TRAUMA AXIAL SKELETON

DR MUHAMMAD BIN ZULFIQARPGR III FCPS Services institute of Medical Sciences/

Services Hospital Lahoreradiombz@gmail.comSpecial thanks to Radiology master class

SKULL

• Bones and fractures • X-rays are rarely indicated for detection of

skull fractures. If there is a history of sufficient force to result in suspected fracture then CT is usually required. CT is necessary to look for underlying intracranial haemorrhage.

• Specific X-ray views are required to look for foreign bodies in the scalp

• Normal skull - Lateral• Anatomically the skull has inner and outer surfaces or 'tables' • Skull X-rays show the course of vessels which indent the

inner table• These vascular indentations branch and taper - whereas

fractures do not usually branch or taper

• Normal skull - AP • Sutures have a saw-tooth appearance which distinguishes them from

fractures which form smooth lines

• Skull fractures - AP • The black lines represent skull fractures• These lines are too smooth to be sutures and do not branch like the vascular markings of the

skull

Basal skull fractures

• Fractures of the skull base are not readily visible on plain X-rays. If injury to the skull base is suspected clinically then CT is usually indicated.

• Blood or cerebrospinal fluid (CSF) may leak into the para-nasal sinuses following basal skull fracture. In the context of trauma an air/fluid level seen in the sphenoid sinus is radiographic evidence of basal skull fracture.

• Sphenoid air-fluid level• No fracture is visible• The air-fluid level seen in the sphenoid sinus is due to

haemorrhage or CSF leakage due to basal skull fracture• The other paranasal sinuses also contain blood due to

facial bone injury

• Skull - Depressed fracture • Displaced or depressed skull fractures may result in

overlapping bone which causes white lines of increased density

• Note: The sphenoid sinus is clear - however this does not exclude a basal skull fracture

• Scalp foreign body X-ray • To look for foreign bodies in the scalp specific radiographic settings are

required and the X-ray beam is aimed tangential to the area of injury. It is therefore essential to specify that 'foreign body X-rays' are required.

• Material that is not very dense, such as wood, will not show up on X-ray. Good quality X-rays will show denser material such as glass.

• several foreign body fragments in the scalp - glass in this case

Systematic approach

• There are many complex overlapping bone structures in the face with a highly variable appearance. Radiological findings must be related to clinical features as it is easy to misinterpret appearances.

• Standard views • Occipito-Mental (OM) and Occipito-Mental at

30 degrees angulation (OM30).

Key points

• Relate radiological appearances to clinical features

• Follow the three 'McGrigor-Campbell' lines to look for the common fracture patterns

• The most common fracture configurations are - isolated zygomatic arch fracture - 'tripod' fracture - and 'blowout' fracture

• Check for the 'teardrop' and 'eyebrow' signs

• Occipito-Mental (OM) view - Normal • This view is acquired with the patient looking slightly upwards • Each zygoma and zygomatic arch resembles the head and trunk of an elephant • The blacker areas are the orbits and paranasal sinuses - frontal, nasal/ethmoid, and maxillary • The frontal sinuses are highly variable in appearance

• Occipito-Mental (OM30) view - Normal • This view is acquired at 30º from horizontal with the patient in the same

position as for the OM view • Each infra-orbital canal is part of the floor of the orbit - these carry the maxillary

division of the trigeminal nerve which can be injured as the result of fracture • Note that each maxillary antrum is clear (black)• Other visible structures include the mandible and the odontoid peg

• McGrigor-Campbell lines • The ' McGrigor-Campbell lines' are visible on OM and OM30 views and can act as anatomical references to assess

the facial bones for injury • Upper line - (Red) passes through the zygomatico-frontal sutures (asterisks) and across the upper edge of the orbits• Middle line - (Orange) follows the zygomatic arch (elephant's trunk), crosses the zygomatic bone and follows the

inferior orbital margins to the opposite side • Lower line - (Green) passes through the condyle (1) and coronoid process (2) of the mandible and through the

lateral and medial walls of the maxillary antra on each side • Midline - used to assess symmetry

• Isolated zygomatic arch fracture • Disruption of the middle McGrigor-Campbell

line is due to a comminuted fracture of the right zygomatic arch

• Following the upper and lower lines shows no fracture

Tripod' fractures

• Trauma to the zygoma may result in impaction of the whole bone into the maxillary antrum with fracture to the orbital floor and lateral wall of the maxillary antrum.

