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Updated 9:30 AM September 8, 2009

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Bone experiments help explain knee injuries

Researchers measured the strain placed on ligaments in cadaver knees during simulated sports landing movements to show that no two knees respond the same, and that injury prevention programs should be tailored to individual athletes.

Anterior cruciate ligament (ACL) injuries are the most common form of knee injury and women suffer them eight times more than men. Most ACL injury prevention programs currently are based on gender and on large populations, says Scott Mclean, assistant professor in the School of Kinesiology and lead researcher on a new study. McLean says this approach doesn't fully account for individual knee joint differences and how gender influences these differences.

"We are taking the group-based prevention concept and going one step further to begin to explore the idea of patient-specific injury prevention training programs. We must turn the focus from an overly simplistic, sex-based program, for example, to programs and injury prevention strategies that account for individual joint vulnerabilities," McLean says.

In the study, McLean and his former colleagues at Cleveland Clinic torqued cadaver knees of both genders using a manual loading device, and measured the force in the ACL. They then developed mathematical models from the data to examine differences between male and female ACL injury risk for specific movements.

The researchers found that female ACLs stretch more for a given force than male ACLs, likely due to differences the way the ACL and joint are designed. Injuring the ACL, one of the four major ligaments of the knee, often requires surgery and a long, painful recovery. Later in life an ACL injury can cause osteoarthritis and lack of mobility, which can lead to obesity, diabetes and other problems.

The study also confirms that no two knee joints are alike.

McLean says individual knee geometry is a large part of the ACL injury equation. The study's results showed that male and female ACLs are loaded very differently during sports movements based on the amounts of strain placed on the cadaver specimens.

"We've always needed to clarify underlying causes or mechanisms of ACL injuries before trying to successfully prevent these injuries in both men and women. This study demonstrated that tailoring injury prevention programs to individual joint risk factors may be an important and necessary step," McLean says.

"This research is the first step in helping team physicians and trainers prevent injuries by becoming more aware of the fact that female knees are more vulnerable," says A.J. (Ton) van den Bogert, professor with the Cleveland Clinic Lerner Research Institute, and study co-author. "We hope this can be made more applicable by determining the vulnerability of the knee through methods that can be applied in athletes. Continuing this research with computer models based on detailed MRI images and mechanical stiffness tests on athletes' knee will make that possible."

McLean, who also has an appointment at the Bone & Joint Injury Prevention & Rehabilitation Center, has begun to develop patient-specific computer models based on MRI and CT scans which are fed with an individual's movements. He said that such models could drastically improve ACL injury risk-screening and prevention methods of the future.

"We could take a youth soccer team of 20 players and assess their ACL load response to various sports movements with their very own computer model," McLean says. "From the results, we may find that only 10 youths need targeted training because they were identified by the models as more at risk for injury."

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