Odontoid Fractures: Current Concepts and Treatments

Abstract and Introduction

Abstract

Odontoid fractures represent the most common fractures involving C2 and the most common cervical spine fractures in patients older than 65 years. Despite their increasing frequency, optimal management of these injuries remain a subject to debate. Although types I and III injuries have relatively good healing potential with nonsurgical treatment, type II fractures carry a higher risk for nonunion. In particular, elderly patients are at risk for nonunion or fibrous malunion after nonsurgical treatment; however, increased medical comorbidities and poor bone quality also increase the risks of surgery in this cohort. The high morbidity and mortality associated with these injuries has made it an area of particular interest among spine surgeons. The purpose of this review was to summarize the pathophysiology, evaluation, and diagnosis of these injuries and to review controversies in management and considerations for treatment based on the most recent available literature.

Introduction

Odontoid fractures are the most common fractures of the axis (C2), representing approximately 10% to 20% of all cervical spine injuries, and are the most common type of cervical spine fracture in patients older than 65 years.^[1,2] Odontoid fractures are reaching epidemic proportions among elderly patients, with an incidence growing faster than that of any other spine fractures.^[3] These injuries in the aging population are associated with worsened quality of life and mortality rates similar to that of hip fractures.^[3–5] Despite the increasing burden these injuries pose to patients and the healthcare system, the optimal treatment strategy has remained unclear. Treatment options range from external immobilization in a rigid cervical collar or halo vest to surgical stabilization. Patients' age, comorbidities, and risk factors for nonunion are all important to consider in the management of these injuries.

The purpose of this article was to review the pathoanatomy, evaluation, diagnosis, and management of these injuries; discuss points of controversy regarding treatment; and summarize recent literature that has furthered our understanding of these injuries and their outcomes.

Table 1. An Overview of Techniques for Posterior Atlantoaxial Screw Fixation
Fixation	Start Point	Trajectory	Comments
C1 lateral mass screw	Direct insertion: midpoint of C1 lateral mass, inferior to posterior arch Posterior arch insertion: posterior arch at midpoint of lateral mass Notching technique: 2–3 mm notch over inferior posterior arch, at midpoint of the lateral mass	Sagittal plane: cranially towards inferior half of the C1 tubercle Axial plane: 10°-15° medial	• Typical screw length: 34 to 36 mm • Primary structures at risk: VA; ICA; hypoglossal nerve; C2 nerve root; paravertebral venous plexus • Slight medial angulation is preferred to decrease risk of VA injury (in transverse foramen) and injury to ICA as the screw reaches the far cortex • Screws placed too cranial may violate the atlanto-occipital joint • Direct insertion carries risk for C2 nerve root irritation and bleeding from venous plexus. Decreased risk with posterior arch and notching techniques
C2 pedicle screw	2 mm lateral to the intersection of superior margin of the C2 lamina and midpoint of the C2 pars, mediolaterally	Sagittal plane: 30° to 45° cranially, toward inferior half of C1 tubercle axial plane: 30° to 45° medial	• Typical screw length: 30 to 35 mm • Pedicle diameter evaluated preoperatively using axial CT images • Primary structure at risk: vertebral artery • Superior biomechanics versus pars, interlaminar screws • More accessible start point versus C2 pars screws
C2 pars screw	2–3 mm superior and 2–3 mm lateral to junction of inferior C2 lamina and C2–3 facet joint	Sagittal plane: 30°-40° cranially, parallel to C2 pars Axial plane: 5°-15° medial	• Typical screw length: 16–18 mm • Pars diameter evaluated preoperatively using sagittal CT images • Primary structure at risk: vertebral artery • Better to err too medial (toward canal) with screw placement than too lateral (toward VA) because there is more room in the canal before reaching the cord • Start point more distal than pedicle screws and requires more dissection
C2 laminar screw	Junction between lamina and spinous process Note: screw should be superior or inferior enough to accommodate a second screw	Follow spinolaminar angle Optimal screw end point: superior to pars and C2 lateral mass	• Typical screw length: 25 to 35 mm • May use 2 crossing screws (bilateral lamina) or 2 parallel screws (unilateral lamina) • May be used in cases with aberrant VA anatomy or insufficient pars/pedicles • Decreased bending/rotational biomechanical strength versus pedicle/pars screws • Increased implant irritation in thinner patients, may interfere with onlay bone grafting
C1-C2 transarticular screw	3 mm lateral, 2 mm superior to medial C2–3 facet joint	Sagittal plane: 40°-60° cranially toward inferior half of C1 tubercle Axial plane: 0°-5° medial	• Typical screw length: 36–46 mm • Provides excellent biomechanical stability and high fusion rates • Carries highest risk for VA injury • Steep screw trajectory; technically challenging. • Screws placed too caudal within C1 may have inadequate purchase leading to failure in extension • Contraindications: aberrant vertebral artery anatomy, VA ectasia within the transverse foramen, and significant cervicothoracic kyphosis

