Systematic Interpretation of the Spinal Radiograph

Authors: Bruce W Martin, John P Sloan / Editor: Helen Yasmin Sultan / Reviewer: Grace McKay, Jolene Rosario / Code: C3AP1c, MuC5, MuP1, MuP3, SLO1, SLO3, SLO4, SLO5, TP2Published: 18/02/2022

Traumatic neck and back pain are common presentations to the emergency department. A systematic approach to the interpretation of the spinal radiograph can help to identify potentially devastating though fortunately uncommon serious injuries.

Spinal column fractures are common in trauma and may be present in up to 10% of all trauma admissions [1]. 2 large multi-centre studies conducted by NEXUS and Canadian Cervical Spine [2, 3] relayed that cervical spine fractures are present in 2% of all patients presenting with traumatic neck pain.

Because spinal column fractures are associated with significant mortality and morbidity, it is essential that Emergency Physicians feel confident in requesting and interpreting spinal imaging correctly.

Introduction

The neck is a highly mobile structure, with an arc of 140° lateral rotation, 80° of lateral flexion, and 100° of flexion/extension in the sagittal plane. Subsequently the neck is susceptible to significant injury when subject to traumatic forces.

Different movements take place at cervical spine levels

  • Nodding movements occurs at the cranio-cervical joint
  • Lateral flexion occurs at the 3rd to 7th cervical vertebrae.
  • The principal fulcrum of flexion in the adult cervical spine occurs at C5/6.

Rotational movements occur throughout the lower cervical vertebrae, but principally at the atlanto-axial joint.

Structured Assessment

Not all patients presenting with neck pain following trauma will require imaging of their cervical spines, and the Emergency Physician should use a structured assessment to assist in identifying patients who require imaging.

The National Institute for Health and Clinical Excellence (NICE) have published guidance on appropriate imaging for practice in England and Wales [4]. These are based on the Canadian Cervical Spine Rules [3].

Image: Taken from NICE Clinical Guideline 56. Head injury: triage, assessment, investigation and early management of head injury in infants, children and adults [4].

Click on the image to enlarge.

X-ray Interpretation

Where plain radiography is indicated, three films are taken of the cervical spine: lateral, anteroposterior (AP) and open mouth (peg) views.

This combination allows for good visualisation of the entire cervical spine. A lateral view in isolation will only detect 75% of c-spine injuries.

The x-rays can be interpreted using the ABCD system:

Adequacy/Alignment

Bones

Cartilage

Dense soft tissues

Learning Bite

All plain radiographs of the spine may be assessed using the ABCD system.

Adequacy/Alignment

Adequacy

An adequate image should includethe entire cervical spine from the occipital condyles to the top of T1 vertebral body.

You should also ensure that there is adequate exposure of the spinous processes and the soft tissues anterior to the vertebral bodies.

Alignment

To check alignment, four lines should be drawn

  1. Anterior aspect of the vertebral body – this marks the line of the anterior longitudinal ligament
  2. Posterior aspect of the vertebral body – this marks the line of the posterior longitudinal ligament and is the anterior limit of the spinal canal
  3. Spino-laminar line – the junction of the laminae and the spinous processes. This is also the posterior limit of the spinal canal
  4. Spinous process line

Click on the x-ray to enlarge.

Special Consideration: Harris Ring

The body of C2 should have a visible ring on the lateral view – the Harris ring [5].

Click on the x-ray to enlarge.

This may be incomplete between the 5 and 7 o’clock position in the normal x-ray. However, if there is disruption elsewhere, this should raise suspicion for a fracture.

Learning Bite

The Harris ring may be incomplete at the 5-7 o’clock position but should be complete elsewhere.

Cartilage

Although cartilage itself is not visible on plain imaging, the cartilaginous spaces should be assessed for uniformity.

Special note should be made of the following:

  • The distance between the vertebral bodies from C2/3 onwards. This should be similar at all levels
  • The C1/2 articulation. The distance between the anterior margin of the odontoid process and the posterior portion of the arch of C1 should be no greater than 3 mm in the adult spine
  • The facet joints. Assess for uniformity at each level

Click on the x-ray to enlarge.

Special Consideration: Atlanto-occipital Subluxation

Atlanto-occipital dislocation is usually a fatal injury. Rarely, however, there may be subluxation at the atlanto-occipital joint without such devastating effects. This is a potentially life-threatening injury which can be difficult to detect.

