Serious Neck Injury to the Dens, aka Odontoid Process

Depiction of a cervical spine, including the atlanto axial joint at the top of the neck.
Depiction of a cervical spine, including the atlanto axial joint at the top of the neck.. MediaForMedical/UIG/Universal Images Group/Getty Images

The Odontoid Process, aka, the Dens

The odontoid process, also known as the dens, is an upward projectile of bone that arises from the front part of the center of the axis vertebra. (The axis is the 2nd highest spinal bone.)

The atlas is the first (topmost) bone of your neck; it sits on top of the axis. (The skull sits on top of the atlas.) The dens projects into a central space in the atlas, and this is how the bones of the atlantoaxial joint fit together.

Unlike most other spinal vertebrae, the atlas does not have a vertebral body. Instead, iis shaped like a ring that (as mentioned above,) is hollow in the center, and through which the odontoid process passes. This arrangement allows for a lot of freedom of motion between the combination of head, first vertebra (atlas), and 2nd vertebra (axis). In fact, the atlantoaxial joint is the most mobile (and complex) joint in the spine.

The odontoid process provides a pivot point -  called an axis of motion - around which the skull and the first cervical vertebra (the atlas) rotate and turn. 

Injuries to the Odontoid Process

A number of injuries can affect the dens, including trauma that pushes the top of the skull down, which may in result in the dens being pushed into the brain stem.  This will likely cause death.

Stress or injury to ligaments that hold the movement of the atlantoaxial joint in check can destabilize the dens, allowing it to disrupt the cervical spine.

  This may cause paralysis.

Dislocation between the atlas and the axis.  This is a very serious, rare injury that at the least will damage your spinal cord.  Dislocations are a hyperflexion injury.

Other types of ligament injuries include stress or stretch that may cause excessive motion in the atlantoaxial joint.

And the dens can be fractured, either at the top point, at its base on the axis or on the body of the axis. Fractures are thought to be a shearing injury; they sometimes accompany a dislocation and other times not. When a dislocation is accompanied by a fracture, the odds of your spinal cord remaining intact are better than in the case of a pure dislocation between the atlas and axis. 

According to Ochoa in his article, "Surgical management of odontoid fractures," which was published in the July 2005 issue of the journal Injury, odontoid fractures account for approximately 20% of all cervical fractures. Marcon, et. al., in their article entitled “Fractures of the cervical spine,” published in the November 2013 issue of Clinics, estimate the incidence of this injury a little lower at 5% to 15%. 

Dens fractures are categorized by their height, a factor which may predict the prognosis as well as determine the treatment for the injury.

  • Type I - A fracture of the upper part of the process (the tip.) 
  • Type II: A Fracture at the base of the dens.
  • Type III: A fracture occurring in body of the axis underlying the dens.

Treatment may take the form of surgery or wearing a brace.  It is, of course, best to consult with your spine specialist when deciding what to do about a dens injury, as this is a very complicated and delicate area.

Injury to the dens can significantly alter your life.  You can learn more about how people live with this injury by reading my review of  The Body Broken, by Lynne Greenberg.  The Body Broken is an autobiography about one woman's heart rendering experience with a dens injury: 

Other types of neck fractures include, but are not limited to:

Source

Ishii T, Mukai Y, Hosono N, Sakaura H, Fujii R, Nakajima Y, Tamura S, Sugamoto K, Yoshikawa H. Kinematics of the subaxial cervical spine in rotation in vivo three-dimensional analysis. Spine (Phila Pa 1976). 2004 Dec 15;29(24):2826-31.

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