WOMAC: how to calculate and interpret the 3 subscales in osteoarthritis

What is the WOMAC?

The WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) was developed by Bellamy et al. (1988) as a patient-reported outcome instrument for patients with knee and hip osteoarthritis. It evaluates three domains — pain, stiffness and physical function — on a Likert scale of 0 (no symptoms) to 4 (extreme symptom).

It is the most validated instrument for monitoring outcomes in total knee and hip arthroplasty, and one of the most widely used in osteoarthritis clinical trials worldwide.

💡 WOMAC vs KOOS

The Pain, Stiffness and Function subscales are equivalent between WOMAC and KOOS, but with opposite direction: in the inverted WOMAC 100 = best; in the original WOMAC 0 = best.

The 3 subscales (LK 3.1 version)

Subscale	Items	Raw maximum	Focus
A — Pain	p1–p5 (5 items)	20	Pain at rest, stairs, at night, sitting, standing
B — Stiffness	s1–s2 (2 items)	8	Morning stiffness and after rest
C — Physical Function	f1–f17 (17 items)	68	Stairs, rising, walking, getting in/out car

Calculate the WOMAC for free

Apply the questionnaire online and get the score with exportable PDF.

Open calculator → Share

Formula and score inversion

Formula per subscale — normalised and inverted version

Score = 100 − [(Raw sum / Subscale maximum) × 100]

100 = no symptoms | 0 = worst possible state
Likert items: 0 = none, 1 = mild, 2 = moderate, 3 = severe, 4 = extreme

There is no official composite score — each subscale is interpreted independently.

Ad space

Clinical interpretation

Score (inverted 0–100)	Interpretation	Suggested management
70–100	Good function	Periodic monitoring
40–69	Moderate limitation	Conservative treatment, physiotherapy
0–39	Significant limitation	Priority specialist evaluation

Estimated MCID: 10–12 points for Physical Function; 8–10 points for Pain (Bellamy, 2002).

Use in total knee arthroplasty

Timepoint	Expected score (Physical Function)
Pre-operative	35–50 pts
3 months post-TKA	55–70 pts
6 months post-TKA	65–80 pts
12 months post-TKA	70–85 pts

The WOMAC is the most commonly used primary endpoint in total knee and hip arthroplasty studies, required by most national and international arthroplasty registries.