There should be no more than 12 mm between:

  1. The tip of the basion and the tip of the dens (i.e. the basion-dental interval – see caption)
  2. The tip of the basion to the posterior axial line [6] (i.e. the basion-posterior axial line interval – see caption)

Image: Harris’ measurements – basion-dental interval and basion-posterior axial line interval are both 12 mm [6]. Also known as the ‘rule of twelve’

Dense Soft Tissues

The Dense Soft Tissues between the larynx and the spine should be examined. If there is swelling or distortion, this can indicate an underlying fracture.

Learning bite:

In neck flexion, there may be an apparent increase in the soft tissue anterior to C1 and C2. This is most marked in young children due to the laxity of their soft tissues. The x-ray above demonstrates anterior soft tissue swelling in a 1-year-old (click on the x-ray to enlarge). The neck should be extended to eliminate physiological rather than pathological soft tissue enlargement.

Concavity of the soft tissue above and below the arch of C1 suggests a physiological rather than a pathological cause however a high suspicion of injury is advised.

Adequacy/Alignment

Adequacy

An adequate AP view should demonstrate the inferior border of C2 to the top of T1. In practice however, the upper portion of the spine is often missed

Click on the x-ray to enlarge.

Alignment

To check alignment, three lines should be drawn

  1. Spinous process alignment – these should be in alignment with no lateral deviation
  2. Foramina line on right
  3. Foramina line on left

Click on the x-ray to enlarge.

Bones

Each bone should be fully assessed for injury or structural abnormalities.

Cartilage and Dense Soft Tissues

Cartilage

The cartilaginous spaces should be assessed to ensure uniformity between each vertebrae. Each cartilaginous space should appear symmetrical.

Dense soft tissues

The prevertebral soft tissues should be assessed for oedema or haematoma formation.

Learning Bite

Use the ABCD system for the AP view as well as the lateral.

Adequacy/Alignment

Adequacy

An adequate open mouth view should demonstrate the whole of the odontoid process of C2 and the lateral masses of C1 and C2

Alignment

The lateral masses of C1 should line up with the lateral masses of C2.

Click on the x-ray to enlarge.

Bones

The odontoid process should be scrutinised thoroughly for fractures by working around the outline of the odontoid process and then the body of C2. Peg fractures occur most commonly at the base.

Click on the x-ray to enlarge.

Be aware of the possibility of Mach effect resembling a fracture.

Learning bite:

Be aware of the ‘Mach effect’ wherebynormal structures (typically the base of the skull) superimpose the Peg and falsely resemble an odontoid base fracture.

Click on the x-ray to enlarge.

The Mach effect occurs when the superimposition of normal structures gives the appearance of a fracture. Most typically, this occurs when the base of the skull gives the appearance of an odontoid base fracture.

Cartilage and Dense Soft Tissues

Cartilage

There should be uniformity of the distance between the odontoid process and the ring of C1. Asymmetry may occur secondary to rotation, but the lateral masses should be closely inspected for any malalignment.

Dense soft tissues

The paravertebral soft tissues should be examined for any oedema or haematoma.

Introduction

Occasionally the initial AP, lateral and open mouth views do not fully visualise the cervical spine. In these circumstances repeating the films whilst pulling caudally on the arms may improve the images, but it may be necessary to take additional views such as ‘swimmer’s views’and ‘oblique views’

If the images are still inadequate then a CT spine may be arranged

The most common views taken are swimmer’s views (see x-ray) and oblique views.

Click on the x-ray to enlarge.

Swimmer’s View

How is the swimmer’s view taken?

The swimmer’s view is taken with one arm held by the side and the other extended to 180° at the shoulder.

It is used to delineate the cervico-thoracic junction and the lower cervical vertebrae.

The key to identifying the correct vertebrae is finding the prominent spinous process of C7 and the first rib (Fig 2).

Once these have been identified, the ABCD system can be used for further evaluation

Click on the x-ray to enlarge.

Oblique View

Oblique films are uncommonly used in the UK due to the availability of CT, however oblique views may be obtained in the following situations:

  • To image the cervico-thoracic junction when other views have been unhelpful
  • To clearly visualise the exit foramina
  • To assess the facet joints in suspected unifacet dislocation

Introduction

The paediatric cervical spine has many mechanical differences from that of the adult [7-10]:

  • Relatively large head leading to higher fulcrum of flexion (C2/3)
  • Horizontally aligned facet joints
  • Underdeveloped uncinate process leading to flatter articular surface
  • Anterior ‘wedging’ of vertebral bodies
  • Cartilaginous synchondrosis at the junction of the odontoid peg and C2 vertebral body
  • Less rigid ligamentous support & weak supportive muscles

Assessment

The principles of assessment of the paediatric cervical spine x-ray are identical to those of the adult:

Adequacy/Alignment

Bones

Cartilage

Dense Soft Tissues

Separate guidance exists on when to image the cervical spine in paediatric trauma.

