Facet Dislocation

7/29/2019 Facet Dislocation

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' 1.4.2013


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Osteology

The cervical spine contains 7 vertebral bodies C1 (atlas) C2 (axis) C1 to C7

have a transverse foramen vertebral artery travels through transverse foramen of C1 to C6

C2 to C6 have bifid spinous process

C7 despite having a transverse foramen, the vertebral artery does NOT travel

through it in the majority of individuals there is no C8 vertebral body although there is a C8 nerve root

Alignment Normal sagittal lordosis (measured from C2 to C7) Spinal Canal

normal diameter is 17mm


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Subaxial Cervical Spine (C3 to C7)

have a transverse foramen vertebral artery travels through transverse foramen of C1 to C6

C2 to C6 have bifid spinous process

C6 contains palpable carotid tubercle which is a valuable landmark for anterior

approach to cervical spine

C7 nonbifid spinous process despite having a transverse foramen, the vertebral artery does NOT travel through it

in the majority of patients there is no C8 vertebral body although there is a C8 nerve root

The superior articular facets of the subaxial cervical spine (C3-C7) areoriented in a posteromedial direction at C3 and posterolateral direction atC7, with a variable transition between these levels


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KINEMATICSRotation decreases caudally due to greater inclination of facet joints


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DEFINITION

Loss of the ability of the spine under physiological loadsto maintain relationships between vertebrae in such away that the spinal cord or nerve roots are not damagedor irritated, and deformity or pain does not develop(White and Panjabi - clinical instability)

The supporting structures of the lower cervical spine canbe divided into two groups

anterior and posterior

A motion segment is made up of two adjacent vertebraeand the intervening soft tissues.

If a motion segment has all the anterior elements and oneposterior element intact, or all the posterior elementsand one anterior element intact, it can remain stableunder physiological loads (White and Panjabi)


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Radiographically,cervical spine instabilityis indicated by thehorizontal translation ofone vertebra relative to

an adjacent vertebragreater than 3.5 mm onthe lateral flexion-extension viewInstability also isindicated by more than

11 degrees of angulationof one vertebra relative toanother

a score of 5or moreindicatesinstability.

Checklist for the diagnosis of clinicalinstability of the lower cervical spine


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Represent spectrum of Osteoligamentous pathology that includes

Unilateral facet dislocation most frequently missed cervical spine injury on plain x-rays leads to ~25% subluxation on x-ray associated with monoradiculopathy that improves with traction

Bilateral facet dislocation leads to ~50% subluxation on x-ray

often associated with significant spinal cord injury Facet fractures

more frequently involves superior facet may be unilateral or bilateral

Epidemiology Location

~75% of all facet dislocations occur within the subaxial spine (C3 to C7) 17% of all injuries are fractures of C7 or dislocation at the C7-T1 junction

this reinforces the need to obtain radiographic visualization of the cervico-thoracicjunction

Mechanism flexion and distraction forces +/- an element of rotation


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Physical exam

Monoradiculopathy

seen in patients with unilateral dislocations

C5/6 unilateral dislocation

usually presents with a C6 radiculopathy

weakness to wrist extension

numbness an tingling in the thumb

C6/7 unilateral dislocation

usually presents with a C7 radiculopathy

weakness to triceps and wrist flexion numbness in index and middle finger

Spinal cord injury symptoms

seen with bilateral dislocations

symptoms worsen with increasing subluxation


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5 Classification developed through the years

1. Holdsworth's classification 1970

2. Allen's classification 19823. Harris' classification 1986

4. The Subaxial Cervical Spine Injury Classification System(SLIC) 2007

5. Cervical Spine Injury Severity Score (CSISS) 2006


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Sir Frank Holdsworth published his classification in 1970.The classification was for spinal trauma in general and therefore also included cervical spinal

injuries.

Pure flexion injuries : Pure flexion injuries and results in a crushing of the anterior part ofthe vertebra (a wedge fracture). This fracture remains stable because the posterior ligament

complex is intact

Flexion-rotation injuries : The flexion of the spine causes With the additional rotation of thespine and the rupture of the posterior ligament complex flexion-rotation injury results in adislocation of the articular processes and the rupture of the intervertebral disc.

