Why Women suffer more Knee Injuries

Lisa

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Female athletes are up to eight times more likely to suffer knee injuries during their careers than males, and now researchers may be closer to understanding why.

A recent study of 10 female and 10 male NCAA athletes completed within the Department of Biomedical Engineering at the Cleveland Clinic found that female athletes tend to land from a jump with a more flexed ankle, the foot rolling outward with an elevated arch, and more knee abduction and knee internal rotation compared to male athletes.

When fatigued, differences between women and men in these movements and loads were even larger, possibly explaining why females may be at greater risk of non-contact anterior cruciate ligament (ACL) injury during landing

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exile

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Very interesting and important result if it can be sustained.

But then the question is, why are women more likely to land in that configuration? The article didn't even speculate, so far as I can tell...
 

Kacey

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I'm not overly surprised - I did some research in the past when I've injured my own ACL, and here are some of the things I've found:

Young Women at Greater Risk of ACL Tears
"Women are anywhere between two and eight times more commonly injured in regards to their ACL than males are. There's several suspected answers, but the most common reason where the research is heading right now, is what are known as neuromuscular differences. In other words, the way women's muscles fire around the knee the quadriceps or hamstring muscles in response to a stress to the knee joint. And there's been shown to be several differences between males and females."
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By: Owen Anderson

It's sad but true: female athletes who take part in sports involving jumping and 'cutting' (football, basketball, volleyball, gymnastics etc) have a risk of knee injury that is 4-6 times higher than for men taking part in the same activities1.
In the USA, the knee injury rate among female collegiate athletes runs at a stunning one per 1,000 'athlete-exposures' (an 'athlete-exposure' is simply a workout or competition). With over 100,000 college women taking part in organized sports each year, there are more than 10,000 knee injuries per year - or more than 1,000 per month (given a nine-month school year).

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Wider Female Pelvis A Factor?

Why are females at greater risk of ACL trouble? The reason is unclear, but some sports medicine experts think it is primarily because of anatomical differences.

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Intercondylar Notch:
  • For one thing, the intercondylar notch - a small chasm at the bottom of the femur through which the ACL passes - tends to be smaller in females than in males6. Thus it is theoretically possible that during cutting and jumping movements, the narrow female notch may fray and weaken the ACL. Any fraying of the ACL would tend to be more serious in female athletes since the female ACL is usually a smaller structure.
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Pelvis:
  • Also, the wider female pelvis tends to exaggerate the angle made at the knee between the femur and tibia when the foot is planted on the ground, increasing inward pressure on the knee and external rotation of the tibia, and thus placing excessive stress on the ACL7.
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Lax ACL:
  • Even more interesting is the theory that the ACL is more lax in females than males - and therefore more susceptible to overstretching8. There are receptors for both estrogen and progesterone on the ACL and the theory suggests that increases in one or both of these hormones may slacken the ACL, heightening the risk of damage. It is known that a woman's ligaments tend to loosen up as a result of the hormonal changes associated with pregnancy, so this theory is not too far-fetched and, if true, would also suggest that the risk of injury would vary with the menstrual cycle9.
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Leg Strength:
  • Studies from the University of Michigan have shown that female athletes have less strength in their leg muscles and slower muscle-reaction times than males, which would increase the risk of ACL trauma.
 

exile

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This is very interesting, Kacey, but it is also a bit troubling, because the information in your post suggests that the problem is due to neuroanatomical differences between men and women so far as the ACL itself is concerned, whereas the study Lisa posted seems to locate the primary difference in the way female athletes land from a jump—foot position. It could be both are right, but the material in your post seems to identify the crucial difference in angle not at the foot but again, at the knee. So it looks like there's something additional going on...

Also, I'm confused by the point made about weaker leg strength in female athletes. Is that supposed to be relative to body weight? Because if so, it conflicts with results I've seen repeatedly confirmed, which is that women have the same number of fast-twitch muscles below the waist per lb of body weight as men do. And it's the fast-twitch muscles which are developed by strength training. So there looks like a contradiction of sorts here...?

It's so hard to get a unified story out of these exercise physiology types!
 

Kacey

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This is very interesting, Kacey, but it is also a bit troubling, because the information in your post suggests that the problem is due to neuroanatomical differences between men and women so far as the ACL itself is concerned, whereas the study Lisa posted seems to locate the primary difference in the way female athletes land from a jumpfoot position. It could be both are right, but the material in your post seems to identify the crucial difference in angle not at the foot but again, at the knee. So it looks like there's something additional going on...

I've seen some of each... I can only speculate that the different configuration of the knee joint and the angle of the thigh from the hip due to the width of the pelvis combine to change the landing angle - thus leading to greater injury from the jump foot position in addition to greater physiological risk. But that's pure speculation on my part.

