About the Ottawa Ankle Rules
The Ottawa Ankle Rules are the most widely validated clinical decision rule in emergency medicine, developed by Ian Stiell and colleagues at the University of Ottawa and published in JAMA in 1992. The rules identify which patients with acute ankle or midfoot injury require X-ray imaging to evaluate for fracture — and more importantly, which patients can safely forgo imaging without missing clinically significant injuries.
Before the Ottawa Ankle Rules, ankle X-rays were ordered for virtually every ankle injury presenting to the emergency department, despite the fact that only 10–15% of patients ultimately had fractures. The rules were developed to reduce this unnecessary imaging burden while maintaining clinical safety. Prospective implementation studies have consistently demonstrated reductions in ankle X-ray ordering of 30–40% without any missed clinically significant fractures.
The rules have been validated in over 50 prospective studies encompassing more than 15,000 patients, across multiple countries and health systems. A 1994 meta-analysis in JAMA by Bachmann et al. confirmed sensitivity of 98–100% for malleolar zone fractures and 99% for midfoot fractures — among the highest sensitivities ever reported for a clinical prediction rule.
The Two-Rule Structure
The Ottawa Ankle Rules consist of two independent sub-rules that can each trigger independently:
| Sub-Rule | Positive Criteria (any one) | Recommendation |
|---|---|---|
| Ankle series | Age ≥55 OR can't bear weight ×4 steps OR lateral malleolus tenderness OR medial malleolus tenderness | X-ray indicated |
| Foot (midfoot) series | Base of 5th metatarsal tenderness OR navicular tenderness | X-ray indicated |
| Both negative | All six criteria absent | No X-ray needed |
How to Use the Ottawa Ankle Rules
Apply the rules to adults (≥18 years) presenting with acute ankle or midfoot pain after injury. Assess each criterion systematically:
- Age ≥ 55: The age criterion was added in the 1993 revised rules. Older patients have lower bone density and higher fracture risk even with low-mechanism injury.
- Ability to bear weight: Ask whether the patient was able to bear weight immediately after injury. Then observe 4 steps in the ED. The patient must be able to transfer weight to the injured limb twice on each foot — limping is acceptable. If they cannot, the criterion is positive.
- Lateral malleolus tenderness: Palpate the posterior 6 cm and tip of the lateral malleolus (fibula). Tenderness must be bony — not soft tissue. Press firmly with one finger tip along the posterior edge.
- Medial malleolus tenderness: Palpate the posterior 6 cm and tip of the medial malleolus (tibia). Same technique as lateral — posterior edge and tip only.
- Base of 5th metatarsal: Palpate the styloid process at the proximal base of the 5th metatarsal. This is the lateral bony prominence about 6–7 cm distal to the lateral malleolus tip.
- Navicular: Palpate the navicular bone on the dorsomedial midfoot — the prominent bony bump on the medial side of the foot approximately 3–4 cm distal to the medial malleolus.
Sensitivity, Specificity, and the Design Intent
The Ottawa Ankle Rules were deliberately designed to have near-perfect sensitivity at the expense of specificity. The design intent is to safely rule out fractures when all criteria are negative — not to predict who will have a fracture when criteria are positive.
| Metric | Ankle Series | Foot (Midfoot) Series |
|---|---|---|
| Sensitivity | ~98–100% | ~99% |
| Specificity | ~40% | ~40% |
| Negative Predictive Value | Very high — safe to rule out fracture | Very high — safe to rule out fracture |
| Positive Predictive Value | ~15% (most positives won't fracture) | ~15–20% |
When a patient screens positive, most will not have a fracture — X-rays are ordered because the rule cannot safely rule it out, not because it predicts one.
When NOT to Apply the Ottawa Ankle Rules
The rules have several well-documented exclusion criteria where clinical judgment or imaging without rule application is appropriate:
- Children under 18: Open growth plates (physis) produce Salter-Harris fractures that may not be detected with adult rules. Use clinical judgment or pediatric-specific tools.
- Intoxicated patients: Unreliable exam — patient cannot accurately report pain. Do not apply the rule; clinical assessment is impaired.
- Altered mental status: Same rationale as intoxication — subjective reporting of tenderness is unreliable.
- Distracting injuries: Ipsilateral or more painful injury may mask ankle tenderness. The rule requires valid tenderness assessment.
- Initial pain score of 0: If the patient reports no pain at all, the rules were not designed for this presentation.
- Isolated skin injuries: Rules apply to bone tenderness, not cutaneous lesions.
- Injury more than 10 days old: The original validation enrolled acute injuries; delayed presentations with chronic swelling may confound tenderness assessment.
- Re-injury with prior known fracture: Underlying structural changes may alter presentation.
Clinical Pearl: Malleolar vs. Midfoot Zones
A common error is conflating the ankle and foot series. The two sub-rules are anatomically and structurally independent. A patient may require an ankle X-ray but not a foot X-ray, or vice versa, or both, or neither. Palpation of both zones is required for each visit regardless of the primary complaint location — midfoot fractures are commonly missed because clinicians focus only on the ankle.
The most commonly missed fracture in ankle injury evaluation is a base of 5th metatarsal avulsion fracture — the peroneus brevis tendon avulses the styloid process with ankle inversion. This fracture is detected by the Ottawa midfoot rule (5th metatarsal base tenderness), not the ankle rule.
Evidence and Guideline Endorsement
The Ottawa Ankle Rules are endorsed by the American College of Emergency Physicians (ACEP), the British Medical Journal's Best Practice guidelines, and are cited in the NICE guidelines for ankle injury management. They are among the most studied clinical prediction rules in medicine. A 2003 systematic review (Bachmann et al.) covering 27 studies and 15,581 patients confirmed consistent sensitivity above 98% across diverse populations and settings.
References
Stiell IG, Greenberg GH, McKnight RD, 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. doi:10.1016/S0196-0644(05)82656-3
Stiell IG, McKnight RD, Greenberg GH, et al. Implementation of the Ottawa ankle rules. JAMA. 1994;271(11):827–832. doi:10.1001/jama.1994.03510350037034
Bachmann LM, Kolb E, Koller MT, Steurer J, ter Riet G. Accuracy of Ottawa ankle rules to exclude fractures of the ankle and mid-foot: systematic review. BMJ. 2003;326(7386):417. doi:10.1136/bmj.326.7386.417
Stiell IG, Clement CM, Grimshaw J, et al. Implementation of the Canadian C-Spine Rule: prospective 12 centre cluster randomised trial. BMJ. 2009;339:b4146. (Comparative rule implementation methodology)