Clinical Decision-Making
Ottawa Ankle and Knee Rules: When to X-Ray in the ED
The Ottawa Ankle Rules and Ottawa Knee Rule are bedside clinical decision instruments that safely identify which ankle and knee injuries require radiography. Properly applied, they have near-100% sensitivity for clinically significant fractures while reducing unnecessary X-rays by 30–40%.
TL;DR: The Ottawa Ankle Rules and Ottawa Knee Rule are bedside clinical decision instruments that safely identify which ankle and knee injuries require radiography. Properly applied, they have near-100% sensitivity for clinically significant fractures while reducing unnecessary X-rays by 30–40%. The rules are only valid in adults (≥18) and adolescents with closed growth plates.
The Imaging Overuse Problem
Acute ankle and knee injuries are among the most common ED presentations. Only 15% of ankle injuries and 5–7% of knee injuries involve a fracture requiring specific management.
Ottawa Ankle Rules
X-ray is required ONLY if ANY of the following are present:
Ankle Series
| Location | Criterion |
|---|---|
| Lateral malleolus zone | Bone tenderness along posterior edge or tip (distal 6 cm) |
| Medial malleolus zone | Bone tenderness along posterior edge or tip (distal 6 cm) |
| Either zone | Inability to weight-bear (4 steps) immediately and in ED |
Foot Series
| Location | Criterion |
|---|---|
| Navicular zone | Bone tenderness at the navicular |
| Base of 5th metatarsal | Bone tenderness at the base |
| Either zone | Inability to weight-bear immediately and in ED |
Ottawa Knee Rule
X-ray is required ONLY if ANY of the following are present:
| Criterion | Detail |
|---|---|
| Age ≥55 years | Age alone triggers imaging |
| Isolated patella tenderness | No other bony tenderness |
| Tenderness at head of fibula | Proximal lateral leg |
| Inability to flex knee to 90° | Active flexion in ED |
| Inability to weight-bear | Cannot take 4 steps |
Implementation Evidence
- Radiography rates reduced by 26–40% without missing significant fractures
- Sensitivity: 97–100% for clinically significant fractures
- Specificity: ~30–40%
When the Rules Don't Apply
- Age <18 with open growth plates
- Intoxication / altered mental status
- Distracting injury
- Neurovascular deficit
Evidence and Guidelines
- Stiell IG, Bennett C. Acad Emerg Med. 2007;14(11):955–959. PMID: 17923717.
- Paradis M, et al. JMIR Mhealth Uhealth. 2018;6(6):e10263. PMID: 29891469.
- Bachmann LM, et al. BMJ. 2003;326(7386):417. PMID: 12595378.
- Stiell IG, et al. JAMA. 1996;275(8):611–615. PMID: 8594242.
References
- Stiell IG, Bennett C. Acad Emerg Med. 2007;14(11):955–959.
- Paradis M, et al. JMIR Mhealth Uhealth. 2018;6(6):e10263.
- Bachmann LM, et al. BMJ. 2003;326(7386):417.
- Stiell IG, et al. JAMA. 1996;275(8):611–615.