The concept of a three column spine ¹ is a familiar one when evaluating a CT or MRI examination. This anatomical concept can also be applied to the lateral radiograph.

▪ Anterior column The anterior longitudinal ligament, the anterior part of the annulus fibrosus, and the anterior two thirds of the vertebral body.

▪ Middle column The posterior longitudinal ligament, the posterior part of the annulus fibrosus, and the posterior margin of the vertebral body.

▪ Posterior column The facet joints, the pedicles, and the posterior ligaments.

AP view—thoracic vertebrae

In the thoracic spine the soft tissue shadow of the left paraspinal line (aka paravertebral stripe) should be closely applied to the vertebral bodies. This line is produced by the interface between the paravertebral soft tissues and the adjacent lung.

On the right side there is no visible paraspinal line ⁵^,⁶.

AP view—lumbar vertebrae

In the lumbar region the pedicles should become gradually wider apart when descending from L1 to L5.

In the lumbar spine there is no visible paraspinal line.

Analysis: the checklists

▪ A step-by-step analytical approach when evaluating the plain films may provide an immediate indication that a potentially catastrophic injury has occurred.

▪ The AP projection can provide useful information, but the lateral radiograph is invariably the more useful. 70–90% of detectable plain film abnormalities will be shown on the lateral projection ⁷^,⁸. Also, it is the lateral radiograph to which the three column stability principle¹^–³ is applied:

“Instability is present if any two of the three columns are disrupted”

On the lateral view

Look for:

▪ Loss of height or wedging of a vertebral body: this is evidence of a compression fracture. Wedging may be associated with loss of the normal concavity of the posterior aspect of the vertebral body ⁹. This loss indicates significant posterior displacement of the middle column.

▪ Fragment(s) of bone detached from the anterior aspect of a vertebral body.

▪ More than one abnormality. The importance of recognising all of the radiological abnormalities that may be present is explained under stability (pp. 209–210).

Wedge compression fracture of a lumbar vertebra.

L1 wedge compression fracture.

Wedge compression fractures.

▪ Top left: two fragments have been detached. Two columns are disrupted… the anterior and middle columns. Unstable.

▪ Top right: Several fragments. The posterior margin of L1 is disrupted and bulges into the spinal canal. Two column disruption. Unstable.

▪ Bottom left and right: Large fragment in canal. Two columns disrupted. Unstable.

On the AP view

Thoracic spine

Look for:

▪ Localised displacement or widening of the thoracic paraspinal lines. In the context of trauma, displacement or bulging should be regarded as indicating a paraspinal haematoma resulting from a vertebral body fracture.

Thoracic and/or lumbar spine

Look for:

▪ Abnormal widening of the distance between the pedicles. This indicates that vertebral fragments have splayed apart.

▪ Fracture of a transverse process. This can be subtle; careful windowing on the digital images will usually be necessary.

The image on the left is normal. Note that the left paraspinal line (arrowheads) parallels the lateral margin of the vertebral bodies. Further laterally, is the vertical shadow of the descending aorta.

The image on the right is abnormal. There is a bulge of the left paraspinal line (arrowheads) caused by a haematoma resulting from the fracture of T6 vertebra. The haematoma has caused the right paravertebral stripe to appear as a bulge (arrows) in this patient. Normally, the right paravertebral stripe is not visible.

Left: T12 fracture. The vertebra has lost height. Note that the pedicles have been splayed apart. Right: fracture of a lumbar vertebra. The pedicles have been splayed apart. Normally, the pedicles gradually splay apart very slightly from L1 to L5, but there should not be any sudden widening as shown here.

Fractures of the right-sided transverse processes of L2, L3, and L4 vertebrae (arrows).

Most commonly these fractures result from rotation or extreme lateral bending.

Helpful hint: In the context of high energy trauma (and multiple injuries) the detection of transverse process fractures should raise the possibility of a major injury lower in the lumbosacral spine. See “sentinel sign”, p. 211.

The common injury

There is only one common—ie regularly occurring—vertebral fracture.

Osteoporotic compression fractures¹⁰.

□ Vertebral compression fractures are common in an ageing population.

