Effect of the Oral Contraceptive Pill on Ligamentous Laxity

OBJECTIVE: Women are 4 to 8 times more likely to sustain a serious knee injury than their male counterparts. Previous studies have found that female sex steroids affect ligamentous tissue properties. The hypothesis is that there exists a difference in ligamentous laxity between oral contraceptive pill (OCP) users and nonusers. DESIGN: Blinded, single-factor, posttest-only control group design. SETTING: McGill University Sport Medicine Clinic, Montreal, Que-bec, Canada. PARTICIPANTS: One hundred twenty-seven female McGill University varsity athletes. INTERVENTIONS: Participants filled out a screening questionnaire and underwent KT-1000 measurements by 1 blinded examiner. Exclusion criteria related to underlying knee pathology, and hormonal factors were identified with the questionnaire. MAIN OUTCOME MEASUREMENTS: Independent sample, 2-tailed t tests were performed on the nondominant knee data of the OCP users and nonusers. RESULTS: Mean anterior translations at 67 N were 3.00 +/- 1.04 mm for the OCP users and 3.86 +/- 1.72 mm for the nonusers (P = 0.011); at 89 N, 3.98 +/- 1.13 mm vs. 4.83 +/- 1.82 mm, respectively (P = 0.018). Mean anterior translations at 67 N were 2.95 +/- 0.93 mm for the non-menstruating OCP users and 3.86 +/- 1.72 mm for the nonusers (P = 0.008); at 89 N, 3.88 +/- 1.06 mm vs. 4.83 +/- 1.82 mm, respectively (P = 0.011). CONCLUSIONS: Oral contraceptive pill use yielded statistically significant decreases in anterior translation of the tibia as compared with nonusers. The OCP may have a role to play in the prevention of ACL injuries by prophylactically targeting 1 of the variables responsible for the increased ACL injury rates in women.