Testosterone may increase rat anterior cruciate ligament strength

Background Women are more likely than men to injure the anterior cruciate ligament (ACL). Human and animal trials have linked circulating estradiol to injury rate and ligament strength. Fewer studies have examined the role of testosterone. The purpose of this study was to determine if male rats with normal testosterone levels would have stronger ACLs than castrated rats. Methods Eight castrated (group C) and eight normal (group N) 12-week-old, male Sprague–Dawley rats were used for the study. Mean testosterone levels were 0.14 ng/mL (95% CI: 0.10 to 0.17) in group C and 3.54 ng/mL (95% CI: 1.32 to 5.76) in group N. After euthanasia, ACL cross-sectional area was calculated, and a servohydraulic material testing unit was used to measure ligament properties. Results Specimens from both groups had similar cross-sectional area, but N specimens showed greater mean load-to-failure (34.5 N [95% CI: 31.6 to 37.4] vs 29.2 N [95% CI: 27.9 to 30.6]) and ultimate stress (38.7 MPa [95% CI: 34.1 to 43.3] vs 31.8 MPa [95% CI: 29.8 to 33.8]). Mean energy was 27.7 mJ (95% CI: 23.1 to 32.2) in the N group and 23.4 mJ (95% CI: 18.2 to 28.6) in the C group. Conclusions Rats with normal circulating testosterone had higher ACL load-to-failure and ultimate stress, indicating that testosterone may influence ACL strength and the injury rate of the ligament.