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Thursday, March 16, 2000

Gender difference found in shoulder laxity, stiffness

Research has shown disproportionately high rates of non-contact anterior cruciate ligament (ACL) injuries in NCAA intercollegiate female athletes. Increased ligamentous laxity and/or decreased stiffness of the female knee have been identified as possible predisposing factors for sustaining injury.

A study presented in poster exhibit 261 is the first to identify significant gender differences in laxity and stiffness at the shoulder.

Fifty-one subjects (28 females, 23 males, median age 22 ` 2.8 years) with no history of shoulder injury or long-term participation in overhead sports were recruited for this study. Both shoulders (N=102) were evaluated for laxity and stiffness in the anterior and posterior directions using an instrumented arthrometer that measures humeral head displacement (mm) relative to applied loads (N).

A slow progressive load from 0-134 N was applied to the proximal humerus to simulate the A/P drawer stress tests. The mean humeral head displacement averaged over all levels of force and the slope of the linear portion of the load-displacement curve (stiffness) were used for statistical analysis. A single group factorial ANOVA design was employed. Multiple paired t-tests revealed no significant differences in laxity or stiffness between right and left shoulders (p-value range=0.14 to 0.73).

Differences in laxity were observed between males and females in the anterior and posterior directions [F(1,392)= 11.9, p=.0006, males anterior=8.3 2.2 mm, females anterior =11.4 2.8 mm, males posterior=9.6 2.9 mm, females posterior=10.9 3.5 mm]. Differences in joint stiffness were observed between males and females in the anterior and posterior directions [F(1,98 =8.0, p=.006, males anterior=20.5 5.0 N/mm, females anterior = 16.3 4.2 N/mm, males posterior=20.1 5.3 N/mm, females posterior=22.1 6.9 N/mm).

"Our findings at the glenohumeral joint are consistent with those of the knee revealing increased laxity and decreased stiffness in females," said Eric L. Sauers, MS, ATC, doctoral candidate in sports medicine, College of Health and Human Performance, Oregon State University, who presented the study. "These data demonstrate that females exhibit greater anterior laxity than males with an associated decrease in anterior joint stiffness. Our findings may indicate an increased risk for instability in females, especially those participating in overhead-throwing sports."

Co-authors of the study are Paul A. Borsa, PhD, ATC, shoulder kinematics laboratory, division of kinesiology, University of Michigan; Derald E. Herling, PhD, assistant professor, department of mechanical engineering, Oregon State University; and Rick D. Stanley, MD, Mid-Valley Orthopaedics, Albany, Ore.

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Last modified 06/March/2000 by IS