□ Many/most of these fractures are clinically silent. Approximately 30% of people sustaining a fracture will be symptomatic and usually present with back pain.

□ Radiologically the appearance on the lateral radiograph is that of a wedge compression fracture.

Compression fracture of a mid thoracic vertebra.

In this example a haematoma bulges the left paravertebral stripe. In practice such a haemorrhagic bulge is rare unless high energy trauma has occurred.

Elderly patient with severe back pain.

Compression fractures (vertebral flattening) of T11 and T12 vertebrae.

Less frequent but important injuries

Fractures following trauma

These important injuries are all consequent on high energy trauma. The forces acting at the time of a particular injury can be very complex.

Assessment:

▪ First, look for distinct fracture patterns.

▪ Second, assess stability by evaluating the three columns.

Distinct fracture patterns…

Flexion compression injury (wedge fracture) of L2 vertebra.

Radiological pattern: The anterior aspect of the vertebral body loses height, but the posterior part does not.

Vertical compression injury (burst fracture) of L1 vertebra.

Radiological pattern: Severe comminution and flattening of a vertebral body. Often caused by a fall from a height and landing on the feet.

Flexion/distraction injury (Chance-type) fracture.

In this case of L3 vertebra.

Radiological pattern: This is a shearing injury. Various patterns occur ¹¹^,¹².

One fairly common pattern: The vertebral body fractures transversely, with the spinous process and the postero-superior aspect of the vertebral body also fractured. Classically a head-on car crash with the upper torso hurled forwards whilst the pelvis is held by a lap seat belt.

Fracture dislocation injury. In this case affecting the T12/L1 level. (Additional vertebral fractures are also evident.)

Radiological pattern: A fracture and subluxation (or dislocation) of one vertebra on another.

Assessing stability by evaluating the three columns…

When a radiographic abnormality is detected it needs to be categorised as showing either a stable or an unstable appearance. Assess each of the three columns on the lateral radiograph (p. 200). In general, the term ‘stable injury’ should only be applied to minimal/moderate compression fractures with an intact posterior column.

The three columns are normal in this illustration. The alignment, the shape, and the contours of these vertebrae are seen to be anatomical. The assessment of each column on every lateral radiograph is a most important task. If a disruption of any two of the three columns is detected then the injury will be classified as unstable.

Instability is present if any two of the three columns are disrupted.

Left: vertebral body fracture. Two columns are disrupted. Unstable injury. Right: vertebral body fracture. Two columns are disrupted. Unstable injury.

Stability following high energy trauma

Wedge fracture.	Many are stable. Nevertheless, the clinical significance of a particular wedge fracture may be underestimated. These fractures will occasionally cause middle column bone fragments to intrude into the spinal canal.
Burst fracture	Invariably unstable.
Chance-type fracture:	Unstable. Usually disrupted posterior and middle columns; frequently, the anterior column is also involved.
Fracture dislocation injury	Highly unstable.
Transverse process fracture	As an isolated finding this is a stable injury.

Pitfalls

The right paraspinal line

This line is situated adjacent to the thoracic vertebrae and it is not seen in normal individuals. There is one exception: it may be visualised in some middle-aged and elderly patients because the pleura is displaced by age-related lateral osteophytes¹³. In these patients the visible right paraspinal line does not signify pathological tissue.

Dismissing transverse process fractures as trivial

If transverse process fractures are seen after high energy trauma. then it is important to assess the lumbosacral junction appearances most carefully¹⁴. Following severe high energy trauma transverse process fractures may be overlooked, or dismissed as minor, particularly in the presence of pulmonary, abdominal, vascular, or brain injury. Lumbosacral junction dislocation (a rare injury) frequently has fractures of several transverse processes on the AP view. This has given rise to the term “sentinal sign”.

Schmorl’s nodes¹⁴

These are focal indentations of the vertebral body end plates seen at all ages but most commonly in younger people. The aetiology of Schmorl’s nodes is controversial and their clinical importance remains undecided. They are a relatively common finding in the thoracic and lumbar spine. A Schmorl’s node should not be read as an important pathological finding.

Two patients with irregular indentations on the end plates of several vertebral bodies. Schmorl’s nodes.

Accident and Emergency Radiology A Survival Guide

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