By Dr. Richard Cunningham | Vail-Summit Orthopaedics & Neurosurgery (VSON)
ACL injuries are common in active patients of all ages, but research consistently shows that ACL injuries in female athletes occur at significantly higher rates compared to men. Many theories exist to explain this gap including anatomy, strength differences, and landing mechanics, yet an additional factor has gained more attention in recent years: hormones. More specifically, how fluctuations throughout the menstrual cycle may influence ligament laxity and possibly contribute to female ACL injuries.
Below, Dr. Richard Cunningham answers common questions about how hormones can affect the knee and what female athletes can do to reduce the risk of an ACL tear. These insights are especially valuable for anyone seeking to better understand ACL tears in women and the role hormonal cycles may play.
Why Are ACL Injuries More Common in Women Than Men
There are multiple contributing factors cause including anatomical, biomechanical, and neuromuscular. Wider hips with a resultant knock-kneed alignment, differences in landing patterns, and quadriceps dominance can all increase stress on the ACL. However, hormone fluctuations that occur naturally throughout the menstrual cycle may also affect ligament tension.
Dr. Cunningham explains, “We have long known that ACL injuries in female athletes occur at higher rates. Certain phases of a woman’s menstrual cycle may increase laxity within the knee, making the ACL slightly more vulnerable to tear.”
How Do Hormones Affect the ACL
The ACL contains receptors that respond to various hormones. Relaxin is a hormone that women produce normally as it facilitates childbirth by increasing the laxity of pelvic ligaments. In one study, cells from female ACL’s were exposed to Relaxin and there were cellular changes that were induced. Namely, there was a decrease in certain types of collagen, which provides structural integrity to ligaments. This change caused increased laxity in the ACL, which is a risk factor for tearing one’s ACL. It should be noted that these same changes were not observed when male ACL cells were exposed to Relaxin. In another study, there was a markedly higher average serum Relaxin concentration in female athletes that had just torn their ACL compared to female athletes that had not torn their ACL.
Dr. Cunningham notes, “When relaxin levels were high, female athletes had a four times higher risk for sustaining an ACL tear.”
This hormonal connection is an ongoing area of sports medicine research especially as clinicians continue to study women and ACL tears in competitive environments.
Is There a Certain Time in the Menstrual Cycle When Injury Risk Is Higher
A meta-analysis looking at 21 studies and over 60,000 female patients found that the lowest risk interval in the menstrual cycle for sustaining an ACL injury was during the luteal phase (post ovulation days 14-28 of a 28 day cycle), although the strength of evidence generating this data was low.
Are Birth Control Pills Protective
There is emerging research suggesting that hormonal contraceptives may help stabilize hormonal fluctuations which could lead to slightly lower rates of women sustaining ACL tears. Since birth control maintains more consistent hormone levels, it may reduce some of the ligament laxity changes seen during natural cycling.
Two case control studies in a systemic review found that oral hormonal contraceptives could lower risk of sustaining an ACL injury by up to 20%. However, in another study comparing the ACL injury rate between over 2 million women who started oral contraceptives and over 600,000 women who received an IUD, there was no difference in the risk of ACL injury over a 14 year time period.
Dr. Cunningham emphasizes that decisions about contraception must be individualized. “Although some early research hints at a possible potential protective benefit, any benefit appears small and therefore these medications should never be relied upon as a primary method for preventing female ACL injuries. Birth control choices should be based on overall health needs with input from both a primary care provider and gynecologist.”
What Can Female Athletes Do To Reduce ACL Injury Risk
Female athletes can decrease overall ACL injury risk with targeted training. Research shows that neuromuscular training programs can significantly reduce ACL injuries in female athletes by improving strength, balance, and landing mechanics.
Effective strategies include:
Strength Training
Focus on core, glutes, hamstrings, and hip stabilizers to help prevent increased knee valgus (knock-kneed alignment) when landing can reduce strain on the ACL.
Landing Mechanics
Avoid landing in the back seat as then one cannot adequately absorb and dissipate ground reaction forces. Training to help one maintain your center of gravity over your feet when landing is helpful.
Balance and Proprioception
Use single leg exercises to improve stability during cutting and pivoting to limit awkward landings.
Dr. Cunningham shares, “When athletes train the right muscles, they can significantly reduce the risk of ACL tears, and this is a more effective preventative measure to address rather than regulating one’s hormones.”
Should Women Avoid Sports During High Relaxin Phases
No. Female athletes should never feel limited by their menstrual cycle. Instead, the goal is awareness. Recognizing when the body may be more vulnerable simply encourages athletes to double down on technique and proper warm up routines.
“Women are incredibly strong competitors” says Dr. Cunningham. “Understanding how hormones influence the knee is not about restriction, it is about preparation. Knowledge allows athletes to stay confident, safe, and performing at their best.”
When Should an Athlete Seek Evaluation
If you experience knee pain, swelling, instability, or a popping sensation during sport it is important to be evaluated quickly. Early diagnosis and advanced treatment options help protect long term function and athletic performance.
About Dr. Richard Cunningham
Dr. Richard Cunningham is a board certified orthopedic surgeon and sports medicine specialist at Vail Summit Orthopaedics and Neurosurgery. He is nationally recognized for his expertise in ACL reconstruction, cartilage restoration, and complex knee injuries. Dr. Cunningham is dedicated to evidence based care and helping athletes of all ages prevent injuries and return to the activities they love with confidence. Contact his team today!