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THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 10 - OCTOBER 1, 1999


Training Programs May Lower Women's ACL Injury Risk

Noncontact anterior cruciate ligament (ACL) injuries are believed to be two to six times more common in women than in men, particularly in basketball, Alpine skiing, volleyball, and apparatus gymnastics (1-3). The reasons for this gender inequity remain unclear, but at a Maryland conference in June, about 20 experts agreed that neuromuscular differences are probably the major factor.

This consensus seems likely to increase interest in programs designed to prevent noncontact ACL injuries through preseason conditioning and/or instruction in how to respond to hazardous situations. A few programs developed in recent years have shown promising results.

What Does Research Say?

Much research on women's higher rate of noncontact ACL injuries has discounted proposed causes or is inconclusive. Intercondylar notch configuration has been suggested as a potential factor, but research has been contradictory. Some studies have suggested "loose-jointedness" as a cause, while others have shown no relationship between joint laxity and injury.

Another proposed explanation is that women's quadriceps muscles are stronger than their hamstrings, and the strength imbalance contributes to ACL injuries. However, this has not been shown to cause ACL injuries in women or in athletes in general. In 1996, Huston and Wojtys (4) reported that female athletes tend to fire their quadriceps in response to anterior tibial translation, which can overload the ACL when the knee is at or near extension (men's hamstrings fire instead).

Researchers are also looking for differences in injury biomechanics. In general, the three main noncontact injury mechanisms are planting and cutting, straight-knee stopping, and one-step landing with the knee hyperextended (6).

In one of the few studies to probe for biomechanical differences, Australian researchers (6) recently analyzed knee joint kinematics during the sidestep cutting maneuver in 16 men and 14 women. They found greater intrasubject variability in knee rotation in women than men. However, they determined that this resulted from the women's lesser experience with cutting relative to the men, not from inherent differences, and they concluded that differences in ACL injury risk are not likely to be explained by differences in knee motion during cutting (though their study didn't actually analyze ACL injury risk). The authors concluded that skill-specific training would increase experience levels and possibly decrease variation in knee joint kinematics.

Mark R. Hutchinson, MD, director of sports medicine services, assistant professor of orthopedics and sports medicine, and head team physician at the University of Illinois in Chicago says he believes the bottom line is that the cause of increased ACL injuries is multifactorial. "Neuromuscular causes are a factor, but the training will not bring women's injuries down to men's rates," he says, noting that possible hormonal causes are another area of increased interest and study.

Hutchinson says his female athlete patients are benefiting from training programs, which have become more numerous and visible since Sports Illustrated published an article in 1995 on ACL injuries in women. In 1996, Italian researchers (6) showed that balance-board training decreased ACL injuries.

Success in Cincinnati

In 1995, researchers at the Cincinnati Sportsmedicine and Orthopaedic Center tested a jump training program designed to improve landing mechanics and increase lower-extremity strength in female athletes (7). The study examined the effects of jump training on 11 female volleyball players and compared them with 9 untrained, weight-matched male athletes. Researchers found that jump training decreased landing forces by 22% and decreased medial and lateral knee movements by about 50%. The program, which also involved stretching and strength training, increased hamstring strength in trained women to equal that of untrained men and eliminated side-to-side differences in hamstring-quadriceps strength ratios in women.

The impressive results led to the development of a formal jump training program—Cincinnati Sportsmetrics—that is available on videotape and comes with a training manual. (For ordering information, contact the Cincinnati Sportsmedicine Research and Education Foundation at 513/346-7290, extension 3707. The cost is $39.)

An added bonus is that the program enables participants to jump higher, says Timothy E. Hewett, PhD, coauthor of the study and director of the center's applied research division. "It's a good thing to have performance goals for training in addition to the goal of injury prevention," he says.

For best results, the researchers advise starting the program 6 to 8 weeks before the season. Training sessions consist of 30-minute bouts of stretching and jumping, followed by a 30-minute rest, then 30 minutes of strength training. The workouts are performed 3 days a week on alternate days. Verbal and visual cues are used to help athletes change their jump patterns (eg, "Recoil like a spring," "Land softer and quieter").

Improvements seen with Cincinnati Sportsmetrics in the lab translate into fewer knee injuries in the field, according to a study presented in July in Vancouver at the annual meeting of the American Orthopedic Society for SportsMedicine (8). The study involved 1,263 athletes from Cincinnati-area high schools. Subgroups included women who underwent preseason training, untrained women, and untrained men. The injury incidence for untrained women was 3.7 times higher than for trained females, and the incidence in trained women was 1.2 times higher than in men.