This injury is unstable

Extension injuries : Rupture of the anterior longitudinal ligament and intervertebral disc. Theposterior ligament complex is not injured and the injury is stable as long as the cervical spineis not extended. Extension of the cervical spine may cause an extension injury

Compression injuries : Occur when force is applied longitudinally to the cervical spine and

one or the other vertebral end plate fractures and the nucleus of the disc is forced into thevertebral body which explodes(a burst fracture).The ligaments are intact and the injury is stable.

Shearing injuries : When a powerful force is applied to the posterior part of the neck, theviolence may cause a shearing injury, whereby the upper vertebra is forced anteriorly relativeto the lower vertebra, the articular processesf racture and all ligaments rupture. When thisinjury occurs in the cervical spine, it is unstable


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In 1982, Ben Allen et al published the classification of Closed, Indirect Fractures andDislocations of the Lower Cervical Spine.

They hypothesise that the mechanism that causes an injury can be deduced from theradiographical findings, that similar injuries are caused by similar mechanismsand that within each injury class there is a spectrum of injury which ranges fromtrivial to severe

Compressive flexion (5 stages)

Vertical compression (3 stages)Distractive flexion (4 stages)

1. Facet subluxation

2. Unilateral facet dislocation

3. Bilateral face dislocation 50% displacement

4. Complete dislocation Compressive extension (5 stages)

Distractive extension (2 stages)

Lateral flexion (2 stages)


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D-F injuries are characterized by a failure of the posterior ligamentous complex,evidenced by an increased spacing of the spinous processes and a Facetsubluxation or dislocation.

There may be a blunting of the anterior-superior margin.

With increasing stage, there is also an increasing anterior motion of the superiorvertebral body.

The injury mechanism was known in 6 cases and

in each the impact came to the back of the head when the neck was in flexion

Stage 1: Facet subluxation, gapping of the spinousprocess ligaments, indicating failure of the posteriorligamentous complex, with or without someblunting of anterosuperior vertebral bodyStage 2: Unilateral facet dislocation, usually

posterior ligamentous complex is intact,rotational deformity.Stage 3: Bilateral facet dislocations, 50% translationof upper vertebral body on lower one.Stage 4: Close to 100% translation of upper vertebralbody on lower one, appearance of a so-called

floating vertebra.


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In 1986, Harris et al published A Practical Classification of Acute Cervical SpineInjuries

The classification has 7 main categories with subgroups.Flexion (5 subgroups)

- Bilateral interfacetal dislocation :

Dislocation of facet joints bilaterally with rupture of all ligamentousstructures

Flexion rotation- unilateral interfacetal dislocation, resulting in rupture of the posterior

ligament complex. The anterior ligament complex may also be ruptured

Extension-rotation

Vertical compression (2 subgroups)

Hyperextension (7 subgroups) Lateral flexion

Diverse or imprecisely understood mechanisms (2 subgroups)


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Vaccaro et al published the Subaxial Cervical Spine Injury Classification System in2007

Its a comprehensive classification system, incorporating pertinent characteristics

for generating prognosis and courses of management

Three major injury characteristics were identified as critical to clinical decision1. morphology as determined by the pattern of spinal column disruption on

available imaging studies

2. Integrity of the disco-ligamentous complex represented by both anterior andposterior ligamentous structures as well as the intervertebral disk

3. neurological status of the patient

These three injury characteristics were recognized as largely independent predictors of

clinical outcome. Within each of the three categories, subgroups were identified and

graded from least to most severe


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The sum of the 3 classes in the SLIC scale is then computed and confounders

are noted.If the score is between 1-3, the patient does not receive surgery, while for ascore 5 surgery is recommended


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Published by Moore et al in 2006.They propose a scoring system where 0-5 points are given based on the

severity of the fracture and ligamentous injury in 4 spinal columns(anterior, posterior, right pillar, left pillar),

with 0 being no injury and 5 being the worst possible injury in theaffected column.

