The Science Behind Leigh Halfpenny's Heartbreaking Injury

Wales suffered a disastrous blow to its Rugby World Cup hopes after star full-back Leigh Halfpenny was carried off on a stretcher during their warm up against Italy on Saturday, September 5th. An awkward turn on his leg was all it took to tear his ACL, one of the most dreaded injuries in professional sport.

ACL stands for anterior cruciate ligament, one of the two cruciate ligaments that sit directly between the femur and the tibia. The ACL acts like super strength elastic, preventing the femur and tibia from stretching apart while allowing the knee joint to flex. Put simply, it takes on 85% of the work holding the two halves of your leg together.

When the ACL is torn, it’s agonising. The leg bones are no longer held properly in place, leading to increased stress on the surrounding structures, particularly the cartilage within the knee. A tear to the ACL is accompanied by intense swelling and a popping noise which – I can tell you from having suffered two myself – you never forget.

ACL injuries are infamous for knocking out athletes, typically requiring surgery and, at the very least, six months of recovery before returning to full activity. Despite their frequency in sports, 80% of ACL injuries happen without any contact with other players. For Halfpenny, it was one awkward step that twisted his knee in the wrong direction, stretching the ACL to breaking point.

Most of the time it’s a bad landing from a jump that tears the ACL. Landing with a straight leg or bending the leg inwards twists the knee in the wrong direction, putting more load on the ACL than it can bear.

In day to day life we don’t tend to do a lot of jumping, so it’s far less common outside of sports. They can pop up in runners and even boxers on rare occasions but mostly you’re at risk if you play rugby, football, skiing, basketball or any activity that involves a lot of jumping and – most importantly – landing.

If you’re at risk, there are steps you can take to prevent an ACL injury. Exercises that work out the quads and glutes such as leg presses, extensions, lunges and squats can build up strength in the leg, fortifying it against unwelcome twists and turns.


But even the strongest legs won’t protect you if your landing technique is stressing out your ACL. Women should pay special attention here as anatomical and biomechanical differences make their knees more likely to bend inwards, resulting in ACL injuries being up to three times more common in women.

Luckily, landing technique is something that can be practised and perfected.

Here at West London Physiotherapy, we use slow motion video to record your jumping and landing, then we can analyse it frame by frame to show you exactly where and when you’re putting unsustainable stress on your knee. Once we’ve pinpointed the problem, we can gradually train you to bend the knee correctly with every landing until it becomes habit. If you’re an athlete, this is career saving training.

Even with world class training and exercise, accidents happen, as we saw with Halfpenny. The wisdom of how ACL injuries are treated, however, may be changing.

A recent case study showed an anonymous pro footballer recovering from a torn ACL without any surgery. Using just physical rehabilitation, he was able to return to the sport within eight weeks, with no issues found at his 18 month follow up. Usually, in eagerness to fix the problem ASAP, athletes are rushed to surgery within days so we rarely get see what could be achieved with physiotherapy alone.  While we should always be cautious of individual case reports it is worth consideration.

Orthopaedic surgeons might disagree, but there’s a movement towards seeing how well an ACL injury can be rebuilt through strengthening exercises alone before deciding whether it’s worth resorting to surgery and its months long recovery.

I’m sure Halfpenny would love to be able to go back to rugby within eight weeks, so it’s going to be very interesting to see how this approach evolves in sports physiotherapy.


david wynne physiotherapist knightsbridge

David Wynne BSc (Physio) MSc (Sports and Exercise Medicine) MCSP MHCP

Musculoskeletal and Sports Physiotherapist, Research Lead at West London Physiotherapy


For any other questions regarding this topic please do not hesitate to contact West London Physio on 0207 937 1628 or email David at