Table 1. An Overview of Techniques for Posterior Atlantoaxial Screw Fixation

Fixation

Start Point

Trajectory

Comments

C1 lateral mass screw

Direct insertion: midpoint of C1 lateral mass, inferior to posterior arch
Posterior arch insertion: posterior arch at midpoint of lateral mass
Notching technique: 2–3 mm notch over inferior posterior arch, at midpoint of the lateral mass

Sagittal plane: cranially towards inferior half of the C1 tubercle
Axial plane: 10°-15° medial

• Typical screw length: 34 to 36 mm
• Primary structures at risk: VA; ICA; hypoglossal nerve; C2 nerve root; paravertebral venous plexus
• Slight medial angulation is preferred to decrease risk of VA injury (in transverse foramen) and injury to ICA as the screw reaches the far cortex
• Screws placed too cranial may violate the atlanto-occipital joint
• Direct insertion carries risk for C2 nerve root irritation and bleeding from venous plexus. Decreased risk with posterior arch and notching techniques

C2 pedicle screw

2 mm lateral to the intersection of superior margin of the C2 lamina and midpoint of the C2 pars, mediolaterally

Sagittal plane: 30° to 45° cranially, toward inferior half of C1 tubercle
axial plane: 30° to 45° medial

• Typical screw length: 30 to 35 mm
• Pedicle diameter evaluated preoperatively using axial CT images
• Primary structure at risk: vertebral artery
• Superior biomechanics versus pars, interlaminar screws
• More accessible start point versus C2 pars screws

C2 pars screw

2–3 mm superior and 2–3 mm lateral to junction of inferior C2 lamina and C2–3 facet joint

Sagittal plane: 30°-40° cranially, parallel to C2 pars
Axial plane: 5°-15° medial

• Typical screw length: 16–18 mm
• Pars diameter evaluated preoperatively using sagittal CT images
• Primary structure at risk: vertebral artery
• Better to err too medial (toward canal) with screw placement than too lateral (toward VA) because there is more room in the canal before reaching the cord
• Start point more distal than pedicle screws and requires more dissection

C2 laminar screw

Junction between lamina and spinous process
Note: screw should be superior or inferior enough to accommodate a second screw

Follow spinolaminar angle
Optimal screw end point: superior to pars and C2 lateral mass

• Typical screw length: 25 to 35 mm
• May use 2 crossing screws (bilateral lamina) or 2 parallel screws (unilateral lamina)
• May be used in cases with aberrant VA anatomy or insufficient pars/pedicles
• Decreased bending/rotational biomechanical strength versus pedicle/pars screws
• Increased implant irritation in thinner patients, may interfere with onlay bone grafting

C1-C2 transarticular screw

3 mm lateral, 2 mm superior to medial C2–3 facet joint

Sagittal plane: 40°-60° cranially toward inferior half of C1 tubercle
Axial plane: 0°-5° medial

• Typical screw length: 36–46 mm
• Provides excellent biomechanical stability and high fusion rates
• Carries highest risk for VA injury
• Steep screw trajectory; technically challenging.
• Screws placed too caudal within C1 may have inadequate purchase leading to failure in extension
• Contraindications: aberrant vertebral artery anatomy, VA ectasia within the transverse foramen, and significant cervicothoracic kyphosis