Also, I'm confused by the point made about weaker leg strength in female athletes. Is that supposed to be relative to body weight? Because if so, it conflicts with results I've seen repeatedly confirmed, which is that women have the same number of fast-twitch muscles below the waist per lb of body weight as men do. And it's the fast-twitch muscles which are developed by strength training. So there looks like a contradiction of sorts here...?

It's so hard to get a unified story out of these exercise physiology types!

As far as that potential contradiction goes - although the proportion of fast-twitch fibers may be the same by weight, women are generally less muscular than men - women who lift weights are often aiming for a sleeker, less bulky look than men, and therefore tend to complete more reps at lighter weights, which changes the build-up of muscle tissue, and therefore overall strength. Also, in general, women weigh less than men, so while they may have the same potential number of fast-twitch fibers per pound, the average woman will still less overall strength.
 
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Lisa

Lisa

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Kacey's post is great. Exile you, yet again, bring up some excellent points as well.

I can't find the study, I read it years ago while in nursing school. It related the injuries to women's knees not only to weaker/smaller leg muscles, wider pelvis' but also on the fact that women have a lower center of gravity then men because we carry a larger amount of our body weight in our hips.
 

exile

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I've seen some of each... I can only speculate that the different configuration of the knee joint and the angle of the thigh from the hip due to the width of the pelvis combine to change the landing angle - thus leading to greater injury from the jump foot position in addition to greater physiological risk. But that's pure speculation on my part.

Yes... that has the ring of truth. Makes much senseLisa's original study didn't address the point, but it's true that the difference in the landing angle her study talks about is fixed at the moment of landing. They probably haven't gotten to the point of tracking it all the way through the jump, lol!



Kacey said:
As far as that potential contradiction goes - although the proportion of fast-twitch fibers may be the same by weight, women are generally less muscular than men - women who lift weights are often aiming for a sleeker, less bulky look than men, and therefore tend to complete more reps at lighter weights, which changes the build-up of muscle tissue, and therefore overall strength. Also, in general, women weigh less than men, so while they may have the same potential number of fast-twitch fibers per pound, the average woman will still less overall strength.

You're right, that's bound to be the case, actuallymen tend to weight-train for bulk. Women very possibly train more for endurance (except for women shot-putters, discus throwers and other athletes who must train for explosive lower-body strength).

What you say makes very good sense all round...
 

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I was just reading an article the other day in an old Runner's World and it mentioned that your shoes may also contribute to the problem. That a lot of manufacturer's will just take a men's shoe and slap "women's colors" on it and sell the shoe as a woman's shoe, but that that can cause problems cause it assumes things like the location of arches and the amount of pronantion between men's and women's feet are the same...
 

Kembudo-Kai Kempoka

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It's not really news for geeks in sports physio land. Wider pelvis requires a steeper incline toward the midline to get the feet under the body, which requires a greater valgus angle at the knee.

In general, women are also more flexible than men...even men who stretch; if Lisa and I start the same yoga program at the same time, she'll be at a 3 year landmark when I'm at my year mark, and we'll both have the same number of mat hours.

Bigger valgus with more flexible muscles = that funny angle that's hard on the ladies' knees. One researcher who noted an increase with knee problems among college volleyball players practicing plyometric box jumps recommended landing with the feet wider than natural, so as to decrease the load on an increased valgus knee. Knee complaints dropped by over half.

Take care of your knees; you need them.

D.
 

exile

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It's not really news for geeks in sports physio land. Wider pelvis requires a steeper incline toward the midline to get the feet under the body, which requires a greater valgus angle at the knee.

In general, women are also more flexible than men...even men who stretch; if Lisa and I start the same yoga program at the same time, she'll be at a 3 year landmark when I'm at my year mark, and we'll both have the same number of mat hours.

Bigger valgus with more flexible muscles = that funny angle that's hard on the ladies' knees. One researcher who noted an increase with knee problems among college volleyball players practicing plyometric box jumps recommended landing with the feet wider than natural, so as to decrease the load on an increased valgus knee. Knee complaints dropped by over half.

Take care of your knees; you need them.

D.

This is very interesting... what strikes me is that if you just look at a number of men and women at random, it isn't especially clear that women's hips are all that much wider in relation to their height, say, then men's are. I'd be interested in seeing this difference quantified, but if it were any larger than 10% overall I'd be surprised. But apparently, that small difference, and the consequent small difference in angular alignment that Dave has commented on, is enough to make a major impact on the numbers distinguishing men's ACL injury rate from women's. These very small differences seem to get leveraged into major outcomes...
 
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