30 years with the Knee injury and Osteoarthritis Outcome Score (KOOS).

This narrative review describes the development and use of patient-reported outcomes over 30 years, focusing on the Knee injury and Osteoarthritis Outcome Score (KOOS). KOOS is a five-subscale patient-reported instrument intended for use from the time of knee injury to the development of osteoarthritis. Numerous studies have confirmed that the psychometric properties of the KOOS and its short-form KOOS-12 are acceptable. More recent research has focused on the use and interpretation of KOOS scores in clinical trials using thresholds, such as minimal important differences, patient-acceptable symptom states, and treatment failure. As an indication of KOOS's popularity, the total 3854 PubMed results for KOOS have increased exponentially since the first KOOS paper was published 25 years ago and now seem to have plateaued at around 650 annually. The selected articles are not based on a systematic search, but on the author's own publications, reading, and literature search that grew organically from that.