"I don't think we can prevent all knee injuries, but we can certainly make a dent," Hewett says.

Protecting Skiers' Knees

Though initial reports indicate that a training program may decrease injuries in sports such as basketball and volleyball, "skiing is a different animal than other sports," Hewett says.

Preseason conditioning programs don't reduce knee injuries in Alpine skiing, says Robert Johnson, MD, an orthopedic surgeon at the University of Vermont who has published several studies on ski injuries. "Many claims have been made, but none have ever been proven," he says. "World-class skiers have the highest ACL injury rates, and they're the best trained and the strongest."

Carl F. Ettlinger, MS, a colleague of Johnson's and director of Vermont Safety Research in Underhill Center, Vermont, says that though knee injuries in skiing aren't strictly women's injuries, women have two-and-a half times the risk of men. "It would be naive to say this is not a female injury," he says. Given equal skill levels, women are more likely to injure their ACLs, whereas men are more likely to sustain fractures and other blunt-impact injuries, Ettlinger says.

ACL injuries on the ski slope often result not from falling but from an attempt to recover from a loss of balance. "People get off balance, they get injured, then they fall," he says.

Ettlinger and colleagues have developed an injury-prevention pamphlet and video that teach skiers how to correct poor ski technique and better respond to dangerous situations. The method has been shown to reduce ACL injuries in ski-area employees (9). "But we've never gotten clearance to do this with a large population," Ettlinger says.

A detailed description is available on Vermont Ski Safety's Web site (https://www.vermontskisafety.com). Free brochures are available at ski shops and ski areas, and an instructional video with pamphlets is available for purchase by healthcare professionals and ski instructors who wish to make group presentations.

Lisa Schnirring
Minneapolis

References

  1. de Loes M: Epidemiology of sports injuries in the Swiss organization, Youth and Sports, 1987-1989: injuries, exposure, and risks of main diagnoses. Int J Sports Med 1995;16(2):134-138
  2. Zelisko JA, Noble HB, Porter M: A comparison of men's and women's professional basketball injuries. Am J Sports Med 1982;10(5):297-299
  3. Arendt E, Dick R: Knee injury patterns among men and women and in collegiate basketball and soccer: NCAA data and review of literature. Am J Sports Med 1995;23(6):694-701
  4. Griffis ND, Nequist SW, et al: Injury prevention of the anterior cruciate ligament, abstracted, in American Orthopaedic Society for Sports Medicine: Meeting Abstracts, Symposia, and Instructional Courses. 15th Annual Meeting, Traverse City, MI, June 19-22, 1989
  5. Huston LJ, Wojtys E: Neuromuscular performance characteristics in the elite female athlete. Am J Sports Med 1996;24(4):427-436
  6. McLean SG, Neal RJ, Myers PT: Knee joint kinematics during the sidestep cutting maneuver: potential for injury in women. Med Sci Sports Exerc 1999;31(7):959-968
  7. Caraffa A, Cerulli G, Projetti M, et al: Prevention of anterior cruciate ligament injuries in soccer: a prospective controlled study of proprioceptive training. Knee Surg Sports Traumatol Arthrosc 1996;4(1):19-21
  8. Hewett TE, Stroupe AL, Nance TA, et al: Plyometric training in female athletes: decreased impact forces and increased hamstring torques. Am J Sports Med 1996;24(6):765-773
  9. Hewett TE, Riccobene JV, Lindenfeld TN: A prospective study of the effect of neuromuscular training on the incidence of knee injury in female athletes, abstracted, in American Orthopaedic Society for Sports Medicine: Meeting Abstracts, Symposia, and Instructional Courses. 25th Annual Meeting, Vancouver, British Columbia, June 1999
  10. Ettlinger CF, Johnson RJ, Shealy JE: A method to help reduce the risk of serious knee sprains incurred in alpine skiing. Am J Sports Med 1995;23(5):531-537


Athletic Field Surfaces: New Products, Old Questions

Artificial turf has been a point of contention between players who think the surface causes more injuries and athletic administrators who want to make fields last longer. Now, the two sides have an opportunity to compromise by using new surfaces that blend natural and artificial grasses. Meanwhile, research on the injury risks posed by different surfaces and shoe types continues.

Hybrids and Portables

Sports turfs that are part natural and part artificial started appearing on US fields in 1996, though the products had been used in Europe for several years before that. SportGrass sod (SportGrass, Inc, Gaithersberg, Maryland) is grown in a sand-based medium on top of plastic. Polypropylene "grass" blades are tufted within the sand layer, which allows the roots of the real grass to grow down through the synthetic blades and the woven backing.

