Risk factors for a common knee injury among athletes

Main Category: Sports Medicine / Fitness
Article Date: 08 Apr 2005 - 14:00 PDT


The US Army, Navy and Air Force academies - fierce rivals on the sports field - soon will cooperate on a $2.8-million study of risk factors for a common knee injury among athletes.

The study, led by researchers at the University of North Carolina at Chapel Hill Injury Prevention Research Center, Duke University and Andrews Air Force Base, will enroll 4,800 male and female cadets during a four-year period, beginning at their summer entry into the academies.

The prospective cohort study will focus on human movement risk factors involved in injuries to the knee's anterior cruciate ligament, or ACL. The ACL is one of two ligaments that cross within the knee joint to prevent the leg bone (tibia) and thighbone (femur) from slipping forward or backward out of the joint. Most ACL injuries are sports-related, and most occur when there is no direct physical contact between athletes.

Studies have shown that the injury rate to the knee's ACL is up to eight times higher for women than it is for men, particularly in sports requiring stopping and jumping tasks, as in basketball, soccer and volleyball. Such injuries often require surgery and prolonged rehabilitation.

The study findings will offer a basis for shaping effective ACL injury prevention training programs for individuals engaged in vigorous physical activity, including male and female athletes.

"This is the largest prospective cohort study put in place to address risk factors for ACL injury," said the study's principal investigator, Dr. Stephen W. Marshall, who is an assistant professor of epidemiology at UNC's School of Public Health and assistant professor of orthopedics at UNC's School of Medicine.

He also is co-chief of biostatistical services at the Injury Prevention Research Center, which is hosting the study.

"The study promises to give us exciting new information based on science that can be used to refine existing ACL injury prevention programs. It will help define what aspects of human movement may predispose an individual to be at greatest risk for ACL injury and how to lower that risk," Marshall said.

Findings from earlier biomechanical studies at UNC and elsewhere indicate that the increased risk for ACL injury in women may be largely due to neuromuscular factors such as muscle strength and human movement. These gender differences "are particularly evident in the landing phase of a jump," Marshall said. "We therefore propose that poor technique when landing from a jump may be a useful marker of neuromuscular factors associated with an increased risk for ACL injury."

Maj. Anthony I. Beutler, director of sports medicine at Andrews Air Force Base's Malcolm Grow Medical Center, coordinates activities involving two of the three military sites in the study. Dr. Darin Padua, assistant professor in UNC's department of exercise and sport science, designed and supervises the physical testing component of the baseline data collection protocol.

Dr. William E. Garrett Jr., professor of orthopedic surgery at Duke University and renowned for his expertise in ACL injury and sports medicine, is a consultant to the study.

Upon entry into the study, academy cadets will complete a baseline questionnaire that collects basic demographic data, as well as information on their injury history and recent sports participation. In addition, participants will complete motion analysis, muscle strength tests and postural alignment assessments.

The performance task used in the motion analysis protocol is a simple jump from a 12-inch box to the floor. This is a standardized jump-landing task designed to simulate the forces on the ACL during vigorous physical activity. The study participant jumps down from the elevated take-off box and lands on a force plate. He or she then immediately jumps vertically as high as possible.

The force plate and a transmitter, in combination with sensors worn by the participant, will provide data on kinematics (body motion) and kinetics (forces affecting motion) of the lower limb. Two cameras will record the jump so that a standardized tool for scoring poor jump-landing technique can help analyze the jump from video replay at a later date.

Other risk factors, including demographic, hormonal and anatomical, also will be examined, as will a comparison of elements that determine poor jump-landing technique between women and men and its prevalence.

Preliminary findings based on 118 U.S. Naval Academy study participants showed one sustained ACL injury during their first year of follow-up (summer 2003-June 2004).

"Ultimately, this research will make a significant contribution to our understanding of the causes of ACL injury, with particular regard to those risk factors that appear to predispose women to those injuries," Marshall said.

The study's feasibility is due largely to the opportunity to enroll a large number of very physically active men and women and to readily track over time any ACL injuries that may occur, as these will be treated in the central orthopedics department of each service academy, he added.

"This study provides a way for the Army, Navy and Air Force to come together and do good science. Competition between the service academies is healthy, but cooperation is also part of the game."

Along with Marshall and Padua, UNC researchers include Drs. Bing Yu, associate professor of allied health sciences in the School of Medicine; Kevin M. Guskiewicz, professor of exercise and sport science in the College of Arts and Sciences; Shrikant I. Bangdiwala, research professor of biostatistics in the School of Public Health; Kelly Evenson, research associate professor of epidemiology in the School of Public Health; and Susan H. Wolf, research associate in the department of epidemiology.

At the military study sites, in addition to Buetler, are, from the U.S. Naval Academy, Cmdr. Scott Pyne, Cmdr. David Keblish and Greg Calhoon; from the U.S. Air Force Academy, Maj. John Tokish and Maj. Timothy Mazzola; and from the U.S. Military Academy at West Point, Col. Dean Taylor, Dr. Sally Mountcastle, Lt. Col. Tom DeBerardino, Lt. Col. Bradley Nelson and Lt. Col. Paul Stoneman.

Affiliated investigators at other institutions, in addition to Garrett, include Dr. Barry Boden of the Orthopedics Center in Rockville, Md.; Dr. James Onate of Old Dominion University; Drs. Brent Arnold and Scott Ross of Virginia Commonwealth University; Dr. Marjorie King of Plymouth State University; Dr. Alison Toth of Duke Sports Medicine Center; and Dr. Donald Kirkendall, a private consultant.

Funding for the study comes from the National Institute of Arthritis and Musculoskeletal and Skin Diseases, a component of the NIH. The American Orthopedic Society for Sports Medicine provided funds for a preliminary pilot investigation conducted in 2003-2004.

By LESLIE H. LANG
UNC School of Medicine

Note: Contact Marshall at (919) 966-1320 or smarshall@unc.edu. To view a photo of a jump-landing task in pilot data collection at the U.S. Naval Academy, click on unc.edu/news/pics/other/acl040505.jpg

School of Medicine contact: Les Lang, (919) 843-9687 or llang@med.unc.edu

Contact: L.H. Lang
llang@med.unc.edu
919-843-9687
University of North Carolina School of Medicine
http://www.med.unc.edu

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