Fracture Odontoid

C2 develops from four ossification centres at birth, one for each neural arch, one for the body and one for the odontoid process. The odontoid process itself forms from two separate ossification centres that fuse in the midline by the 7 fetal month, but occasionally can persist as a vertical lucent cleft in the odontoid (Ogden 1984). A secondary ossification centre appears at the tip of the odontoid process between 3 and 6 years of age and fuses by 12 years. This can be mistaken for an avulsion fracture (Fig. 7.57). The body of C2 fuses with the odontoid process by 2-6 years leaving a fusion line or remnant of the cartilaginous synchondrosis until 11 years of age and may be confused with a fracture either on radiographs or CT (Fig. 7.58). Pseudofractures of the odontoid process can be produced by the Mach effect by overlapping of the teeth, the posterior arch of Cl, occiput or soft tissues such as the tongue (Fig. 7.59). The neural arches of C2 fuse posteriorly by 2-3 years of age and the body fuses with the neural arches by 3-6 years. Additional ossification centres may be found at the tips of the spinous... 

Fig. 7.58. Sagittal CT reconstruction. Almost fused synchondrosis between the body of C2 and the odontoid process simulating a fracture in an 11-year-old...

Forces which can cause odontoid fracture are combinations of flexion, extension and rotation of the craniocervical junction. The actual shape and position of the fracture and the final dislocation of the odontoid will be determined by the resultant of the different vectors of forces on the actual position of the neck and head when the impact took place. 

The odontoid can be sheared from the C2 vertebra by its ligaments or may be distracted from it by its apical ligament. The three main types of odontoid fractures are illustrated by Anderson and d Alonzo (1974). 

Others suggest, that in so called type two fractures (fracture at the junction of the odontoid with the body of the axis) early posterior cervical fusion (wiring and onlay bone graft) is more effective (Maiman and Larson 1982). Schiess et al. (1982) believe that surgical fusion should be considered as the initial treatment of all types of odontoid fractures. 

In some cases of odontoid fractures however, antero-posterior dislocations, anterior compression of the cord by displacement of parts of the fractured C2 body, transoral surgery may be indicated (Fang and Ong 1962, O Laoire and Thomas 1982, Lee and Fairholm 1985). In most of the reported cases the traumatic changes were not acute. Anterior compression of the medulla constituted the basis of clinical symptoms, the alignment of the spine remained disturbed, the clinical symptoms either developed or worsened after posterior surgical fixation. 

Fig. 18. Case no. 12. Pre-operative lateral X-ray of the craniocervical region illustrates the fracture of the odontoid accompanied by posterior dislocation of C7...

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