Table 2 Thematic analysis

Shoe inserts require little effort to use

- Not noticing the inserts was perceived as a good thing

- The inserts were comfortable enough to not notice them

- Inserts felt comfortable immediately

- The intervention was straightforward as adolescents did not have to do much apart from keep the shoe inserts in their shoes

- Having inserts fitted to school and sports shoes made it easy to wear them

Perceptions of the program were generally positive

- Best thing about the program: knee pain subsided

- Belief that intervention helped PFP

- Enhanced pain-free exercise participation

- A reduction in symptoms is positive even when PFP is not completely recovered

- The inserts were comfortable but did not help with the pain

- Pain was still present throughout the whole study

- Pain decreased in a few activities, but not in others

Participation in the trial could be made easier

- Questionnaires and logbook were straightforward, and clear

- Logbook was simple

- No difficulties with online questionnaires

- Three shoes with inserts did not limit shoe choice

- Potential barrier with travel to physiotherapy appointments

- Hard to remember to fill in the logbook

- Unsure about how much detail to include in logbook

Warm weather matters

- Summer affected the use of the inserts

- Negative view of warm climate and having to wear closed-in shoes

- Cold weather would have made adolescents more likely to wear the shoe inserts

Life happens

- Forgot logbook between houses

- Grew out of shoes and inserts

- Unsure if knee pain stopped because of inserts or “growing out of it”

- Started exercising more which helped with pain

- Confounding factors changed lifestyle (e.g. COVID-19)