What is a type III odontoid fracture?

Type III Odontoid Fracture Definition

A type III odontoid fracture extends through the body of the C2 vertebra (axis), passing through predominantly cancellous bone below the base of the odontoid process, distinguishing it from type I fractures (through the tip of the odontoid) and type II fractures (through the base/neck of the odontoid). 1, 2

Anatomical Classification

• Type III fractures are defined by their extension into the vertebral body of C2, involving the cancellous bone rather than the cortical bone at the odontoid base 1, 2
• These fractures account for a subset of odontoid injuries, which collectively represent approximately 20% of all cervical spine fractures 2
• The fracture line passes through the axis body itself, which has better healing potential due to the rich cancellous bone and larger surface area for bony union 1, 2

Important Subtype Recognition

Not all type III fractures behave the same—high-energy complex fractures with lateral mass comminution (>50%) or secondary fracture lines into the pars interarticularis represent a distinct subgroup with significantly higher failure rates. 3

Standard Type III Fractures

• Simple fracture lines extending into the C2 body without comminution 1
• Typically result from low-energy mechanisms, particularly falls in elderly patients (82% of cases) 1
• Median patient age is 72 years with 56% having severe comorbidities 1

Complex Type III Fractures

• Defined by lateral mass comminution exceeding 50% or secondary fracture lines into pars interarticularis or vertebral body 3
• Result from high-energy trauma mechanisms 3
• Represent 51% of type III fractures in trauma center populations 3
• Carry a 21% failure rate with nonoperative treatment, requiring delayed surgical stabilization 3

Vertically Unstable Type III Fractures (Rare)

• Extremely rare subtype with vertical distraction similar to atlanto-occipital dislocation 4
• Can present with quadriparesis and brainstem deficits 4
• Requires urgent surgical stabilization rather than standard external immobilization 4
• Failure to recognize this pattern can result in devastating iatrogenic neurological injury including quadriplegia and fatal brainstem palsies 4

Critical Imaging Pitfall

Beware of "high and shallow based" type III fractures that extend minimally into the C2 body—these behave biomechanically like type II fractures with increased nonunion risk despite their type III classification. 2

• The depth of extension into the vertebral body determines healing potential 2
• Shallow fractures closer to the odontoid neck may require surgical management despite technical type III classification 2