Odontoid Fractures

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Continuing Education Activity

The odontoid process, or dens, is a superior projecting bony element from the second cervical vertebrae (C2, or the axis). The first cervical vertebrae (atlas) rotates around the odontoid process to provide the largest single component of lateral rotation of the cervical spine. Fracture of the odontoid process is classified into one of three types, which are type I, type II, or type III fractures, depending on the location and morphology of the fracture. The most common mechanism of injury is a hyperextension of the cervical spine, pushing the head and C1 vertebrae backward. This activity reviews the etiology, presentation, evaluation, and management of fractures of the C2 dens and reviews the role of the interprofessional team in evaluating, diagnosing, and managing the condition.


  • Describe the unique vertebral anatomy of the second cervical vertebra (axis), including the odontoid process.
  • Discuss the components of proper evaluation and assessment of a patient presenting with a potential odontoid process fracture, including any indicated imaging studies.
  • Summarize the treatment and management strategies available for C2 odontoid fractures based on the specific fracture type.
  • Discuss the importance of interprofessional team strategies for improving care coordination and communication to aid in prompt diagnosis of C2 odontoid fracture and improving outcomes in patients diagnosed with the condition.


The odontoid process, or dens, is a superior projecting bony element from the second cervical vertebrae (C2, or the axis). The first cervical vertebrae (atlas) rotates around the odontoid process to provide the largest single component of lateral rotation of the cervical spine. Fracture of the odontoid process is classified into one of three types: type I, type II, or type III fractures, depending on the location and morphology of the fracture.[1]


Odontoid fractures occur as a result of trauma to the cervical spine. In younger patients, they are typically the result of high-energy trauma, which occurs as a result of a motor vehicle or diving accident. In the elderly population, the trauma can occur after lower energy impacts such as falls from a standing position. The most common mechanism of injury is a hyperextension of the cervical spine, pushing the head and C1 vertebrae backward. If the energy mechanism and resulting force are high enough (or the patient's bone density is compromised secondary to osteopenia/osteoporosis), the odontoid will fracture with varying displacement and degrees of comminution. 

The odontoid fracture can also occur with hyperflexion of the cervical spine. The transverse ligament runs dorsal to (behind) the odontoid process and attaches to the lateral mass of C1 on either side. If the cervical spine is excessively flexed, then the transverse ligament can transmit the excessive anterior forces to the odontoid process and cause an odontoid fracture.[1]


Odontoid fractures account for 20% of cervical spine fractures in the adult population and are the most common fracture subtype in geriatric patients (≥ 65 years).[2] The axis (C2) is the most common vertebra to be involved in cervical spine injuries, and odontoid fractures account for 50% of all C2 fractures.[3] This shows bimodal distribution with peaks among early adults and the elderly population.[2]

Odontoid fractures result from an interaction between the load magnitude and bone quality.[4] This results from high-impact forces in young cohorts but with trivial injuries among elders. Hyperextension injury causes the skull and C1 arch to cause traction at the odontoid process, while the hyperflexion injury causes the transverse ligament to limit the posterior movement of dens.[5] Type II is the most common of the types of odontoid fractures and accounts for over 50% of all odontoid fractures. Type III odontoid fractures make up most of the remaining odontoid fractures. Type I odontoid fractures are rare.[1] Road traffic accidents are accountable for the majority of cases.[3] In a study comprising more than 30,000 patients, the average age of the cohorts was 77, and 54% were females.[6]


Advanced age and large occiput-C2 angles are predictive of the odontoid fracture angle.[7]

The atlantoaxial joint and fractured segment all move in unison, causing unbearable pain during neck movements.[5] The nonunion rate following conservative management can be as high as 90% owing to thin bony trabeculae and watershed zone at the base of dens.[5]

Non-operative management of odontoid fractures can result in the following:

  • Solid fusion
  • Unstable nonunion, or
  • Fibrous nonunion.[8]

The fusion is governed by the following:

  • Pattern of injury
  • Fracture subtype
  • The slope of the fracture line
  • Angulation (more or less than 11 degrees
  • Displacement (more or less than 5 mm)
  • Blood supply
  • Bone quality, and
  • Age of the fracture and that of the patient.[2]

History and Physical

Younger patients with an odontoid fracture typically have identifiable recent trauma (motor vehicle accident, sports-related impact, diving accident, fall from a height or downstairs). Older patients tend to have less resilient bones and can sustain an odontoid fracture after minor trauma, including falling from ground level or running into a door or cabinet. However, older individuals can also sustain an odontoid fracture from recent injuries similar to those of younger people. 