Open mouth views are recommended only for those aged 10 or over.

Image: A normal 11-year-old in lateral view.

Click on the image to enlarge.

Adequacy/Alignment

Adequacy

As in the adult, you should ensure that the entire cervical spine from the occipital condyles to the top of T1 is visible

Alignment

The same lines should be drawn as in the adult spine:

  1. Anterior aspect of the vertebral body
  2. Posterior aspect of the vertebral body
  3. Spino-laminar line
  4. Spinous process line

True Subluxation/Pseudosubluxation

In some cases, there may be displacement of the anterior and posterior lines of the vertebral body due to either true subluxation or pseudosubluxation.

To differentiate between true subluxation and pseudosubluxation:

  • Evaluate the anterior soft tissue spaces for signs of swelling
  • Draw a line (the spino-laminar line) between C1 to C3, this should pass no more than 1 mm anterior to the spino-laminar line at C2 (the ‘Swischuk line’) [11]. If this distance is >1mm, then suspect subluxation.
  • Pseudosubluxation should recover with repositioning of the head in extension

Learning Bite

Pseudosubluxation occurs most commonly at C2/3. It may be distinguished from true subluxation by the use of the Swischuk line, the absence of anterior soft tissue swelling and resolution in extension. If doubt persists, expert advice should be sought.

Bones

As in the adult, each bone should be fully assessed for injury or structural abnormalities. Important points to note are:

  • The anterior wedging of the vertebral bodies
  • The apophyses of the vertebrae may be seen at the anterior aspect of the vertebral body

Image: Pseudosubluxation in a 7-year-old. Click on the x-ray to enlarge.

Cartilage

As the child’s spine matures, cartilage becomes ossified, leading to a more adult appearance. Before this, the cartilaginous spaces are larger in the child than in the adult.

The space between adjacent vertebrae is larger.

The space between C1 and C2 anteriorly may be as much as 5 mm.

Image: X-ray of a 7-year-old.

Click on the x-ray to enlarge.

Dense Soft Tissues

The soft tissue anterior to the vertebral bodies may become distorted due to its relative laxity and due to distress.

Physiological rather than pathological soft tissue enlargement should be eliminated by taking the neck out of flexion. Concavity of the soft tissue above and below the arch of C1 suggests a physiological rather than a pathological cause, but in all cases, there should remain a high suspicion of injury. Image: Anterior soft tissue swelling in a 1-year-old.

Click on the x-ray to enlarge.

Special Consideration: SCIWORA

Spinal Cord Injury Without Obvious Radiological Abnormality (SCIWORA) refers to the situation that may arise in children in which the initial radiographs are normal despite clinical evidence of cord injury [12].

The anatomical and physiological features outlined earlier predispose the developing spine to significant movement without causing bony injury. This may lead either to ischaemic cord injury or direct traction injury to the cord.

SCIWORA can occur at any age but is most common in younger children [13-15].

If SCIWORA is suspected, an MRI of the cervical spine may demonstrate the underlying injury.

Burst (Jefferson) Fracture

Injuries to the atlas are typically caused by axial loading to the head. These result in a burst fracture – often known as a Jefferson fracture.

The typical radiological findings are:

  • Overlap of the lateral masses of C1 on C2 on the peg view
  • On the lateral view, there is disruption to the pars of C1 and soft tissue oedema anterior to the upper cervical spine

CT will demonstrate the fracture clearly.

Although Jefferson fractures are potentially unstable fractures, the patient frequently has no neurological symptoms at presentation due to the widening of the spinal canal and exit foramina.

C2 Fracture

C2 is most commonly fractured at the odontoid process. This fracture is usually evident on the open mouth view (click on the x-ray to enlarge). The lateral view should also be closely inspected for displacement of the posterior vertebral line, a disrupted Harris ring, and soft tissue oedema.

Peg Fractures

Peg fractures are classified according to the Anderson and D’Alonzo system [16].

