Last Updated on February 26, 2025
Odontoid fractures are fractures of dens or odontoid process of the axis vertebra or C2. Dens is a strong, tooth-like process projecting upwards from the body of the axis.
Odontoid fractures account for 10-15% of all cervical fractures. These are the most common fractures of the axis vertebra and the most common cervical spine fracture in the elderly
These fractures occur in young patients and the elderly in a bimodal fashion. Whereas in young patients the fractures are a result of high-energy trauma to the head leading to cervical hyperflexion or hyperextension, in elderly people these occur by simple fall. Elderly people also have higher morbidity and mortality.
These fractures are less common in children.
These fractures can alter the movements of the cervical spine leading to pain, instability, and neurologic deficits.
Relevant Anatomy
The odontoid process or dens is a projection from the Axis vertebra. The axis is the second vertebra and is also called C2. It consists of two parts, the odontoid process and the body. The dens is about 15mm in length and about 10 mm in anteroposterior width. It sticks up from the front of the C2 vertebra and fits into a groove in the C1 vertebra. It acts as the pivot for the C1 vertebra. Together C1 and C2 participate in rotation and flexion extension movements.
The dens along with other ligaments provide stability to the occiput-C1-C2 region. These ligaments are
- Transverse ligament
- Primary stabilizer of the atlantoaxial joint
- Checks anterior translation of the atlas
- Apical ligaments
- Alar ligaments
The transverse ligament is the primary stabilizer of the C1-C2 joint and limits the anterior translation of the atlas. Alar and apical ligaments limit the rotation of the atlas.
Vertebral and carotid arteries form the main source of blood supply to odontoid. The anterior ascending artery and posterior ascending artery are branches of the vertebral artery beginning at the level of C3. They ascend anterior and posterior to the odontoid and meet superiorly to form an apical arcade.
The apex of the odontoid is supplied by branches of the internal carotid artery and the base is supplied by branches of the vertebral artery. A vascular watershed exists between the apex and the base of the odontoid. This limited blood supply in this watershed area is thought to affect the healing of type II odontoid fractures.
C1-C2 contributes about 10 degrees of flexion extension, 5o degrees of rotation, and nothing to lateral bending movement.
Pathophysiology
Trauma is the main cause of odontoid fractures. It is a high-energy injury in young people whereas in old age a simple fall could lead to the fracture. Very rarely, conditions like metastases can give rise to pathological fractures.
Fractures result from sudden hyper-flexion or hyper-extension.
Hyperflexion leads to anterior displacement and is associated with transverse ligament failure and atlantoaxial instability.
The base of the odontoid is considered more vulnerable (Hence type II fractures are more common) due to
- High biomechanical stress
- Watershed area- limited regenerative capacity and less trabecular bone
- Degenerative changes
Neurologic deficits are less common in adults. But younger patients, due to high energy often have subluxation of the odontoid and hence have a higher incidence of neurologic injuries.
Os Odontoideum is a congenital condition due to a failure of fusion at the base of the odontoid but new evidence has suggested the likelihood of residual old traumatic process. An os odontoideum can be divided into two main types. It could be confused with odontoid fractures and the treatment is mostly observation
Risk Factors
The following factors could increase the risk of odontoid fracture occurrence.
- Risk Factors
- Age
- Bone fragility
- Degenerative changes
- Metastatic disease of C2
Classification of Odontoid Fractures
Anderson and D’Alonzo
- Type I Odontoid Fractures: These types of odontoid fractures involve the tip of dens at the insertion of the alar ligament. These are usually stable fractures but may be associated with atlanto-occipital dislocation. These constitute about 5% of odontoid fractures. Generally, it is a stable fracture.
- Type II Odontoid Fractures: These are the most common odontoid fractures and account for 60% of the cases. Fractures occur at the base. These fractures are associated with a higher rate of nonunion.
- Type III Odontoid Fractures: Accounts for 30% of the fractures. Fractures occur through the body of C2 and do not involve dens. These are unstable fractures as the atlas and occiput can now move together as a unit
Roy-Camille
- Type I: oblique linear fracture, line slopes forward, with dens displaced anteriorly
- Type II: oblique linear fracture, the line slopes backward, with dens displaced posteriorly
- Type III: horizontal fracture line and the dens can be either anterior or posterior
Thus Roy-Camille et al modified Anderson and D’Alonzo type II fractures depending on the fracture orientation
Grauer
Grauer et al modified Anderson and D’Alonzo’s classification to better differentiate between type II and type III. They said that fractures at the base of the odontoid and involving the body that are shallow and do not involve the superior articular facets should be considered type II, and only fractures of the body involving the superior facets should remain type III.
