Normal Features of the Lateral X-ray

The lateral x-ray ( Figures 3-8 through 3-13 ; see also 3-19 and 3-20 ) provides information about gross fractures, as well as alignment of vertebral bodies relative to one another. In addition, prevertebral soft tissue widening may suggest soft-tissue hematoma or swelling, a surrogate marker of fractures that may themselves be invisible on plain film. The x-ray must visualize the cervical spine from the skull base to the C7-T1 (cervical seventh vertebra–thoracic first vertebra) junction. This is not an arbitrary definition of an adequate plain film. An x-ray that fails to visualize the entire cervical spine and its junctions with the adjacent skull and thoracic spine may miss injuries. Widening of the space between the C1 vertebra and the skull base may be a subtle indication of a devastating occipital–cervical dissociation—although this injury is usually clinically evident with a moribund patient with quadriplegia. At the caudad end of the cervical spine, it is essential to visualize the C7-T1 junction to avoid missing subluxation of these vertebral bodies relative to one another. This injury is made more likely by the sudden change in the mobility of the spine, from the highly mobile cervical spine to the relative immobile thoracic spine, which is supported by the buttresses of the ribs.

Adequate and inadequate lateral cervical spine x-rays.

A, An adequate lateral cervical spine x-ray, showing the entire cervical spine and its cephalad border (the skull base) and caudad border (T1). B, The image is inadequate because C1 and T1 are not seen fully. Fractures or subluxation at these locations would be missed. The x-ray should be repeated, perhaps using special views such as the swimmer’s view to visualize the C7-T1 junction, or computed tomography could be used.

Interpretation of the lateral cervical spine x-ray.

A normal lateral cervical spine x-ray, with (A) and without (B) labels.

The spine should be inspected for four curved, roughly parallel lines:

• 1
  

  Anterior longitudinal ligament line (follows the anterior border of the vertebral bodies)

  
  
• 2.
  

  Posterior longitudinal ligament line (follows the posterior border of the vertebral bodies)

  
  
• 3.
  

  Spinolaminar line (follows the anterior border of the posterior spinous processes, where the lamina converge)

  
  
• 4.
  

  Spinous processes line (follows the posterior border of the posterior spinous processes and does not fully parallel the other lines due to the increasing length of the spinous processes from C1 to C7)

  
  

  The spinal canal, which houses the spinal cord, lies between lines 2 and 3.

  
  

  If all lines are intact, the vertebral bodies should be properly aligned and the spinal canal should be preserved.

Evaluation of predental space.

On lateral cervical spine x-ray, the predental space should be evaluated. Several injury patterns can widen this space. Fracture of the ring of C1 can allow the anterior portion of the ring to migrate anteriorly with respect to the dens. Dens fracture can allow posterior migration of the dens relative to the ring of C1. Subluxation of the transverse ligament can allow widening of this space. Patients with rheumatoid arthritis are at particular risk of this latter abnormality.

Prevertebral soft tissues.

The lateral cervical spine x-ray should be examined for the width of prevertebral soft tissues. Widening suggests cervical spine injury with prevertebral soft-tissue swelling or hematoma, even in the absence of visible fracture. Lack of widening is relatively reassuring, as a fracture or ligamentous injury would be expected to be accompanied by some degree of soft-tissue swelling or hemorrhage.

In adults, soft tissues should be less than 7 mm in width at C2 and less than 5 mm at C3 and C4.

A rule of thumb in children is that the prevertebral soft tissues should be less than half the width of the adjacent vertebral body. False widening may be seen on expiratory films in children younger than 2 years, particularly if images are obtained during crying, which creates forced expiration.

A normal lateral cervical spine image shows a gentle cervical lordosis—a curve with its convex border oriented anteriorly (see Figure 3-10 ). This lordosis may be straightened slightly due to the presence of the cervical collar. When all cervical vertebrae are intact and in normal alignment with one another, this cervical lordosis results in four parallel curved lines, for which the lateral x-ray should be inspected (the numbered lines in Figure 3-10 ):

• 1.
  

  The anterior longitudinal ligament line, which follows the anterior border of the vertebral bodies.

  
  
• 2.
  

  The posterior longitudinal ligament line, which follows the posterior border of the vertebral bodies.

  
  
• 3.
  

  The spinolaminar line, which follows the anterior border of the posterior spinous processes, where the lamina converge.

  
  
• 4.
  

  The spinous processes line, which follows the posterior border of the posterior spinous processes. It does not fully parallel the other lines because of the increasing length of the spinous processes from C1 to C7. The space between the posterior longitudinal ligament line and the spinolaminar line is the spinal canal. If these lines are intact and parallel, the spinal canal should be intact, and the spinal cord should be safely contained within it.