• The displaced zygoma is detached from the maxillary bone, the inferior orbital rim, the frontal bone at the zygomatico-frontal suture, and from the zygomatic arch. The result is said to liken a 'tripod', but in reality these fractures are often more complex than is appreciated on plain X-ray. 'Quadripod' would perhaps be a more accurate term as four fractures may be visible.

• 'Tripod' fracture • 1 - The zygoma (asterisk) is separated from the frontal bone at

the zygomatico-frontal suture • 2 - Comminuted fracture of the zygomatic arch • 3 - Orbital floor fracture• 4 - Breach of the lateral wall of the maxillary antrum

• Maxillary antrum fluid level• A fluid level of blood seen in the maxillary antrum may be the only obvious sign of fracture• 'Tripod' fracture• A - Widened zygomatico-frontal suture• B - Zygomatic arch fracture• C - Orbital floor fracture• D - Lateral maxillary antrum wall fracture

Orbital 'blowout' fractures

• Trauma to the orbit may lead to increased pressure in the orbit such that the thin bone of the orbital floor bursts. This manifests as the 'teardrop' sign which is due to herniation of orbital contents into the maxillary antrum.

• Orbital 'blowout' fracture- Teardrop sign • On the left a 'teardrop' of soft tissue has

herniated from the orbit into the maxillary antrum

• Orbital emphysema • Occasionally a 'tripod' or 'blowout' fracture will cause a leak of air from the

maxillary antrum into the orbit. This can have the appearance of a dark 'eyebrow'. • Orbital emphysema - 'Eyebrow' sign• Fractures are visible of the lateral wall of the maxillary antrum and of the orbital

floor• Air has leaked into the orbit and is seen as an area of comparative low density -

the 'eyebrow' sign• There is also increased soft tissue density due to swelling, and increased density

of the maxillary antrum due to blood

• Fracture mimics • X-ray appearances can easily be misinterpreted unless a systematic approach is used to

look for the common fracture patterns. Any suspected injury should be correlated to the clinical features. Overlying structures such as sutures should not be interpreted as fractures.

• The eye is drawn to the dark irregular line passing across the orbit which is the normal coronal suture

• A systematic approach reveals a tripod injury with a large fracture of the orbital floor

Mandible fractures

• The mandible can be considered as an anatomical ring of bone, stabilised at each end at the temporomandibular joints. A break of the ring in one place will usually be accompanied by further break in the ring elsewhere. If you see one fracture, look for a second fracture, or a dislocation of the temporomandibular joint.

Orthopantomogram (OPG) and Mandible views.

• Both views are necessary because fractures are often only seen on one image. The OPG is a panoramic view acquired with the camera panning around the patient.

• Whenever one fracture is seen - check for a second fracture or dislocation at the temporomandibular joint

• Normal mandible - Orthopantomogram (OPG)

• Follow the cortical edge all the way around the mandible

• Check the temporomandibular joints

• Asterisks = Inferior alveolar canal - the course of the inferior alveolar nerve

• OPG - Normal temporomandibular joint• The condyle of the mandible meets the glenoid

fossa of the temporal bone to form the temporomandibular joint (TMJ)

• Normal mandible - Mandibular view• Follow the cortical edge all the way around

the mandible

• Mandible fracture - OPG• (Same patient as image below)• A fracture of the left mandible body is easy to see• On the right the cortical outline is difficult to follow at the

base of the condyle (?) - but no second fracture is readily seen

• Mandible fracture - Mandibular view• (Same patient as image above)• On this view the right condylar fracture is

more easily seen

Cervical spine - Normal anatomy

• Clinical considerations are particularly important in the context of Cervical spine (C-spine) injury. This is because normal C-spine X-rays cannot exclude significant injury, and because a missed C-spine fracture can lead to death, or life long neurological deficit.

• Clinico-radiological assessment of spinal injuries should be managed by experienced clinicians in accordance with local and national clinical guidelines. Imaging should not delay resuscitation.

• Further imaging with CT or MRI (not discussed) is often appropriate in the context of a high risk injury, neurological deficit, limited clinical examination, or where there are unclear X-ray findings.

Standard views• The 3 standard views are - Lateral view - Anterior-Posterior (AP)

view - and the Odontoid Peg view (or Open Mouth view). In the context of trauma these images are all difficult to acquire because the patient may be in pain, confused, unconscious, or unable to cooperate due to the immobilisation devices.

