Avulsion Fracture of the Extensor Digitorum Brevis: Location and Treatment
An avulsion fracture of the extensor digitorum brevis occurs at the dorsolateral aspect of the calcaneus where this muscle originates, and conservative treatment with elevation, supportive bandaging, and early mobilization is the recommended approach for most cases.
Anatomic Location
The extensor digitorum brevis muscle originates from the dorsolateral surface of the anterior calcaneus. The avulsion fracture occurs at this specific origin point, typically on the superior-lateral aspect of the calcaneus 1, 2. This injury is located:
- Below the anterior talofibular ligament on physical examination
- Visible on routine dorsoplantar foot radiographs and/or anteroposterior ankle views 2
- Distinct from the anterior process of the calcaneus (which is more medial and anterior)
Key Diagnostic Pitfall
This fracture is frequently misdiagnosed as a lateral ankle sprain because the mechanism of injury (supination/inversion forces) and initial symptoms are identical 1. The critical distinguishing feature is that maximal tenderness is confined to the area below the anterior talofibular ligament rather than over the ligament itself 1.
The fracture can also be confused with an os peroneum or anterior process calcaneal fracture on imaging 2.
Mechanism of Injury
This injury occurs from inversion/supination forces applied to the ankle, identical to the mechanism causing lateral ankle sprains 1, 2. The sudden forceful contraction or stretch of the extensor digitorum brevis muscle during ankle inversion causes the bony fragment to avulse from its calcaneal origin.
Incidence: This fracture was identified in approximately 10% of emergency room patients with clinically suspected ankle fractures following inversion injuries 2.
Treatment Approach
Conservative Management (First-Line)
Conservative treatment is recommended for the vast majority of cases 1, 3, 2. The standard protocol includes:
- Elevation of the affected extremity
- Supportive bandaging or immobilization
- Early activity/mobilization as tolerated 2
- Weight-bearing as pain permits
This approach addresses the injury as primarily a diagnostic challenge rather than a treatment challenge 3.
Surgical Intervention (Selective Cases)
Surgery may be necessary only in specific circumstances 1:
- Large avulsed fragments with significant displacement
- Symptomatic malunions that develop after failed conservative treatment
- Persistent pain or functional limitation despite adequate conservative management
The evidence does not specify exact size thresholds for surgical intervention, but the general principle is that small, minimally displaced fragments heal well conservatively.
Clinical Pearls
Examination Findings
- Point tenderness specifically over the dorsolateral calcaneus (at the EDB origin)
- Tenderness below (inferior to) the anterior talofibular ligament, not over it
- Pain with resisted toe extension may be present
- Swelling localized to the lateral hindfoot/sinus tarsi region
Imaging Strategy
Following ACR guidelines for acute ankle trauma 4:
- Standard ankle radiographs (AP, lateral, mortise views) will demonstrate the fracture
- Dorsoplantar foot view provides optimal visualization 2
- No advanced imaging (CT/MRI) is typically required for diagnosis or treatment planning
- The fracture appears as a small bony fragment separated from the dorsolateral calcaneus
Common Pitfall to Avoid
Do not dismiss this as a simple ankle sprain based solely on mechanism. Any patient with persistent lateral hindfoot pain after inversion injury should have radiographs that include adequate visualization of the anterior calcaneus 1, 2. The injury is easily overlooked if the clinical suspicion is low and imaging is limited to standard ankle views without foot views.
Prognosis
With appropriate conservative management, these fractures typically heal without long-term sequelae. The emphasis on early activity 2 suggests that prolonged immobilization is unnecessary and potentially counterproductive. Patients can generally return to activities as symptoms allow, with the fracture healing occurring over the standard 6-8 week timeframe typical for small avulsion fractures.