Scientific Article   |    
Gender Differences in Muscular Protection of the Knee in Torsion in Size-Matched Athletes
Edward M. Wojtys, MD; Laura J. Huston, MS; Harold J. Schock, BS; James P. Boylan, BS; James A. Ashton-Miller, PhD
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Investigation performed at the University of Michigan, Ann Arbor, Michigan

Edward M. Wojtys, MD
Laura J. Huston, MS
Harold J. Schock, BS
MedSport, 24 Frank Lloyd Wright Drive, Ann Arbor, MI 48106. E-mail address for E.M. Wojtys: edwojtys@umich.edu. E-mail address for L.J. Huston: huston@umich.edu

James P. Boylan, BS
James A. Ashton-Miller, PhD
Biomechanics Research Laborarory, University of Michigan, 3208 G.G. Brown, Ann Arbor, MI 48109-2125. E-mail address for J.A. Ashton-Miller: jaam@umich.edu

The authors did not receive grants or outside funding in support of the research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

A commentary is available with the electronic versions of this article, on our web site (www.jbjs.org) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).

J Bone Joint Surg Am, 2003 May 01;85(5):782-789
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Background: Female athletes who participate in sports involving jumping and cutting maneuvers are up to eight times more likely to sustain a rupture of the anterior cruciate ligament than are men participating in the same sports. We tested the hypothesis that healthy young women are able to volitionally increase the apparent torsional stiffness of the knee, by maximally activating the knee muscles, significantly less than are size-matched men participating in the same type of sport.

Methods: Twenty-four NCAA (National Collegiate Athletic Association) Division-I athletes (twelve men and twelve women) competing in sports associated with a high risk of injury to the anterior cruciate ligament (basketball, volleyball, and soccer) were compared with twenty-eight collegiate endurance athletes (fourteen men and fourteen women) participating in sports associated with a low risk of such injuries (bicycling, crew, and running). Male and female pairs were matched for age, height, weight, body mass index, shoe size, and activity level. Testing was performed with a weighted pendulum that applied a medially directed 80-N impulse force to the lateral aspect of the right forefoot. The resulting internal rotation of the leg was measured optically, to the nearest 0.25°, at 30° and 60° of knee flexion, both with and without maximal activation of the knee muscles.

Results: Maximal rotations of the leg were greater in women than in men in both the passive and the active muscle state (16% and 27% greater [p = 0.01 and p = 0.02], respectively). Moreover, female athletes exhibited a significantly (18%) smaller volitional increase in apparent torsional stiffness of the knee under internal rotation loading than did the matched male athletes (p = 0.014); this was particularly the case for those who participated in sports involving jumping and pivoting maneuvers (42% difference between genders, p = 0.001).

Conclusions: The collegiate female athletes involved in high-risk sports exhibited less muscular protection of the knee ligaments during external loading of the knee than did size and sport-matched male athletes.

Clinical Relevance: Improving active muscle protection of the knee during training and rehabilitation might help to decrease rates of knee injury.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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