Contraceptives and knee injury link found

Oral contraceptives appear to reduce the severity of anterior cruciate ligament (ACL) injuries in female athletes, a large population study reveals.

Tears in the major stabilising knee ligament occur regularly during team sports that involve sudden changes in direction. The injury prevents nearly one in two players from returning to competitive sports, and up to half develop arthritis within 10 to 20 years.

Intriguingly, females are up to eight times more likely to tear the ligament than males. This has prompted researchers to explore whether hormones might be involved, and whether contraceptive pills – which suppress hormonal peaks during the menstrual cycle – might reduce that risk.

Using a national US database, Steven DeFroda and colleagues from Brown University, Rhode Island, analysed a decade of prescription and insurance details from more than 165,000 female patients aged 15 to 49 years.

Half the women used common oral contraceptives. Overall, they were 18% less likely to need reconstructive surgery for ACL damage compared to those who didn’t take the pill.

Specifically, 465 women in the oral contraceptive group needed surgery during the 10-year study compared to 569 in the control group.

Closer inspection revealed the result was driven by females aged 15 to 19. This group, which is at highest risk for ACL damage, had a 63% lower rate of surgery.

Previous observational research has reported similar findings. Other studies have found the hormones oestrogen and relaxin weaken the structural integrity of ACL tissue and are associated with higher likelihood of tears. 

Anatomical differences, body mass index and mode of landing during sport have also been linked to increased risk of knee injuries.

And, as the authors note, oral contraceptives are not without their own risks – which include heart attack, stroke and depression.

Nonetheless, DeFroda and colleagues suggest the findings underline the benefits for professional female players of taking the pills.

“While clinical evidence is limited, there should be consideration for [oral contraceptive pill] usage in elite high school and college aged athletes, especially those who are at risk of ACL tear,” they conclude.

It’s important to note the research is observational – so does not establish cause and effect – and only controlled for a limited number of other factors such as age and other health conditions.

Notably, the study did not differentiate between athletic, recreational or accidental ACL tears, nor factor in different activity levels between the groups. Further, it only studied women with injuries that required surgery.

The study is published in The Physician and Sports Medicine journal.