• Additional views• If the lateral view does not show the vertebrae down to T1 then a

repeat view with the arms lowered or a 'Swimmer's view' may be required.

• Lateral view• The lateral view is often the most informative image. Assessment

requires a systematic approach.

Key points

• Normal C-spine X-rays do not exclude significant injury

• Clinical considerations are of particular importance when assessing appearances of C-spine X-rays

• Look at all views available in a systematic manner

C-spine - Systematic approach

• Coverage - Adequate? • Alignment - Anterior/Posterior/Spinolaminar • Bones - Cortical outline/Vertebral body height • Spacing - Discs/Spinous processes • Soft tissues - Prevertebral• Edge of image

• C-spine systematic approach - Normal Lateral 1• Coverage - All vertebrae are visible from the skull base to the

top of T2 (T1 is considered adequate) • - If T1 is not visible then a repeat image with the patient's

shoulders lowered or a 'swimmer's' view may be necessary

Approach• Alignment - Check the Anterior line (the line of the anterior

longitudinal ligament), the Posterior line (the line of the posterior longitudinal ligament), and the Spinolaminar line (the line formed by the anterior edge of the spinous processes - extends from inner edge of skull).

• - GREEN = Anterior line• - ORANGE = Posterior line• - RED = Spinolaminar line• Bone - Trace the cortical outline of all the bones to check for

fractures• Note: The spinal cord (not visible) lies between the posterior and

spinolaminar lines

• C-spine systematic approach - Normal Lateral 2 • Disc spaces - The vertebral bodies are spaced apart by

the intervertebral discs - not directly visible with X-rays. These spaces should be approximately equal in height

• Prevertebral soft tissue - Some fractures cause widening of the prevertebral soft tissue due to prevertebral haematoma

• - Normal prevertebral soft tissue (asterisks) - narrow down to C4 and wider below

• - Above C4 ≤ 1/3rd vertebral body width• - Below C4 ≤ 100% vertebral body width• Note: Not all C-spine fractures are accompanied by

prevertebral haematoma - lack of prevertebral soft tissue thickening should NOT be taken as reassuring

• Edge of image - Check other visible structures

• C-spine normal anatomy - Lateral (detail)• Bone - The cortical outline is not always well defined but forcing your eye

around the edge of all the bones will help you identify fractures• C2 Bone Ring - At C2 (Axis) the lateral masses viewed side on form a ring

of corticated bone (red ring ) • This ring is not complete in all subjects and may appear as a double ring• A fracture is sometimes seen as a step in the ring outline

• AP view • Although often less informative than the lateral view this view may nevertheless

provide important corroborative information - a systematic approach is required.

Approach to C-spine• C-spine systematic approach - Normal AP • Coverage - The AP view should cover the whole C-spine and the

upper thoracic spine• Alignment - The lateral edges of the C-spine are aligned (red lines ) • Bone - Fractures are often less clearly visible on this view than on

the lateral• Spacing - The spinous processes (orange) are in a straight line and

spaced approximately evenly• Soft tissues - Check for surgical emphysema• Edges of image - Check for injury to the upper ribs and the lung

apices for pneumothorax

Odontoid peg/Open mouth view

• Although called the 'odontoid peg' view the odontoid peg is often obscured on this view by overlapping structures such as the teeth or occiput. Many refer to this view as the 'open mouth' view. Its primary purpose is to view lateral mass alignment.

• Even if a fracture of the odontoid peg is present it is often not visible with this view. If a peg fracture is not visible, but is suspected clinically by a senior clinician, then further imaging with CT should be considered.

• C-spine normal anatomy - Open mouth view• This view is considered adequate if it shows the alignment of the lateral

processes of C1 and C2 (red circles)• The distance between the peg and the lateral masses of C1 (asterisks)

should be equal on each side• Note: In this image the odontoid peg is fully visible which is not often

achievable in the context of trauma due to difficulty in patient positioning

• Open mouth view - Rotated • The distance between the peg and the lateral processes is

not equal - compare A (right) with B (left)• This is because when the image was acquired the patient's

head was rotated to one side• Alignment of the lateral processes can still be assessed and is

seen to be normal

'Swimmer's' view

• This is an oblique view which projects the humeral heads away from the C-spine. A swimmer's view may be useful in assessing alignment at the cervico-thoracic junction if C7/T1 has not been adequately viewed on the lateral image, or on a repeated lateral image with the shoulders lowered.

