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 can be made with standard lateral and open-mouth odontoid radiographs. Some fractures may be difficult to visualize on Xrays 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. Patient 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 fractures in the elderly Demographics occur in bimodal fashion in elderly and young patients elderly common, often missed, and caused by simple falls associated with increased morbidity and mortality compared to younger patients with this injury young patients result from blunt trauma to head leading to cervical hyperflexion or hyperextension children rare and almost occur at site of basilar synchondrosis Etiology Pathophysiology mechanism displacement may be anterior (hyperflexion) or posterior (hyperextension) anterior displacement is associated with transverse ligament failure and atlanto-axial 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 fx on xray treatment observation Anatomy Osteology axis has odontoid process (dens) and body contains a transverse foramen which vertebral artery travels through embryology develops from five ossification centers subdental (basilar) synchondrosis is an initial cartilaginous junction between the dens and vertebral body that does not fuse until ~6 years of age secondary ossification center appears at ~ age 3 and fuses to the dens at ~ age 12 Arthrology C1-Dens anterior dens articulates with anterior arch of C1 CI-C2 articulation is a diarthrodial joint C2-3 joint participates in subaxial (C2-C7) 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 internal carotid artery base supplied from branches of vertebral artery 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 Bend 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 fx of tip of odontoid. Due to avulsion of 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 blood supply). Type III Fx extends into cancellous body of C2 and involves a variable portion of the C1-C2 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 fracture line from anterosuperior to posteroinferior. Treatment is with anterior odontoid screw (if adequate bone density). Type IIC Fracture from anteroinferior to posterosuperior, or 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-section area of spinal canal at this level Imaging Radiographs required views AP, lateral, open-mouth odontoid view of cervical spine optional views flexion-extension radiographs are important to diagnose occipitocervical instability in Type I fractures and Os odontoideum instability defined as atlanto-dens-interval (ADI) > 10mm space available for cord (SAC) < 13mm findings fx pattern best seen on open-mouth odontoid 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 neurologic symptoms present Treatment Treatment Overview Table Type I Collar Type II (age < 40) Halo Vest Type II (40-80) Surgery Type II (> 80 years) Collar Type III Collar Nonoperative observation alone indications Os odontoideum assuming no neurologic symptoms or instability hard cervical orthosis indications Type I Type II in elderly who are not surgical candidates union is unlikely, however a fibrous union should provide sufficient stability except in the case of major trauma Type III no evidence to support Halo over hard collar technique typically worn for 6-12 weeks halo immobilization indications Type II young patient with no risk factors for nonunion contraindications elderly patients do not tolerate halo (may lead to aspiration, pneumonia, and death) technique typically work for 6-12 weeks Operative posterior C1-C2 fusion indications Type II fractures with risk factors for nonunion indicated in patient 50-80 Type II/III fracture nonunions Os odontoideum with neurologic deficits or instability anterior odontoid screw indications Type II fractures with risk factors for nonunion AND acceptable alignment and minimal displacement (reduction obtained) anterior oblique fracture pattern fracture line is perpendicular to screw trajectory patient body habitus must allow proper screw trajectory outcomes associated with higher failure rates than posterior C1-2 fusion transoral odontoidectomy indications severe posterior displacement of 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-C2 posterior fusion approach posterior midline cervical approach stabilization technique sublaminar wiring techniques (Gallie or Brooks) require postoperative halo immobilization and rarely used posterior C1-C2 segmental fixation C1 lateral mass screws 10 degrees medial, 22 degrees cephalad avoid perforation of anterior cortex of C1 lateral mass due to potential internal carotid arteryinjury C2 fixation options include C2 laminar screws C2 pedicle screws C2 pars scews (most common) posterior C1-C2 transarticular screws construct contraindicated in patients with an aberrant vertebral artery outcomes C1-C2 fusion will lead to 50% loss of neck motion Higher fusion rate in elderly compared to anterior fusion Anterior odontoid screw approach anterior approach to cervical spine technique single screw adequate pros & cons associated with higher failure rate than posterior C1-2 fusion advantage is preservation of atlantoaxial motion Transoral odontoidectomy technique usually combined with posterior stabilization procedure Complications Nonunion overall incidence 33% (up to as high as 88% in some studies) risk factors Type II fractures with posterior displacement ( > 2 mm) strongest predictor of nonunion age > 40 years ≥ 5 mm displacement (>50% nonunion rate) delay in treatment ( > 4 days) angulations > 10° smoker Mortality overall patient > 80 year of age do poorly with operative or nonoperative treatment especially with halo orthosis