Ottawa Rules Calculator
Ankle & Knee Fracture Triage Decision Tool
Body Region
Select injured area
Clinical Criteria
Select findings present
Triage Summary
Positive Criteria0
Regionankle
Sensitivity~100%
Guidelines & Evidence
Verified
Last Review: 2026-07-17
When to Use
When to Use
Acute ankle injury (within 10 days) presenting to emergency department or clinic
Acute knee injury (within 7 days) with suspicion of fracture
Patients aged 18+ with blunt trauma mechanism
Clinical decision-making for radiography referral in acute musculoskeletal injuries
Reducing unnecessary X-ray utilization in emergency triage
Exclusion Criteria
Patients under 18 years of age
Injuries older than 10 days for ankle / 7 days for knee
Isolated skin injuries (lacerations, abrasions, burns)
Gross deformity or obvious fracture on examination
Multiple injuries distracting from the ankle or knee exam
Altered mental status or intoxication
How it Works
Ankle Rules
Bone tenderness at posterior edge or tip of lateral malleolus (distal 6 cm)
Bone tenderness at posterior edge or tip of medial malleolus (distal 6 cm)
Bone tenderness at base of 5th metatarsal (midfoot zone)
Bone tenderness at navicular bone (midfoot zone)
Inability to bear weight both immediately and in emergency department (4 steps)
Knee Rules
Patient aged 55 years or older
Isolated tenderness of patella (no other bone tenderness)
Tenderness at fibular head
Inability to flex knee to 90 degrees
Inability to bear weight both immediately and in emergency department (4 steps)
Decision Logic
Ankle X-ray required if ANY tenderness in malleolar zone OR inability to weight bear
Foot X-ray required if ANY tenderness in midfoot zone OR inability to weight bear
Knee X-ray required if ANY of the 5 criteria is positive
100% sensitivity for clinically significant fractures when applied correctly
Clinical Pearls
Key Considerations
The rules have 100% sensitivity for detecting fractures — a negative rule effectively rules out fracture
Specificity is approximately 40-50% for ankle and 30-40% for knee rules
Application in patients over 55 retains sensitivity but specificity decreases
The rules apply only to blunt trauma — not pathologic fractures or stress fractures
Weight-bearing is defined as ability to transfer weight twice (4 steps total), not necessarily unaided
Tenderness must be over bone, not soft tissue
Clinical Impact
Implementation of the Ottawa Rules reduces unnecessary ankle radiography by 30-40% and knee radiography by 20-30%, resulting in significant cost savings and reduced emergency department wait times.
Next Steps
Clinical Actions
01
If ANY criterion positive: obtain standard radiography (AP, lateral, and mortise views for ankle; AP and lateral for knee)
02
If ALL criteria negative: radiography can be safely deferred; diagnose as soft tissue injury
03
For ankle injuries with negative rules: treat with RICE protocol and early mobilization
04
For knee injuries with negative rules: treat symptomatically and provide crutches if needed
05
Arrange orthopedic follow-up if fracture is identified on radiography
06
Document application of the Ottawa Rule in clinical notes
The Evidence
Primary Reference
Decision rules for the use of radiography in acute ankle injuries: refinement and prospective validation
Stiell IG et al. • JAMA. 1993;269(9):1127-1132 — Derivation and validation of the Ottawa Ankle Rules
Implementation of the Ottawa Knee Rule for the use of radiography in acute knee injuries
Stiell IG et al. • JAMA. 1997;278(23):2075-2079 — Validation of the Ottawa Knee Rules
Validation Evidence
Sensitivity: 98-100% across 30+ clinical studies
Specificity: 40-50% for ankle, 20-30% for knee
Inter-observer reliability: kappa 0.85-0.95
Reduction in X-ray utilization: 30-40% for ankle, 20-30% for knee
Adopted by ACEP, NICE, and multiple national emergency medicine guidelines
Origins & History
Historical Background
The Ottawa Ankle Rules were developed in 1992 by Dr. Ian Stiell and colleagues at the Ottawa Hospital Research Institute, University of Ottawa, Canada. The knee rules followed in 1995. They represent one of the most successful and widely implemented clinical decision rules in emergency medicine.
Last Comprehensive Review: 2026-07-17