The first US installation of a competing product, the Grassmaster System (Clark Companies, Delhi, New York) took place this year at the Binghamton Mets Stadium in Binghamton, New York. GrassMaster machine operators stitch polypropylene fibers into existing turf. The grass roots entwine with the artificial fibers.

How the new hybrid surfaces will affect injury rates is unknown. I. Martin Levy, MD, an orthopedic surgeon at Montefiore Medical Center in Bronx, New York, who cowrote a two-part series on artificial grass in 1990 (1,2), says he is not aware of any data on injury comparisons between the new hybrid turfs and traditional playing surfaces.

Lambeau Field, home of the Green Bay Packers, has had a SportGrass surface for 3 years, says Packers' head trainer Pepper Burruss, ATC, PT. "I don't have any medical conclusions about the turf," he says. "But players still have concerns about artificial turf. They certainly prefer natural grass."

John N. Rogers, PhD, professor of turf grass management at Michigan State University (MSU) in East Lansing, Michigan, says MSU is evaluating the new turf systems but still uses an artificial surface for games. "Players are positive about these new [hybrid turf] fields. They say it feels like they're playing on grass, but it has the stability of Astroturf," he says, noting that the new surfaces prevent bare spots where the turf wears away during play.

The next turf trend to watch, says Rogers, is portable playing surfaces. For example, the New Orleans Saints tested a portable natural grass "rug" inside the Louisiana Superdome in a preseason game against the Packers on August 28, according to a statement released by the Saints. Also in development are modular removable fields, Rogers says. The grass (or one of the new natural-artificial hybrids) is grown in square, removable containers. "This system is perfect for multiuse stadiums and can respond to changing conditions. You can get underneath to heat, cool, or water them," he says.

Friction and Other Factors

As new products are introduced, debate on the comparative injury risks linked with artificial surfaces and grass continues. Some findings suggest that risks are higher on artificial turf, but the picture remains far from clear.

In the 1990 series (1,2), Levy and his colleagues reviewed the science behind artificial grass and evaluated several epidemiologic reports on turf-related injuries. The authors concluded that the risk of injury was greater on artificial surfaces, but the difference was relatively small: one time-loss injury per team per season, at most.

The MSU football team practices on a grass field and plays its home games on an artificial surface, says Randolph L. Pearson, MD, football team physician and associate professor in the Department of Family Practice at MSU. Though Pearson says some players have difficulty adjusting from grass to artificial turf, the medical staff has seen no differences in injury rates between games played on grass and those played on artificial turf. "This is consistent with literature reports on this topic," Pearson says.

Both Pearson and Burruss say they have concerns about the high level of friction, or "grabbiness," on artificial turf—particularly when the surface is dry and warm. Some teams water the playing surface on warm days, and Burruss says teams often change shoes depending on field conditions. "Our equipment people are like an Indy pit crew. They can change cleats in the blink of an eye if conditions change," he says.

Scranton et al (3) examined turf and shoe variables in noncontact anterior cruciate ligament (ACL) injuries in five seasons in the National Football League. They found that for grass, injuries were more common during games than during practice; for artificial turf, the opposite was true. An editor's note accompanying the study states that the results underscore the difficulty of analyzing a problem that has many uncontrolled variables. The researchers also looked at other factors that influence the shoe-turf interface, including dry versus wet field conditions, shoe design, and the widespread practice of "spatting" (protectively taping) the shoe.

The review found that all players on natural grass who sustained noncontact ACL injuries were wearing a standard seven-cleat grass shoe (47.5%), suggesting that the shoe is a risk factor for injury. The contribution of shoe type to injury risk on artificial surfaces could not be assessed because the amount of exposure in various shoe types was not recorded. Spatting the shoe did not affect injury patterns in games, but in practices, injuries on grass were more common with unspatted shoes, while injuries on artificial turf were more likely to occur with spatted shoes.

Lisa Schnirring

References

  1. Levy IM, Skovron ML, Agel J: Living with artificial grass: a knowledge update. Part 1: basic science. Am J Sports Med 1990;18(4):406-412
  2. Skovron ML, Levy IM, Agel J: Living with artificial grass: a knowledge update. Part 2: epidemiology. Am J Sports Med 1990;18(5):510-513
  3. Scranton PE Jr, Whitesel JP, Powell JW, et al: A review of selected noncontact anterior cruciate ligament injuries in the National Football League. Foot Ankle Int 1997;18(12):772-776


Field Notes

Multiple Concussions Linked to Neurologic Deficits
College football players who sustain two or more concussions are at risk for long-term neurologic symptoms, especially if they had a preexisting learning disability, researchers from the Henry Ford Health System in Detroit reported in the September 8 issue of The Journal of the American Medical Association.

