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Dens Fracture

- See:
       - Anatomy of C2
       - Development of Dens
       - Odontoid view:
       - Pediatric Dens Frx:

- Discussion:
    - odontoid fractures are the most common upper Cervical Spine fractures;
    - remeber rule of thirds - cervical cord occupies a 1/3 of canal, dens occupies a 1/3, and the remaining 1/3 is empty;
    - mechanism:
           - flexion loading is the cause in the majority of patients, and results in anterior displacement of the dens;
           - extension loading (forward fall onto forhead) occurs in a minority of patients, and results in posterior displacement of the dens;

- Normal Views:  

- Classification: (from Anderson LD, D'Alonzo RT (1974))
- Type I:
    - this form of dens fracture is rare;
    - oblique avulsion frx of tip of dens caused by an avulsion of alar ligament;
           - type I frx is avulsion of alar lig off one side of tip of dens;
           - alar ligaments connect the dens to the occiput.
    - alar ligaments connect the dens to the occiput;
    - evaluation should include dynamic lateral views to rule out anterior subluxation of C1;
    - may be associated with occipitoatlantal dislocation (unstable injury);
    - treat with a semirigid collar;
    - cervical collar for symptomatic management is usually sufficient.
    - ref: Fractures of the Odontoid Process of the Axis

- Type 2 Dens Frx:

- Type III:
    - extends into the vertebral body of C2
    - this frx allows the Atlas and the occiput to move as a unit, hence it is mechanically unstable - heals well w/ immobilization;
    - any combination of angulation and translation can occur;
    - cervical orthosis may be most appropriate in select pts w/ stable, impacted frxs, particularly elderly patients.
            - frequent f/u is recommended for patients treated in this manner.
    - healing in fully anatomic position is not likely w/o prolonged traction;
    - most typical treatment is 12 weeks of immobilization w/ halovest, and majority of patients heal by bony union;
    - anterior screw fixation:
          - in the study by Henry et al, 81 patients with odontoid fractures underwent anterior screw fixation.
                 - 29 patients had type II fractures and 52 patients had type III fractures;
                 - 92% of patients achieved bony union at an avg of 14 weeks;
                 - two patients required seceondary posterior fusion;
                 - full range of motion was restored in 43 patients;
          - ref: Fixation of odontoid fractures by an anterior screw.

- Associated Injury:
    - Atlas Frx: (see: Jefferenson Frx)
           - halovest until the C-1 arch is healed, then a posterior C-1 & C-2 arthrodesis if the dens has not healed;
           - it is prudent to obtain a CT scan of the C-spine, in all patients w/ a dens frx, esp if C1-C2 fusion is being considered;
    - Transverse Ligament Rupture:
           - may occur in 10% of patients w/ type II dens fracture;
           - MRI is used to make the diagnosis;
           - non operative treatment would be expected to result in atlantoaxial instability;
    - Pharangeal Injury:
    - ref:
           Transverse atlantal ligament disruption associated with odontoid fractures
           Posterior atlanto-occipital dislocation with fractures of the atlas and odontoid process
           Odontoid Fracture Associated with a Pharyngeal Tear. A Case Report.

C2 Vertebral Fractures in the Medicare Population

Fractures of the dens. A multicenter study.

Avascular necrosis of the proximal end of the dens. A complication of halo-pelvic distraction.

Odontoid fractures, with special reference to the elderly patient.          

Anterior stabilization for acute fractures and non-unions of the dens.

Injuries of the atlas and axis. A follow-up study of 85 axis and 10 atlas fractures.

Non-union of fractures of the atlas