PFP is occurring as early as late elementary school, calling into question traditional “overuse injury” therapies.
By Nicole Wetsman, Lower Extremity Review August 2018
Patellofemoral pain is a common condition among adolescents, with nearly 7% of the today’s adolescent population affected.  It’s a particular burden for girls—it affects as many as 10% of adolescent female athletes,  and the pain likely shuts them out of sports at a similar rate to anterior cruciate ligament tears, said Frances Gavelli PhD, a staff scientist in the Functional and Applied Biomechanics (FAB) Section at the National Institutes of Health. “And the prognosis is much worse,” she said.
But despite the prevalence of patellofemoral pain in young athletes, and the damage it can do, there’s very little information available on the condition in that particular group because nearly 95% of the research has been done in adults. 
However, there’s increasing interest from clinicians and researchers in patellofemoral pain in children, and particularly young girls. Patellofemoral pain presents differently in adolescents than in adults, and children’s continued growth through puberty complicates the condition further. Efforts to understand patellofemoral pain in this population are designed to help clinicians and trainers prevent and treat it while keeping kids of both genders active in sports and pain-free.
“It’s really starting to come to the forefront,” Gavelli said.
|Cause and effect|
|Until recently, the scientific community often considered patellofemoral pain in adolescents to be an overuse injury, Gavelli said. That classification derived largely from a 1985 study that determined that the pain was a “benign, self-limiting condition,” that would resolve on its own over time. |
However, a 2016 paper in the American Journal of Sports Medicine complicated that perspective: the authors queried 504 adolescents with knee pain, following up two years later, and found that those with pain from diagnosed patellofemoral syndrome at baseline were more likely to also report pain at follow up than those with other types of knee pain—indicating that the condition did not resolve on its own. Furthermore, those with patellofemoral pain were more likely to have reduced or stopped participation in sports than those with other types of knee pain. 
In adults, the current leading theory for the cause of patellofemoral pain is improper tracking and kinematics in the lower extremity, Gavelli said. Kinematics may play some role in the genesis of the condition in adolescents, as well, and any type of improper tracking is likely to cause pain, she said. But the size of the patella relative to the femur, the shape of the patella, or other, structural issues might be a factor as well. “You could have multiple subgroups,” she said.
What is increasingly clear, though, is that patellofemoral pain in children and adolescents should not be managed in the same way as patellofemoral pain in adults. An analysis of the literature published in 2015 in the journal Sports Medicine showed that adolescents had a different success rate from exercise treatment than adults.  “Kids are not just little adults,” Gavelli said.
Still unpublished research, in addition, found that the abnormal lower limb tracking patterns seen in adults with patellofemoral pain were different than those seen in adolescents, Gavelli said. “There appears to be kinematics unique to adolescents” she said. “And it’s really messy as they age into adulthood.”
|Pain, kinematics, growth and puberty|
|Patellofemoral pain can begin young, with cases initially appearing in elementary and early middle school-aged kids—indeed, earlier in the maturation cycle than previously thought. “Most of the new cases are occurring in the younger, growing years,” said Gregory Myer, PhD, FACSM, CSCS*D, Director of Research and the Human Performance Laboratory for the Division of Sports Medicine at Cincinnati Children’s Hospital Medical Center. Understanding the way pain, and the causes of pain, change as kids grow and go through puberty is a key area of inquiry.|
Some early studies are starting to address those questions. In a small, pilot study from Carlson et al at the FAB Section at the National Institutes of Health, researchers analyzed the kinematic patterns of ten adolescent female knees with patellofemoral pain when the subjects were an average of 14 years old, and then again when they were an average of 18.5 years old. The knees with pain had abnormal tracking patterns at baseline and did not convert to a more normal pattern at follow-up, when the subjects were entering adulthood. At follow up, the women reported that their symptoms had resolved, though not entirely; importantly, all reported that they had reduced their physical activity levels. The results were published in February 2017 in the Orthopaedic Journal of Sports Medicine. 
“It seems like reduction in pain was there, but the kinematics hadn’t changed, which is why pain didn’t go fully away,” said Gavelli, who works with the study authors at the NIH. That finding indicates that maltracking contributes to patellofemoral pain but leaves room for overuse to remain a factor. “It could be that there is an overuse component, and when you reduce activity, the pain does reduce,” Gavelli said. But it’s possible that the pain doesn’t go away entirely because the tracking problems persist, she said. “It’s likely a multi-part answer.”
An August 2018 study conducted by Myer and published in the American Journal of Sports Medicine added to those findings. The team looked at the landing profiles of more than 500 high school female athletes and classified them by risk, at the hip or the knee, for developing patellofemoral pain. Their mechanics were re-examined at follow up, and analysis showed that the athletes who started with high-risk knee profiles stayed the same as they went through puberty. Athletes who started with high-risk hip profiles, however, saw their mechanics shift to low-risk after puberty. “The hip group tended to get better with maturation,” Myer said. The study did not track changes in pain between baseline and follow-up. 
The results from the two studies are not necessarily inconsistent, though Myer’s study showed that mechanics changed during growth for one group, and the Carlson NIH study did not find any mechanical changes. According to Gavelli, there are likely a constellation of factors that could drive patellofemoral pain, and the causes might be different for each individual patient. “We need to have a holistic approach,” she said.
|Treatment and prevention|
|The emerging research suggests a need for new treatment approaches to patellofemoral pain in adolescents. “The original concept of overuse, and to let them rest, may not be a good functional intervention,” Gavelli said. Removing kids from sports might help pain, but it could also have a significant impact on other aspects of their health, their future in their chosen sport, and their academic opportunities, she said.|
Playing through significant pain isn’t a good strategy, either, so clinicians should work to identify conservative treatment strategies that can return kids to their chosen activity. “Like we do with ACL tears—can we repair it quickly and let them play in a way that they’re not hurting themselves further,” she said.
However, because the condition is multifaceted, there won’t be a one-size-fits-all treatment. Researchers should study a roster of potential therapies, and then determine in which kids they work and why. “Maybe orthotics, or gait retraining, or strengthening,” Gavelli said. “Then, you see which is best for each child. We’ll try one thing, and if it doesn’t work, we’ll try something else. You’ll have a list of options,” she said.
Myer’s study pointed to individualized treatment approaches, as well, indicating that girls with aberrant hip mechanics should be managed differently than girls with aberrant knee mechanics.
At the moment, however, it is not clear what the treatment options might be; currently there is no evidence to say what might work. “I don’t have a prescription yet,” Gavelli said.
Myer said he hopes to approach the problem from the other side, by working to develop prevention strategies, rather than wait and react to pain when it appears.
“We want to do specific training that can reduce the incidence of [patellofemoral pain],” Myer said. It’s still to early to say what that might be, but it would likely include strength and stability exercises, and might be similar to the strategies used to prevent ACL tears. “We want to build an athlete that can tolerate the demands of any sport,” Myer said.
Because the condition can appear so young, preventative measures should start early, before kids are fully grown, Myer said. By the time young athletes reach and pass through puberty, there are already cases of knee pain. “If we wait until late middle or early high school, we’re going to be too late,” he said.
|Nicole Wetsman is a freelance writer in New York|
Source Lower Extremity Review