Type I Fractures involve the upper portion of the odontoid process only. These are stable injuries, but there is a risk of avascular necrosis.
Type II Fractures involve the base of the odontoid process. These are unstable injuries and usually require operative intervention.
Type III Injuries extend into the body of C2. These are stable injuries.

 

Avulsion Fractures

The anterior longitudinal ligament provides a high degree of stability to the cervical spine.

Disruption of this may cause avulsion fractures to the end plates of the cervical vertebrae.

Although their appearance on x-ray may appear trivial, these are potentially unstable injuries and require further evaluation.

Click on the x-rays to enlarge.

Fig 1: Avulsion C6 superior end plate AP Fig 2: Avulsion C6 superior end plate lateral

 

Importance of Studying the X-ray Fully

It is essential to ensure that having identified one injury, the rest of the x-ray is studied carefully.

What fractures can be identified in the x-ray?

In this patient, there is a fracture of the inferior aspect of the anterior vertebral body of C2, but there is also a fracture through the posterior arch of C2.

Click on the x-ray to enlarge.

Hangman’s Fracture

A ‘Hangman’s fracture’ is an injury to the arch of C2 usually associated with anterior displacement of C2 on C3. Patients typically present with no neurological deficit at presentation due to the opening up of the spinal column.

Thorace-lumbar Spine

Cervical spine fractures are associated with other, non-contiguous fractures in approximately 10% of trauma patients [1,13]. It is essential that patients with cervical spine fractures also have imaging of their thoraco-lumbar spine.

The thoraco-lumbar spine is inherently more stable than the cervical spine. When injuries do occur, they may be associated with significant trauma, and therefore patients with these injuries have a high risk of associated organ damage.

The exception to this is in patients with osteoporosis. The thoracic spine is particularly vulnerable to osteoporosis, which can lead to wedge fractures from relatively minor, or indeed no trauma.

X-ray Interpretation

Thoraco-lumbar spine radiographs are interpreted in much the same way as those of the cervical spine:

Adequacy/Alignment

Bones

Cartilage

Dense soft tissues

Some differences apply to each area, most notably the specific anatomical features and the surrounding soft tissue planes.

Click on the x-rays to enlarge.

Fig 1: Normal lumbar AP view Fig 2: Normal lumbar lateral view

 

Adequacy

An adequate thoracic spine x-ray should incorporate the 1st lumbar vertebra. It is frequently difficult to visualise the upper thoracic vertebrae on the lateral film however due to overlying bone and soft tissue.

An adequate lumbar spine x-ray should include the upper part of the sacrum however a ‘pelvis’ x-ray is best to examine the sacrum.

Fig 1: Markedly displaced fracture of T3, not well visualised on lateral view Fig 2: Markedly displaced fracture of T3, clearly visible on AP view

 

Alignment

Again, it is important to note the alignment of the anterior and posterior limits of the vertebral bodies on the lateral view.

On the AP view, the spinous processes should be aligned, as should the pedicles on both sides of the spinal column. Note that these are not parallel lines as the vertebrae become wider as the spinal column progresses caudally.

Cartilage

As in the cervical spine, the intervertebral space should be assessed for asymmetry and discrepancies between vertebrae.

On both the lateral and the AP view, the spinous processes should be approximately the same distance apart.

Dense Soft Tissues

There is a visible parasternal soft tissue shadow on the left of the thoracic spinal column. This is produced by the edge of the left lung. Where this is present bilaterally, or where there is localised swelling of this, an underlying haematoma secondary to a fracture should be suspected.

Click on the x-ray to enlarge.

Learning Bite

Left-sided parasternal soft tissue shadowing may be normal. If visible on the right, underlying pathology should be suspected.

The Three-column Concept

The three-column concept, as described by Denis [17], is one commonly used method for determining the stability of thoraco-lumbar spine fractures. The spinal column is divided into three columns, with the middle column acting as a fulcrum between the others.

The posterior column consists of the pedicles, transverse processes, laminae, facets and spinous processes.

The middle column comprises the posterior portion of the vertebral body and the posterior longitudinal ligament.

The anterior column consists of the anterior longitudinal ligament and the anterior portion of the vertebral body.

Denis Classification

Several classification systems exist for the type of fracture present in the thoraco-lumbar spine, reflecting difficulty in reaching consensus.

The Denis classification divides these injuries into four types, according to the mechanism of injury and the resultant effects [17]:

  • Compression injuries
  • Burst fractures
  • Seat-belt type injuries
  • Fracture dislocations

Compression Injuries

Compression fractures are commonly associated with underlying osteoporosis, particularly in the thoracic region.

