Fracture Classification

Craniocervical Junction

Occipital condyle fractures are classified into 3 types.

• Type I = comminuted fractures due to axial loading; stable if contralateral side is intact

• Type II = occipital condyle fracture with skull base fractures; most of these are stable

• Type III = avulsion fracture due to tensile force on alar ligaments; may show occipitocervical instability

Recent data (Maserati 2009) suggests that initial evaluation should be primarily concerned with identification of craniocervical malalignment. Fusion or halo used in patients with initial scans show fracture and malalignment with rigid cervical collar with delayed imaging follow-up for all others.

Atlantooccipital Disassociation (Dislocation)/C0-C1 Distraction Injury

Complete (disassociation) or partial (subluxation) ligamentous disruption between occiput and C1, which can occur in 1 of 3 directions: (1) Anterior superior displacement of cranium relative to spine most common; (2) pure distraction injury with superior displacement of cranium; or (3) posterior dislocation of cranium which is least common.

Numerous measurement techniques have been used to assess craniovertebral junction trauma, many of which were 1st defined in the plain film era. Many of these measurements have been superseded by the direct soft tissue visualization afforded by CT and MR. There is reasonable literature support for use of the following measurements.

Basion-dental interval (BDI) is abnormal if > 10 mm on sagittal CT.

Summed condylar displacement (sum of the bilateral distances between midpoint of occipital condyle and C1 condylar fossa) is abnormal if > 4.2 mm.

Single side condylar distance measurement of > 2 mm is also considered abnormal in adults. The 2-mm upper limit of C0-C1 spacing also applies to children up to 18 years of age.

Other measurements such as the Powers ratio and Lee lines do not have sufficient sensitivity and specificity to recommend their use. The Harris “rule of 12” for the BDI and basion-axial interval are for plain film use only and so are very limited given the use of CT for acute trauma evaluation.

C1 Fractures

• Anterior arch = vertical or transverse with avulsion from longus colli

• Anterior arch bilateral fractures with posterior atlantoaxial dislocation = plow fracture

• Lateral mass = stable if lateral ring intact; rare

• Posterior arch = common

• Jefferson = combined lateral mass displacement relative to C2 of 6.9 mm indicates disruption of transverse ligament and potential for instability

Atlantoaxial Instability

• Nonphysiologic motion between C1-C2

• Wide variety of causes

• → transverse ligament rupture (most common)

• → odontoid fracture

• → unstable Jefferson fracture

• → fracture of lateral mass of C1 or C2

• → unilateral alar ligament rupture

• → alar and tectorial membrane rupture

Classification of Atlantoaxial Rotatory Fixation (Fielding 1977)

• Type I = rotation about dens without anterior translation [no increase in atlantodental interval (ADI)]

• Type II = rotation about 1 lateral mass with anterior translation of 3-5 mm (ADI) (transverse ligament injury)

• Type III = rotation about lateral mass with anterior translation > 5 mm (transverse and alar ligament injury)

• Type IV = posterior dislocation of C1 behind dens (rare, usually fatal)

Odontoid

• Type I = avulsion at tip of odontoid

• Type II = transverse fracture of dens above C2 body

• Type III = fracture involving superior portion of C2 body

C2 Ring Fractures (Effendi 1981)

• Type I = bilateral pars fractures with < 3-mm anterior subluxation (stable)

• Type II = displacement of pars fracture + anterior translation of C2 with discoligamentous injury

• Type III = pars fractures with C2-C3 facet dislocations

C2 Body Fractures (Fujimura 1996)

• Type I = extension teardrop fracture of anterior inferior endplate of C2

• Type II = horizontal shear fracture through body (more caudal than type III odontoid fracture)

• Type III = C2 body burst fracture

• Type IV = unstable sagittal cleavage fractures