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Getting Back in the Game

Adam King is expanding the scope on ACL rehab in female athletes. 

Adam King standing in a corridor

Adam King, assistant professor of kinesiology, studies how young female athletes recover — or don’t — from ACL surgeries.
Photo by Mark Graham


Wincing as an athlete goes down clutching a knee is a familiar experience for most sports fans. Accounting for about half of all knee injuries, the dreaded anterior cruciate ligament, or ACL, tear is often the culprit. 

Many athletes who tear an ACL never regain their former abilities. Others reinjure the same knee after recovery despite a rehab team’s judgment that they are ready to return to play.  

Adam King wants to help prevent such damaging outcomes in one especially vulnerable population: young female athletes. The assistant professor of kinesiology is studying the movement not only of the knee, but also of multiple interacting body segments at once. His is a departure from the usual sports rehab, which typically focuses just on the injured joint. What he learns could help those rehabbing an ACL injury to prepare for a safer return to competition.    

“How your knee moves is influenced by your trunk, by your pelvis, by your thigh, by your shin,” said King, a former collegiate football and basketball player. By better understanding how these body parts influence one another, King aims to redesign what athletes do to recover from injuries.  

One of several tough ligaments that join the upper and lower leg bones at the knee, the ACL is prone to tearing during collision sports and in those that require fast changes of direction. Girls and young women are especially susceptible, with soccer and basketball players experiencing some of the highest rates of ACL injury. This group is also prone to reinjuring the same or the opposite knee, often within a couple of months of returning to athletics.  

The toll is high. The injury can lead to surgery and a sports hiatus that can last as long as 18 months. After reconstructive surgery, only 65 percent of athletes return to their pre-injury level of sports participation. Female athletes are less likely than males to successfully return to pre-injury levels of activity. Long term, many of these athletes develop arthritis or chronic pain. 

Knee injuries account for a substantial public health impact, said Shiho Goto, a clinical biomechanist at Texas Health Sports Medicine. The sizable likelihood of reinjuring an ACL leads to an unfortunate pattern: Athletes “are so happy to get released, but two months later they come back for another surgery,” she said, adding that many use the injured limb less because they fear another painful incident. 

When it comes to deciding when an athlete can return to play after an injury, there isn’t much solid data. Reinjury of the ACL is also common — about 20 percent overall, and higher among athletes who are younger — so the decision is especially difficult. 

To better inform these decisions, King compared coordination patterns between two groups of young female athletes: those who had experienced an athletics-related ACL injury and those who had not. The injured athletes had completed reconstructive surgery and rehab, and their rehab providers had deemed them ready to return to sports based on traditional measures such as strength, range of motion and ability to perform key actions. 

Using motion-capture technology, King’s team analyzed the athletes’ body movements in the drop-landing task, in which a person jumps down from a 30-inch height.  

What physical therapists want to see, King said, are the knees kept wide as the athlete’s feet hit the ground. This position reduces strain on the ACL ligament. And, indeed, the athletes in the post-rehab group were doing that, successfully avoiding the higher-risk knock-knee movement.  

But King looked at the bigger picture.  

“We want to look at the lower extremity as a full system, not necessarily isolate a specific joint and say that that is the risk factor,” he said. 

He examined how body segments move relative to each other over time, Goto said, not, say, single joint angles at discrete time points. “That’s a very different way to look at the movement,” she said. 

When King and TCU graduate students Kelci Hannan and Hadley Lindley examined motion-capture data, they spotted something: The athletes who had completed rehab may have been keeping their knees in proper form, but they were moving their thighs and lower legs differently from their uninjured counterparts. The difference in alignment could be a clue to a previously unrecognized vulnerability. 

King has not yet confirmed whether the difference in motion correlates with a higher injury risk. His team is gathering data on athletes earlier in rehab, checking to see if these unusual coordination patterns are present at an early stage and whether they can be linked to known risk factors for reinjury.  

“My assumption is, yes, it is [linked] and that we can find new ways to rehab them and get them ready to return to sport,” he said. “But that’s a little bit down the road.” 

by Jenny Blair