The 4 spinal columns where defined to include the followingstructures:

Anterior: vertebral body, vertebral disc, anterior and posteriorlongitudinal ligaments, uncinate processes and transverseprocesses

Posterior: the spinous process, the laminae, the posteriorligamentous complex and the ligamentum flavum

Lateral pillars: lateral masses, pedicle, transverse processes,superior and inferior articular processes and the facet capsules.

The scores are then summed to a final injury severity score.


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Radiographs Lateral shows subluxation of vertebral bodies Unilateral dislocations lead to ~ 25% subluxation Bilateral facet dislocation leads to ~ 50% subluxation on xray

CT scan Valuable in demonstrating

Bony anatomy of the injury Malalignment or subtle subluxation of facet Facet fracture

Fracture of the pedicle or lamina on axial images MRI

Indications are controversial but include Acute facet dislocation in patient with altered mental status Failed closed reduction and before open reduction to look for disc herniation Any neurologic deterioration is seen during closed reduction

Timing Timing of MRI depends on severity and progression of neurologic injury MRI should always be performed prior to open reduction or surgical stabilization

Valuable in demonstrating Disc herniations Extent of posterior ligamentous injury


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Nonoperative cervical orthosisor external immobilization (6-12 weeks)

indications facet fractures without significant subluxation, dislocation, or kyphosis

Operative Closed reduction followed by surgical stabilization

Indications awake and cooperative patient with unilateral facet dislocation awake and cooperative patient with bilateral facet dislocation

Outcomes 26% of patients will fail closed reduction and require open reduction unilateral dislocations are more difficult to reduce but more stable after reduction bilateral dislocation are easier to reduce (PLL torn) but less stable following

reduction

Open reduction and surgical stabilization Indications

patient with mental status changes and facet dislocations patients who fail closed reduction unilateral facet fracture with significant subluxation, kyphosis, or radiculopathy bilateral facet fractures lateral mass dissociations


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Closed reduction gradually increase axial traction with the addition of weights perform serial neurologic exams and plain radiographs after addition of each weight abort if neurologic exam worsens and obtain immediate MRI

Anterior open reduction & ACDF indications

facet dislocations reduced through closed methods with an anterior disc herniation unilateral facet dislocations that fail closed reduction with an anterior disc herniation

anterior open reduction techniques reduction technique involves distracting vertebral bodies with caspar pins and then rotating the proximal pin

towards the side of the dislocation not effective for reducing bilateral facet dislocations

Posterior reduction & instrumented stabilization indications

when unable to reduce by closed or anterior approach no anterior compression (no disc herniation)

technique performed with lateral mass screws usually have to fuse two levels due to inadequate lateral mass purchase at level of dislocation

Combined anterior decompression and posterior reduction / stabilization indications

when anterior disc herniation present that requires decompression in patient that can not be reduced throughclosed or open anterior technique

technique go anterior first, perform discectomy, position plate but only fix plate to superior vertebral body this way the plate will prevent graft kick-out but still allows rotation during the posterior reduction this technique eliminates the need for a second anterior procedure


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Denis' Three-Column TheoryThree-column concept divides a spinal segment into three parts:

anterior ALL,anterior annulus fibrosus, and the ant. part of thevertebral body

middle - PLL, post. annulus fibrosus, and the post. wall of thevertebral body

posterior post. bony complex (post. arch) with the post. lig complex:supraspinous , interspinous, capsule, and lig flavum


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According to Denis' system, spinal traumas are classifiedto minorand majorinjury based on their potential risks to cause instability

Each type of fracture also may be divided some subclasses based on severity ofthe damage.

In terms of their instability risk as follows (from the most stable to the most instable):

wedge fracture < burst fracture < seat-belt-type fracture < fracture dislocation


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A failure under compression of the anterior column.

The middle column is intact and acts as a hinge.

There may be a partial failure of the posterior column,indicating the tension forces at that level.

Competent middle column prevents the fracture from

subluxation or compression of the neural elementsby retropulsion of the fragments of the posterior wallinto the canal.

Four subt pes of compression fractures can be identified


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Four subtypes of compression fractures can be identified:

Type A - involvement of both end plates

Type B - involvement of superior end plate Type C - inferior end plate

Type D - buckling of anterior cortex w/ both end platesintact.


