Actually, there has been some debate about whether oral contraceptives (birth control pills) may increase the risk of knee (anterior cruciate ligament or ACL) injuries. Scientists are studying whether or not ups and downs in hormone levels could be a risk factor for ACL injuries.
The basis for the possible link between hormones and knee injuries was discovered several years ago. Researchers found receptors on ACL for two hormones: estrogen and relaxin. Relaxin does produce a relaxation effect on ligaments. But the exact meaning of this relationship remains unknown.
A recent study comparing women taking oral contraceptives and who had ACL injuries with women taking oral contraceptives without ACl injuries did not find any effect caused by the birth control pills. All the women included in the study were either dancers or jumping athletes.
What they did find was that dancers had a low rate of ACL injuries. The authors offered several theories for the low rate of ACL injuries among dancers. First, dance training focuses on balance, alignment, footwork, and control. All of these skills may improve balance to a precise level needed to land single-leg jumps without injury. Second, dancers practice hundreds of jumps every day.
Third, jump practice progresses over time with supervision and guidance of an experienced dance instructor. And finally, unlike athletes, dancers practice the same steps in a routine. There are no surprise or unexpected movements to respond to. Rarely is there contact between two female dancers to cause an ACL injury.
The low incidence of ACL injuries among dancers points to different training techniques between dancers and other athletes. For dancers, monitoring fatigue and focusing more attention on reducing fatigue may be of benefit. Taking oral contraceptives is not advised for the purpose of preventing injuries.