What is a trimalleolar fracture?

Definition of a Trimalleolar Fracture

A trimalleolar fracture is defined as an ankle fracture involving three malleoli: the medial malleolus, lateral malleolus, and posterior malleolus of the distal tibia. This type of fracture represents one of the more severe patterns of ankle fractures, typically resulting from high-energy trauma 1.

Anatomical Components of a Trimalleolar Fracture

• Lateral malleolus: Fracture of the distal fibula
• Medial malleolus: Fracture of the medial aspect of the distal tibia
• Posterior malleolus: Fracture of the posterior aspect of the distal tibia

Diagnostic Approach

Initial Assessment

When a trimalleolar fracture is suspected:

1. Apply the Ottawa Ankle Rules (OAR) to determine the need for radiographic imaging:

   • Inability to bear weight immediately after injury, OR
   • Point tenderness over the medial malleolus, posterior edge or inferior tip of the lateral malleolus, talus, or calcaneus, OR
   • Inability to ambulate for 4 steps in the emergency department 1

2. The OAR have high sensitivity (92-99%) for detecting ankle fractures with negative predictive values of 97-99% 1

Imaging

• Standard radiographic views: Three views are typically required:

  • Anteroposterior view
  • Lateral view
  • Mortise view (ankle in 15-20° internal rotation) 1

• Weight-bearing radiographs (if possible) provide critical information about fracture stability

  • A medial clear space <4 mm confirms stability 1

• CT scanning is often needed for:

  • Preoperative planning
  • Assessment of posterior malleolus fragment size and position
  • Evaluation of complex fracture patterns 1

Clinical Significance

Trimalleolar fractures are:

• The least common type among ankle fractures 2, 3
• More frequently seen in females than males 2
• Associated with high-energy trauma mechanisms 2, 3
• Often associated with ankle dislocation or instability 1

Prognostic Factors

Negative prognostic factors for trimalleolar fractures include:

• Age over 61 years
• BMI > 40
• ASA > 1 (American Society of Anesthesiologists classification)
• Type C fracture (according to Danis-Weber classification)
• Presence of fracture dislocation 4

Treatment Considerations

• Trimalleolar fractures typically require surgical management with open reduction and internal fixation (ORIF) 5
• The management of the posterior malleolus fragment remains controversial and depends on:
  • Fragment size
  • Ankle joint stability
  • Presence of talar subluxation 5

Clinical Pitfalls

1. Missed diagnosis: The posterior malleolus fracture may be overlooked if proper radiographic views are not obtained
2. Underestimating instability: Even with appropriate fixation of medial and lateral malleoli, ankle instability may persist if a significant posterior malleolus fragment is not addressed
3. Delayed rehabilitation: Prolonged non-weight-bearing can lead to muscle wasting and reduced ankle range of motion 2

Trimalleolar fractures require careful assessment, appropriate imaging, and often surgical management to restore ankle stability and function, with rehabilitation tailored to the specific fracture pattern and fixation method.