Summary Atlas Fractures & 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 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 each other. Stable injuries can be treated with immobilization in a cervical collar. Unstable injuries require either halo-vest immobilization or surgical stabilization with a fusion. Epidemiology Incidence make up ~7% of cervical spine fractures atlas fractures make up to 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 (20-30s) 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 injury mechanisms ~85% of cases associated with MVC ground level falls in elderly patients osteoporosis predisposes to low energy fractures injury biomechanics hyperextension forehead blow injury posterior arch remains static anterior arch continues to move posterior arch injury higher occurence with low-energy falls higher association with odontoid fractures 30% less energy requirement to cause atlas fracture when cervical spine is in extension compared to neutral lateral compression anterior arch fractures 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 fx 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 availabe for spinal cord at C1 Anatomy Bony anatomyAtlas osteology atlas (C1) is a ring containing two articular lateral masses it 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 Occ-C1 joint and crosses sulcal groove sulcal groove is a common site for posterior arch injuries/fractures Ligamentous anatomy occipital-cervical junction and atlantoaxial junction are coupled intrinsic ligaments are located within the spinal canal, 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 occipitalcervical 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 occipitoatlantal joint (Occ-C1) occipital condyles articulate with C1 superior articular processes provides ~50% of cervical spine flexion and extension range of motion 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 atlantodens joint synovial joint aticulation between the dens (C2) and the anterior arch of the atlas enable ~50% of cervical spine rotation Classification Landells Atlas Fractures Classification Type 1 Isolated anterior or posterior arch fracture.Most common injury pattern"Plough" fracture is an isolated anterior arch fracture caused by a force driving the odontoid through the anterior arch. Stable injuryTreat with hard collar. Type 2 Jefferson burst fracture with bilateral fractures of anterior and posterior arch resulting from an axial load.Stability determined by the integrity of transverse ligament. If intact, treat with a hard collar. If disrupted, halo vest (for bony avulsion) or C1-2 fusion (for intrasubstance tear)(see Dickman classification below). Type 3 Unilateral lateral mass fx. Stability determined by the integrity of the transverse ligament. If stable, treat with a hard collar. If unstable, halo vest. Dickman Transverse Ligament Injuries Classification Type 1 Intrasubstance tear. Treat with C1-2 fusion. Type 2 Bony avulsion at tubercle on C1 lateral mass. Treat 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 nerualgia/palsy occipital neuralgia occipital numbess occipital alopecia (rare) vertebral artery dissection loss of consciousness double vision vertigo Physical exam neuro deficits uncommon in isolated C1 fractures associated C2 fractures have a higher risk of neuro deficit vertebral artery injury vertigo diploplia 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 radiographs oblique radiographs 60-degree oblique radiographs to indetify posterior arch fractures open-mouth odontoid open-mouth odontoid view important to identify atlas fractures optional views flexion-extension views identify late instability following nonoperative treatment findings increased widening of C1 lateral masses compared to C2 (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 atlantodens interval (ADI) measured on lateral radiographs and flexion-extension views < 3 mm = normal in adult (< 5mm 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 views if sum of lateral mass displacement is > 6.9 mm (rule of Spence) or 8.1mm with radiographic magnification (rule of Heller) then a transverse ligament rupture is assured and the injury pattern is considered unstable retropharyngeal soft tissue measured on lateral radiographs 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 should be ordered for 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 should be ordered in any case there is a confirmed fracture of the atlas 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 increaed 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 fx (intact transverse ligament) stable Jefferson fx (Type II) (intact transverse ligament) stable Type III (intact transverse ligament) Dickman type II TAL injuries technique controversy exists around optimal form of immobilization hard cervical collar typically used in stable fracture patterns with intact transverse ligament halo vest typically used in 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's fractures higher association with neurologic injury some authors prefer Occ-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 serioes preserves C1-2 motion technique anterior and posterior techniques described transoral approach further randomized trials needed to ascertain role of this treatment Techniques Posterior C1-C2 fusion preserves motion compared to occipitocervical fusion fixation C1 lateral mass - C2 pedicle screw construct (Harm's 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 (C0-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 increased the 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 so it is important to clear expeditiously Pseudoarthrosis Stiffness loss of ~50% of cervical rotation with C1-2 arthrodesis loss of ~50% cervical flexion with Occ-C2 arthrodesis Infection a complication of surgical treatment higher infection rates in patients treated with posterior approaches Prognosis Natural history (conservative treatment) 8-20% complaints of neck stiffness 14-80% complaints of neck pain ~34% complaints of 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