Atlas Fractures & Transverse Ligament Injuries - Spine

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 anatomy
  Atlas 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
    
    runsvertically 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 injury
Treat 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

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T

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 injury Treat 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%)