Summary Atlas fractures and transverse ligament injuries are traumatic injuries usually caused by high-energy trauma with axial loading in young patients (Jefferson fracture) or low-energy falls in the elderly. Due to the capacious nature of the spinal canal at this level, these injuries usually present with neck pain without neurological deficits Diagnosis is often missed with plain radiographs, so a CT scan may be required to make the diagnosis. An open-mouth odontoid radiograph is useful to evaluate for disruption of the transverse ligament, which leads to lateral displacement of the lateral masses relative to one another Stable injuries can be treated with immobilization in a cervical collar. Unstable injuries require either halo-vest immobilization or surgical stabilization with fusion Epidemiology Incidence ~7% of cervical spine fractures atlas fractures comprise 25% of the injuries of the craniovertebral junction 1-3% of all spinal injuries commonly missed due to inadequate imaging of occipitocervical junction Demographics bimodal age distribution early adulthood (20-30 y/o) high-energy axial loading mechanism elderly low-energy, ground-level fall predisposed to injury from osteoarthritic bone changes limited mobility gait imbalance ETIOLOGY Pathophysiology mechanism most commonly associated with high-energy injuries ~85% of cases associated with MVC ground level falls in elderly patients osteoporosis predisposes to low-energy fractures injury biomechanics hyperextension blow to the forehead injury posterior arch remains static anterior arch continues to move posterior arch injury higher occurrence with low-energy falls higher association with odontoid fractures 30% less energy required to cause an atlas fracture when the cervical spine is in extension compared to neutral alignment lateral compression anterior arch fracture lateral distraction comminuted lateral mass fracture axial compression blow to the vertex leads to Jefferson burst fracture Associated conditions spine fracture 50% have an associated spine injury 40% associated with axis fracture closed head injuries neurologic injury risk of neurologic injury is low due to large space for the spinal cord at this level injuries tend to increase the area available for spinal cord at C1 Anatomy Bony anatomy atlas osteology atlas (C1) is a ring containing 2 articular lateral masses lacks a vertebral body or a spinous process embryology forms from 3 ossification centers anatomic variation incomplete formation of the posterior arch is a relatively common anatomic variant and does not represent a traumatic injury C1 transverse foramen houses vertebral artery makes acute posteromedial bend around occiput-C1 joint and crosses sulcal groove sulcal groove is a common site for posterior arch injuries/fractures Ligamentous anatomy occipitocervical junction and atlantoaxial junction are coupled intrinsic ligaments are located within the spinal canal and provide most of the ligamentous stability. They include: transverse ligament primary stabilizer of atlantoaxial junction prevents posterior migration of the odontoid into the spinal canal connects the posterior odontoid to the anterior atlas arch, inserting laterally on bony tubercles of the lateral mass paired alar ligaments connect the odontoid to the occipital condyles relatively strong and contributes to occipitocervical stability apical ligament relatively weak midline structure runs vertically between the odontoid and foramen magnum tectorial membrane connects the posterior body of the axis to the anterior foramen magnum and is the cephalad continuation of the PLL Articulations atlanto-occipital joint (occiput-C1) occipital condyles articulate with C1 superior articular processes provides ~50% of cervical spine flexion and extension true synovial joint contains anterior and posterior joint capsules atlantoaxial joints (C1-2) facet joints articulation between the inferior facet of C1 and superior facet of C2 biconcave synovial joint atlanto-odontoid joint synovial joint articulation between the dens (C2) and the anterior arch of the atlas enable ~50% of cervical spine rotation Classification Landells Classification for Atlas Fractures Type 1 Isolated anterior or posterior arch fractureMost common injury pattern"Plough" fracture is an isolated anterior arch fracture caused by a force driving the odontoid through the anterior archStable injuryTreat with hard collar Type 2 Jefferson burst fracture with bilateral fractures of anterior and posterior arch resulting from an axial loadStability determined by the integrity of transverse ligamentIf intact, treat with a hard collarIf disrupted, halo vest (for bony avulsion) or C1-2 fusion (for intrasubstance tear). See Dickman classification below Type 3 Unilateral lateral mass fractureStability determined by the integrity of the transverse ligamentIf stable, treat with a hard collarIf unstable, halo vest Dickman Classification for Transverse Ligament Injuries Type 1 Intrasubstance tear Treat with C1-2 fusion Type 2 Bony avulsion at tubercle on C1 lateral massTreat with halo vest (successful in 75%) Presentation History high-energy injury MVC fall from ladder ground level fall elderly patients Symptoms neck pain cervical spinal muscle spasms limited neck motion C2 neuralgia/palsy occipital neuralgia occipital numbness occipital alopecia (rare) vertebral artery dissection loss of consciousness double vision vertigo Physical exam neurologic deficits uncommon in isolated C1 fractures associated C2 fractures have a higher risk of neurologic deficit vertebral artery injury vertigo diplopia blindness ataxia bilateral weakness dysphagia nausea C2 nerve palsy decreased sensation in the occipital region neck flexion and extension weakness Imaging Radiographs recommended views lateral oblique 60° oblique radiographs to identify posterior arch fractures open-mouth odontoid important to identify atlas fractures optional views flexion-extension identify late instability following nonoperative treatment findings increased widening of C1 lateral masses compared to C2 (lateral mass displacement (LMD)) increased distance of the atlantodental interval (ADI) fracture