Introduction Short-term self-reported changes may be more strongly associated with long-term prognosis as they describe a disease trajectory and not a state. This study aimed to investigate the association between Global Rating of Change (GROC) after 4 weeks and the outcome after 12 months among adolescents with non-traumatic knee pain (Patellofemoral Pain (PFP) or Osgood-Schlatter (OSD)).

Material and Methods We included data from two prospective clinical trials including adolescents (aged 10–14 years) with PFP (N=151) or OSD (N=51) who underwent a self-management rehabilitation programme including education and exercise. Primary outcome was a 7-point GROC ranging from “much improved” to “much worse”. Adolescents were considered to have a successful outcome if they reported being “much improved” or “improved”. Outcomes were collected after 4 weeks and 12 months.

Results Among adolescents with an unsuccessful outcome after 4 weeks (58% of all adolescents), 78% had a successful outcome after 12 months. Among those with a successful outcome after 4 weeks (42% of all adolescents), 94% had a successful outcome after 12 months. Having a successful outcome after 4 weeks increased the relative risk of a successful outcome after 12 months (relative risk 1.21 (95%CI: 1.07–1.38) and absolute risk difference: 16%.

Conclusion Self-reported improvement after 4-weeks of treatment is associated with better outcomes after 12 months. Importantly, despite no improvement after 4 weeks, a large proportion of adolescents between 10 and 14 years of age will report improvement after 12 months. This highlights the importance of following the rehabilitation programme irrespective of short-term improvements.