- Type I: Fracture above the inferior aspect of C1
- Type IIA: Transverse fracture without comminution and displacement <1mm
- Type IIB: Anterior superior to posterior inferior transverse fracture and/or displacement >1mm
- Type IIC: Anterior inferior to posterior superior or comminuted fracture
- Type III: Includes at least one of the superior articular facets
Clinical Presentation
Elderly patients present with a history of accidental falls and complaints of neck pain, especially in the movement of the neck. There may be a history of dysphagia or difficulty in swallowing. It suggests the formation of hematoma.
In elderly patients., associated neurologic injury is less common.
Younger patients often sustain high-energy trauma and typically present with other injuries in addition to neck injuries. These patients have However, younger patients have a higher incidence of spinal injury.
Spinal cord injury symptoms may include
- Abnormal reflexes
- Imbalance
- Clumsy movements
- Weakness in the hand and upper extremity
- Altered sensations
Imaging
Xrays
AP, lateral, open-mouth odontoid view of the cervical spine is commonly done in injury to the upper cervical spine and odontoid fractures. The fracture pattern is best seen on an open-mouth odontoid view.
Flexion-extension radiographs are important to diagnose occipitocervical instability in Type I odontoid fractures and Os odontoideum.
X-rays may miss undisplaced odontoid fracture; therefore, a CT scan is considered the gold standard. If significant odontoid displacement is present or there is a neurological injury, it is important to assess the degree of cord compression and the integrity of associated craniocervical junction ligaments.
Cervical instability is suggested by the following findings
- Atlanto-dens-interval > 10mm
- Space available for cord < 13mm
CT
It is the study of choice and is much better at stability assessment. CT angiogram is useful to locate vertebral arteries when screw insertion is planned.
MRI
MRI is indicated in the presence of a neurological deficit to assess the injury to the neural structures.
Differential Diagnosis
Os odontoideum
It is a recognized anatomical variant of the normal odontoid process due to the failure of fusion of the ossification center of the odontoid tip and vertebral body. This makes the odontoid process appear detached from the vertebral body, resembling a type II odontoid fracture.
Persistent Ossiculum Terminale
The failure of fusion of the ossification center of the rostral tip of the odontoid process to the remaining odontoid process can lead to a persistent gap between the odontoid process and the tip of the odontoid process mimicking a type I odontoid fracture.
Treatment of Dens Fractures
Nonoperative Treatment
Odontoid fractures can be treated conservatively or using surgical methods. The type of fracture, spinal instability, and patient-related issues might affect the choice of conservative or operative treatment.
The treatment aims at spinal realignment, fusion of the broken bone, and if required, decompression. Even achieving a fibrous union can result in fracture stability.
Therefore, the patients who have adequate alignment, no dynamic instability, and neurological deficits should be treated with conservative methods.
• Absence of neurological deficits
Surgical treatment is more commonly employed in type II fractures, especially in the age group between 40-80 years. Type I and III are more commonly treated with conservative treatment. Surgical treatment is favored in the presence of a neurologic deficit. However, type I fractures associated with C0–C1 (occiput-cervical) vertical instability or ligamentous injury may require a craniocervical junction fusion.
Older people with limited life expectancy and who are not fit for operative treatment medically should be treated conservatively.
Patients who cannot tolerate long-term solid external fixation can be candidates for surgery.
Nonoperative treatment involves observation only, collar or halo vest application.
- Observation: Os Odontoideum patients require observation in most cases
- Collar or Hard cervical Orthosis: Type I fractures, Type II fractures in greater than 80 years of age, Type III patients
- Halo Vest: Type II fractures in <40 years of age, Type III fractures. In this age group, the risk of nonunion is less.
External immobilization is not tolerated well by some patients. They become a candidate for surgery.
The orthosis is worn for 6-12 weeks.
Operative Treatment
Unstable or irreducible fractures, nonunion, or those patients with neurological deficits should be treated surgically.