• The view is difficult to achieve, and often difficult to interpret. If plain X-ray imaging of the cervico-thoracic junction is limited then CT may be required.

• C-spine normal anatomy - ' Swimmer's' view • Oblique image with the humeral heads projected away from the C-spine• The cervico-thoracic junction can be seen• Check alignment by carefully matching the corners of each adjacent vertebral body - anteriorly and

posteriorly

C1 fracture

• Injury to C1(atlas) results in loss of integrity of its ring structure. The ring expands and loses alignment with the adjacent occipital bone above, and C2 below. This is most readily appreciated on the open mouth view which shows that the lateral masses of C1 no longer align with the lateral masses of C2, and that the spaces between the peg and the C1 lateral masses are widened.

• C1 'Jefferson' fracture - Open mouth view• The space between the odontoid peg of C2 and the

lateral masses of C1 is widened on both sides (arrows)• The lateral masses of C1 are both laterally displaced and

no longer align with the lateral masses of C2 (red rings)

• C2 fractures • Fractures of C2 (axis) may involve the odontoid peg, vertebral body, or

the posterior elements.• The C2 bone 'ring' is incomplete due to a fracture • The odontoid peg is displaced posteriorly

• C2 odontoid peg fracture - Open mouth view

• Displaced fracture of the odontoid peg

• It is uncommon to see such an obvious fracture on the open mouth view - many fractures of the odontoid peg are more readily seen on the lateral view

• C2 'hangman' fracture• The so called 'hangman' fracture results from a high force hyperextension injury.

The fracture involves the pedicles of C2 and often results in anterior displacement of the body and peg of C2.

• Loss of alignment at C2/C3 with anterior displacement of C2 (large arrow) • Following the cortical outline of C2 (white line) reveals discontinuity due to a

fracture

• 'Extension teardrop' fracture - Lateral view• Hyperextension may result in avulsion of the anterior corner of a

vertebral body - most commonly C2. The anterior longitudinal ligament remains attached to the bone fragment which is separated from the vertebral body.

• A fracture fragment is seen at the anterior/inferior corner of C2 resembling a 'teardrop'

• C-spine 'flexion teardrop' fracture • This fracture may occur at any level between C3 and C7. It is a highly unstable injury with a

high incidence of associated spinal cord injury.• Following the outline of the vertebral bodies shows an anterior - inferior C6 vertebral corner

'teardrop' fracture fragment • The facet joint of C6/C7 is widened - compare with level above•

• C-spine dislocation injury • It is possible to sustain

severe C-spine or spinal cord injury without evidence of a fracture. Dislocations may be transient with spontaneous relocation of the joints at the time of injury. Occasionally there may be locking or 'perching' of the facet joints preventing the bones from returning to their normal positions. This may be unilateral or bilateral.

• Bilateral perched facets - Lateral view

• (Same patient as image below) • Loss of alignment of all three lines

at C5/C6 with 'perching' of the C5 facet on the C6 facet (ring)

• No fracture is visible• The prevertebral soft tissue is

widened due to a haematoma • Note• The spinal canal lies between the

posterior (Orange) and spinolaminar (Red) lines

• Derangement of the spinal canal due to this injury results in a high incidence of spinal cord injury

• Bilateral perched facets - AP view • (Same patient as image above) • There is widening of space between the C5 and C6 spinous processes (SP) with loss of normal

alignment • Again no fracture is demonstrated

• Pre-vertebral soft tissue• At the level of C3 the prevertebral soft tissue is thickened

- ( >1/3rd the width of the vertebral body)• This soft tissue swelling is the only visible sign of injury • CT showed a fracture at C4 not visible on the plain X-ray • Note• Not all C-spine fractures are accompanied by prevertebral

haematoma• Lack of prevertebral soft tissue thickening should NOT be

taken as reassuring

• Pre-vertebral soft tissue• Thickening of the pre-vertebral soft tissues is

occasionally the only X-ray sign of a C-spine fracture.

• Spinous process 'clay-shoveller's' fracture • Isolated fractures of the spinous processes are often difficult to identify, especially

at the cervico-thoracic junction where they may be obscured by overlying soft tissues. A specific check is necessary of the cortical outline of each spinous process.

• These avulsion injuries are traditionally known as 'clay-shoveller's' fractures due to the mechanism of repeated forceful flexion associated with shovelling.