Researchers evaluated 393 NCAA Division 1A football players over two seasons, according to a press release from the Henry Ford Health System. Players were interviewed about their medical history and took written and oral neuropsychological tests to establish baseline functioning. Athletes who sustained concussions during football season repeated the tests.

Athletes' postconcussion test performance was poorer in verbal learning, memory, and speed of information processing, and the deficits lasted up to 5 days. The 20% of players who had had two or more concussions during their football careers demonstrated the greatest long-term neurologic damage when compared with controls.

Michael W. Collins, PhD, the study's lead author, said in the press release that researchers were perplexed by the finding that athletes who had learning disabilities showed greater neurologic deficits after concussions. "We don't know whether [previous] concussions cause learning disability or players with a learning disability are more vulnerable to sustaining concussions," said Collins, who is a fellow in the Division of Neuropsychology at Henry Ford Health System.

The practical implication of the study is that baseline neuropsychological testing and retesting after a concussion are useful tools for making return-to-play decisions, Collins said. (See "Baseline Neurologic Testing Grows: Pro Teams Lead the Way," July 1998, page 13.) Confusion, memory loss, and slowed mental processing are concussion symptoms, and he said injured athletes should be free of all symptoms before returning to play.

In another study that appeared in the same issue of JAMA, researchers from the Netherlands found that amateur soccer players performed less well on neuropsychological tests than a control group of swimmers and runners. Of the 33 soccer players tested, 27% had sustained one concussion and 7 had had two to five concussions during their careers.

Psychological Traits Predict Athletic Success
Psychological attributes are more important than physical prowess in the development of young athletes, according to a survey of coaches by researchers from Loyola Marymount University in Los Angeles. The report was presented in August at the American Psychological Association annual meeting in Boston.

Shari Young Kuchenbecker, PhD, and her coauthors asked 658 coaches of young athletes to characterize a young athlete with winning potential from a list of 64 psychological and 64 physical characteristics. The top psychological attributes were: a love for playing (43%), positive attitude (32.7%), coachability (29.8%), self-motivation (27.4%), and being a team player (25.7%). Coaches were also asked to cite the most damaging forces; the top two selections were criticism (16.8%) and pressure (12.2%). The physical skills that were rated as important for success were "natural physical athlete" (10.2%), good eye-hand coordination (8.8%), and good coordination for age (8.8%).

Exercise and the Colon
Though some runners have cramps and diarrhea during races, colon contractions in untrained people seem to slow down during exercise, according to a University of Iowa Health Care study published in the May issue of the American Journal of Physiology.

According to a press release from the University of Iowa College of Medicine in Iowa City, investigators used slim, solid-state probes to measure the colon activity in 11 healthy, nonathletic adults before, during, and after they engaged in three different levels of aerobic activity on stationary bikes at 15-minute intervals.

The researchers found that colon function slowed during exercise, but normal colon contractions returned after exercise. "One implication of the study is that regular physical exercise may benefit people in terms of normal colonic activity," said Satish S.C. Rao, MD, PhD, an internist and lead investigator, in the press release. "By extension, this may help decrease a person's chances of colon cancer."

Does Higher SPF Lead to Longer Sun Exposure?
Using a sunscreen with a high sun-protection factor (SPF) may encourage longer sun exposure and thus increase the risk of skin cancer, according to a report published in the August issue of the Journal of the National Cancer Institute.

In a double-blind, randomized trial, researchers assigned French and Swiss participants to receive an unlabeled SPF 10 (n=44) or SPF 30 (n=42) sunscreen before their summer vacation. At the end of the vacation period, those assigned the SPF 30 sunscreen had spent significantly more cumulative hours in the sun than participants assigned the SPF 10 sunscreen (72.6 hours versus 58.2). The two groups had equal numbers of sunburns.

In an accompanying editorial, Karen M. Emmons, PhD, and Graham A. Colditz, MD, DrPH, wrote that people should continue to use sunscreen but reduce their overall sun exposure, regardless of SPF. Emmons is associate professor of health and social behavior and Colditz is associate professor of epidemiology at the Harvard School of Public Health in Boston. They also called for stronger federal sun safety initiatives.


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