Ottawa Ankle Rules
Clinical decision rules to determine if ankle or midfoot X-rays are needed after injury. Sensitivity approaches 100% for clinically significant fractures.
Ankle X-ray Series
An ankle X-ray is indicated if there is pain in the malleolar zone AND any of the following:
Foot X-ray Series
A foot X-ray is indicated if there is pain in the midfoot zone AND any of the following:
⚠️ Exclusions: These rules apply to adults (≥ 18 years, though validated in children ≥ 5). Do NOT apply if: patient is intoxicated, has multiple painful injuries, diminished sensation, or presents > 10 days after injury.
Disclaimer: For educational purposes only. Not a substitute for clinical judgment.
About This Tool
What Are the Ottawa Ankle Rules?
The Ottawa Ankle Rules (OAR) are a set of clinical decision rules developed by Stiell et al. at the Ottawa Civic Hospital in 1992 to guide the use of radiography in patients with acute ankle and midfoot injuries. Before these rules, nearly all patients with ankle injuries received X-rays, despite fracture rates of only 15%. The OAR provide a highly sensitive screening tool to identify patients who can be safely discharged without radiographic imaging, reducing healthcare costs, ED wait times, and unnecessary radiation exposure.
How the Rules Work
The rules are divided into two series. An ankle X-ray is only indicated if there is pain in the malleolar zone AND either bone tenderness at the posterior edge/tip of the lateral malleolus, bone tenderness at the posterior edge/tip of the medial malleolus, or inability to bear weight for four steps both immediately after injury and in the ED. A foot X-ray is only indicated if there is midfoot pain AND either bone tenderness at the base of the 5th metatarsal, bone tenderness at the navicular, or inability to bear weight. If none of these criteria are met, imaging is not required.
Validation and Impact
The Ottawa Ankle Rules are among the most extensively validated clinical decision rules in medicine, with over 40 external validation studies across multiple countries and healthcare settings. They have a pooled sensitivity of approximately 98–100% for detecting clinically significant fractures (those requiring specific treatment), with a specificity of about 40–50%. Implementation studies have demonstrated a 30–40% reduction in ankle radiography rates without any increase in missed fractures. The rules have been successfully applied in both adult and pediatric populations (validated in children ≥ 5 years).
🔑 Clinical Pearls
- Bone tenderness must be palpated at the POSTERIOR edge or TIP of the malleoli — ligament tenderness alone does not count.
- "Weight-bearing" is defined as taking 4 steps — even limping or partial weight-bearing satisfies this criterion.
- The rules should not be applied to patients who are intoxicated, have altered mental status, have multiple painful injuries, or present more than 10 days after injury.
- Implementation tip: post the rules in triage areas to allow nurses to apply them before physician evaluation, further reducing unnecessary imaging.
Key References
- Stiell IG, et al. A study to develop clinical decision rules for the use of radiography in acute ankle injuries. Ann Emerg Med. 1992;21(4):384-390.
- Stiell IG, et al. Implementation of the Ottawa Ankle Rules. JAMA. 1994;271(11):827-832.
- Bachmann LM, et al. Accuracy of Ottawa ankle rules to exclude fractures of the ankle and mid-foot: systematic review. BMJ. 2003;326(7386):417.
Formula last verified: February 2026