Sternum

• Fractures of the sternum are often due to direct trauma such as a road traffic crash, but may also be caused by chest compressions in cardiopulmonary resuscitation.

• Standard view• Lateral - Sternal fractures are generally only visible

with a lateral view. In the context of suspected sternal injury a chest X-ray is also indicated. Severe chest trauma may require further imaging with thoracic spine X-rays and/or CT.

Key points

• Look for a step in the cortex of the sternum• Don't mistake the sternomanubrial junction

for a fracture

Sternum - Normal - Lateral• Note the normal sternomanubrial joint which

should not be mistaken for a fracture

• Sternal fractures • Check for a step in the cortex of the sternum. Swelling

of the surrounding soft tissue can accompany bone fracture.

• A step in the cortex of the sternum indicates a fracture

Ribs

• Standard view • Chest X-ray - A chest X-ray is not indicated for suspected

uncomplicated rib fractures. This is because rib fractures are often undisplaced and therefore not visualised, and, even if a fracture is visible, management is unchanged. Rib fractures are often seen as an incidental finding on X-rays of the chest, shoulder or thoracic spine.

• If there has been trauma with a suspected complications such as pneumothorax or haemothorax then chest X-ray is indicated.

• Severe thoracic injury often requires CT examination.

Key points

• Chest X-ray is not indicated for suspected uncomplicated rib fractures

• Chest X-ray is indicated for thoracic injury with suspected complications

Rib fractures - Chest X-ray (detail)• Multiple displaced lower left rib fractures are

visible

Subtle rib fracture - Shoulder X-ray • The clavicle fracture is obvious• A subtle rib fracture is also seen• Note: Always check for a second injury

Rib fractures and chest pain

• Rib fractures are often found unexpectedly in patients with chest pain as they may occur without a clear history of trauma. Patients treated with steroids may sustain a rib fracture as the result of minor trauma, for example on coughing.

Unexpected rib fracture - Shoulder X-ray • This patient presented with no clear history of trauma and

complained of shoulder pain• Shoulder examination was unremarkable

Complications of rib fractures

• If more than a simple rib fracture is suspected then a chest X-ray may be indicated to look for a pneumothorax or haemothorax.

• A chest X-ray alone cannot determine if a pleural effusion is a haemothorax or simple fluid , however in the context of significant chest trauma this is often a reasonable assumption.

• Rib fractures with haemothorax - Chest X-ray

• Multiple rib fractures are accompanied by a small pleural effusion - likely a haemothorax

• Rib fracture with pneumothorax - Chest X-ray• A minimally displaced rib fracture is visible• This fracture is complicated by a haemothorax and a pneumothorax with surgical emphysema

Thoracolumbar spine -

• Normal anatomy • In the context of trauma similar principles apply to imaging

both the Thoracic spine (T-spine) and the Lumbar spine (L-spine). The plain X-ray anatomy and appearances of injuries to both these areas are discussed together.

• In correct management of patients with spinal injury may lead to, or exacerbate, neurological deficit. Therefore patients with suspected spinal injury should be managed by experienced clinicians in accordance with local and national clinical guidelines. Imaging should not delay resuscitation.

Thoracolumbar spine -

• Further imaging with CT or MRI (not discussed) is often appropriate in the context of a high risk injury, neurological deficit, limited clinical examination, or where there are unclear X-ray findings.

• Good views of the T-spine and L-spine are difficult to achieve in the context of trauma. Clinical assessment is also often limited by distracting injuries or reduced consciousness. The clinico-radiological assessment of suspected T-spine or L-spine injuries therefore depends on careful consideration of both the clinical and radiological findings.

Key points

• Use a systematic approach• Correlate radiological findings with the clinical

features• If 'instability' is suspected then further

imaging with CT should be considered • If you see one fracture - check for another

Thoracolumbar spine - Systematic approach

• Coverage - Adequate? • Alignment - Anterior/Posterior/Lateral• Bones - Cortical outline/Vertebral body height • Spacing - Discs/Spinous processes/Pedicles• Soft tissues - Paravertebral• Edge of image

Thoracic spine - Standard views

• AP and Lateral - Assess both views systematically (see box).

• Images of the thoracic and lumbar spine are often large and the bones should be scrutinized in detail (see images below).

• Note: The upper T-spine may not be visible on the lateral view - if injury is suspected here then a swimmer's view may be helpful.

