Women’s Rate of Knee Injuries Studied

Coming down from a layup may be harder on women’s knees than men’s because women do it wrong, a study suggests.

But other new research indicates that women’s greater rate of injuries to the anterior cruciate ligaments, which bind the upper and lower leg bones together at the knee, also may be due to different patterns of muscle use--or simply being in worse physical shape.

“Women are seeing higher forces transmitted across the joint, and their ability to protect the joint needs to be better,” said Dr. Edward M. Wojtys of the University of Michigan.

Wojtys and his colleagues looked at the angle of the knee as 10 men and 10 women jumped down from heights of about 10, 20 and 30 inches.

At the 20- and 30-inch distances, women landed more straight-legged than did men, the researchers found. The knee angle was about 7 degrees for women but about 16 degrees for men.

In a sense, landing straight-legged misses the point of having a knee. The leg should act as a shock absorber in falls, bending to reduce the impact. A straighter landing puts more impact on the joint.

A small difference in knee angle creates a far bigger difference in impact, because more of the weight of the falling body is absorbed by the joint, Wojtys said.

Women especially need to protect their knees, but there is no solid research on how to do it, Wojtys said. It may not be as simple as putting more bend into the knee. Women may also need to build strength and endurance, and to put extra effort into practicing the moves in their sports, he said.

“It’s not just strength--it’s probably the integration of the muscles, which muscles you call upon and, more importantly, the reflex patterns, which are pre-programmed,” Wojtys said. “The key thing is, we have to learn what this desired pattern is before we teach it, and at this point, we don’t know for sure.”

Wojtys presented his findings at the Orlando, Fla., meeting of the American Academy of Orthopaedic Surgeons.

Another study presented at the meeting looked at muscle differences between 25 female and 26 male collegiate athletes. Using equipment to evaluate nerve and muscle activity, the researchers watched the athletes do knee bending and extension exercises.

Women tended to rely on the quadriceps muscles in the front of the leg, more than did men, said Dr. Klane White of UC San Diego. The hamstrings in back are supposed to work with the quadriceps to stabilize the leg. So if women can be taught to change their muscle movements, they might reduce their risk of ACL injuries, he said.

A third study at the conference examined the risk of ACL injuries among men and women. The four-year look at West Point students by West Point doctors found an injury rate of 0.04% for females but only 0.027% for males.

And a separate study, not presented at the conference, suggested that women’s leg injuries in general may be related to their not being in as great a shape as they could be. In this project, researchers followed 509 men and 352 women through eight weeks of Army basic training. The study was being published in the American Journal of Preventive Medicine.

The study did not look at the anterior cruciate ligament specifically, but did look at visits to clinics, many of them for leg injuries such as stress fractures, which are small but painful bone cracks.

Women had about twice the rate of injuries that men did, and the women’s rate of injury that cost at least one day of lost duty was 2.5 times higher, the study found.

However, the apparent sex difference seems to be really a difference in strength and fitness, said researcher Nicole S. Bell of Social Sectors Development Strategies, Boston, a contract research organization that worked on the project with the Army.

“The people who ran slow got hurt regardless of whether they were male or female,” Bell said. “The people who ran fast did not get hurt regardless of gender.”