Prospective Correlation Between Serum Relaxin Concentration and Anterior Cruciate Ligament Tears Among Elite Collegiate Female Athletes

Background: The female anterior cruciate ligament may be more susceptible to injury than the male anterior cruciate ligament because of the gender-specific expression of receptors for relaxin, a collagenolytic hormone that promotes remodeling of the anterior cruciate ligament. Purpose: This study was undertaken to investigate whether collegiate female athletes with elevated serum relaxin concentrations (SRC) sustain anterior cruciate ligament tears at an increased rate compared with those with lower SRC. Study Design: Cohort study (prognosis); Level of evidence, 2. Methods: From 2005 to 2010, 143 Division I female athletes from 2 universities participating in sports at high risk for anterior cruciate ligament tears (basketball, lacrosse, field hockey, soccer, gymnastics, and volleyball) were recruited to participate. Questionnaires and urine luteinizing hormone (LH) tests were used to determine participants' anterior cruciate ligament injury and menstrual history and to identify their mid-luteal phase or projected cycle days 21 to 24. Serum samples were obtained for progesterone and relaxin ELISA (enzyme-linked immunosorbent assay) analysis. Participants were monitored for anterior cruciate ligament injury over their 4-year National Collegiate Athletic Association athletic career. Results: A total of 128 participants completed the study and were eligible for data analysis. The cumulative incidence of complete anterior cruciate ligament tear over the 4-year study period was 21.9%, and varied significantly by sport (P < .001). The mean SRC for athletes with anterior cruciate ligament tears (6.0 +/- 8.1 pg/mL) was significantly higher than that for those without anterior cruciate ligament tears (1.8 +/- 3.4 pg/mL; P = .013). In subgroup analysis of the 46 athletes who had detectable SRC, the cumulative incidence of anterior cruciate ligament tear was 14 of 46 (30.4%); the mean SRC among athletes with anterior cruciate ligament tears (14 of 46) was 12.1 +/- 7.7 pg/mL and without anterior cruciate ligament tears (32 of 46), 5.7 +/- 3.6 pg/mL (P = .002). When 6.0 pg/mL was set as the SRC cutoff for screening athletes for risk of anterior cruciate ligament tear in the subgroup with detectable relaxin levels, the test had 71% sensitivity, 69% specificity, 52% positive predictive value, 88% negative predictive value, and a relative risk of 4.4. These values were significant by x(2) test (P = .003) and receiver operating characteristic analysis (P = .002). Conclusion: Elite female athletes with anterior cruciate ligament tears have higher SRC than those without tears. Those with an SRC greater than 6.0 pg/mL had over 4 times increased risk for a tear. Clinical Relevance: Females with higher serum relaxin levels may be at increased risk for anterior cruciate ligament tears. Further investigation of the clinical utility of SRC testing is warranted.