On physical exam, patients may note cervical neck pain, which is worse with motion. They can also have dysphagia due to a retropharyngeal hematoma or associated parapharyngeal swelling. Less commonly, the patient may have myelopathic spinal cord injuries such as paresthesias in the arms and/or legs, weakness of the arms and/or legs, or other neurologic dysfunctions. There are fewer spinal cord injuries in odontoid fractures due to the relatively large cross-sectional diameter of the spinal canal at the level of the odontoid process compared to the diameter of the spinal cord.


 X-rays of the cervical spine constitute lateral, anterior-posterior (AP), and open-mouth views. Although radiographs yield lower sensitivity and specificity rates when compared to computed tomogram (CT) scans, experienced clinicians and practitioners can still appreciate suspected injury without CT utilization. In addition, flexion-extension radiographs should be obtained in the setting of suspected occipitocervical instability (useful in type I odontoid fractures or the setting of os odontoideum). Initial stability on upright radiographs is associated with stability on follow-up.[9]

Computerized tomography (CT) spine - provides the best resolution of the bony elements allowing for the identification and characterization of an odontoid fracture. This also allows recognition of anatomic anomalies, such as the defect of the posterior arch of C1, that can help plan the management strategies.[10] CT angiography is justified in cases with fracture extension within the vicinity of the vascular zone and assessing the course of the vertebral artery during posterior fixation.[11]

Magnetic resonance imaging- to assess the integrity of the transverse ligament well as the cord among patients presenting with neurological deficits.[12] 

Classification of Odontoid Fractures

  1. Type I- involves the apex of the dens and is mostly stable. If instability due to the avulsion of the alar ligament is suspected, dynamic radio imaging is advocated.
  2. Type II- involves the neck of the odontoid process. They are categorized depending on the pattern of the fracture line into anterior oblique, posterior oblique, and horizontal variants.[5] They are the most common subtype and are mostly considered unstable. Type IIA variant has comminuted fractures at the base of the dens and is unstable.[5]

Grauer Classification

  • Type IIA- non-displaced and no comminution
  • Type IIB- fracture line running anterosuperior to the posteroinferior direction
  • Type IIC- Fracture line running anteroinferior to posterosuperior direction, or with significant comminution.[13][14]

      3. Type III- fracture extends into the body of C2.[14] Non-surgical treatment remains the preferable option for the majority of these patients.[15]

Treatment / Management

Achieving fracture stability is the mainstay of management.[2] The fibrous union can provide adequate stability.[9][16] Without instability on flexion/extension views or ligamentous injury on an MRI scan, a rigid brace or halo vest can be used to promote healing of the fracture, which may occur in 12 weeks.[9]

A conservative approach may be justified for patients with the following:

  • Good alignment with
  • No dynamic instabitiy
  • No deficits.[8]

Type I and Type III fractures Halo fixation or cervical traction and rigid cervical collar result in fusion in:

  • 100% of type 1 in the majority of cases
  • Approximately 90% of type III fractures, and
  • 60% of type II fractures.[12]

A cervical collar is biomechanically superior to halo orthoses with minimal risk of concurrent device-related complications.[2] Soft collars provide comparable benefits in aged patients compared to rigid collars.[17] The use of halo-vest was not associated with increased mortality.[18]Conservative treatment and surgery had similarly low in-hospital mortality.

