ACL Tears Part 2: Why women are 3.5 times more likely to tear an ACL than men

Posted on: September 19th, 2013 by Dr. Geoffrey S. Van Thiel

Perhaps, that number shocks you: 3.5 times more than men.  Well, to a certain extent, it should.  But some people claim even higher numbers up to eight times as likely, though the data do not necessarily support those claims.  Season risk over the course of the year for a female soccer player is about 5%, whereas it”s about 1.5% in males.

In my own clinic, my patient ratio matches the data in the younger athletes: many more female ACL tears.

This topic is particularly important because a female athlete who tears one ACL is at a much higher risk of tearing her other ACL as well.  We don”t really know why that is, but it”s a fact.

People theorize about factors that predispose women to an ACL tear, but it’s still a new science, and because it’s a new science, ACL injuries in women receive a great deal of attention, as they should.

But ACL studies are difficult because you need so many patients in order to see a difference between types of treatment.  So the studies looking at this problem will observe 1000 female athletes.  Maybe fifty have an ACL tear, and they look at the difference between what the fifty did versus the 1000.

What we do know is that much of the injury rate is due to muscle control problems and the alignment of the lower extremity.

Some of the best data that exists is in soccer and basketball, especially since Title IX came out.  More even participation between the sexes in those sports means researchers have more data.

It’s possible since more women participate in team-based sports than before that more women experience ACL injuries, but when you equalize the numbers, percentages remain constant, which can mean only one thing: participation cannot account for the injury rates.  An anatomical reason must exist.

In the following video, you will see a typical ACL injury in women’s soccer.  The player cuts and pivots, leading to an ACL tear.

What the science shows and theories claim

Females tend to have a higher Q angle, which means that the knee is a little more valgus.  A more common term for valgus is “knock-kneed.”

Females tend to have their knees a little closer together than males in relation to the hip and ankle.  It”s just how they were made.  It does not mean a problem or an issue exists.

On the downside, that increased Q angle/alignment puts more torque and torsion on the ACL when a female lands from a jump, or pivots or cuts.

A narrower space for the ACL

In the middle of knee, the ACL is in a tunnel of sorts.  The ACL attaches to the lower bone, goes through a tunnel, and attaches to the upper bone.
[blockquote]Females tend to have a narrower tunnel in the middle of the knee.[/blockquote]
One theory suggests the ACL impinges on the corner of the tunnel which may contribute over time to a weakened and eventually torn ACL.

Sadly for many female athletes, the fact that sometimes people with more of a narrow tunnel have a higher rate of ACL injury is a new revelation.  To make that next jump to confirm why that occurs is the next step in research.

The narrower tunnel could cause the ACL to “bump” against the tunnel wall, leading to a weaker and more-likely-to-tear ACL.  Maybe you’ve been running your whole life, and every step bumps the ACL.  Then when you have that one episode when you cut or pivot, the ACL may just fail and tear.

As an orthopedic surgeon we understand it more and more as we go through and see more tears.

A smaller ACL

Based on MRI studies, females tend to have a smaller ACL than males, even when accounting for differences in body weight and height.  When we adjust for weight and height, the female ACL has a smaller diameter.

Varying estrogen levels

The female ACL has estrogen receptors on it inside the knee.  These receptors cause the ACL to stretch when estrogen levels increase, and some studies propose that increased levels of estrogen put female athletes at a higher risk of a tear.

Think of the ACL as a rubber band.  If the rubber band stretches, it’s chance of breaking also increases.  It’s the same with the ACL, and estrogen may contribute to that stretching.

That said, this is a theory (backed by evidence), but it has not yet been proven.

The female body has estrogen receptors all over the body, so some take that to explain why females in general are more susceptible to injuries anywhere on the body than men, not just the ACL.

Incorrect Muscle Control of the leg is a contributing factor

A non-anatomic–but structural issue–in many female athletes is the muscle control of the leg.  Using video analysis of female athletes jumping, cutting, landing, or pivoting, we have found that female athletes tend to land in certain ways:

  • with their legs a little more straight
  • With their hips a little more internally rotated
  • With their hips flexed a little more, meaning they are leaning forward.

This is a position of danger for the ACL, adding much more torque and stress.

Ultimately, the muscles around the leg help to stabilize the ACL.  So muscle control and activation­–how those muscles react to landing, jumping, cutting, and pivoting–protect and give secondary stabilization to the knee.

Prevention Programs will help reduce injury

If you are competing in sports, you should participate in an ACL prevention program.  They provide immediate benefits because the training solves many of the muscle control issues faced by female athletes.

This research has sparked the creation of preventative exercises and protocols for female athletes.  Some research says training doesn’t make a difference, but other research says coaches, therapists, physicians, and athletic trainers need to focus on training people to feel their bodies in space.

Trainers can accomplish that by:

  • Training athletes with appropriate mechanics
  • Training athletes to pay attention to know where the foot is when landing
  • Training athletes to know where the knee is when landing.
  • To overall protect the ACL through strength training

Many prevention programs last for about eight weeks and should be completed prior to the beginning of the season.  These programs provide players with better knee control and stability, and they decrease a player’s chance of a tear.

A female soccer player should start ACL preventative exercises eight weeks before the season begins.  This will give her better knee control, better stability of the knee, and less chance of a tear.

All of the exercises in prevention programs can be done in a home-based or school-based environment.  You don”t need specific equipment.

Prevention programs require commitment and time; they are quite involved and can require explanation from an athletic trainer, coach, or physical therapist. Because of that, participation and compliance rates are lower than they should be.

If you decide to be a part of a program, stay motivated.  Persevere.  Your ACL will thank you.

Mind and body matter in training

Training your mind to control your body is a major component of the programs.  For example: jump off a box and land multiple times. Do that to the point that you think every time about your knee being directly center over your foot when you land.

Also, focus on hamstring strengthening.  When the ACL stretches, the brain will tell the hamstring muscles to activate in order to prevent a tear. You want your backup system to function well and be strong; otherwise, it”s not really going to do all that much to protect you from injury.

Especially in females, there is a difference in the ratio between the quadriceps and the hamstrings.  The quadriceps tend to be stronger than the hamstrings.  Female athletes should focus on hamstring strength.  Do lunges, squats, etc.

Again, think about how the knee is positioned over the foot.  A female (or male) could do one hundred squats in a day, but if she internally rotates her hip and allows her knee to go to the inside of her foot, she has put her ACL at risk and hasn’t done anything to decrease her chance of a tear.

5 things to consider and know before you begin a prevention program

  1. Make sure you talk to someone who knows what they are talking about.
  2. This training is mental and physical.  You may get the physical portion down, but you might not have the proper mental training.
  3. Your mind often needs to retrain the muscles to move differently, and that”s something where a second pair of eyes really helps.
  4. Do video analysis of your jumping and landing.  Slow that down and look at the relationship between each joint and muscle.  Then you can identify areas for improvement.
  5. Do another video analysis showing the improvement.  We”re visual people.  It really helps to know what this should look like, and that”s where a trainer and a camera come in handy.

Have you experienced an ACL tear as a female athlete?  Share about it in the comments.  Also, feel free to ask questions or add some other things to consider.

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