Bringing female athletes to sports medicine research

Researchers at MUSC aim to correct research desert in sports injuries specific to women

by Celia Spell

Whether an athlete spends their high school years bouncing basketballs, slamming soccer balls or tossing tennis balls, they often cross pollinate the school sports arena with different teams based on season and time of year. Particularly gifted athletes, however, pour their time into a single high school sport year-round, and as that number grows so do the overuse injuries that go alongside specializing too early.

The Data Resource Center for Child & Adolescent Health found that 55% of children played a sport in 2019, but only 33% of girls played one. And a study from 2015 found that athletes with a serious overuse injury were twice as likely to be specialized in one sport. In that study, while the female participants under 18 spent overall less time each week being physically active than the male participants, there were still more girls with serious overuse injuries than boys, which echoed what Harris Slone, M.D., an associate professor in orthopaedic surgery and sports medicine at the Medical University of South Carolina, had been seeing.

Despite different rates of injury, types of injury and rates of recovery related to their sport, Slone found the research surrounding these differences particularly lacking. And that led him to dive deeper into a research topic that is not often specifically studied in sports medicine: young female athletes.

The crucial anterior cruciate ligament

Commonly known as the ACL, the anterior cruciate ligament stabilizes the knee and connects the femur to the tibia. This strong band of tissue is commonly injured during sports that involve directional changes or sudden stops, like basketball, tennis, volleyball or soccer.

Research is continuously finding that in addition to improper form, faulty equipment and poor conditioning, being female is a risk factor for ACL injuries, but Slone also saw a dearth of studies that examined sex-specific differences in recovery from this type of knee injury.

In his recent paper, he looked specifically at ACL reconstruction using a quadriceps tendon autograft and the recovery differences between young male and female athletes. He compared the recovery of strength, the range of motion and stability of the knee following surgery.

“With the ACL specifically, young females have a higher incidence of tears when compared to male athletes of the same age,” he said.

He says the discrepancy between injury rates is likely due to both anatomic and neuromuscular differences between men and women. Anatomically, the ACL is smaller in women, which predisposes it to tear. Women’s hips are also wider, and tend to be more “knock kneed” which can stress the ACL during landing or pivoting, compared to men who tend to be more “bow-legged.”

There are also differences in the ways that men and women play sports. The way an athlete runs, jumps and pivots can predispose them to knee injuries, and Slone has found that such a predisposition happens more in women. With proper coaching and training from an early age though, some of these jump mechanics can be altered, but more research is needed to further understand how best to do so.

After surgery, men and women are both able to recover the strength in their ligaments, but men tend to recover more quickly. Women generally have less quad strength and a greater loss of knee extension after ACL reconstruction as well, and Slone points to that loss of extension as the crux. “Why is that important?” he asks. “Well, it’s important because we know that patients who attain that early terminal knee extension do better, and patients that have good quad strength tend to do better in terms of recovery.”

Imbalances in either knee or leg after surgery can also lead to either reinjury or injury of the uninjured knee, so retaining as much of the original strength or laxity as possible after surgery is a priority in the case of ACL reconstructions.

By endeavoring to provide specific recovery guidelines to both men and women, Slone and his research team conducted a study with equal participants of each sex, whereas most studies in the field of sports medicine have predominantly used male athletes as participants. Slone hopes that by providing guidelines that address female athletes specifically, his patients can recover from ACL reconstruction smoothly and quickly regardless of their sex.

Microinstability in the hip

W. Michael Pullen, M.D., is also an assistant professor in orthopaedic surgery and sports medicine at MUSC Health, like Slone, and he is seeing more and more young female athletes with overuse injuries in his clinic.

Through the literature and his research, Pullen has seen that female athletes have different rates of certain injuries — either overuse injuries or sports-related injuries — than their male counterparts.

He conducted a study specifically addressing the hip and found differences between men and women. Female athletes were more likely to have increased laxity and be diagnosed with hip microinstability when undergoing hip arthroscopy.

Orthopaedic surgeons often perform minimally invasive arthroscopies on their patients to either view the joint more closely or alleviate pain. Using a few small incisions, physicians can access the hip with a camera or with surgical tools with less risk and a shorter recovery period for the patient according to the American Academy of Orthopaedic Surgeons. During the procedure, physicians like Pullen and Slone must briefly dislocate the hip, a process also known as a distraction, and Pullen and his research team found that it was more often easier to dislocate the hip joints of women because their ligaments were looser.

In recent years physicians have started looking at hip microinstability as a cause for dislocation, and while the definition is still loosely defined, it is becoming more accepted as an official diagnosis according to a paper in the Journal of Hip Preservation Surgery. Microinstability occurs with repetitive motions over time, like with athletes, or when strong forces are exerted on the body, as in a car wreck. With young athletes, it is more common in sports like golf, gymnastics, football, baseball and tennis, and it can cause pain or hip dislocation. When Pullen and his research team looked at ligament laxity and ease of dislocation during arthroscopies, they found that being female was a risk factor.

Both gender and practicing a sport intensely with wear on the hip can affect the stability of the hip joint. “Hip microinstability tends to affect women at a considerably higher rate than men,” Pullen said. “And a lot of that is just due to the natural laxity that occurs in their hip capsules. Female gender is one of the more common risk factors.”

Looking at oral contraceptives

With hormones at the heart of many of these differences in ligament laxity or loss of strength after surgery, Slone will next be researching the effect of oral contraceptives on sports injury. He has seen healthy female athletes experience blood clots after their injury or while recovering from surgery, and oral contraceptives that contain estrogen increase that risk.

He is looking at how the common combination pill of progesterone and estrogen affects the clotting cascade in the blood once the knee becomes immobilized. Potential suggestions to combat the increase in risk could be to temporarily change to a progesterone-only medication after injury or to prescribe blood thinners until the patient has recovered.

“I want to look at young female athletes in their 20s or 30s who are most likely to sustain an ACL tear or undergo a knee surgery,” he said. “I want to look at the risks associated with that, and we’ve seen that if a patient has more than one risk factor, including oral contraceptives, diabetes or smoking, they have double the risk of experiencing a blood clot after injury.”

Laxity can also change throughout the course of the monthly female hormone cycle, according to Pullen, which can put athletes at greater risk for injury at various times each month.

“The stability of the joints in female athletes can ebb and flow throughout the month as their hormone levels change,” Pullen said. “But it would be challenging to modify someone’s training schedule alongside their hormone levels. It is definitively something that is an emerging science though as we have more and more young female athletes.”

He’d like to see where that growing section of research will take us in the future, as the effects of excess estrogen on the system are not as carefully studied in sports medicine.

By performing new studies and gathering data in this under-researched area, more specific interventions and guidelines can be made to keep female athletes healthy and safe, and Slone and Pullen are taking a step in that direction.