Women's football: Why are there so many knee injuries?

Last month, England international Rachel Unitt ruptured an anterior cruciate ligament in her knee for the second time in 16 months.

Another long lay-off could signal the end of a career for the 32-year-old who has earned 102 caps for her country.

More worryingly, she is the fourth Notts County player to suffer the injury this season and the ninth player to be injured in this manner during 2014 in the Women's Super League (WSL) top division.

On the face of it, their plight could be viewed as bad luck. But is there more to it than that?

The hips don't lie

Research by world governing body Fifa has suggested that female footballers are between two and six times more likely to suffer this injury because of physiological differences such as generally wider hips, which increase the leg's angle into the knee, and under-developed muscles which prevent the knee from turning in upon landing.

However the rate of injuries to the whole body for women is lower than for men.

There has been a sharp increase in serious knee injuries since the women's game moved to a semi-professional league in the summer of 2011.

Not all clubs in the WSL keep historical records on these injuries, but the Football Association does. Their figures show that in the opening WSL season just one England international suffered an ACL injury, but that rose to five last season and six this season.

"Broadly speaking, there are two ways that you can tear your ACL," says former England chief medical officer Pippa Bennett, who worked with ex-England manager Hope Powell. "Landing from a jump with a straighter knee and cutting and turning with your knee falling inwards a little bit. This is what we call an increased valgus angle.

"I was with the England teams for 15 years and on average, we would probably have four or five players in the team who have had an ACL injury at some point in their career. So we do see these spikes and troughs."

Research has suggested that female footballers are between two and six times more likely to suffer an ACL injury

Elle Turner is a sports scientist at Manchester City Women's team, which joined the WSL this season. She says that when she started working with the squad last January, there were players who she considered "an ACL injury waiting to happen."

"In football, you get forces going through the body at four times the body mass and if players are not able to move correctly, that's when the risk goes through the roof for injuries," she says.

"A lot of female footballers have poor hamstrings and poor gluteus medius muscles, which are the muscles at the side of the hips that correct the knee and brings it back into alignment. So we work on them on a daily basis."

Too much football?

There are concerns in the game that more could be done to protect players, with the spike in knee injuries this season coinciding with an increased load on the players' bodies. Liverpool Ladies won their first title last season after committing to full-time training. This season, many other teams have followed suit in an attempt to usurp Matt Beard's side, who will battle it out with Chelsea and Birmingham for the title next weekend.

Effectively, some players have gone from part-time to full-time footballers in a matter of months. Is it too much, too soon?

As Professional Footballers' Association chief executive Gordon Taylor says: "Everybody wants to see the women's game progress. But on the other hand, it doesn't want to progress on the back of a lot of injuries that are unnecessary."

Helen Vaughan, lead physiotherapist at Manchester City adds: "I definitely think that the increase could be discussed as a factor. We know movement patterns and the quality of movement is lost when players fatigue so I think a big part of it is fitness levels."

Add in a clustered schedule, which the likes of Beard have criticised before, and it is a potentially risky cocktail.

The move to a summer league three years ago has been classed a success by many in the game as it avoids fixture clashes with men's teams and the risk of waterlogged pitches in winter. With nearly all teams renting stadiums from lower league men's teams, though, they still have to fit in their matches around other schedules and allow a break in the middle of the season so that pitches can seed.

Even so, Bennett says that more medical advice should be taken on board when deciding the fixture list. During her time at the FA, she says her medical team were not consulted about the schedule.

Rachel Unitt (right) has only played seven times for Notts County because of knee injuries

"There are loads of factors that go into scheduling matches, not purely the science and medicine behind it," she adds. "Accessibility to pitches, TV rights etc… but certainly some input medically would be a benefit I'm sure in the future."

FA director of women's football Kelly Simmons accepts that striking the right balance is a "challenge". Yet she insists that the FA now works together with the elite unit at St George's Park and is attempting to establish an even spread of matches.

"If you're asking England manager Mark Sampson or the elite unit, they'd probably say one fixture a week is ideal," she says. "Outside of that then maybe no more than a midweek fixture every other week so you've always got that chance to build in recovery timing."

Plastic pitches

Another factor that could have direct impact on Sampson, too, is the use of synthetic pitches. Research has shown that injuries tend not to be more common than on grass but a PFA study says that players feel less sure about artificial surfaces.

Liverpool and Everton both use a 3G pitch in the WSL, with the sides being hit by five ACL injuries between them in the past two seasons. Synthetic turf will also be used at the 2015 World Cup in Canada, a decision that has seen a group of players suing Fifa in protest.

Sampson, though, has said he has no issue with the plans, saying the surface may actually help his team.

"Some people can adapt to changing between surfaces well, certainly the younger players that went to the under 20s World Cup in Canada last August came back saying it was fine," says Bennett. "They are young players, they can adapt.

"As we get older, the ability of our muscles, our tendons, our ligaments, our bones, to adapt to the change of surface actually becomes more difficult.

"As a medic we want to get the players fit but their long-term health has got to be paramount as well.

England captain Steph Houghton says that no players 'deserve' to suffer an ACL injury

"Every club needs to invest in a really good backroom staff to look after their female players."

One club which has embraced that is Manchester City, with players there having access to the medical care and facilities which minimise the risk.

As club and England captain Steph Houghton says: "I feel that as a squad we are generally one of the best prepared teams in the league.

"It's upsetting when you see some of your close friends getting ACLs and you think, they don't deserve it.

"Nobody deserves to have an injury like that. It is something we've got to try and combat."

Whether it is changes to training, pitches or scheduling which is needed, it is clear that there is a willingness from all sections of English football to ensure that the number of ACL injuries this season remains an anomaly.

For more on the issue watch the Women's Football Show on iPlayer.