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?
The results of this study are very interesting as is the question that the discussant poses regarding how a clinician would begin to apply the results of hormonal screening to injury prevention initiatives. I, however, would like to comment on a different aspect of the study. Twenty-two percent of the female intercollegiate athletes in this study suffered an ACL injury. That value is incredibly high compared to other trials assessing ACL injury risk. The value is usually in the range of 1 to 2 percent of female athletes will tear their ACLs in a given year. This huge discrepancy makes me ask if this sample of athletes in this study is truly a representative sample of female college athletes.
Since the study was conducted over a 4 year time frame, wouldn't that make it about 4% of athletes per year (on average)? Granted, this is still quite a bit higher than 1-2%, but I almost wonder if that could be a representative sample because I would not be surprised if the incidence was increasing. Purely on speculation, it would be logical to assume that an increase in the rate of sedentary lifestyle would correlate with an increase in faulty biomechanics. As disuse atrophy starts to cause an increased rate of poor mechanics, the ACL incidence may increase. The kicker here is whether or not the athletes participated in an ACL prevention program, which brings this discussion back to what other factors may be involved.
Timothy & Jay-Thanks for your interest in the post. Great comments. The prevalence does seem unusually high. I recently saw a couple of articles citing a significant jump (near doubling) in prevalence rates in females between 2000-2005 within the age range of 14-21. Clinically there seems to be some evidence of an increased incidence rate as well. Is anyone else seeing this trend?