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The ABCs of ACL injuries in women

Since the Title IX Educational Assistance Act—which mandated equal funding for women's sports—was passed in 1972, the number of female athletes suffering from anterior cruciate ligament (ACL) injuries has soared.

I see several of these injuries every week among both men and women. Several studies have compared the incidence of ACL injuries between males and females and findings indicate women experience anywhere between four and 11 times as many of these injuries as men. Interestingly, before adolescence, the rate of injury is about the same; but at about age 12, the rate of injuries in girls begins to outpace those in boys.

What is an ACL injury?
The ACL is one of the four major ligaments in the knee and more susceptible of the two ligaments that connect the thigh bone (femur) with the shin bone (tibia), beneath the kneecap. The ACL is more likely to be stretched or fully torn during sports that involve jumping or quick changes of direction. Basketball and soccer are the kinds of sports in which these injuries are most prevalent.

Why women?
There are three broad theories about why this difference between the genders exists. The first has to do with the anatomical differences between the sexes. Because women's pelvises are wider than men's, the angle at which the femur and the tibia meet at the knee is sharper, resulting in a more “knock-kneed” alignment in women. The knees rotate in and the bottom of the leg splays out, creating more potential for excess stress on the ACL. Further, the ligament may be smaller in women and the notch through which it passes to connect the bones may be smaller; these factors may also make women more vulnerable to injury.

The second theory suggests female hormones may play a role. Ligaments like many other tissues, may be affected by hormone levels. ACL injuries occur more frequently to women in the ovulatory phase of their menstrual cycles. The female hormones estrogen and progesterone relax muscles, ligaments, and joints, resulting in an increase in joint mobility that could place women at risk. Hormonal changes could have other effects as well—perceptual and concentration deficits and neuromuscular changes, for example.

The third theory, which I consider the most likely and which the study conducted at the University of Cincinnati College of Medicine puts forth, is that as girls enter adolescence, their neuromuscular development differs from boys.

In order to shift direction quickly, it's important for your muscles to fire at precise moments in perfect synchronization. If this precision does not occur, then instead of the muscles taking the brunt of the movement in, for instance, a sudden change of direction, the ligaments and bones absorb the impact.

For uncertain reasons, women do not seem to have this neuromuscular precision developed to the extent that men do. It might be hormonally mediated, because young males have testosterone and this plays a vital role in muscular development. Studies that have examined how men and women land from a jump show that women tend to use less hip and ankle musculature, exposing the knee to greater amounts of uncontrolled movement.

What can be done to prevent injuries?
There has been documented success with a training program that takes into account form, flexibility and plyometric strength. This program is essentially a progressive jump-training program that emphasizes form and technique of jumping and landing. Jump training led to a significant decrease in the incidence of ACL injury among female athletes. Other benefits include increased overall strength of the hamstrings and an increase in vertical jump.

For girls who intend to pursue the kinds of sports that place them at risk for ACL injuries, training with a specialist who understands jump training may greatly reduce their vulnerability to injury.

Treating ACL injuries
Many of the body's ligaments will heal after injury if the patient rests and keeps the affected area immobilized. Unfortunately, ACL tears do not heal on their own. Once the ACL is torn, the stability of the knee is compromised. Sudden, pivoting movements may be difficult and the affected knee is more prone to cartilage tears, which can lead to subsequent arthritis.

The decision to have reconstructive surgery is dependent on several factors. Some patients who experience ACL tears are able to resume normal daily activities without surgical repair of this ligament. If a patient intends to resume participation in sports that stress the knee, however, surgery is generally indicated. Of course the patient must be willing to participate in a period of postoperative rehabilitation.

Advances in arthroscopic surgical technology allow for minimally invasive surgery, resulting in smaller incisions, less post-operative pain and quicker recovery. Although the gender difference in injury rate exists, studies show that the success rate of ACL reconstructive surgery is the same between men and women. Currently about 100,000 reconstructive surgeries are performed in the U.S. each year.

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Dr. Medvecky is an attending orthopaedic surgeon at Yale-New Haven Hospital and an assistant professor of orthopaedic surgery at the Yale University School of Medicine.