The criteria for labeling a fracture unstable is
- Fracture is older than 6 months
- Irreducible fracture on traction
- Comminuted fracture
- Rupture of the transverse ligament
- Dens displacement 6 mm or more
- Fracture angulation greater than 10 degrees
- More than 2mm fracture gap
- More than 2 mm lateral gap
Anterior versus Posterior surgery
Odontoid fractures can be surgically approached from the anterior or posterior side. Both approaches have their uses, limitations, and surgical procedure profiles.
The anterior approach is mainly used for fracture fixation of the odontoid process and excision of the odontoid fragment.
The posterior approach is used for C1-C2 fusion.
The posterior fusion has been shown to have higher union rates and lower surgery rates than anterior screw placement in patients who are older than 60 years. Hence, posterior fixation is preferable.
The anterior screw fixes the fracture without affecting C1-C2 motion unlike C1–C2 fusion surgery.
Sometimes screw insertion is supported with bone cement.
However, anterior screw fixation is contraindicated in patients with transverse ligament injury, as well as for comminuted fractures.
Posterior surgery can be undertaken for any of the odontoid fracture types and can be performed in different ways.
Anterior screw fixation is associated with greater failure of surgery than posterior C1-C2 fusion.
Anterior Odontoid Screw Fixation
This involves the surgical fixation of the fracture. This is done in patients with type II fractures with minimum risk factors for nonunion and acceptable alignment. The fracture pattern should provide good screw placement. The method is preferred, especially in Roy Camille type I and II [Also termed in literature as Roy Camille IIA and IIC fractures] where screw placement perpendicular to fracture is possible.
One or two large odontoid screws (usually one is sufficient) are placed caudal–cranially in the direction of the odontoid from an anterior cervical approach. Cement augmentation may be done in the selected cases like the presence of bone cysts, metastatic fracture, and the presence of osteoporosis.
The procedure is associated with higher nonunion rates. transverse ligament should be intact for performing this surgery. This procedure should not be done if atlantoaxial dislocation is associated.
The procedure is not done in children younger than 6 years of age.
C1-C2 Trans-articular Screw Fixation
Screws are inserted caudally and slightly lateral to the anterior C1–C2 articular joints. it can be used as an additional procedure when screw fixation is not adequate. It can also be used for C1-C2 fixation when posterior anatomy is in favor of the procedure.
Posterior C1-C2 fusion
This involves the fusion of the first and second vertebra posteriorly. This treatment is considered in patients with
- Type II fractures with risk factors for nonunion( in the age group 50-80 years)
- Type II/III fracture nonunions
- Os odontoideum with neurologic deficits or instability
- Type I with atlantooccipital instability (extremely rare)
A posterior midline approach is used.
Stabilization procedures
- Sublaminar wiring technique
- Requires postoperative halo immobilization
- Rarely used
- Posterior C1-2 segmental fixation
- Uses screws and bars to construct
- C1 lateral mass screws (the carotid artery may be at risk)
- C2 screws may be laminar or pedicle or pars (most common)
- Posterior C1-2 trans articular screws
Fusion of C1 and C2 leads to about 50% loss of neck motion.
Transoral Odontoidectomy
A severe posterior displacement of dens with spinal cord compression and neurologic deficits may warrant odontoid removal though the procedure is rarely done due to the high complication rate. C1 laminectomy will provide sufficient decompression of the spinal canal and is preferred.
Transoral odontoidectomy is usually combined with a posterior stabilization procedure
Complications
Nonunion is the biggest unwanted outcome. The nonunion is mostly seen in type II fractures with
- Posterior displacement of more than 2 mm
- More than 5mm of displacement
- Angulation greater than 10 percent
- Smoker
- Delay in treatment
References
- Charles YP et al. Mortality, complication, and fusion rates of patients with odontoid fracture: The impact of age and comorbidities in 204 cases. Arch. Orthop. Trauma Surg. 2019, 139, 43–51. [Link]
- Salottolo K et al. Epidemiology of C2 fractures and determinants of surgical management: Analysis of a national registry. Trauma Surg. Acute Care Open 2023, 8, e001094. [BMJ]
- Iyer S, Hurlbert RJ, Albert TJ. Management of odontoid fractures in the elderly: A review of the literature and an evidence-based treatment algorithm. Neurosurgery 2018, 82, 419–430. [JNS]
- Huybregts JG et al. The optimal treatment of type II and III odontoid fractures in the elderly: An updated meta-analysis. Eur. Spine J. 2023, 32, 3434–3449.