• Thoracic spine systematic approach - • Lateral and AP• Coverage - The whole spine is visible on

both views• Alignment - Follow the corners of the

vertebral bodies from one level to the next• Bones - The vertebral bodies should

gradually increase in size from top to bottom

• Spacing - Disc spaces gradually increase from superior to inferior - Note: Due to magnification and spine curvature the vertebral bodies and discs at the edges of the image can appear larger than those in the centre of the image

• Soft tissues - Check the paravertebral line (see AP image below)

• Edge of image - Check the other structures visible

• Thoracic spine systematic approach - • Lateral and AP• Coverage - The whole spine is visible on

both views• Alignment - Follow the corners of the

vertebral bodies from one level to the next• Bones - The vertebral bodies should

gradually increase in size from top to bottom

• Spacing - Disc spaces gradually increase from superior to inferior - Note: Due to magnification and spine curvature the vertebral bodies and discs at the edges of the image can appear larger than those in the centre of the image

• Soft tissues - Check the paravertebral line (see AP image below)

• Edge of image - Check the other structures visible

• T-spine normal anatomy - Lateral (detail) • Alignment - Vertebral body alignment is assessed by carefully matching the anterior and

posterior corners of the vertebral bodies with the adjacent vertebra• Bones - Gradual increase in vertebral body height from superior to inferior • Spacing - Disc spaces gradually increase in height from superior to inferior • VB = Vertebral body, P = Pedicle, SP = Spinous process (ribs overlying)• F = Spinal nerve exit foramen

• T-spine normal anatomy - AP (detail)• Alignment - The vertebral bodies and spinous processes (SP) are aligned • Bones - The vertebral bodies and pedicles are intact• Other visible bony structures include the transverse processes (TP), ribs, and the costovertebral and

costotransverse joints• Spacing - Each disc space is of equal height when comparing left with right. The pedicles gradually

become wider apart from superior to inferior • Soft tissue - Note the normal paravertebral soft tissue which forms a straight line on the left - distinct

from the aorta

Lumbar spine - Standard views

• AP and Lateral• The whole L-spine should be viewed in both

views. • Divergence of the X-ray beam may limit

assessment of the low lumbar spine levels - a further 'coned lumbosacral view' centred at the level of the lumbosacral junction may be helpful.

• L-spine systematic approach - Lateral

• Coverage - The whole L-spine should be visible on both views

• Alignment - Follow the corners of the vertebral bodies from one level to the next (dotted lines)

• Bones - Follow the cortical outline of each bone

• Spacing - Disc spaces gradually increase in height from superior to inferior - Note: The L5/S1 space is normally slightly narrower than L4/L5

• L-spine systematic approach - Lateral• Coverage - The whole L-spine should

be visible on both views• Alignment - Follow the corners of the

vertebral bodies from one level to the next (dotted lines)

• Bones - Follow the cortical outline of each bone

• Spacing - Disc spaces gradually increase in height from superior to inferior - Note: The L5/S1 space is normally slightly narrower than L4/L5

• L-spine normal anatomy - Lateral (detail)• Check the cortical outline of each vertebra• The facet joints comprise the inferior and superior articular processes of each

adjacent level• The pars interarticularis literally means 'part between the joints'• P = Pedicle• SP = Spinous process

• L-spine systematic approach - Normal AP

• Alignment - The vertebral bodies and spinous processes are aligned

• Bones - The vertebral bodies and pedicles are intact

• Spacing - Gradually increasing disc height from superior to inferior. The pedicles gradually become wider apart from superior to inferior - Note: The lower discs are angled away from the viewer and so are less easily assessed on this view

L-spine normal anatomy - AP (detail)• Check carefully for pedicle integrity and

transverse process fractures

Three column model

• The clinico-radiological assessment of thoracolumbar spine stability is usually performed by spinal surgeons with the help of radiologists.

• A simple model commonly used for assessment of spinal stability is the 'three column' model. This states that if any 2 columns are injured then the injury is 'unstable'. This theory is an over simplification if applied to plain X-rays alone. It is important to be aware that some injuries are not visible on X-ray and that 2 and 3 column injuries may be underestimated as 1 or 2 column injuries respectively.

• If spinal instability is suspected on the basis of clinical or radiological grounds then further imaging with CT should be considered.

