Effect of testosterone on the female anterior cruciate ligament

1 Department of Physiology and 2 Department of Physical Therapy and Rehabilitation Science, University of Maryland School of Medicine, Baltimore, Maryland Submitted 8 December 2004 ; accepted in final form 15 March 2005 ABSTRACT Injuries to the anterior cruciate ligament (ACL) result in immediate and long-term morbidity and expense. Young women are more likely to sustain ACL injuries than men who participate in similar athletic and military activities. Although significant attention has focused on the role that female sex hormones may play in this disparity, it is still unclear whether the female ACL also responds to androgens. The purpose of this study was to determine whether the female ACL was an androgen-responsive tissue. To identify and localize androgen receptors in the female ACL, we used Western blotting and immunofluorescent labeling, respectively, of ACL tissue harvested during surgery from young women ( n = 3). We then measured ACL stiffness and assessed total testosterone (T) and free [free androgen index (FAI)] testosterone concentrations, as well as relative estradiol to testosterone ratios (E 2 /T and E 2 /FAI) at three consecutive menstrual stages ( n = 20). There were significant rank-order correlations between T (0.48, P = 0.031), FAI (0.44, P = 0.053), E 2 /T (–0.71, P < 0.001), E 2 /FAI (–0.63, P = 0.003), and ACL stiffness near ovulation. With the influences of the other variables controlled, there were significant negative partial rank-order correlations between ACL stiffness and E 2 /T (–0.72, P < 0.001) and E 2 /FAI (–0.59, P = 0.012). The partial order residuals for T and FAI were not significant. These findings suggest that the female ACL is an androgen-responsive tissue but that T and FAI are not independent predictors of ACL stiffness near ovulation. Instead, the relationship between T, FAI, and ACL stiffness was likely influenced by another hormone or sex hormone binding globulin. androgen receptor; gender differences; immunofluorescence; free androgen index Address for reprint requests and other correspondence: W. Romani, Univ. of Maryland School of Medicine, Dept. of Physical Therapy, 100 Penn St., Baltimore, MD, 21201 (e-mail: wromani{at}som.umaryland.edu )