How ankles can save footballers’ knees

Maths meets Carlton, AFL fights ACL

AFL knee injuries could be dramatically reduced if physiotherapists paid more attention to ankles, a Melbourne mechanical engineer has found. He is now trialling the mathematical models to help Carlton Football Club predict and screen for players at most risk of knee injuries.

Hossein Mokhtarzadeh has demonstrated that the ankle is key to preventing knee injuries that cost the Australian football codes tens of millions of dollars a year. As a University of Melbourne post-doctoral fellow at the Australian Institute for Musculoskeletal Science, Hossein is hoping to expand his work into protecting the anterior cruciate ligament (ACL) against injury by developing exercises to strengthen critical muscles supporting the ankle joint. He also has a vision for a mechanical bracing system for those who may not be able to train their muscles to a sufficient level.

“We are improving our mathematical models to predict and screen for athletes who are at a high risk of injury while they play,” says Hossein. “If we could prevent just half of the knee injuries in Australian football, we would save more than $60 million a year and a lot of pain.”

Hossein is one of 12 early-career scientists unveiling their research to the public for the first time thanks to Fresh Science, a national program sponsored by the Australian Government through the Inspiring Australia initiative.

ACL injuries—tears and ruptures—typically occur when athletes abruptly change their direction of movement, such as in landing. “Landing is an inevitable physical activity in sports, such as football, basketball and volleyball. And, when landing, the ACL is one of the knee structures most susceptible to injury, with a higher rate of incidence among female athletes,” Hossein says.

So, Hossein filmed athletes landing using a motion capture system, and measured their landing force with a detector plate on the ground. He then used the data he collected to customise a pre-existing mathematical model of the interactions of leg muscles and bones. It allowed Hossein to calculate the forces in each of the muscles during the landing motion. From that Hossein developed another model to determine the force on the ligament itself.

Using this data and information from previous studies, Hossein designed a series of experiments on the limbs of pig carcasses to determine the actual injury mechanism. “I found that if you fix the shin bone at the ankle so it doesn’t rotate, you need to increase the level of force to cause injury to the ACL. So this protects the ACL.”

“There is a limitation, however, because if you continue, you can cause other forms of damage. There is a kind of trade-off.”

Until now, says Hossein, no-one has recognised the significant role in protecting the ACL played by the soleus, a large muscle behind the calf at the back of the lower leg which runs from below the knee to the heel. It is critical to ankle joint stability, but in terms of ACL injury it has been neglected because it doesn’t span the knee, just the ankle joint. “But we found that it contributed up to 30% of the force required for protection.”

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