ACL injuries - Why is the prevalence higher in women?

The story is all too familiar, a promising young athlete lands awkwardly in a game, hears a ‘pop’ followed by sudden pain and development of swelling. Sometimes, an opponent falls on the athlete, causing the knee to ‘shift’. In either case, the season is over and the athlete’s future is now in question.

It is doubtful that anyone involved in athletics today is unfamiliar with the letters ACL– Anterior Cruciate Ligament. The ACL is injured in 1 of every 3000 individuals each year, and are classified as either Contact or as Non-contact injuries. Contact injuries are those in which one athlete collides with another. Approximately 70% of ACL injuries, however, are Non-contact injuries–the athlete plants his foot, pivots, and then feels something ‘pop’. Shockingly, perhaps, female athletes sustain Non-contact ACL tears at a rate 5 times higher than their male counterparts.

Why?

There are many theories, and over the last two decades, many studies have attempted to answer this simple question. Some have implicated the supposed negative effects of oestrogen (and other hormones associated with menstruation) on ligament strength. Others have suggested that the increased width of a woman’s pelvis was responsible for the greater stress on a woman’s ACL. More recently, attention has focused on evaluating the manner in which young athletes perform simple tasks such as running and jumping. Recent evidence demonstrates that male and female athletes perform these tasks differently.

The answer

Overwhelmingly, female athletes put greater stress on their knees (and particularly the ACL) as a result of different biomechanics. Three factors in particular have been identified:

No easy explanation

Women may be more prone to non-contact ACL injuries because they run and cut sharply in a more erect posture than men, and bend their knees less when landing from a jump.

Why women and girls are more prone to ACL injuries than men and boys defies easy explanation is also likely due to a number of anatomical and hormonal differences between men and women:

• Narrower intercondylar notch and smaller ACL: Not only does the intercondylar notch (the groove in the femur through which the ACL travels) tend to be smaller in women, but so is the ACL itself, leading it more prone to injury.
• Wider pelvis: Women typically have a wider pelvis, which makes the thigh bones angle downward more sharply than in men. The greater the so-called ‘Q’ angle, the more pressure is applied to the inside (medial aspect) of the knee, which can cause the ACL to tear.
• More lax ligaments: Women’s ligaments tend to have more ‘give’ (laxity) than men’s. Excessive joint motion combined with increased flexibility may be a significant contributing factor in the higher rate of torn ACLs among women.
• Slower reflex time: Research shows that the muscles stabilizing the knee may take a millisecond longer to respond in women than in men. Scientists suspect that this small difference in contraction time also leads to a higher rate of injury.
• Changes in oestrogen levels: Recent studies have suggested that changes in oestrogen levels during a woman’s menstrual cycle may affect ACL strength, predisposing women to the higher injury rate. A 2007 article in The British Journal of Sports Medicine, however, found “no conclusive evidence directly linking an increase in ACL injury to a predictable time in the menstrual cycle.”
• Running and landing techniques: Females’ knees are less bent when jumping and landing. plus they jump and run with the soles of the feet in a more rigid position and directed away from the body’s centre of gravity.

In light of these findings, we not only have a better understanding of the answer to the question: ‘Why are ACL tears more common in female athletes?’, but also the ability to prescribe a ‘cure’. Even more exciting, the cure is not some new, outlandish, complicated, surgical procedure requiring months of recovery, but a preventative rehabilitation program that can be performed by any athlete.

See our next Blog about prevention measures…..