Indications for Surgery in Type II Fractures

  • Unstable fracture
  • Irreducible fracture
  • Nonunion, and
  • Patients with deficits.[5]

Criteria of instability

  • Fracture age equal to or more than six months 
  • Comminuted fracture
  • Rupture of the transverse ligament
  • Non-reducible or mal-aligned fracture pattern,
  • Dens displacement more or equal to 6 mm,
  • Angulation greater more or equal to 10 degrees or
  • Fracture gap more than or equal to 2 mm
  • Lateral mass gap  >2 mm.[19][20]

Both anterior and posterior fixation techniques have equivalent clinical results.[5] Anterior odontoid screw fixation preserves neck movements while providing fusion rates of  80%–100%.[5]

The posterior inferior fracture type and concurrent tear of the transverse ligament are selected for the posterior fixation.[5]Historically, posterior cervical fusion was undertaken by Brooks, Gallie, and later Dickman and Sonntag methods incorporating the use of sublaminar wires and bone grafts, providing a fusion rate of 86%. This was followed by a transarticular screw, as described by Jeanneret and Magerl, which provided almost 100% fusion.[12] The Goel-Harms technique (C1 lateral mass and C2 pedicle screws) is now an excellent alternative to anterior fixation.[21][22] After the advent of the Goel posterior joint manipulation technique, most of the once irreducible atlantoaxial dislocations (AAD) could be reduced, and the need for transoral odontoidectomy became almost nil.[23] Bone grafting provides long-term stability.[12] Sublaminar wiring can impinge upon the spinal canal, and C1-2 joint fusion restricts neck ranges of movements.[12]

Nakanishi described the technique of anterior odontoid screw fixation.

Anterior fixation is advocated for:

  • Fractures < 6 months old and
  • Anterior-inferior sloping fracture line,
  • Transverse without any comminuting segments at the base.[2][5]

There is no need for bone grafting and minimal risk of injury to the vertebral artery. There are also mild limitations in functional abilities following the procedure.[24]

Prerequisites for the anterior odontoid screw fixation include:

  • Intact transverse ligament, and
  • Reduction and proper alignment following traction.[5]

The bicortical purchase and superior and posterior breach of the odontoid tip significantly govern postoperative alignment.[25] Lag, Herbert, and Acutrak screws are used for anterior odontoid fixation.[26][27] Both single or two-screw anterior odontoid screws have shown similar clinical results.[12] There are anatomical limitations and variability in the placement of two odontoid screws.[28][29]

Subsets not appropriate for anterior odontoid screw fixation include:

  • Type II-a fractures
  • Rupture of the transverse ligament
  • Associated atlantoaxial dislocation
  • Osteopenia
  • >6 months of injury
  • Anterior oblique fracture slope
  • Short neck
  • Barrel-shaped chest, and
  • Severe kyphosis.[5][19]

Recent advances in assisting instrumentation include:

The odontoid screw fixation technique is not recommended for children under six years old.[36] This technique is feasible for children aged 6 to 18 years old; appropriate screw diameter, length, and angle according to the actual CT measurement result is critical.[36]An anterior approach is more suitable for younger cohorts.[2]

There is a level II recommendation for surgical stabilization in geriatric patients due to the high risk of high nonunion.[5] Meta-analysis has revealed better fusion with posterior fixations.[5] There is a high risk of reoperation rates owing to osteopenia following anterior odontoid fixation.[22] There is also an increased risk of postoperative pneumonia, swallowing dysfunction, and increased technical problems.[2][19]

There is marked variation in the treatment strategies as well as follow-up and imaging algorithms.[37] Major comorbidities and older age are significant factors in refraining from surgical fixation.[38] The proportion of crossover from primary external immobilization to surgery was 14.4%, whereas the proportion of revision surgery in the primary surgical group was 9.5%.[39] Operative treatment has shown an average increase of 3.7% per year; operative management nearly doubled between 2003 to 2017 for managing geriatric odontoid fractures.[6] [Level 3] Increased sagittal balance and bone fusion within the atlantodental interspace confer a high risk of nonunion.[40] Duration from injury to surgery > 7 days appears to have a 48 times higher risk for nonunion in elderly patients despite anterior odontoid screw fixation.[41]

Differential Diagnosis

Some entities can be mistaken for an odontoid fracture. It is important to recognize these to avoid unnecessary interventions.

