3 May 2019
It’s every athlete’s worst nightmare, a knee injury that puts them on the bench for the rest of the season or worse permanently. Anterior cruciate ligament (ACL) injuries are one of the most common knee injuries in young athletes. They have a huge impact on an athlete’s career, as many as 45% of athletes with an ACL tear do not return to athletic competition. Ligaments are a type of fibrous tissue that connects bones to one another. Ligaments allow for the movement in joints as well as stabilizing them. There are three bones in the knee, the thigh bone (femur), the shinbone (tibia) and the kneecap (patella). The ACL connects the femur and the tibia and is found in the middle of the knee joint while the patella sits on top of the ACL to provide protection. ACL injuries occur in younger athletes that play high impact sports that involve jumping, pivoting and changes in direction. Examples of sports where this type of injury is common include basketball, soccer, volleyball and handball.
The only treatment options available include non- operative strategies such as knee braces and physiotherapy. Once the ACL is torn it cannot repair itself and as a result, athletes often undergo ligament reconstruction surgery. This is where a ligament from a different part of the body (or a ligament taken from a donor cadaver) is used to replace the damaged ACL.
Women seem to be at a higher risk of ACL tear with some studies saying that they are 2 to 8 times more likely to sustain an ACL injury compared to men. There is no difference in the rate of ACL tears between boys and girls prior to puberty and this has prompted researchers to speculate that the difference in hormonal regulation between men and women may be responsible for this difference.
Estrogen is speculated to be involved with numerous aspects of the knee joint development, such as the tensile strength of ligaments, muscle development and joint alignment. There are physiological differences between the ACL in men and women and this suggests that estrogen may impact cellular remodeling of the ligament. This may ultimately impact how the ligament functions when it is under physiological stress. There is a special type of cell within the knee known as fibroblast, these cells are responsible for the production of collagen. Collagen is the protein that is used to construct and repair ligaments. It has been shown that the fibroblasts in the knee have estrogen receptors and can, therefore, respond the estrogen directly. When there is a lot of estrogen present the fibroblasts no longer produce collagen and this affects the structural and mechanical properties of the ACL.
It has been suggested that different phases of the menstrual cycle and the resulting fluctuations in hormone levels may impact ACL injury risk. There has been conflicting evidence on this topic and a consensus has yet to be reached by scientists. This line of investigation has led researchers to wonder if stabilizing these hormonal fluctuations in women with oral contraceptives may help lower the risk of ACL injury.
In a recent US study published in The Physician and Sportsmedicine, scientists used information from a national database to determine if contraceptives could have a protective effect against ACL tears. The group use the PearlDiver database which stores information such as patient demographics and prescription records. The group searched the database for women between the ages of 15 and 49 who were taking the most common oral contraceptives that contained both estrogen and progesterone. They made sure the women selected had taken the contraceptives at least one year before any reported ACL injury. The scientists then matched this group with a control group of patients who were not taking contraceptives but had a similar BMI and age. Each group consisted of 82,874 patients. The scientists then looked up how many patients in each group had undergone ligament reconstructive surgery. The group found that there was an 18% reduction in the risk of an ACL tear that required surgical intervention in women who took oral contraceptives. The scientists also showed that women between the ages of 15-19 had the best protective effect when using oral contraceptives. This age group had a reduction of 63% in ACL tears that required surgery.
There were some limitations with the study, mainly the database used did not provide researchers with information on the level of activity for the women participating in the study. If there are more women who are active in the group that did not take contraceptives they may inherently be at a higher risk of getting an ACL injury. It is possible that this may account for the differences seen in the two populations. Although the data presented here holds promise for mitigating the risk of ACL tears, particularly in younger athletes, it does require further clinical validation. A randomized clinical trial that frequently collects biological samples to analyses hormone levels may be a good starting point for a more robust analysis.
Dr DeFroda, the lead author, said in a press release, “With careful assessment of the risks, injury risk reduction could be another way in which female athletes may benefit from their (oral contraceptive) use”