Note the wedge shape appearances of T5 and T6 on the lateral view, and the loss of height of T6 on the AP view.

Click on the x-rays to enlarge.

Fig 1: T5 and 6 wedge, lateral view Fig 2: T5 and 6 wedge, AP view

 

Burst Fractures

Burst fractures are associated with widespread damage to the vertebra.

In this patient, there is expulsion of bone fragments of L3 into the spinal column on the lateral view. On the AP view, there is obvious lateral displacement, but one should also note the wide distance between the pedicles.

Click on the x-rays to enlarge.

Fig 1: Burst fracture, lateral view Fig 2: Burst fracture, AP view

 

Seat-belt Type Injuries

Flexion-distraction injuries are caused by flexion of the spine around an anterior fulcrum. This fulcrum may be within the anterior column, or anterior to this as in a Chance fracture.

Radiologically, there is separation of the posterior elements and compression of the anterior column. These commonly occur from lap-belt injuries in cars, and typically affect the thoraco-lumbar junction. There is a high incidence of associated intra-abdominal injury.

Fracture Dislocations

The images below demonstrate complete disruption to the T3/T4 junction.

On the lateral view (Fig 1) and the AP view (Fig 2) the injury is poorly demonstrated but it, and the resultant cord damage, is clearly visible on the MR scan (Fig 3).

Click on the images to enlarge.

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  1. Amin O. Epidemiology of spinal injury in adults. Faculty of Accident and Emergency Medicine (FAEM), 2005.
  2. Hoffman JR, Mower WR, Wolfson AB, et al. Validity of a set of clinical criteria to rule out injury to the cervical spine in patients with blunt trauma. National Emergency X-Radiography Utilization Study Group. N Engl J Med. 2000 Jul 13;343(2):94-9.
  3. Stiell IG, Wells GA, Vandemheen KL et al. The Canadian C-spine rule for radiography in alert and stable trauma patients. JAMA. 2001 Oct 17;286(15):1841-8.
  4. National Institute for Health and Clinical Excellence. Head injury: assessment and early management. NICE guideline [CG176]. London, 2014, Last updated: 13 September 2019.
  5. Harris JH Jr, Burke JT, Ray RD, Nichols-Hostetter S, Lester RG. Low (type III) odontoid fracture: a new radiographic sign. Radiology. 1984 Nov;153(2):353-6.
  6. Harris JH Jr, Carson GC, Wagner LK. Radiologic diagnosis of traumatic occipitovertebral dissociation: 1. Normal occipitovertebral relationships on lateral radiographs of supine subjects. AJR Am J Roentgenol. 1994 Apr;162(4):881-6.
  7. Lebwohl NH, Eismont FJ. Cervical spine injuries in children. In: Weinstein SL, ed. The Pediatric Spine. Principles and Practice. 2nd edn. Philadelphia: Lippincott Williams & Wilkins, 2001:555.
  8. Fesmire FM, Luten RC. The pediatric cervical spine: developmental anatomy and clinical aspects. J Emerg Med. 1989 Mar-Apr;7(2):133-42.
  9. Bonadio WA. Cervical spine trauma in children: Part I. General concepts, normal anatomy, radiographic evaluation. Am J Emerg Med. 1993 Mar;11(2):158-65.
  10. Roche C, Carty H. Spinal trauma in children. Pediatr Radiol. 2001 Oct;31(10):677-700.
  11. Swischuk LE. Anterior displacement of C2 in children: physiologic or pathologic. Radiology. 1977 Mar;122(3):759-63.
  12. Pang D, Wilberger JE Jr. Spinal cord injury without radiographic abnormalities in children. J Neurosurg. 1982 Jul;57(1):114-29.
  13. Martin BW, Dykes E, Lecky FE. Patterns and risks in spinal trauma. Arch Dis Child 2004;89:860-865.
  14. Kokoska ER, Keller MS, Rallo MC, Weber TR. Characteristics of pediatric cervical spine injuries. J Pediatr Surg. 2001 Jan;36(1):100-5.
  15. Patel JC, Tepas JJ 3rd, Mollitt DL, Pieper P. Pediatric cervical spine injuries: defining the disease. J Pediatr Surg. 2001 Feb;36(2):373-6.
  16. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974 Dec;56(8):1663-74.
  17. Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine (Phila Pa 1976). 1983 Nov-Dec;8(8):817-31.

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