Problem: Adolescent patellofemoral pain (PFP) is a major problem worldwide and affects 7% of adolescents. Adolescents with PFP have long-lasting severe pain and low quality of life. Current treatment is ineffective for more than 60% and new treatment approaches are needed.

Solution: A novel multidimensional diagnostic approach combining imaging, physical activity level and pain sensitisation in adolescents with PFP. This approach will enable the identification of adolescents with PFP who benefits from a new treatment strategy using activity modification to reduce loading of the patellofemoral joint and graded exercises to improve loading capacity.

Participants:

Adolescents will be recruited from a population-based cohort from Aalborg and Copenhagen consisting of a total of 16 public schools. This cohort will allow for recruitment of adolescents with PFP from the following categories 1) adolescents not participating in sport outside school; 2) adolescents involved in sports a minimum of 3 times per week. In addition, a randomly recruited age- and gender-matched pain-free group from the same cohort will be recruited to form a control group.

Protocol:

All adolescents will be requested to complete an online questionnaire on current pain problems. If they report having knee pain they will be telephoned. The telephone interview will collect an anamnesis and the adolescents and their parents will be invited to a clinical examination if they have anterior knee pain with an insidious onset and with duration of more than 6 weeks. If the adolescents are diagnosed with PFP they are invited to participate in the project.

Baseline measurements:

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.

Main study:

Adolescents with PFP will be asked to participate in main study which investigates the effect of early activity modification and graded exercises among adolescents with patellofemoral pain.

Using a prospective cohort design the investigators will investigate the effect of a novel treatment strategy aimed at temporary reduction in the loading of the patellofemoral joint by activity modification. After inclusion, the custody holder and the adolescent with PFP will be informed to begin a 4 week activity modification period and avoid all sports activity including school sports. This protocol will cause a temporary reduction in the loading of the patellofemoral joint. At 4 weeks they are instructed to begin a predefined training protocol involving graded exercises. The purpose of the graded exercises is to increase loading capacity of the tissue around the knee.

Inclusion Criteria:

• 10-14 years of age
• insidious onset of anterior knee or retro- patellar pain of more than 6 weeks duration
• provoked by at least two of the following situations: prolonged sitting or kneeling, squatting, running, hopping or stair climbing; tenderness on palpation of the patella, pain when stepping down or double leg squatting

Exclusion Criteria:

• Concomitant injury or pain from the hip, lumbar spine or other knee structures
• previous knee surgery
• self-reported patellofemoral instability
• current use of physiotherapy for treating knee pain
• A diagnosis of other knee conditions that may present as anterior knee pain (Mb. Osgood Schlatter, iliotibial band syndrome, sinding-larsen-Johansson, patella tendinopathy or similar).