Os Odontoideum 

Os odontoideum is a recognized anatomical variant of the normal C2 odontoid process. During the development, there are multiple ossification centers in the spine, with one being in the odontoid process, one in the odontoid tip, and one in the vertebral body. If the ossification centers in the odontoid process and the vertebral body fail to fuse, then the odontoid process (dens) can appear to be detached from the vertebral body and mimic a type II odontoid fracture. In younger children, complete ossification of the spine has not yet occurred, and the normal growth pattern and ossification can also mimic a type II odontoid fracture.

Persistent Ossiculum Terminale 

The rostral tip of the odontoid process has a separate ossification center during development from the remaining odontoid process. When the two ossification centers fail to fuse, there can be a persistent gap between the odontoid process and the tip of the odontoid process, which can mimic a type I odontoid fracture.


Children achieve stable fusion with halo immobilization. However, patients over 50 years of age have 21 times high risk of nonunion with halo immobilization.[12]

The fusion rate is 88% when the surgery is performed within six months of allowing a fusion rate of 88%, but it drops to 25% when surgery is performed more than 18 months after injury.[12] If a patient fails external immobilization and is within six months of the injury, anterior odontoid screw placement is still an option.

Displaced distal fracture segment or facetal malalignment causing cervicomedullary compression and irreducible despite traction previously required transoral resection preceding posterior fusion. Anterior extrapharyangeal open reduction and internal fixation have now been introduced to manage the same.[42]


Mortality at the time of injury is observed in 25% to 40% of patients.[43]

Most of the survivors are usually neurologically intact. However, this can harbinger the risk of instability at the atlantoaxial region and spinal cord injury, causing Brown-Sequard syndrome, spinal Cord transection, cruciate paralysis, myelopathy, and persistent disabling neck pain in around 25% of patients.[12][44][45]

There can be concurrent injuries associated with and complicating the odontoid fractures, which include:

  • Anterior cervical wedge fracture
  • Atlanto occipital dissociation
  • Cervical burst fracture
  • Cervical facet dislocation
  • Cervical spinous process fracture
  • Extension cervical teardrop fracture
  • Flexion cervical teardrop fracture 
  • Hangman's fracture
  • Isolated transverse process fractures, and
  • Jefferson fracture

Deterrence and Patient Education

Postoperatively, patients should be monitored for retropharyngeal hematoma, dysphagia, aspiration, vocal cord paralysis, and surgical site infections. The patient needs to understand these signs and symptoms and contact their surgeon's office immediately if these present.

Enhancing Healthcare Team Outcomes

Odontoid fractures most often occur as a result of trauma to the cervical spine. Patients are often younger. The clinicians must work together in a coordinated interprofessional team approach to care that minimizes the risk of further injury. Trauma nurses are responsible for cervical spine immobilization—radiologists review X-rays and scans. Neurosurgeons and orthopedists provide definitive care. Physiatrists and rehabilitation nurses coordinate care and feedback to the interprofessional team. Often pharmacist assists the team in helping to maintain pain control in the acutely injured patient. Nurses can serve as the liaison point between the various disciplines, assist in patient assessment and during surgery, monitor patients, and answer patient questions. All care team members must maintain accurate and updated patient records so that every team member is operating from the same information. This interprofessional team approach will lead to improved patient outcomes. [Level 5]

(Click Image to Enlarge)
Anderson and D'Alonzo classification of odontoid fractures.
Anderson and D'Alonzo classification of odontoid fractures.
Contributed by Steven O Tenny, MD, MPH, MBA

(Click Image to Enlarge)
Odontoid fracture
Odontoid fracture
Contributed by Sunil Munakomi, MD

(Click Image to Enlarge)
Odontoid fracture
Odontoid fracture
Contributed by Sunil Munakomi, MD
Article Details

Article Author

Steven Tenny

Article Author

Sunil Munakomi

Article Editor:

Matthew Varacallo


11/16/2022 10:57:23 AM

PubMed Link:

Odontoid Fractures



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