ACL Injury – female hormones at fault?
Researchers have known for decades that women are more likely than men to suffer injury to the anterior cruciate ligament (ACL) — the ligament responsible for stabilizing the knee during jumping, landing, pivoting, and changing speeds. But the reasons behind this difference are still fuzzy.
Dr. Sandra Shultz has been at the forefront of these investigations since the late 1990s, looking specifically at how hormones might affect knee laxity in women.
“We’ve learned that laxity varies greatly among men and women,” Shultz says. “Women naturally have greater laxity than men. That’s important because research shows that greater laxity increases the risk of injury.”
Laxity refers to the amount of existing ligament looseness. With knees, laxity impacts stability. People with greater laxity tend to land more stiffly, and the knee collapses inward. Injuries occur when the force of impact on the knee overwhelms what the ACL can handle — often, the ligament just isn’t strong enough.
Shultz is investigating the potential for hormones to influence that laxity. Past research has shown that more injuries occur during the first half of a woman’s menstrual cycle compared to the second. Shultz’s team hypothesized that the reason might lie in fluctuations in estrogen, progesterone, testosterone, and possibly relaxin, the hormone most responsible for ligament laxity during pregnancy.
To test these changes, the team gathered blood samples from female undergraduate students, measuring their knee laxity on the same days the samples were drawn. They then identified the days of minimum and maximum laxity in each female’s cycle. On those days, subjects were asked to perform a landing maneuver while the researchers measured their lower extremity movement patterns. As expected, on days of maximum laxity, subjects exhibited movement patterns that are associated with a higher risk for injury.
The researchers assessed each subject’s hormone levels and other blood markers on days of minimum and maximum laxity. What they found? Not only do hormone changes correlate with changes in observed laxity, they also correlate with changes in collagen metabolism — in a way that can alter the makeup and structural integrity of soft tissue. These changes most likely contribute to a structurally weaker ligament and render the knee less mechanically stable at certain times of the month.
Dr. Randy Schmitz, Shultz’s colleague, is also adding to what researchers know about ACL injury and recovery. He’s following women who’ve had surgery for ACL injury to observe how their knee cartilage changes in the six months post-operation. He wants to know whether those early changes can predict how the subjects will walk over time. Such knowledge could impact rehabilitation.
Figuring out better ways to treat or possibly prevent ACL injuries in females is critical, Shultz says, because the impact is lifelong. The majority of ACL injuries happen between ages 14 and 15, and arthritis sets in within 10 years to 15 years. That means injured young women can have arthritic knees — and face a future of knee replacements — by age 30.
Having a greater understanding of the variability of who’s at risk will help Shultz and her team better understand who to target for intervention. “These injuries add up to missed time in sports and activities and an increase in potential long-term complications,” Shultz says. “Ultimately, we want to understand what factors increase knee laxity, and then determine if laxity can be changed or not through prevention and strengthening, since some evidence suggests that more muscle mass around the knee is associated with less knee joint laxity.”
Taken together — and individually — the ongoing work inside labs led by Rhea, Etnier, Shultz, and Schmitz continues to move the needle in the right direction for what we know about healthy movement and how the human body and brain can help themselves. Over time, their investigations hold great promise for combatting and, potentially, preventing and conquering some of the most common causes of impaired motion that both men and women face.
by Whitney L.J. Howell
Since its early days, UNCG has had a strong reputation for excellence in sports, sports medicine, and movement-related health. Today’s kinesiology department has not let that legacy fade. Instead, the faculty are picking up the mantle and carrying it to exciting new places.
Maintaining optimal movement is crucial at any age. It’s vital that we know what impacts motion, how we can preserve it, and — in the worst case scenarios — how to recapture it after injury. Unexpectedly, the big answers aren’t coming in the form of little pills or injections. They’re taking shape as high-tech solutions merged with interventions based on personal physical effort.
At every turn, UNCG is leading the charge not only for the healthy to hold onto their capabilities, but for the injured and cognitively-impaired to reclaim their abilities as well.