involving the posterior or anterior arch concomitant spine injuries C2 injuries subaxial spine injuries occipitocervical distraction/dissociation measurements atlantodental interval (ADI) measured on lateral and flexion-extension views <3 mm = normal in adult (<5 mm normal in child) 3-5 mm = injury to transverse ligament with intact alar and apical ligaments >5 mm = injury to transverse, alar ligament, and tectorial membrane sum of lateral mass displacement (LMD) measured on open-mouth odontoid view if sum of lateral mass displacement is >6.9 mm (rule of Spence) or 8.1 mm with radiographic magnification (rule of Heller), then a transverse ligament rupture is assumed and the injury pattern is considered unstable retropharyngeal soft tissue measured on lateral radiograph increased thickening of retropharyngeal soft tissue (>9.5 mm) suggests an anterior arch injury sensitivity radiographs have a lower sensitivity of detecting unstable atlas fractures than CT and MRI CT indications every case of suspected cervical spine injury study of choice to delineate fracture pattern and identify associated injuries in the cervical spine good study to assess for pseudospread of the atlas in pediatric patients thin slices parallel to the C1 arch represents asymmetric growth of the atlas compared to the axis greater atlantal overhang of the lateral masses views sagittal reconstructions occult horizontal fractures of the anterior arch axial reconstructions identify Dickman II injuries to the TAL coronal reconstructions determine total lateral mass displacement angiogram assess the presence of a vertebral artery injury findings fractures involving the anterior and posterior ring lateral mass fractures increased radial displacement of the C1 fracture fragments (unstable) bone avulsion injuries of the tubercle (TAL insertion) sagittal split fractures of the lateral mass sensitivity highly sensitive at detecting fractures lower sensitivity than MRI at detecting TAL injuries MRI indications any case there is a confirmed fracture of the atlas to rule out associated unstable ligamentous injuries views sagittal and coronal views increased T2 signal in the TAL suggests intrasubstance injury findings TAL injuries increased T2 signal intensity in the TAL on the sagittal and coronal views spinal cord injury edema increased T2 signal intensity in the spinal cord hematoma depends on age of injury prevertebral soft tissue swelling increased prevertebral soft tissue T2 signal intensity at C1-2 more sensitive at detecting injury to transverse ligament increased T2 signal intensity in the TAL is suggestive of injury Treatment Nonoperative hard collar vs. halo immobilization for 6-12 weeks indications stable type I fracture (intact transverse ligament) stable Jefferson fracture (type II, intact transverse ligament) stable type III (intact transverse ligament) Dickman type II TAL injuries technique controversy exists about the optimal form of immobilization hard cervical collar typically used in stable fracture patterns with intact transverse ligament halo vest typically used when the transverse ligament is compromised reduce with halo traction before immobilization immobilization for 3 months require post-treatment flexion-extension radiographs to assess for late instability Operative posterior C1-C2 fusion vs. occipitocervical fusion indications unstable type II (controversial) unstable type III (controversial) Dickman type I TAL injuries combined C1 and C2 fractures most often type II odontoid and Hangman fractures higher association with neurologic injury some authors prefer occiput-C2 fusion as opposed to C1-2 fusion no significant downside and lower risk of revision surgery technique may consider preoperative traction to reduce displaced lateral masses C1 internal fixation indications C1 lateral mass split fractures (controversial) described in a few small case series preserves C1-2 motion technique anterior and posterior techniques described transoral approach further randomized trials are needed to ascertain the role of this treatment Techniques Posterior C1-C2 fusion preserves motion compared to occipitocervical fusion fixation C1 lateral mass to C2 pedicle screw construct (Harms' technique) may be sufficient if adequate purchase with C1 lateral mass screws 10° medial screw trajectory protects the internal carotid artery C1-2 transarticular screw placement sublaminar wiring not commonly performed in isolation need intact posterior arch Occipitocervical fusion (occiput-C2) used when unable to obtain adequate purchase of C1 (comminuted C1 fracture) leads to significant loss of motion fixation occipital plate C1 lateral mass screws C2 pedicle screws C1 internal fixation anterior and posterior approaches described standard posterior approach fixation plate and screw construct screw and rod construct screws alone Complications Vertebral artery injury rare complication with displaced posterior ring fractures fractures involving the sulcal groove Neurologic injury rare in isolated atlas fractures radial displacement of fracture can compromise surface area of the spinal canal Cock Robin deformity displaced unilateral sagittal split lateral mass fracture occipital condyle settles onto the C2 superior articular facet treat with occipitocervical fusion +/- osteotomy to correct the deformity Nonunion ~20% of cases treated nonoperatively Neck pain present in 20-80% of patients after immobilization Delayed C-spine clearance higher rate of complications in patients with delayed C-spine clearance; important to clear expeditiously Pseudoarthrosis Stiffness loss of ~50% of cervical rotation with C1-2 arthrodesis loss of ~50% cervical flexion with occiput-C2 arthrodesis Infection a complication of surgical treatment higher infection rates in patients treated with posterior approach Prognosis Natural history with conservative treatment 8-20% report neck stiffness 14-80% report neck pain ~34% report activity limitations contact athletes may not return to play Prognostic variables stability dependent on degree of injury and healing potential of transverse ligament worse long-term patient reported outcomes in fractures with >7 mm of displacement