Type I:
fractures of the anterior arch

Type II:
fractures of the posterior arch (usually bilateral)

Type III:
fractures involving the anterior and posterior arch (Jefferson burst fracture)
-Type IIIa: intact transverse atlantal ligament
-Type IIIb: disrupted transverse atlantal ligament complex

Type IV:
fractures of the lateral mass

Type V:
isolated fractures of the C1 transverse process (rare)