KOOS (Knee injury and Osteoarthritis Outcome Score)

Developed by Ewa Roos and colleagues in 1994–1995 and first published in 1998, the Knee injury and Osteoarthritis Outcome Score (KOOS) was designed to capture patient-centered outcomes across the full spectrum of knee pathology—from acute ligamentous and meniscal injury through end-stage osteoarthritis. Its 42 items are grouped into five independently scored subscales: Pain (KOOS Pain), Other Symptoms (KOOS Symptoms), Function in Daily Living (KOOS ADL), Function in Sport and Recreation (KOOS Sport/Rec), and Knee-Related Quality of Life (KOOS QOL). Because the WOMAC Osteoarthritis Index is embedded within the KOOS, clinicians can derive a WOMAC score from KOOS responses without administering a separate instrument.

The KOOS is entirely self-administered, typically requiring 10–15 minutes to complete. Each item uses a five-point Likert response scale; raw scores are then normalized to a 0–100 scale per subscale. No single composite KOOS score is reported—each subscale stands alone, reflecting the multidimensional nature of knee health. A 12-item short form (KOOS-12) and a physical-function short form (KOOS-PS) are available when brevity is required, and a pediatric adaptation (KOOS-Child) exists for younger populations.

Psychometric validation has been conducted across more than twenty independent studies globally, confirming reliability, responsiveness, and construct validity in populations undergoing ACL reconstruction, meniscectomy, and total knee replacement, as well as in patients with primary osteoarthritis. The instrument is licensed through Mapi Research Trust (ePROVIDE) and is freely available for non-commercial clinical and research use; Microsoft Excel–based scoring software is available at koos.nu.

Payers and accreditation bodies increasingly require documented PRO data to justify ongoing care, authorize surgery, and benchmark quality under value-based care contracts. When KOOS subscale scores are collected at defined intervals—preoperative, 6-month, and 1-year—they create an auditable outcomes trail that supports medical necessity for procedures such as arthroscopic meniscus repair (CPT 29882), ACL reconstruction (CPT 27407), or total knee arthroplasty (CPT 27447). Absent this documentation, claims for elective knee procedures face higher denial rates and post-payment audit risk. Additionally, registries such as the American Joint Replacement Registry (AJRR) accept KOOS data for longitudinal benchmarking, meaning incomplete or mis-timed collection can invalidate a practice's quality-reporting submission.