• Three column model - Anatomy • Anterior column = Anterior half of the vertebral bodies and soft tissues • Middle column = Posterior half of the vertebral bodies and soft tissues • Posterior column = Posterior elements and soft soft tissues

• Three column model - Fracture simulation

• Injuries 1 and 2 affect one column only and are considered 'stable'

• 1 - Spinous process injury • 2 - Anterior compression

injury • Injuries 3 and 4 affect

two or more columns and are considered 'unstable'

• 3 - 'Burst' fracture • 4 - Flexion-distraction

fracture - 'Chance' type injury

• Three column model - Fracture simulation

• Injuries 1 and 2 affect one column only and are considered 'stable'

• 1 - Spinous process injury

• 2 - Anterior compression injury

• Injuries 3 and 4 affect two or more columns and are considered 'unstable'

• 3 - 'Burst' fracture • 4 - Flexion-distraction

fracture - 'Chance' type injury

Thoracolumbar spine

Injury classification • The 'three column model' (see previous page) can be used to form a

basic classification of thoracolumbar spinal injuries (see box). This page also discusses osteoporotic fractures, and fractures of the transverse and spinous processes.

• Spinal injuries which are seen to disrupt structures of 2 or more columns are considered 'unstable'. If the middle column is seen to be injured it is usually taken that another column must be injured even if no anterior or posterior column fracture is visible.

• If an injury is seen which disrupts 1 column then a second fracture is also present in approximately 15% of cases. If a 2 column injury is seen then likelihood of a second fracture increases to 40%.

• RULE: If you see one fracture - check for another

Basic thoracolumbar spine injury classification

• 1 column - Anterior compression (or isolated spinous process injuries)

• 2 column - Burst injuries • 3 column - Flexion-distraction 'Chance-type'

injuries

1 Column - Anterior compression injury

• Anterior compression injury is a common fracture pattern which results from traumatic hyper-flexion with compression. Although considered 'stable' the greater the loss of height anteriorly the greater the risk of middle column involvement. X-ray may underestimate the extent of injury and so if there has been high risk injury or other suspicion of instability then CT should be considered.

Anterior compression injury - L-spine - Lateral • (Same patient as image below)• A poorly defined dense (white) fracture line is visible with a

detached fracture fragment (asterisk)• L1 has lost height anteriorly and there is disruption of the

anterior column only

Anterior compression injury - L-spine - AP• (Same patient as image above)• Loss of vertebral body height can be seen but

the fracture is not visible on this view

2 column - 'Burst' fracture

• 'Burst' fractures result from high force vertical compression trauma. Posterior displacement of vertebral body fracture fragments into the spinal canal leads to a high risk of spinal cord or nerve root damage.

• Thoracolumbar 'Burst' fracture - Lateral • (Same patient as image below)• Both the anterior and middle columns are disrupted • Injury has resulted in increased kyphosis• A large vertebral body fragment is displaced anteriorly

• Thoracolumbar 'Burst' fracture - AP • (Same patient as image above)• The T12 vertebral body has lost height and the adjacent rib is fractured• The interpedicular width should increase gradually from superior to inferior (white dotted lines)• At the level of the fracture there is sudden widening of the interpedicular width - Note: This sign is not always visible

in burst fractures• The normal paravertebral soft tissues (asterisks) is widened by a paraspinal haematoma at the level of the fracture

3 column - Flexion-distraction fracture

• Flexion-distraction injuries are associated with high force deceleration injuries and are most common at the thoracolumbar junction. Also known as 'Chance-type' fractures (after the radiologist who first described them) these injuries are unstable and carry a high risk of neurological deficit and abdominal organ injury.

• The 'fracture' line may pass through the disc rather than the vertebral body, and so there may not be visible bone injury of the anterior column.

• Flexion-distraction / 'Chance' fracture - Lateral• All three columns are disrupted• A = Widened spinous processes (SP) indicating disruption

of the interspinous ligaments at the level of the fracture • B = Normal interspinous distance

• Flexion-distraction / 'Chance' fracture - AP • The interspinous distance is increased at the level of

the fracture• In this case the pedicles and transverse processes have

been split horizontally

Osteoporotic 'insufficiency' injuries

• Thoracolumbar spine injuries are very common in patients with osteoporosis. Common fracture patterns include 'wedge' injuries and 'biconcave' fractures.

