Introduction In sports physiotherapy, medicine and orthopaedic randomised controlled trials (RCT), the investigators (and readers) focus on the difference between groups in change scores from baseline to follow-up. Mean score changes are difficult to interpret (‘is an improvement of 20 units good?’), and follow-up scores may be more meaningful. We investigated how applying three different responder criteria to change and follow-up scores would affect the ‘outcome’ of RCTs. Responder criteria refers to participants’ perceptions of how the intervention affected them.

Methods We applied three different criteria—minimal important change (MIC), patient acceptable symptom state (PASS) and treatment failure (TF)—to the aggregate Knee injury and Osteoarthritis Outcome Score (KOOS₄) and the five KOOS subscales, the primary and secondary outcomes of the KANON trial (ISRCTN84752559). This trial included young active adults with an acute ACL injury and compared two treatment strategies: exercise therapy plus early reconstructive surgery, and exercise therapy plus delayed reconstructive surgery, if needed.

Results MIC: At 2 years, more than 90% in the two treatment arms reported themselves to be minimally but importantly improved for the primary outcome KOOS₄. PASS: About 50% of participants in both treatment arms reported their KOOS₄ follow-up scores to be satisfactory. TF: Almost 10% of participants in both treatment arms found their outcomes so unsatisfactory that they thought their treatment had failed. There were no statistically significant or meaningful differences between treatment arms using these criteria.

Conclusion We applied change criteria as well as cross-sectional follow-up criteria to interpret trial outcomes with more clinical focus. We suggest researchers apply MIC, PASS and TF thresholds to enhance interpretation of KOOS and other patient-reported scores. The findings from this study can improve shared decision-making processes for people with an acute ACL injury.