Adolescents and adults with patellofemoral pain exhibit distinct patellar maltracking patterns

Background: Chronic idiopathic patellofemoral pain is associated with patellar maltracking in both adolescents and adults. To accurately target the underlying, patient-specific etiology, it is crucial we understand if age-of pain-onset influences maltracking. Methods: Twenty adolescents (13.9 +/- 1.4 years) and 20 adults (28.1 +/- 4.9 years) female patients with idiopathic patellofemoral pain (age-of-pain-onset: < 14 and > 18 years of age, respectively) formed the patient cohort. Twenty adolescents and 20 adults (matched for gender, age, and body mass index) formed the control cohort. We captured three-dimensional patellofemoral kinematics during knee flexion-extension using dynamic MRI. Patellar maltracking (deviation in patient-specific patellofemoral kinematics, relative to their respective age controlled mean values) was the primary outcome measure, which was compared between individuals with adolescent-onset and adult-onset patellofemoral pain using ANOVA and discriminant analysis. Findings: The female adolescent-onset patellofemoral pain cohort demonstrated increased lateral (P = 0.032), superior (P = 0.007), and posterior (P < 0.001) maltracking, with increased patellar flexion (P < 0.001) and medial spin (P = 0.002), relative to the adult-onset patellofemoral pain cohort. Post-hoc analyses revealed increased lateral shift [mean difference +/- 95% confidence interval =-2.9 +/- 2.1 mm at 10 degrees knee angle], posterior shift [-2.8 +/- 2.1 mm,-3.3 +/- 2.3 mm &-3.1 +/- 2.4 mm at 10 degrees, 20 degrees& 30 degrees], with greater patellar flexion [3.8 +/- 2.6 mm & 5.0 +/- 2.8 mm, at 20 degrees& 30 degrees] and medial spin [-2.2 +/- 1.7 mm &-3.4 +/- 2.3 mm at 20 degrees& 30 degrees]. Axial-plane maltracking accurately differentiated the patient age-of-pain-onset (60-75%, P < 0.001). Interpretation: Age-of-pain-onset influences the maltracking patterns seen in patients with patellofemoral pain; with all, but 1, degree of freedom being unique in the adolescent-onset-patellofemoral pain cohort. Clinical awareness of this distinction is crucial for correctly diagnosing a patient's pain etiology and optimizing interventional strategies.