Fractures of the Odontoid Process (Dens)

A high association exists with other cervical spine fractures.

There is a 5% to 10% incidence of neurologic involvement with presentation ranging from Brown-Séquard syndrome to hemiparesis, cruciate paralysis, and quadriparesis.

Vascular supply arrives through the apex of the odontoid and through its base with a watershed area in the neck of the odontoid.

High-energy mechanisms of injury include motor vehicle accident or falls with avulsion of the apex of the dens by the alar ligament or lateral/oblique forces that cause fracture through the body and base of the dens.

Classification (Anderson and D’Alonzo) (Fig. 9.8)

Type I: Oblique avulsion fracture of the apex (5%)

Type II: Fracture at the junction of the body and the neck; high nonunion rate, which can lead to myelopathy (60%)

Type III: Fracture extending into the cancellous body of C2 and possibly involving the lateral facets (30%)

Subclassification of type II odontoid fractures (Grauer et al.) based on fracture obliquity and displacement. They further clarified the Type II fracture as any fracture that does not extend into the

C1–C2 facet articulation, even if it involves a portion of the body of C2.

Type IIA: Minimally or nondisplaced fracture with no comminution

Type IIB: Displaced fracture with superior to posterior–inferior oblique fracture line

Type IIC: Displaced fracture with anterior–inferior to posterior–superior oblique fracture line

Treatment

Type I: If it is an isolated injury, stability of the fracture pattern allows for immobilization in cervical orthosis.

Type II: This is controversial, because the lack of periosteum and cancellous bone and the presence in watershed area result in a high incidence of nonunion (36%). Risk factors include age >50 years, >5-mm displacement, and posterior displacement. It may require screw fixation of the odontoid or C1–C2 posterior fusion for adequate treatment.

Nonoperative treatment is halo immobilization. Type IIB is more amenable to anterior screw fixation. The obliquity of the fracture line in Type IIC is less amenable to the lag technique of anterior screw fixation.

Type III: There is a high likelihood of union with halo immobilization owing to the cancellous bed of the fracture site.