• Thoracic spine - 'Wedge' compression fracture• Note the low density (blackness) of the vertebral bodies• The vertebral body has lost height anteriorly• Kyphosis is increased

• Lumbar spine - Biconcave fracture• Note the low density (blackness) of the vertebral bodies• Compression injuries of both the superior and inferior endplates of the

vertebral body have resulted in a biconcave appearance• The vertebral body has also lost height anteriorly - compare to level

below (superimposed dotted line)

Other fractures

• Spinal fractures may be isolated to the spinous or transverse processes.

• Transverse process fractures are often not visible with X-ray - (only seen on CT), and are often associated with other fractures - so if seen are a prompt to recheck all X-ray images available and consider further imaging. Transverse process fractures are also associated with injury to the kidneys.

• Transverse process fracture - Lumbar spine AP

• Multiple fractures of the transverse processes are seen on one side

• Spinous process fracture - Lumbar spine - Lateral

• Only 1 column is visibly injured but further imaging should be considered

Sacrum and Pelvis

Anatomy• The bony pelvis comprises the two hemi-pelvic

bones which are bound anteriorly at the pubic symphysis and posteriorly at the sacroiliac joints.

• As with other anatomical bone rings if a fracture is seen in one place a careful check should be made for a second fracture, or for disruption of the pubic symphysis or sacroiliac joints.

Key points

• If there is one pelvic fracture - look for another fracture, or disruption of the pubic symphysis or sacroiliac joints

• Carefully check the arcuate lines of the sacrum

• Pelvis anatomy - Normal AP

• The 2 hemi-pelvis bones and the sacrum form a bone ring bound posteriorly by the sacroiliac joints and anteriorly by the pubic symphysis

• Each obturator foramen is also formed by a ring of bone

• Hemi-pelvis anatomy - Normal AP

• Each hemi-pelvis bone comprises 3 bones - the ilium (white), pubis (orange) and ischium (blue)

• The 3 bones fuse to form the acetabulum - the pelvic portion of the hip joint

• ASIS = Anterior Superior Iliac Spine = attachment site for sartorius muscle

• AIIS = Anterior Inferior Iliac Spine = attachment site for rectus femoris muscle

• Hemi-pelvis anatomy - Normal AP

• Each hemi-pelvis bone comprises 3 bones - the ilium (white), pubis (orange) and ischium (blue)

• The 3 bones fuse to form the acetabulum - the pelvic portion of the hip joint

• ASIS = Anterior Superior Iliac Spine = attachment site for sartorius muscle

• AIIS = Anterior Inferior Iliac Spine = attachment site for rectus femoris muscle

Pubic ramus fracture

• Fractures seen in the superior or inferior pubic ramus are usually accompanied by another fracture of the other ramus on the same side. These are very common fractures in the elderly.

• Pubic ramus fracture

• The obturator ring is incomplete on the right

• A fracture passes through the superior and inferior pubic rami

• Compare with the normal left side

Pelvic fractures

• Fractures to the pelvis are highly variable in appearance depending on the mechanism and force of injury. Careful examination of the cortical surfaces of the bony rings will reveal most fractures.

• The extent of injury is often underestimated on plain radiographs.

• Acetabular fracture• A tiny step in the cortical edge of the pelvic ring

reveals a fracture which passes into the acetabulum• The fracture passes to the obturator ring and then

through the inferior pubic ramus

Pelvis diastasis

• High force injury to the bony pelvis may result in "diastasis" (separation) at the pubic symphysis or a sacroiliac joint.

• Pelvis diastasis • Both the pubic symphysis and the right

sacroiliac joint are widened• There is complete separation of the right

hemi-pelvis from the axial skeleton

• Avulsion injuries • In young athletically active

individuals avulsion injuries may occur, most frequently at the ASIS, and occasionally at the AIIS.

• ASIS (anterior superior iliac spine) avulsion fracture

• A small fragment of bone has detached from the pelvis

• All or part of the sartorius tendon origin will be attached to the bone fragment

• Note the normal appearance of the unfused iliac crest apophysis in this male teenager

Sacral injuries

• Fractures of the sacrum may be isolated or accompany pelvis fractures. They are easily missed unless a specific check of the arcuate lines is made on every pelvic X-ray.

• Pelvis anatomy - Sacrum - Normal AP• The sacrum and the iliac bones overlap to

form the sacroiliac joints• The arcuate lines of the sacrum are the roofs

of the sacral exit foramina which carry the sacral nerve roots

• Sacral fracture- AP pelvis• Loss of the smooth arcuate lines is a sign of

sacral fracture

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