Prospective correlation between serum relaxin concentration and anterior cruciate ligament tears among elite collegiate female athletes

Dragoo JL, Castillo TN, Braun HJ, Ridley BA, Kennedy AC, & Golish SR. American Journal of Sports Medicine. 2011. 39:2175-2180. doi: 10.1177/0363546511413378

It is a well-known fact that anterior cruciate ligament (ACL) tears are more common in females than males.  This increased risk has been attributed to many factors that have been investigated including biomechanics as well as hormonal differences.  The purpose of this study was to prospectively investigate whether female collegiate athletes with higher levels of relaxin, a hormone associated with tissue turnover, were more susceptible to ACL tears than those with lower levels of relaxin. Baseline serum samples were collected from 128 female athletes in high-risk sports (e.g., soccer, basketball) and injury incidences were followed over a 4-year period. The serum samples were collected during the mid-luteal phase of the menstrual cycle because this is when relaxin is known to peak. For athletes on hormonal contraception or not experiencing a regular cycle the timing of serum collection were standardized. Serum relaxin concentrations were analyzed using assays.  Over the 4-year period, 28 (22%) of 128 athletes suffered ACL tears.  Serum relaxin concentrations were high enough to be measured in 46 (36%) of the athletes and not detectable in the other 82 athletes. There were no significant differences in the incidence of ACL tears among those with and without measurable serum relaxin. However, among athletes with detectable relaxin concentrations, athletes who suffered an ACL tear had significantly higher relaxin concentrations compared to those who did not.  Relaxin concentrations were also lower among female athletes on hormonal contraception compared to those who were not on birth control, however, there were no significant differences in the use of birth control between athletes who did or did not tear their ACL. 

As clinicians, this study demonstrates hormonal concentrations may play a role in females’ increased risk of ACL injury. The authors of this study proposed a value of 6.0 pg/mL as a threshold for establishing an increased risk of suffering an ACL tear.  However, the clinical applicability of this seems limited due to the fact that only 36% of the athletes had detectable relaxin concentrations.  Furthermore, ACL incidence did not differ among the athletes who did and did not have detectable concentrations.  Ideally, the identification of a hormonal “at-risk” population may allow for successful interventions targeting prevention to this group.  However, relaxin may not be the best option because it was only detectable in 36% of the females, and would certainly not be detectable in the male population who also suffers ACL injuries.  While relaxin may not be the optimal biomarker for predicting future ACL tears this study is part of an emerging area of research that is trying to use biochemical and genetic biomarkers to predict future injuries or individuals that will take longer to recover. Future studies following high-risk sports should collect a larger scope of information to include multiple risk factors (e.g., biomechanical, joint laxity).  It would also be interesting to see what biochemical concentrations are present the day of injury, in comparison to some of the baseline measures.  Where this study points out the hormonal component, I am not sure it is time to recommend interventions that would include taking something to alter the hormones of an at-risk individual.  What are your thoughts on this?

Written by: Nicole Cattano
Reviewed by: Jeffrey Driban

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Dragoo JL, Castillo TN, Braun HJ, Ridley BA, Kennedy AC, & Golish SR (2011). Prospective correlation between serum relaxin concentration and anterior cruciate ligament tears among elite collegiate female athletes. The American Journal of Sports Medicine, 39 (10), 2175-80 PMID: 21737831