PFP will be diagnosed using eligibility criteria in line with previous clinical trials and commonly accepted criteria. All adolescents with PFP from the cohort will be examined using self-report questionnaires, clinical examination, strength of the hip and knee, MRI and pressure pain thresholds. Pressure pain thresholds will be measured around the knee, lower leg and forearm to assess local and secondary mechanical hyperalgesia and thus the sensitisation of the central nervous pain system. Additionally, cuff-algometry will be used to asses temporal summation of pain during repeated stimuli and conditioned pain modulation. The pain-free control group will be examined using the same measurements. The comparison between adolescents with PFP and the pain-free control group will be used in 1-2 descriptive studies with the main purpose of describing this young population based on self-report questionnaires, MRI-scans, strength of the hip ad knee and pain mechanisms.