How to Differentiate a Foot Fracture from a Sprain
Use the Ottawa Foot Rules to determine if imaging is needed—if positive, obtain foot radiographs (3-view series) which have 99% sensitivity for detecting fractures and are the definitive way to distinguish fracture from sprain. 1
Clinical Decision Algorithm
Step 1: Apply the Ottawa Foot Rules
The Ottawa Foot Rules indicate imaging is needed if the patient has:
- Pain in the midfoot zone AND any of:
- Bone tenderness at the navicular
- Bone tenderness at the base of the 5th metatarsal
- Inability to bear weight both immediately after injury and in the clinical setting (4 steps)
Adding swelling as a criterion increases sensitivity to 100% for the malleolar zone and 50% for the midfoot 1.
Step 2: Check for Exclusionary Criteria
Do NOT use Ottawa Rules if any of these apply 1:
- Age <5 years
- Pregnancy
- Penetrating trauma or skin wounds
10 days since injury
- Return visit for same injury
- Polytrauma
- Altered mental status
- Neurologic abnormality affecting the foot
- Underlying bone disease (osteoporosis, bone tumors)
- Patient transferred with radiographs already obtained
If exclusionary criteria exist, proceed directly to radiography regardless of clinical findings.
Step 3: Imaging When Indicated
Radiography is the gold standard 1:
- Standard 3-view series (AP, lateral, oblique)
- Weight-bearing views when possible, especially for suspected Lisfranc injuries 1
- 99% sensitivity for detecting foot fractures 1
Critical Pitfalls to Avoid
Fractures frequently masquerade as ankle sprains 2, 3, 4. Specific high-risk areas that are commonly missed include:
- Talar dome fractures - Point tenderness over the talus 2
- Lateral/posterior talar process fractures - Deep tenderness anterior to Achilles tendon 2
- Base of 5th metatarsal - Specific point tenderness 4
- Navicular fractures - Midfoot tenderness 4
- Lisfranc injuries - Often subtle; require weight-bearing views to detect widening of tarsometatarsal joint 1, 5
In children and adolescents, what appears to be a lateral ankle sprain may actually be a Salter-Harris type I fracture of the distal fibula (0-57.5% of cases), though recent evidence shows ATFL sprains (76-80%) and osteochondral avulsions (62%) are actually more common 6.
When Ottawa Rules Are Negative
If Ottawa Rules are negative and no exclusionary criteria exist, imaging is not routinely indicated 1. The patient likely has a soft tissue injury (sprain) and can be managed conservatively with:
- Activity modification
- Ice, compression, elevation
- Progressive weight-bearing as tolerated
Special Considerations
Toe and forefoot injuries are not directly addressed by Ottawa Rules 1. If a toe fracture is suspected based on localized tenderness and swelling, obtain radiographs to confirm 1.
Clinical presentation alone cannot reliably distinguish fracture from sprain—this is why the Ottawa Rules were developed and why radiography remains essential when criteria are met 5.