In addition, the lateral film should be examined with attention to the following:

• 5.
  

  The predental space (see Figure 3-11 ), which separates the dens from the anterior ring of C1. Widening suggests dens or C1 ring fracture, or subluxation of the transverse ligament, which binds the dens to the anterior ring of C1. In adults, this space should be no more than 3 mm, and in children it should be no more than 4 to 5 mm.

  
  
• 6.
  

  Prevertebral soft tissues (see Figure 3-12 ). Widening suggests cervical spine injury with soft-tissue swelling or hematoma. In adults, this distance should be less than 7 mm at C2 and less than 5 mm at C3 and C4. In children, a commonly cited distance is less than half the width of the adjacent vertebral body. False widening may occur in children under the age of 2 years if the image is obtained during expiration. Below C4, the airway moves anteriorly, the esophagus occupies the prevertebral space, and soft-tissue widths vary considerably, usually between 10 and 20 mm in adults. Soft-tissue width exceeding the width of the adjacent vertebral body suggests injury.

  
  
• 7.
  

  The spinal facet joints ( Figure 3-13 ), which should overlap like shingles on a roof. Decreased overlap can occur in the case of a jumped or perched facet joint.

  
  

  
  

  
  

  

  
  

  
  

  Assessment of facet joints.

  
  

  A, Lateral cervical spine x-ray. B, Close-up. The facets should overlap like shingles on a roof. In the case of jumped or perched facet joints, the degree of facet overlap at the level of injury will be less than the overlap at uninjured levels. The facets can be recognized by their rhomboid shape in profile. Fracture through the facets and lamina is also common and should be looked for carefully.

  
  
  
  
• 8.
  

  Widening of the distance between posterior spinous processes, which can indicate fracture or ligamentous injury.

Normal Features of the Anterior-posterior X-ray

The AP x-ray ( Figure 3-14 ) provides information about lateral alignment of vertebral bodies with one another. A small number of additional fractures ( particularly oblique fractures) may be noted on the AP x-ray, and subtle abnormalities from the lateral film may be confirmed. The posterior spinous processes should be centered in the midline and aligned with one another. The cortex of each vertebral body should be intact. The height of and spacing between adjacent vertebral bodies should be uniform.

Anterior–posterior (AP) normal cervical spine x-ray.

The AP cervical spine x-ray should be inspected for gross fractures. The intervertebral spacing (double arrows) should be symmetrical if the intervertebral discs (not visible on x-ray) are intact. The posterior spinous processes (black arrowheads) should project directly backward out of the plane of the x-ray and should be aligned with one another. In cases of unilateral jumped facet joint, rotation of one vertebral body relative to the adjacent bodies causes the posterior spinous process to project at an angle and thus not be aligned with the processes of other vertebrae.

Open-Mouth Odontoid X-ray

The open-mouth odontoid view ( Figures 3-15 and 3-16 ) is essential for evaluation of two important injury patterns:

• •
  

  Burst fractures of the C1 ring, also called Jefferson fractures

  
  
• •
  

  Fractures of the odontoid process or dens, which is a structure of C2

Adequate and inadequate open-mouth odontoid view x-ray.

An adequate open-mouth odontoid view must visualize the entire dens and the lateral borders of C1 and C2. An incompletely visualized dens could result in an undiagnosed dens fracture. The lateral borders of C1 and C2 must be seen to assess for misalignment, which can occur in the setting of C1 burst fracture, in which the lateral masses of C1 are displaced laterally.

A, An adequate view. The lateral borders of C1 and C2 are visible and align normally. The spaces between the dens and the lateral masses of C1 are symmetrical. The entire dens is visible and appears intact. B, An inadequate view with the tip of the dens and the lateral masses of C1 and C2 cropped. Alignment and fracture cannot be assessed.

Normal open-mouth odontoid view x-ray.

The open-mouth odontoid view is essential for evaluation of potential dens fractures and fractures of the C1 ring.

A, Routine open-mouth odontoid image. B, Close-up of the region of interest, which includes C2 with the dens, as well as the lateral masses of C1.

The open-mouth odontoid view is so called because it is obtained with the patient’s mouth opened as wide as possible, with the x-ray tube aimed into the open mouth. This gives a direct view of C1 and C2. Issues that may prevent adequate visualization include an obtunded or uncooperative patient who is unable to comply with this maneuver; a patient with trismus, temporomandibular joint disease, or other injuries (e.g., mandibular fractures) that prevent full opening of the mouth; and the presence of significant metal dental work. Sometimes, the cervical spine collar may restrict mouth opening too much to allow an adequate open-mouth odontoid view. When an adequate open-mouth odontoid view cannot be obtained, CT should be performed to avoid a missed injury of C1 or C2.

