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Hormonal Effects on the ACL in Women's Knees

Women athletes tear the anterior cruciate ligament (ACL) of the knee at least twice as often as men in the same sports. Much recent research has tried to figure out why. Many possible reasons have been identified. It is possible that all these factors play some part in women's high number of ACL injuries.

These authors looked closer at the theory that women's hormones make ACL injuries more likely. They specifically looked at a hormone called relaxin. Relaxin is only found in women. Pregnant women produce it at high levels. All women seem to produce it during a certain stage of the menstrual cycle. Research has shown that relaxin affects ligaments. It seems to affect the body's ability to produce and repair collagen. Collagen is the rope-like tissue that forms the strands of ligaments, tendons, and other supportive tissue in the body.

In this study, the researchers studied ACL tissue from women and men undergoing ACL surgery. The tissue was tested in the laboratory to see if relaxin could attach itself to the ACL cells. As expected, the relaxin didn't attach to any of the tissue from male ACLs. But relaxin did bind to certain types of cells in female ACL tissue.

These results proved to the authors that relaxin could be affecting women's ACLs, making them weaker and more prone to injury. The exact way this works is not known. But the authors note that, if relaxin does cause direct damage to the ACL, all women may be at increased risk of injury. And women who use oral contraceptives might be at even higher risk for ACL problems.

References: Jason L. Dragoo, MD, et al. Relaxin Receptors in the Human Female Anterior Cruciate Ligament. In The American Journal of Sports Medicine. July/August 2003. Vol. 31. No. 4. Pp. 577-584.

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