The Effects of Sex Hormones on Physical Characteristics of the Medial Collateral Ligament in Prepubescent Female Rats

Abstract

About 100,000 injuries to anterior cruciate ligaments (ACL) occur annually in the United States, with females reporting an ACL injury rate two to eight times higher than their male counterparts. Many intrinsic and extrinsic factors have been cited to explain the disparity between rates of injury between males and females, such as anatomical differences, joint laxity, training technique, and sex hormones, the focus of the present research. Estrogen has been shown to decrease collagen content within ligament tissue whereas progesterone has been shown to inhibit estrogen and in some cases promote the production of collagen. Testosterone has been linked with increased collagen content, but its effects upon female knee ligaments have not been studied in detail. The present research focused on the role that estrogen, progesterone, and testosterone had, both singularly and in combination, on the physical properties of ligament tissue. Peak levels of estrogen, progesterone, and testosterone were simulated in prepubescent female rats, with treatment groups as follows: estrogen, progesterone, testosterone, estrogen and progesterone, estrogen and testosterone, and control. Mechanical tests on ligaments were subsequently performed after termination to measure ligament laxity and breaking point strength. The results show that estrogen in combination with testosterone or progesterone significantly decreases the breaking point strength in ligaments. Estrogen in combination with testosterone or progesterone and testosterone alone significantly decreased ligament laxity.