrings seemed to be less likely to reinjure their ACLs.

However, he also said the severity of ACL injuries meant more needed to be done to prevent them.

He said some children would have genetic predisposition to such injuries, so if there was a family history of ACL injury parents should encourage the children to do preventative warm-ups.

"I really think that just like we all know about slip, slop, slap, putting on sunscreen, preventing skin cancer, we should know about how to keep the knee fit to prevent sporting injuries," said Dr Roe.

Dr Salmon agreed and said some good prevention programs had been devised.

"Things like a good warm up — not just jumping out of a car and running onto the field, but having a good warm up that involves a lot of change of direction, jumping and agility activities," she said.