Boston University researcher Cara Lewis works with a study participant at the Human Adaptation Lab, which Lewis directs.

Sports Medicine

Would Better Hip Care for Young Female Athletes Prevent Pain and Surgery Later in Life?

Most research into athletes’ hips only studies boys and men. With prevention and better training in mind, Boston University’s Cara Lewis is setting out to change that.

When Cara Lewis was working on her PhD in movement science, one of her mentors gave her some advice that would transform her scholarship: “Study the hip. It’s where it’s at. It controls everything else.” Lewis had noticed this working as a physical therapist, where it seemed like she was always treating lower limb injuries that had originated in the hip.

For the last two decades, Lewis—a Boston University Sargent College of Health & Rehabilitation Sciences professor of physical therapy—has researched the way bodies develop and interventions that improve the lives of individuals with chronic musculoskeletal pain. Her goal: to prevent or slow the progression of damage to bones, muscles, joints, ligaments, and tendons, specifically in the hip.

Lewis’ latest work is derived from a problem she’s observed: current research about hip injuries in athletes focuses almost exclusively on men and boys, when clinical data show that around two-thirds of hip injury diagnoses and surgical interventions are occurring in women and girls. A 2022 study of former world-class athletes in Norway found that 1 in 9 female athletes required hip replacement by age 75, compared to 1 in 12 male athletes.

Lewis has two current research projects—one funded by the National Institutes of Health, and the other by the Arthritis Foundation—that seek to right this wrong. The first studies female athletes ages 8 to 17 to better understand why their hip bone shape develops the way it does, and how participating in a sport—especially soccer or ice hockey—influences that development. A second study examines how a fully developed hip bone in adult female athletes, ages 18 to 30, influences pain, cartilage health, and, ultimately, the onset of osteoarthritis. For the older group, volunteers in Lewis’ study participate in soccer, ice hockey, distance running, or dance.

“Why are we trying to apply data from men to women, especially at a joint where half the joint is the pelvis, and—let’s face it—those [bone structures] are a bit different between men and women?” says Lewis, director of Sargent’s Human Adaptation Lab. “Somebody should study it, especially when we have all these females participating in sport, with participation now about 50-50. It’s time our research caught up with that—and that’s what my team is doing.”

The Body Mechanic

Lewis researches how humans move and bodies function the way a mechanic might study a car—an approach she traces all the way back to her childhood. “My grandfather was an auto mechanic, and I loved watching him work with his hands and figure out systems,” she says. “But I didn’t really want to work with cars; I wanted to work with people and with their bodies. I became a body mechanic, or a biomechanist, so that I could study the way that we move and the way our body functions to allow us to do the things we do.”

She’s observed that when it comes to addressing a patient’s pain, doctors can sometimes jump to an intervention—be it surgical or otherwise—without fully understanding the problem.

“I tend to take the approach of, ‘Let me figure out what’s wrong here,’” she says. “Let me take apart the bicycle to figure out why it’s not working before I put a new chain on it. I want to understand what’s happening, and then we can design the more appropriate intervention.” 

In previous studies, Lewis has highlighted that femoroacetabular impingement (FAI) syndrome, which causes hip pain, is associated with muscle weakness and altered movement patterns during daily tasks, which can act as a precursor to osteoarthritis. While the altered movement is often thought to be a result of the pain, her studies suggest that the movement contributes to the pain. Researchers in her lab have analyzed how muscles like the gluteus medius (located on the pelvis) and piriformis (located in the buttock), along with changes in a person’s gait, affect loading of the lower body joints. They also determined resistance bands offer effective methods for strengthening hip muscles. And Lewis has found that modifying movements in 20- to 30-year-olds can help prevent joint damage, such as acetabular labral tears, which leads to chronic pain and hip replacements later in life.

The hips of female athletes are ripe for a biomechanic’s perspective, she says. A femur, or upper leg bone, that doesn’t move precisely within the acetabulum, or hip socket, can cause hip pain, Lewis says. This can occur when bone coverage in the socket or femur is excessive (FAI syndrome) or insufficient (acetabular dysplasia). 

“In either case, you have to understand the underlying bone shape, or what we call morphology, and how movement is interacting with that,” Lewis says. Which is one of the main reasons Lewis and her team are studying athletes—especially those in sports that put a lot of strain on the hips, like hockey and soccer. Young athletes, she says, tend to move in ways that contribute to impingement rather than decreasing it.

“We know that boys who play soccer or ice hockey intensely—meaning a couple hours a day, multiple days a week—before the age of 12, have increased risk for FAI morphology,” Lewis says. “But there aren’t studies in girls that look at that.”

Female-specific research of the hip is vital, she says, because evolution has resulted in key differences between the sexes: Puberty affects the way girls’ hips develop differently than boys, with changes coming quickly in height and a widening of the pelvis, “which changes how strong your muscles have to be to do the same movements.”

“Because a lot of those changes are at the pelvis, it absolutely is affecting hip function,” Lewis adds. “That’s part of what we’re looking at—this transformation between prepuberty and postpuberty, and what all is changing in there, not only in terms of how they’re moving, but [also] what their bone shape looks like.”

The Next Step: Better Interventions

When research volunteers arrive at Lewis’ Human Adaptation Lab, an MRI is taken to understand the structure of the young athlete’s hip. Next, researchers conduct various movement and balance tests—like jumps and squats—to assess hip strength and range of motion. The athletes in the younger volunteer group go home with an accelerometer that tracks their activity and movement for the following week. 

“We wanted to get [athletes in] sports that have very different requirements of the loading of the hip joint,” Lewis says. “We want to understand how sport-specific loading is affecting these movement patterns. Once we see how their movement is changing, we can figure out how to intervene and how to improve it.”

Ultimately, Lewis hopes her research will result in young female athletes receiving more appropriate training protocols and physical therapy, reducing the need for hip surgeries.

“As a physical therapist, I am pushing for us to have a larger role in prevention and maintenance of health,” she says. “Why can’t we promote hip health by intervening in grade school, teaching girls how to keep their hips healthy, so that the 18-year-old isn’t having surgery?”