Why women are more susceptible to anterior cruciate ligament (ACL) injuries

New research presented today at the 72nd Annual Meeting of the American Academy of Orthopaedic Surgeons includes important findings on the causes of anterior cruciate ligament (ACL) injuries in female athletes, such as posture and body movement. These findings may be key in the effort to find ways to prevent these types of injuries.

The ACL connects the thigh bone (femur) to the shin bone (tibia). Athletes are particularly susceptible to ACL injuries because this ligament can be torn when a person changes direction rapidly, slows down from running or lands from a jump. These tears prevent the knee from being able to support the body, and often require surgical repair.

Women suffer ACL injuries at a significantly higher rate than men. Data collected since 1995 finds that the incidence of ACL injuries among women basketball players is twice that for men, and that female soccer players are four times more likely to experience an ACL tear than their male counterparts.

Much research has been conducted to determine why these differences exist, and how these painful injuries can be prevented.

A team of researchers at the University of North Carolina-Chapel Hill led by Spero G. Karas, MD, assistant professor of orthopaedics at Emory University, Atlanta, examined the mechanical motion of the trunks and hips of 18 female and 17 male elite soccer players as they performed certain athletic tasks. The study found that female athletes tend to hold their trunks and hips in a more erect posture while performing running and jumping maneuvers, suggesting that this difference may contribute to the increased risk of ACL injury.

As the first study to look at the effect of trunk and hip motion on ACL injury, these findings provide a new avenue for physicians and trainers looking to help female athletes protect their ACLs.

"Now knowing that the trunk and hip may be an important variable in this problem, we should consider appropriate intervention strategies," said Dr. Karas. "These would include instructing and training female athletes to perform maneuvers in a less erect posture, stressing the importance of trunk and knee flexion," said Dr. Karas.

Data collected from a separate study conducted by researchers at the Medical College of Ohio, Toledo, suggested that there were inherent gender differences in elite athletes' ability to reproduce various squatting positions, particularly with regard to more erect posturing. Henry T. Goitz, MD, associate professor and chief, orthopaedic sports medicine and director, Center for Performing Arts Medicine, at the Medical College, led the research effort that compared collegiate soccer players -- 33 men versus 33 women.

"The female athlete was able to reproduce deep squatting positions just as well as their male counterpart; however, women do not stay in these bent-knee positions during sport," said Dr. Goitz. "This could be that perhaps women fatigue in these positions more easily than men, or perhaps it is just a habit. If either is the case, female athletes should be conditioned to place themselves in a more protective position in sport activities, and, thereby, reduce ligament injury."

Dr. Goitz's team examined two additional groups in which leg control is an integral part of training -- gymnastics and ballet -- the former with a relatively high ACL injury incidence, and the latter with an extremely low incidence. Data collected from studying 22 elite female gymnasts (level 8 and above) was nearly identical to that of the female college soccer players. Interestingly, when studying eight female professional ballet dancers, this group exhibited superior scores compared to all groups, both men and women. "The training of the female ballet dancer may provide the key to our understanding of ACL injury prevention," explained Dr. Goitz.

Gender differences were also found in the mechanical motion of the knee, according to research conducted by Timothy C. Sell, PhD, PT, research coordinator of the neuromuscular research laboratory at the University of Pittsburgh. He and his team of researchers studied a group of 18 male and 17 female high school basketball players as they performed lateral jumps, a task that is known to cause noncontact ACL injuries. Female athletes were found to bend their knees less and turn them in more than the males, a difference that could be partially responsible for the disparity in the number of ACL injuries.

"Because women are more at risk for ACL injuries, they need to pay particular attention to prevention," said Dr. Sell. "Knowing that there are differences in the way female athletes move can aid in the creation of training programs to reduce the forces that can cause these injuries. This information needs to be shared directly with the coaches and trainers who work with college, high school and even junior high athletes."

Another study has pinpointed an additional method to reduce women's chances of suffering an ACL injury. The primary author of this study, Paul A. Martineau, MD, chief resident in the division of orthopedic surgery at McGill University, Montreal, Canada, determined that taking the oral contraceptive pill may help women reduce their chances of experiencing ACL injuries. The study of 127 female athletes found that those who used oral contraceptives had less knee laxity in their ACLs, making them less likely to suffer injuries to those ligaments.

"While more research needs to be done with a larger group of women for a longer period of time, the preliminary findings are encouraging," Dr. Martineau said. "This study has provided evidence that oral contraceptives may provide women with some protection to the ACL."

An orthopaedic surgeon is a physician with extensive training in the diagnosis and non-surgical as well as surgical treatment of the musculoskeletal system, including bones, joints, ligaments, tendons, muscles and nerves.

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