How menstrual cycle phase and anatomy may have an impact on ACL injuries in females
As the mystery surrounding females' heightened risk of experiencing ACL injuries remains far from resolved, one speculation has arisen in which both the phase of the menstrual cycle and anatomical makeup are thought to play a role in putting females at increased risk due to varying levels of hormones. The belief behind the process of investigating these two subjects is that in order to develop intervention strategies for ACL injury, the particular risk factors must be determined.
In terms of female anatomy, a possible feature that may lead to a greater risk of ACL injury is decreased intercondylar notch width (a section of the femur), which is believed to be indicative of a smaller ACL and inferior structural properties than males. The smaller size of the ACL may cause it to be more prone to injury. Another possible female anatomical risk factor is joint laxity. One study found that the risk of ACL injury was 2.7 times higher in women whose knee laxity values were more than 1 SD from the mean compared with women with decreased knee laxity values. Men, on the other hand, didn't show any relationship between knee laxity and ACL injury. While the affect of anatomical composition still requires further investigation, gender differences such as these indubitably serve some role in giving females additional risks.
A major consensus that is gaining popularity in medical literature is that the likelihood of an ACL injury does not remain constant throughout all phases of the menstrual cycle. Instead, the risk of females injuring their ACLs is actually much greater during the preovulatory phase of the menstrual cycle than the postovulatory phase. A number of studies took measures to analyze the accuracy of this consensus. One used urine levels of estrogen, progesterone and luteinizing hormone metabolites to characterize a participant's menstrual status at the time of injury and concluded that injuries were greater during days 9-14 of the 28-day cycle compared to the final 15 days. Another study involving female alpine skiers used concentrations of progesterone and estradiol, two of the primary hormones involved in menstruation, to figure out the phase in the menstrual cycle at the time of injury. Progesterone levels are low during the preovulatory phase, then rise after ovulation, whereas estradiol levels rise early on, and then drop off slightly at ovulation before rising again during the luteal (final) phase of menstruation. Findings showed that among skiers, based on hormone levels, 74% of women with ACL injuries were in the preovulatory phase, while 26% were in the postovulatory phase.
The direct mechanisms at work that cause a greater likelihood for injury at the preovulatory phase are not entirely understood, but one possible explanation is the unopposed increase in estradiol during this period, while progesterone does not increase until later in the cycle. Hormones such as these and others may have an impact on muscle contraction and may cause stiffness in the knee that can lead to injury. Once again, these open-ended statistics leave many questions unanswered regarding the specific effect of menstrual cycle on ACL injuries; however, the findings should spur further investigation into the subject matter, and for the time being, women should be more careful at times they know they are at a proven increased risk of injury.
-As reported in the Sept./Oct. '08 edition of the Journal Of Athletic Training
-By Greg Gargiulo
