Ottawa knee rule
Need for knee radiographs after acute knee injury in adults
Sources last checked: 2026-11-03
Ottawa knee rule
Need for knee radiographs after acute knee injury in adults
Derived and validated in adults in the emergency department. 'Isolated' patellar tenderness means no other bony tenderness of the knee. 'Unable to bear weight' means unable to take four steps (limping counts as bearing weight). The rule addresses fracture only, not ligament or meniscal injury.
Interpretation
| Rule not applicable | The patient is outside the population the rule was derived and validated in, so the rule makes no statement for this patient. |
|---|---|
| No knee radiograph required by the rule | None of the five findings present. In the 1996 JAMA validation the probability of fracture with a negative rule was estimated at 0 % (95 % CI 0–0.4 %). |
| Knee radiograph series indicated by the rule | At least one of the five findings is present. The rule is calibrated for sensitivity: most patients with a positive rule have no fracture (specificity about 50 %). |
What is the Ottawa knee rule?
The Ottawa knee rule identifies which adults with an acute knee injury need knee radiographs. Stiell and colleagues derived it in 1,047 emergency patients in Ottawa (Ann Emerg Med 1995) and validated it prospectively in 1,096 further patients (JAMA 1996), where it detected all 63 clinically important fractures. Applying it could reduce knee radiography by about 28 %.
When to use it
- Adults with an acute blunt or twisting knee injury in the emergency department, urgent care or general practice.
- Deciding whether a plain knee radiograph is needed before discharge.
- Teaching a structured knee examination: fibular head, patella, flexion and weight-bearing.
When not to use it
- Patients who cannot be examined reliably — intoxication, reduced consciousness, distracting injuries.
- Children, unless a paediatric validation is used locally — the derivation and validation enrolled adults.
- Penetrating trauma, injuries that are days or weeks old, or patients returning for reassessment.
How it is calculated
Knee radiograph if ANY of: age ≥ 55 years; tenderness at the head of the fibula; isolated tenderness of the patella; inability to flex to 90°; inability to bear weight (4 steps) both immediately after injury and in the ED.
Clinical pearls and limitations
- Derived and validated in adults in the emergency department. 'Isolated' patellar tenderness means no other bony tenderness of the knee. 'Unable to bear weight' means unable to take four steps (limping counts as bearing weight). The rule addresses fracture only, not ligament or meniscal injury.
- Age ≥ 55 years alone makes the rule positive — older patients are always imaged under this rule.
- 'Isolated' patellar tenderness means tenderness on the patella and nowhere else on the knee's bony landmarks.
- Weight-bearing means four steps, limping allowed, both straight after the injury and in the department.
- A negative rule excludes fracture, not ligament, meniscal or extensor-mechanism injury; those need clinical follow-up.
- A 2004 systematic review of six adult studies found a pooled sensitivity of 98.5 % and specificity of 48.6 %.
Frequently asked questions
What are the Ottawa knee rule criteria?
Age 55 or older, tenderness at the fibular head, isolated patellar tenderness, inability to flex to 90°, or inability to bear weight for four steps both immediately and in the ED. Any one means a radiograph.
How sensitive is the Ottawa knee rule?
Sensitivity was 100 % in both the derivation and the 1996 validation; a 2004 systematic review pooled 98.5 % across six adult studies.
Does the Ottawa knee rule apply to children?
It was developed and validated in adults. Paediatric use depends on separate validation studies and local protocols.
Can the Ottawa knee rule be used for an ACL or meniscus injury?
No. The rule only decides whether a radiograph is needed to look for a fracture. Soft-tissue injuries are assessed clinically and, where indicated, with MRI.
Evidence and guidelines
- Primary source: Stiell IG, Greenberg GH, Wells GA et al. Prospective validation of a decision rule for the use of radiography in acute knee injuries. JAMA 1996;275(8):611-615. PMID 8594242.
- Stiell IG, Greenberg GH, Wells GA et al. Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med 1995;26(4):405-413.
- Bachmann LM, Haberzeth S, Steurer J, ter Riet G. The accuracy of the Ottawa knee rule to rule out knee fractures: a systematic review. Ann Intern Med 2004;140(2):121-124.
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