Odontoid

Zahn-. tooth, dental, odonto-, toothed, notched, zatm hnlich, a. toothhke, (Anat.) odontoid. Zatmarzt, m. dentist, zatmkrzthch, a. dentist s, dental. 

MPS IV A Morquio A Distinctive skeletal abnormalities, corneal clouding, odontoid hypoplasia milder forms known to exist Galactose 6-sulfatase Keratan sulfate, chondroitin 6-sulfate... 

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. 56. Unilateral offset of the lateral masses of Cl and C2 (arrows) due to rotation. The lateral mass to odontoid process distances are unequal...

Fig. 7. 57. a,b Sagittal and coronal CT reconstructions showing two foci of calcification within the ossification centre for the tip of the odontoid process in a 6-year-old. c Unfused, well developed ossification centre for the tip of the odontoid process in a 7-year-old... 

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...

Fig. 7.59. Pseudofracture of the odontoid process produced by the Mach effect from overlapping of the posterior arch of Cl and the occiput...

The ossification centre for the anterior arch of atlas usually appears in the first year but is present in 20% at birth. In a few cases, it may be absent resulting in a failure of anterior fusion leaving a deft. The syndion-drosis at the base of the odontoid with the C2 body fuses between 3-6 years of age but may be ddayed. The vestigial outline of this fusion can be seen up to... 

Type 4 AARF with posterior displacement of the atlas and occurs with a deficiency of odontoid process. This is the least common type. 

Swischuk LE, John SD, Hendrick EP (2000) Is the open-mouth odontoid view necessary in children under 5 years Pediatr Radiol 30 186-189... 

H-Acetyiglucosamme-6-sulfatase (EC 3.1.6.14). Heparan sulfate accumulates. Mild osteochondnxtystro-phy, and presence of hypoplastic odontoid proccss. Fadal features similar to type III a-ViPt mucopolysaccharidosis, or Morquio-Brailsfordsyndrome (variant 1) (see Fig.2). 

The atlantoaxial articulation is specially adapted for (nearly) pure rotation. In addition to the inferior articular facets of the atlas and the superior articular facets of the axis, movement other than rotation is limited by the anteriorly located odontoid process (dens) of the axis. The odontoid process is held close to the anterior arch of the atlas by the transverse ligament of the atlas, which allows only a slight amount of flexion of the atlas on the axis. 

The atlantoaxialjoint never leaves the neutral position, because extension is limited by bony apposition and the odontoid ligament limits flexion. Therefore, the major motion of this Joint is rotation. 

The anterior arch (relevant to this exposure) is 9 mm high and 4 mm thick on average. The posterior surface of the anterior arach articulates with the anterior surface of the odontoid by a small round synovial joint. This is opened during resection. 

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. 

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