Summary Odontoid fractures are relatively common fractures of the C2 (axis) dens that can be seen in low energy falls in elderly patients and high energy traumatic injuries in younger patients Diagnosis may be made with standard lateral and open-mouth odontoid radiographs; however, some fractures may be difficult to visualize on radiographs and require a CT scan to diagnose. MRI is rarely indicated, as these fractures are usually not associated with neurologic symptoms Treatment may be nonoperative or operative depending on the Anderson and D'Alonzo type and risk factors for nonunion. Patients older than 80 have a high morbidity and mortality regardless of nonoperative or operative treatment Epidemiology Incidence most common fracture of the axis account for 10-15% of all cervical fractures most common cervical spine fracture in the elderly Demographics occur in bimodal distribution in young and elderly patients young patients result from blunt trauma to the head leading to cervical hyperflexion or hyperextension elderly patients common, often missed, and caused by simple falls associated with increased morbidity and mortality compared to younger patients with this injury children rare and almost always occur at site of basilar synchondrosis Etiology Pathophysiology mechanism displacement may be anterior (hyperflexion) or posterior (hyperextension) anterior displacement associated with transverse ligament failure and atlantoaxial instability posterior displacement caused by direct impact from the anterior arch of atlas during hyperextension biomechanics a fracture through the base of the odontoid process severely compromises the stability of the upper cervical spine Associated conditions os odontoideum etiology previously thought to be due to failure of fusion at the base of the odontoid evidence now suggests it may represent the residuals of an old traumatic process imaging appears like a type II odontoid fracture on radiographs treatment observation Anatomy Osteology axis has an odontoid process (dens) and body contains a transverse foramen that the vertebral artery travels through embryology develops from 5 ossification centers subdental (basilar) synchondrosis an initial cartilaginous junction between the dens and vertebral body that does not fuse until ~6 y/o secondary ossification center appears at ~3 y/o and fuses to the dens at ~12 y/o Arthrology C1-dens anterior dens articulates with the anterior arch of C1 C1-2 articulation diarthrodial joint C2-3 joint participates in subaxial (C2-7) cervical motion Ligaments occipital-C1-C2 ligamentous stability provided by the odontoid process and its supporting ligaments transverse ligament primary stabilizer of atlantoaxial joint limits anterior translation of the atlas apical ligaments limit rotation of the upper cervical spine alar ligaments limit rotation of the upper cervical spine Blood supply a vascular watershed exists between the apex and the base of the odontoid apex supplied by branches of the internal carotid artery base supplied from branches of the vertebral arteries the limited blood supply in this watershed area is thought to affect healing of type II odontoid fractures Kinematics Normal Cervical Kinematics Flexion/Extension Rotation Lateral Bending Occipitocervical joint (OC) 50 4 8 Atlantoaxial joint (C1-2) 10 50 0 Subaxial spine (C3-7) 50 50 60 Total motion (degrees) 110 100 68 Classification Anderson and D'Alonzo Classification Type I Oblique avulsion fracture of the tip of the odontoid Due to an avulsion of the alar ligament Although rare, atlantooccipital instability should be ruled out with flexion and extension films Type II Fracture through waist High nonunion rate due to interruption of the blood supply Type III Fracture extends into cancellous body of C2 and involves a variable portion of the C1-2 joint Grauer Classification of Type II Odontoid Fractures Type IIA Nondisplaced/minimally displaced with no comminution Treatment is external immobilization Type IIB Displaced fracture with a fracture line from anterosuperior to posteroinferior Treatment is with an anterior odontoid screw (if there is adequate bone density) Type IIC Fracture is from anteroinferior to posterosuperior or a fracture with significant comminution Treatment is with posterior stabilization Presentation Symptoms neck pain worse with motion, especially rotation dysphagia may be present when associated with a large retropharyngeal hematoma Physical exam neurologic deficits very rare due to large cross-sectional area of spinal canal at this level Imaging Radiographs required views AP, lateral, open-mouth odontoid view of the cervical spine fracture pattern best seen on open-mouth odontoid optional views flexion-extension radiographs are important to diagnose occipitocervical instability in type I fractures and os odontoideum instability defined as atlantodens interval (ADI) >10 mm space available for the cord (SAC) <13 mm CT study of choice for fracture delineation and to assess stability of fracture pattern CT angiogram required to determine location of vertebral artery prior to posterior instrumentation procedures MRI indicated if there are neurologic symptoms present Treatment Treatment Overview Type I Collar Type II (<40 y/o) Halo vest Type II (40-80 y/o) Surgery Type II (>80 y/o) Collar Type III Collar Nonoperative observation alone indications os odontoideum assuming no neurologic symptoms or instability hard cervical orthosis indications type I type II fracture in the elderly who are not surgical candidates union is unlikely; however, a fibrous union should provide sufficient stability except in major trauma type III no evidence to support halo over hard collar technique typically worn for 6-12 weeks halo immobilization indications type II fracture in a young patient with no risk factors for nonunion contraindications elderly patients do not tolerate halo immobilization (may lead to aspiration, pneumonia, and/or death) technique typically worn for 6-12 weeks Operative posterior C1-2 fusion indications type II fracture with risk factors for nonunion indicated in patient 50-80 y/o type II/III fracture nonunion os odontoideum with neurologic deficits or instability anterior odontoid screw indications type II fracture with risk factors for nonunion AND one or more of the following acceptable alignment and minimal displacement (reduction obtained) anterior oblique fracture pattern fracture line is perpendicular to screw trajectory patient body habitus allows for proper screw trajectory outcomes associated with higher failure rates than posterior C1-2 fusion transoral odontoidectomy indications severe posterior displacement of the dens with spinal cord compression and neurologic deficits rarely performed due to high complication rate C1 laminectomy typically provides sufficient decompression of the spinal canal and is preferred Techniques Halo immobilization complications pin site infection initial superficial pin infection can be treated with tightening and oral antibiotics C1-2 posterior fusion approach posterior midline cervical approach stabilization technique sublaminar wiring techniques (Gallie or Brooks) requires postoperative halo immobilization and rarely used posterior C1-2 segmental fixation C1 lateral mass screws 10° medial, 22° cephalad avoid perforation of anterior cortex of C1 lateral mass due to potential internal carotid artery injury C2 fixation options include C2 laminar screws C2 pedicle screws C2 pars screws (most common) posterior C1-2 transarticular screws construct contraindicated in patients with an aberrant vertebral artery outcomes C1-2 fusion will lead to 50% loss of neck motion Higher fusion rate in the elderly compared to anterior fusion Anterior odontoid screw approach anterior approach to the cervical spine technique single screw adequate advantages preservation of atlantoaxial motion disadvantages higher failure rate than posterior C1-2 fusion Transoral odontoidectomy technique usually combined with posterior stabilization procedure Complications Nonunion overall incidence 33% (as high as 88% in some studies) risk factors type II fractures with posterior displacement (>2 mm) strongest predictor of nonunion >40 y/o ≥5 mm displacement (>50% nonunion rate) delay in treatment (>4 days) angulation >10° smoker Mortality overall patients >80 y/o do poorly with operative or nonoperative treatment especially with halo orthosis