What are the Ottawa rules for determining when to order an X-ray for ankle or knee injuries?

Ottawa Rules for Ankle and Foot Injuries

The Ottawa Ankle and Foot Rules are highly sensitive (99%) clinical decision tools that should be routinely applied to determine when radiographs are necessary in patients ≥5 years old with acute ankle or midfoot injuries, as they can safely reduce unnecessary X-rays by approximately 30-35% without missing clinically significant fractures. 1

Ottawa Ankle Rules - When to Order Ankle X-rays

An ankle radiograph series is required only if there is pain in the malleolar zone AND any one of the following criteria 1:

• Bone tenderness along the distal 6 cm of the posterior edge of the tibia or tip of the medial malleolus
• Bone tenderness along the distal 6 cm of the posterior edge of the fibula or tip of the lateral malleolus
• Inability to bear weight both immediately after injury AND in the emergency department (unable to take 4 steps)

Ottawa Foot Rules - When to Order Foot X-rays

A foot radiograph series is required only if there is pain in the midfoot AND any one of the following 1:

• Point bone tenderness at the navicular bone
• Point bone tenderness at the base of the 5th metatarsal
• Inability to bear weight both immediately after injury AND in the emergency department (unable to take 4 steps)

Adding the criterion of swelling increases sensitivity to 100% for the malleolar zone and improves specificity, though this is not part of the standard rules 1.

Critical Exclusionary Criteria - When NOT to Apply Ottawa Rules

The Ottawa Rules should NOT be used in the following clinical scenarios 1:

• Penetrating trauma
• Pregnancy
• Any open skin wound
• Patient transferred with radiographs already obtained
• >10 days after trauma
• Return visit for same injury with continued pain
• Polytrauma setting
• Altered sensorium or mental status (head injury, intoxication, dementia)
• Neurologic abnormality affecting the foot (paraplegia, diabetic neuropathy)
• Underlying bone disease (osteoporosis, bone metastases)
• Gross deformity or palpable mass
• Prosthetic hardware present
• Unreliable examination due to multiple injuries 1

In these situations, radiographs should be obtained regardless of clinical findings, as physician judgment must supersede clinical guidelines 1.

Ottawa Knee Rules - When to Order Knee X-rays

For patients ≥18 years old with acute knee pain, knee radiographs are indicated if ANY of the following criteria are met 1:

• Age ≥55 years
• Isolated patellar tenderness (no other bony tenderness)
• Tenderness at the head of the fibula
• Inability to flex knee to 90 degrees
• Inability to bear weight immediately after injury
• Inability to take 4 weight-bearing steps in the emergency department

The Pittsburgh Decision Rule is an alternative that mandates radiographs for patients <12 years old OR >50 years old, as well as those unable to take four weight-bearing steps 1. The Ottawa Knee Rule demonstrates 100% sensitivity with potential to reduce radiographs by 35% 1.

Age-Specific Considerations

• Children >5 years old: Ottawa Rules are validated and effective for both ankle/foot and knee injuries 1
• Children 5-12 years old with knee injuries: Fall outside both Ottawa and Pittsburgh rule age ranges; radiographs may be beneficial despite lack of symptoms 1
• Geriatric patients (≥65 years): Some evidence suggests consideration of mandatory imaging regardless of other criteria, as specificity drops significantly in this population (33% vs 60% in younger patients) 2

Clinical Performance and Validation

The Ottawa Rules demonstrate 1, 3, 4:

• Sensitivity: 96.8-100% for detecting clinically significant fractures
• Specificity: 26-45.8% (intentionally low to maximize fracture detection)
• Negative predictive value: 96.5-100% (extremely reliable when negative)
• Potential reduction in radiographs: 30-35% when properly implemented

Important Clinical Pitfalls

Weight-bearing as sole criterion: When inability to bear weight is the only positive finding, consider reassessment in several days if symptoms persist rather than immediate radiography, as this criterion alone has lower specificity 3. However, if any doubt exists in acute setting, obtain radiographs.

Occult fractures: The Ottawa Rules may identify some patients with occult fractures not visible on plain radiographs; 3D-CT can detect these in patients with positive Ottawa criteria but negative X-rays 4.

Areas NOT covered by Ottawa Rules: The rules do not address trauma to metatarsal heads, toes, or penetrating injuries with concern for foreign bodies—use clinical judgment for these scenarios 1.

Documentation: Proper documentation of all Ottawa Rule criteria significantly improves compliance and appropriate utilization 5.