Five Reasons Why Females Are More Likely to Tear Their ACL

On average, female athletes are 4-5 times more likely to tear their ACL (Anterior Cruciate Ligament) than their male counterparts. 

With over twenty years of experience as the head physician for the U.S. Women’s Alpine Ski Team, Dr. Sterett has been able to pinpoint five factors that contribute to a woman’s higher risk of ACL tears.

1. Women Are More “Knock-Kneed” Than Men

When a person is “knock-kneed,” it means their thighbones curve inwards from the knee to the hip. Since women typically have wider hips than men, they are more prone to either being knock-kneed or having a knock-kneed stance.

Here’s a simple test to tell if you are knock-kneed:

• Stand with your knees together

• Do you stand with your lower legs spread out so there’s a gap between your ankles?

• Is that gap over 3 inches?

If the answer to those two questions is yes, you may be knock-kneed or have a knock-kneed stance. The danger here is, when the knees point inward, it places added stress on the ACL. Additional stress increases the risk of an ACL tear, especially when landing after a jump. 

  2. Women Are More Loose-Jointed

On average, women have more flexibility in their hips and knees. This is great for range of motion, but it also puts female athletes at a greater risk for hyperextension. 

We treat more ACL injuries caused by hyperextension in female athletes than in males. The current thinking is this congenital hyperlaxity is due to hormones that develop in women after puberty, meaning that females are more likely to be “loose-jointed.” 

The risk? Loose-jointed athletes are 4-5 times more likely to tear their ACLs.

To test if you or your loved one is loose-jointed, give yourself a point for each of the following:

You can bend your thumb down to touch the front of your forearm (2 points if you can do so on both thumbs)

• You can bend your pinky back more than 90 degrees from the knuckle (2 points if you can do so on both pinkies)

• Your elbow can hyperextend more than 10 degrees (2 points if you can do so on both elbows)

• Your knee can hyperextend more than 10 degrees (2 points if you can do so on both knees)

• You can place your palms flat on the ground without bending your knees

There are a total of nine points possible in this test. If you score 7 out of 9 possible points, you are loose-jointed.

3. Women Tend to Land More Straight-Legged When Jumping

Biomechanical differences mean that female athletes tend to land more straight-legged when jumping than their male counterparts. Additionally, women’s knees tend to fall inward when:

• Landing

• Bending

• Pivoting

As a consequence, the force on the knees is greater and less evenly distributed. To prevent ACL injuries as a result of landing, we typically recommend the following:

• Properly warming up and cooling down before and after activity

• Learning how to land in a way that your hips and ankles help your knees absorb the force of impact

• Start a strengthening program that focuses on the legs and knees

4. Women Have a Smaller Intercondylar Notch and ACL

The intercondylar notch is a groove that sits in the middle of the two rounded ends of the thigh bone (femur). The ACL passes through this groove, giving the knee stability. Some unavoidable physical factors in females are: 

• Women have a smaller intercondylar notch

• As a result, the female ACL is 30% smaller to accommodate the narrower passage (and for equivalent body mass) 

• The smaller the ACL, the more strain is put on it during twisting motions

• This smaller intercondylar notch and ACL size lead to increased instances of ACL tears

Unfortunately, there isn’t much women can do about these physical risk factors besides standard activity preservation. This means working with your sports medicine team to build and maintain strength in the lower body. 

5. The Menstrual Cycle Can Impact the ACL

A less discussed risk factor in female ACL tears is the menstrual cycle. Here’s how it works:

• Low levels of estrogen and progesterone have been shown to cause an increase in ligament laxity.

• Since estrogen and progesterone are hormones that lower during the first half of the menstrual cycle, this means menstruation can impact the ACL.

• During this period of menses, the ACL is less rigid and more likely to tear.

• As a result, women are four times more likely to tear their ACLs during the first two weeks of their menstrual cycle. 

There are currently several studies on whether contraceptives can decrease this risk. A growing body of research suggests that oral contraceptives, which act to downregulate hormone fluctuations, can have a preventative effect on ACL tears during this time.

Concerns About Your Risk Factors? Contact Team Sterett Today!

Understanding these differences can help female athletes, coaches, and surgeons make some basic changes to pre-season and post-injury treatment plans to lessen these devastating numbers.

If you’re a female athlete concerned about the risk factors associated with tearing your ACL, contact Team Sterett today.