What are the Ottawa Knee Rules?

The Ottawa Knee Rules are validated clinical criteria developed in 1995 at the University of Ottawa to identify which patients with acute knee injuries need radiography. They have near-100% sensitivity for fractures and reduce unnecessary imaging by approximately 25–28%.

Who should NOT be assessed with this tool?

The rules apply to adults (≥18 years) with isolated acute knee injury. Exclude: patients with multiple injuries, patients presenting more than 7 days after injury, pregnant patients, patients with diminished lower-limb sensation due to neurological disorders, and patients with low-energy injuries who return only for recurrence of a chronic condition.

What counts as "age 55 or older" as a criterion?

If the patient is 55 years of age or older at the time of evaluation, this criterion alone is sufficient to indicate a knee X-ray regardless of other findings.

What is the fibular head?

The fibular head is the bony prominence on the outer side of the knee just below the knee joint line. Isolated tenderness at this point (not simply lateral joint-line tenderness) is a positive finding.

How accurate are the Ottawa Knee Rules?

Prospective studies show sensitivity of 97–100% and specificity of 27–49% for clinically significant fractures. A negative result is highly reliable for ruling out fracture; a positive result indicates imaging is warranted but does not confirm fracture.

What is the patella tenderness criterion?

Isolated tenderness of the patella means tenderness localized to the kneecap itself with no other bony tenderness. Diffuse tenderness over the knee that happens to include the patella does not meet this criterion.

Ottawa Knee Rule

Name: Ottawa Knee Rule
Availability: InStock
Author: Nham Vu

Apply the Ottawa Knee Rules to determine whether a knee X-ray is clinically indicated after acute knee injury.

Ottawa Knee Rule Criteria

A knee X-ray is indicated if any one of the five criteria below is present.

Age 55 years or older

Patient is 55 years of age or older at time of evaluation.

Isolated tenderness of the patella

Tenderness on palpation of the patella with no other bony tenderness of the knee.

Tenderness at the head of the fibula

Isolated bony tenderness at the fibular head (outer side of the knee, just below the joint line).

Unable to flex the knee to 90°

Patient cannot flex the injured knee to a right angle due to pain or mechanical block.

Unable to bear weight (4 steps)

Patient cannot take four weight-bearing steps both immediately after injury and in the ED, regardless of limping.

0 of 5 criteria checked

Assessment Result

Check criteria on the left to see the X-ray recommendation.

Clinical note: The Ottawa Knee Rules apply to adults (≥18 years) with isolated acute knee injury presenting within 7 days of trauma. Not validated in children, pregnant patients, those with multiple injuries, or those with neurological deficits affecting lower-limb sensation. Clinical judgment always takes precedence.

Rule Performance Reference

Sensitivity (fracture detection) 97–100%

Specificity 27–49%

Imaging reduction ~25–28%

Population validated Adults ≥18 yrs

Original publication Stiell et al., 1995

Summary

Apply the Ottawa Knee Rules to determine whether a knee X-ray is clinically indicated after acute knee injury.

How it works

Check each Ottawa Knee Rule criterion that is present on examination.
The tool evaluates all five criteria and issues an X-ray recommendation instantly.
A positive result (any criterion met) means a knee X-ray is indicated.
A negative result (no criteria met) suggests fracture is unlikely and imaging can be deferred.
Review the sensitivity and specificity reference panel to understand rule performance.
Reset the form to evaluate a new patient.

Use cases

Triage acute knee injuries in emergency and urgent care settings.
Reduce unnecessary knee X-rays in low-risk adult patients.
Teach medical students validated clinical decision rules at the bedside.
Document clinical reasoning for imaging decisions.
Screen patients before referring for radiography.
Apply evidence-based decision support in sports medicine and primary care.
Confirm clinical reasoning when evaluating isolated knee trauma.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu