(HealthDay News) — Women are more likely than men to suffer a knee injury called an anterior cruciate ligament (ACL) tear. But — surprisingly — the injury occurs the same way in both genders, a new study reveals.

Prior research suggested women are two to four times more likely to suffer ACL tears due to differences in how this type of injury occurs in the sexes, researchers at Duke University, in Durham, N.C., noted.

But that theory is wrong, according to the results of a new study of 15 women and 15 men with torn ACLs. Those prior studies were based on slow-motion replays of injuries, while the new work relied on scans and other advanced techniques.

“Based on watching videos of athlete injuries, previous researchers have suggested that females may have a different mechanism of injury than males. But it’s difficult to determine the precise position of the knee and the time of injury through footage,” said study leader and biomedical engineer Louis DeFrate.

“We used MRI scans taken within a month of the ACL rupture and identified bruises on the surface of the two large bones that collide when the ACL tears — the femur and the tibia — then used 3-D modeling and computer algorithms to reconstruct the position of the knee when the injury occurred,” he explained in a Duke news release.

“Our results suggest that males and females have the same position of injury,” DeFrate said.

The study was published online April 18 in the American Journal of Sports Medicine.

It was long believed that ACL tears were caused by an inward buckling of the knee. However, a previous study by DeFrate and colleagues concluded that landing on a hyperextended knee — when the knee is bent backwards — is what causes an ACL tear.

“In order to develop improved treatment strategies and prevention, we need a clear understanding of what motions are most dangerous for athletes,” DeFrate said.

According to DeFrate, this work provides new evidence that landing on an extended knee may be a dangerous position for ACL tears in both sexes.

ACL Knee Injuries

Knees Are Casualties of Women’s Sports

Active women are at least twice as likely to suffer serious knee injuries as men, but it’s not just athletes who are at risk.

Although female athletes at the high school and college level can suffer serious knee injuries, women who play recreational volleyball or participate in step aerobics also can injure their knees, says the American Academy of Orthopaedic Surgeons (AAOS). A mother who carries her child down a flight of steps and misses the last step also can injure her knee. In short, a knee injury can happen to any woman, no matter how athletic she is.

The chief movements that cause knee problems in women are pivoting and landing from a jump, the AAOS says.

Luckily, women can help protect themselves by getting into better shape, knowing their strength, controlling their weight, and exercising their leg muscles.

Anatomy of the problem

Why are women’s knees, in a sense, their Achilles heel?

Since a woman has a wider pelvis, her femur (thigh bone) descends into the knee at an inward angle.

When a woman becomes fatigued, as during an athletic event, the angle on landing becomes more pronounced, further increasing the chance of injury.

A band of fibrous connective tissue called the anterior cruciate ligament (ACL) passes through a “notch” in the lower end of the thighbone that forms part of the knee. The ligament, one of several that attach the upper and lower leg bones, is about the same size for a woman as a man—but the notch is up to 20% narrower in women. That makes the woman’s ligament more susceptible to tearing.

A woman’s hamstring muscles, at the back of the thigh, are often weak compared with her quadriceps, the muscles at the front of the thigh. The quadriceps pull the bones of the lower leg forward, and the hamstrings pull them back. Hamstring muscles help protect the ACL from injury. When the pulling power is out of balance, the knees suffer.

The muscle imbalance tends to be far worse in women than in men. The imbalance may begin to happen during childhood if girls engage in less physical activity. Exercise can help overcome the problem.

Risk of injury to the ACL appears to be higher during ovulation, when estrogen levels are highest. The ACL appears to respond to estrogen by decreasing cell activity to repair basic ligament fibers called collagen.

Strengthen your legs

Strengthening exercises are especially important for your hamstrings. Try hamstring curls: Lying on your belly, draw your lower legs upward, and try to touch your heel to your buttock. Use resistance equal to about 10% of your body weight. Do a few sets of 10 to 15 repetitions; hold them a second or 2.

Jumping exercises are also critical for building strength and preventing knee injuries. When you land from a jump, keep it soft. Come down on the balls of your feet and slowly roll back to the heel. Keep your knees bent and your hips straight. Try to keep your knee in line with your foot.

Hopping over a cone side to side and forward and backward builds strength and control:

  • Place a 6-inch cone on your left. Hop over the cone with both feet, concentrating on a soft landing. Repeat by hopping back over the cone to the right. Repeat for a total of 20 hops.
  • Place the cone in front of you. Hop over the cone with both feet, then hop backward over the cone. Keep your knees slightly bent when you land. Repeat for a total of 20 hops.
  • Repeat the above forward and backward exercise, but hop with 1 leg at a time. Again, keep your knee slightly bent when you land. Do 20 hops on each leg.

Other knee injuries prevention tips

  • Improve your overall strength and fitness.
  • Know your level of fitness and the demands of your sport or activity.
  • Control your weight. When you walk, each extra pound adds 4 pounds of pressure to the kneecap. That pound adds 20 pounds of pressure when climbing steps.
  • Buy sturdy shoes made for your activity, and replace them when the inner or outer soles appear worn.

More information

The American Academy of Orthopaedic Surgeons has more on ACL injuries.

SOURCE: Duke University, news release, April 18, 2018