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Results from failure under axial load of both the anterior and themiddle columns originating at the level of one or both end-

plates of the same vertebra.Five different types of burst fractures can be described

A: Fracture of both end-plates.

The bone is retropulsed into the canal.

B: Fracture of the superior end-plate.a combination of axial load with flexion.

C: Fracture of the inferior end-plate.

D: Burst rotation.

Could be misdiagnosed as a fracture-dislocation.The mechanism is a combination of axial load and rotation.

E: Burst lateral flexion.

differs from the lateral compression fracture in that it

presents an increase of the interpediculate distance onanteroposterior roentgenogram.


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Both posterior and middle columns fail due to hyper-flexion andsubsequent tension forces.

The anterior part of the anterior column may partially damagedunder compression, but still functions like a hinge.

There is no subluxation, and spine is mainly unstable in flexion.

Seat belt injuries may be divided to two subtypes


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Seat-belt injuries may be divided to two subtypes

One-level injury: It present as a simple fracture going throughbone, or as a ligamentous disruption passing throughposterior ligamentous complex and the intervertebral disc.

Two-level injury: The middle column is ruptured either throughthe bone or the disc


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Presents with failure of all three columns under

compression, tension, rotation, or shear.

It is similar to seat-belt-type injury.

However, the anterior hinge is also disrupted and some

degree of dislocation is present.

There are three subtypes of fracture-dislocations basedon mechanism of injury:flexion rotation

flexion distraction

Shear

Flexion-rotation type fracture-dislocation


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Flexion-rotation type fracture-dislocation.

There is a complete disruption of the posterior and middle columns undertension and rotation. The anterior column may fail in rotation orcompression and rotation. The failure at the level of the middle andanterior columns may occur through the vertebral body or purely throughthe disc.

Flexion-distraction type fracture-dislocation.This injury resembles the seat-belt type of injury with disruption of both the posteriorand middle columns under tension.However, in addition, it presents tear of the anterior annulus fibrosus, and subsequentstripping of the anterior longitudinal ligament during subluxation or dislocation.


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Shear type fracture-dislocation.

This injury results from an extension type ofmechanism in which the anterior longitudinal

ligament is disrupted.The disc is first torn anteriorly to posteriorly until the

continued shearing force translates the upper

segment on top of the inferior segment, or vice versa.

It has 2 subtype:


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It has 2 subtype:(1) In the posteroanterior shear subtype, the segment above is

sheared off forward on top of the segment below. Theposterior arch of the last one or two vertebrae of the uppersegment is usually fractured in the translation, leaving afloating posterior arch behind. The frequency of dural tearand complete paraplegia is very high in this type of fracture.

(2) In the anteroposterior shear, the segment above shears off onthe segment below in a posterior direction. Its posterior archhas nothing to clear during its posterior displacement;

therefore, no free-floating laminae exist.


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Fracture patterns include: Compression fracture

compressive failure of anterior vertebral body without disruption ofposterior body cortex and without retropulsion into canal

Burst fracture fracture extension through posterior cortex with retropulsion into the

spinal canal often associated with complete and incomplete spinal cord injury

Flexion teardrop fracture characterized by fracture of anterior inferior portion of vertebra posterior-inferior corner of body breaks off and is retropulsed

posteriorly often associated with posterior ligamentous injury

associated with SCI unstable and usually requires surgery

Extension teardrop avulsion fracture must differentiate from a true teardrop fracture caused by mild extension injury

small fleck of bone is avulsed of anterior endplate


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Nonoperative Collar immobilization for 6 to 12 weeks

Indications

stable mild compression fractures (intact posterior ligaments & no significantkyphosis) anterior teardrop avulsion fracture

Cxternal halo immobilization Indications

only if stable fracture pattern (intact posterior ligaments & no significantkyphosis)

Operative Anterior decompression, corpectomy, strut graft, & fusion with

instrumentation Indications

compression fracture with 11 degrees of angulation or 25% loss of vertebralbody height

unstable burst fracture with cord compression unstable tear-drop fracture with cord compression minimal injury to posterior elements

Posterior decompression, & fusion with instrumentation Indications

significant injury to posterior elementst i d i t i d

Facet Dislocation

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