Odontoid Fractures

Type I- Stable avulsion fracture at the alar ligament near the tip of the odontoid. The treatment for this type of fracture is the use of a soft collar. There will be significant ligamentous injury, and the physician should be aware of this.

Type II- Fracture at the base of the odontoid process. This is the most common type of odontoid fracture, but is also very troublesome. The nonunion rate of a type II odontoid fracture is 20-80% due to interruption of blood supply. The risk factors for nonunion include patients' age of 60 years or older, more than 6 mm of displacement of the fracture, the pateint is a smoker or has diabetes, reduction of the fracture is not achieved, posterior displacement of the fracture, extension injury (rare), or a delay in treatment. To treat a type II odontoid fracture in a young patient with no nonunion risk, a Halo is used. The patient should be younger than the age of 60, the fracture should be minimally displaced, initial dens displacement should be less than 6 mm, and the reduction should be within one week of the injury if a Halo is going to be used. In this scenario, healing will occur in the majority of cases. In addition, surgery is done if the patient has a nonunion risk, or when reduction of the fracture cannot be achieve or maintained. In this case, the surgery associated with the fracture pattern should be kept in mind. When the fracture pattern allows, anterior screws can be put into the odontoid, in order to preserve the motion of C1-C3. Odontoid screw, rather than fusion, is used in younger patients to avoid the loss of 50% of their neck rotation. Anterior screw fixation should not be used in patients with osteoporosis, in older patients, or in patients with a short neck. However, if the patient has nonunion risks, but the fracture pattern does not allow the placement of an anterior odontoid screw, then a fusion of C1 to C2 should be performed. In general, C1/C2 fusion is used in cases of nonunion, displaced fractures in an older patient, or if there is failure to treat the fracture with a Halo. Fusion of C1-C2 can also be used if the fracture is comminuted and unstable. Posterior C1/C2 fusion can be done with different screw or wire constructs.

A vascular watershed area exists between the apex of the odontoid, which is supplied by branches of the internal carotid artery and the base of the odontoid, which is supplied by branches of the vertebral artery. Type II fracture of the odontoid may get a nonunion due to cortical bone and poor blood supply.

Type III- The fracture extends through the body of C2. This area of the vertebrae is rich in blood supply and, therefore, this fracture heals in the majority of cases. The treatments for a type III odontoid fracture is an external cervical orthosis (especially in an elderly patient or a halo (if the fracture is displaced).

Odontoid fractures in the elderly can occur due to a simple fall, and the diagnosis is usually missed. However, this fracture is associated with increased complications and mortality. A Halo should never be used for an elderly patient. Instead, an external cervical orthosis of some sort should be used. Fibrous union might be adequate if the fracture is not badly displaced, otherwise a fusion of C1/C2 should be done. For example, an 80 year old patient with osteoporosis, who is a smoker, has a displaced odontoid fracture that cannot be reduced. This fracture will lead to nonunion and more complications, and a posterior C1/C2 arthrodesis should be done. In general, if an elderly patient with an odontoid fracture is not a good surgical candidate, then they will be given a cervical orthosis.

A C1/C2 fusion can be done by using transarticular screws, but should not be done if there is no aberrant vertebral artery. Another technique can be done where fusion between C1/C2 is done with the screw placed into the C1 lateral mass and C2 pedicle, plus a bone graft. There is an increased survival rate for the elderly patient that undergoes surgery for type II odontoid fracture.

An odontoid fracture in young children usually occurs around the age of 4. The synchondrosis between the odontoid and the C2 body fuses after this, by the age of 6 years. Physicians may confuse the synchondrosis with a fracture in this age group. The treatment of odontoid fractures in children is done with a Minerva brace or Halo vest. If the fracture is displaced, more pins but less torque should be used, and the pins should be finger tightened on the Halo.

The os odontoidium is an oval shaped structure with sclerotic edges. The os is smaller than the normal dens, and looks like an odontoid fracture. It is a congenital process, but the mechanism that causes an os odontoidium is unknown, although probably developmental or resultant from an old trauma.