KOOS: the 6 subscales and how to interpret each domain
Complete KOOS guide — 6 subscales, formula, MCID and differences from IKDC and WOMAC.
What is the KOOS?
The KOOS (Knee Injury and Osteoarthritis Outcome Score) was developed by Roos et al. (1998) as an extension of the WOMAC, adding two domains — Symptoms and Quality of Life — for younger, more active populations with ligamentous and meniscal injuries.
With 42 items across 6 independent subscales, the KOOS captures distinct dimensions of knee function that a single score cannot represent. There is no official composite score — each subscale is interpreted independently.
The Pain, Stiffness and Function subscales of KOOS are equivalent to those of WOMAC, but with the opposite direction: in KOOS 100 = best.
The 6 subscales
| Subscale | Items | Maximum | What it assesses |
|---|---|---|---|
| S — Symptoms | s1–s7 | 28 | Crepitation, stiffness, swelling, ROM |
| ST — Stiffness | st1–st2 | 8 | Morning stiffness and after rest |
| P — Pain | p1–p9 | 36 | Frequency and intensity of pain |
| A — ADL | a1–a17 | 68 | Daily activities: stairs, squatting |
| SP — Sport/Recreation | sp1–sp5 | 20 | Running, twisting, jumping in sport |
| QoL — Quality of Life | q1–q4 | 16 | Knee awareness, lifestyle modification |
Calculate the KOOS for free
Apply the questionnaire online and get the score with exportable PDF.
Scoring formula
Items: Likert 0 (best) to 4 (worst)
MCID per subscale
| Subscale | MCID |
|---|---|
| Symptoms | 8–10 pts |
| Pain | 8–10 pts |
| ADL | 9–11 pts |
| Sport/Recreation | 10–14 pts |
| Quality of Life | 10–15 pts |
Source: Collins et al., Osteoarthritis Cartilage 2016.
When to use KOOS vs IKDC
| KOOS | IKDC | |
|---|---|---|
| Items | 42 | 18 |
| Subscales | 6 independent | Single score |
| Best for | Osteoarthritis, meniscus, young ACL | ACL, ligaments, general research |
| Quality of life | ✓ (own subscale) | Partially |
| ISAKOS standard | Recommended | Recommended |
References
- 1. Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. “Knee Injury and Osteoarthritis Outcome Score (KOOS) — development of a self-administered outcome measure.” J Orthop Sports Phys Ther, 1998;28(2):88–96.
- 2. Collins NJ, Prinsen CA, Christensen R, et al. “Knee Injury and Osteoarthritis Outcome Score (KOOS): systematic review and meta-analysis of measurement properties.” Osteoarthritis Cartilage, 2016;24(8):1317–29.