PFP etiology differs in adults, kids
By Katie Bell
Patellar maltracking persists in adolescent girls with patellofemoral pain (PFP) even as symptoms improve, according to a study from Maryland, which suggests the etiology of PFP differs between adolescents and adults and should be managed accordingly.
The longitudinal study found no changes in patellar maltracking patterns in 10 knees from six girls with clinically diagnosed PFP as they matured from mid- to late adolescence.
The unchanged patellofemoral maltracking suggests anatomic and kinematic abnormalities contributing to PFP during midadolescence continue during skeletal maturation, rather than evolving to resemble those seen in adults, according to the authors. The findings suggest age of onset is important to PFP’s etiology and that interventions tailored to age-based maltracking patterns may improve outcomes.
Corresponding author Barry P. Boden, MD, who specializes in sports medicine at The Orthopaedic Center, a division of Centers for Advanced Orthopaedics, in Rockville, MD, noted that with PFP, “adolescent-onset is associated with lateral shift or lateral tracking in the trochlea, while adult-onset PFP is associated with patella tilt.”
Boden and colleagues used dynamic magnetic resonance imaging (MRI) to acquire 3D patellofemoral kinematic data during active extension and flexion when participants were aged a mean of 14 years, with follow-up when participants were aged a mean of 18.5 years.
The investigators obtained 3D patellofemoral kinematic parameters with the participants situated supine in an MRI scanner. Participants rhythmically flexed and extended their knees at 30 cycles per minute, with guidance from an auditory metronome. Velocity data in the three cardinal planes were used to identify the position of the patella and tibia relative to the femur during the cycle.
At initial and follow-up visits, investigators evaluated participants’ knees, including Q-angle, assessment for a J-sign, and lateral patellar hypermobility, and recorded age, height, weight, and body mass index. They compared pain score based on a visual analog scale (VAS) and anterior knee pain (AKP) scores across initial and follow-up visits. Participants reported hours spent doing impact and nonimpact physical activities.
All participants reported improved PFP symptoms at follow-up; AKP scores improved 35% and VAS pain scores during provocative activities improved 72%. One participant reported complete resolution of PFP symptoms.
Investigators found no differences in patellar maltracking from initial to the follow-up visits. Meanwhile, a decrease in hours engaged in impact physical activities was reported by all participants at follow-up, with two reporting they discontinued all physical activity.
On initial evaluation, 50% of patients had extreme lateral patellar displacement at 10° of extension; the rest had nonextreme patterns. At follow-up, all participants demonstrated the same kinematic profile as at baseline. The average distance between the tibial tuberosity and trochlear groove at initial and follow-up visits was 11.6 and 13 mm, respectively, for the whole study group, and 14.8 and 14.2 mm, respectively, for the extreme maltrackers. No participant reported a history of dislocation during either visit.
The study, published in February in The Orthopaedic Journal of Sports Medicine, didn’t evaluate dislocaters, who often have patella alta and trochlear dysplasia, Boden said.
Symptom improvement didn’t result from a change in patellofemoral tracking, he said, but rather from other causes, such as reduced participation in impact physical activities.
Physical therapy, including activity modification, is currently the best treatment for PFP in children and adults, said Boden.
“Knee braces can be helpful for stabilizing the patella and providing proprioception, and surgery is helpful in cases that don’t respond to a minimum of six to nine months of nonoperative treatment,” he added. “For the adult, the lateral release may be more appropriate, whereas [centering] the patella may be more appropriate for adolescents.”
Michael Skovdal Rathleff, PhD, associate professor, and Sinead Holden, PhD, visiting researcher, in the OptiYouth research group at the Research Unit for General Practice at Aalborg University in Denmark, said young adolescents with PFP don’t display the same strength deficits as older adolescents or adults with the condition. Although the study didn’t look at strength deficits, Rathleff and Holden said this strength difference calls into question the rationale for focusing on strength training and exercise therapy in these young adolescents.
“To keep youth active, practitioners can focus on helping adolescents control their sports participation and manage load. Initially this can include education about activity modification, enabling them to be physically active in activities that do not aggravate their knee pain, or cause a flare in symptoms,” Rathleff and Holden noted in an email interview. “To support them in returning safely to sport, the focus should be a graded reintegration to previous activity levels, helping them find the ‘sweet-spot,’ rather than an ‘all-or-nothing’ approach to starting and stopping exercise and activity.”
Katie Bell is a freelance writer based in New York City.
Carlson VR, Boden BP, Shen A, et al. Patellar maltracking persists in adolescent females with patellofemoral pain. Orthop J Sports Med 2017;5(2): 2325967116686774.