An adequate open-mouth odontoid view visualizes the entire dens and the lateral margins of both C1 and C2. A fully visualized dens is essential for evaluation of dens fractures. The cortex of the dens should be carefully inspected for defects. Shadows of overlying structures such as central incisors can simulate or hide fractures, so a wide-open view with no overlap of teeth with the dens is desirable. When the ring of C1 is intact, the lateral margins of C1 should align with the lateral margins of C2. When fractured, C1 typically “bursts,” with the fracture fragments spreading outward. Consequently, an indirect sign of C1 fracture is misalignment of the lateral margins of C1 with the lateral margins of C2. Frequently, the lateral margins of C1 appear displaced laterally compared with the lateral margins of C2, although medial displacement of C1 is also possible. This finding may be unilateral or bilateral. When C1 is intact and the patient is facing directly forward, the distance between the dens and the medial borders of the C1 ring should be bilaterally symmetrical. When C1 is fractured, displacement of fracture fragments typically renders this distance asymmetrical. The lateral margins of C1 and C2 may be hidden by radiopaque dental fillings, especially if the patient’s mouth is not fully opened.

The standard three-view series just described is sometimes augmented with additional plain x-ray views. Adding two oblique views allows visualization of the pedicles, lamina, and neural foramina. Although this technique may be useful in selected cases, this “five-view” technique has been compared with the standard three views and does not detect additional injuries at a rate high enough to make five views a useful standard. The five-view series was insensitive (44%) compared with CT in a high-risk group of patients with altered mental status and a high rate of cervical spine injury (>10%). CT should be obtained if subtle lamina, pedicle, or neural foramen injuries are suspected.

In cases in which the C7-T1 junction is not visualized on the lateral x-ray, “swimmer’s” ( Figure 3-17 ) or “traction” views may allow visualization of this region. In a swimmer’s view, the patient is positioned with the arm closer to the x-ray detector raised above the head. This elevates the humeral head above the C7-T1 junction, preventing it from obscuring this area. The opposite arm is held at the patient’s side, resulting in that humeral head lying somewhat lower that the C7-T1 junction. Variations on this theme include having the patient raise both arms directly in front of the body or over the head. In a traction view, a health care worker pulls on the patient’s arms from a position at the foot of the bed, distracting the humeral heads down to reveal the C7-T1 junction – a method now discouraged because of the possibility of worsening spinal injury. When these maneuvers do not allow adequate visualization of C7-T1, CT is indicated. In many cases, these views are skipped in favor of CT. Flexion and extension views ( Figure 3-18 ) are sometimes obtained to assess for ligamentous instability—the evidence for these views is discussed in detail later.

Swimmer’s view x-ray of the cervical spine.

A swimmer’s view is a lateral cervical spine x-ray in which the patient is positioned with one arm raised above the head. This position tilts the shoulder girdle, elevating one humeral head and depressing the other, thus revealing the C7-T1 junction. Other variations on the swimmer’s position are sometimes used, including raising both arms above the head. The swimmer’s view is only necessary when the C7-T1 junction is not visualized on a standard lateral x-ray. Today, computed tomography is more commonly used to visualize this region.

Flexion and extension x-rays of the cervical spine.

Flexion (A) and extension (B) views may be performed to evaluate for ligamentous injury if plain films in neutral position do not show fractures or subluxation but the patient has persistent pain. The patient is asked to flex and extend the cervical spine actively, stopping if pain or neurologic symptoms develop. Subluxation suggests a ligamentous injury. Passive flexion and extension (in which the patient is manipulated by the examiner) should never be used, because this may cause cervical spinal cord injury. The utility of flexion–extension views is an area of controversy, but generally these are not useful in the evaluation of acute trauma because patients with acute pain are often unable to flex or extend sufficiently to exclude ligamentous injury.

Step 1: Examine the Sagittal Computed Tomography Reconstructions

The sagittal CT reconstructions provide detailed information about the AP alignment of the cervical spine, as well as fractures or subluxations that may impinge on the spinal canal. Start your evaluation by selecting bone windows, and then move to a slice in the middle of the sagittal series, corresponding to the midsagittal plane ( Figure 3-19 ). If you are experienced in interpreting cervical spine x-rays, this image should look familiar—it strongly resembles the lateral cervical spine x-ray, without the confusing overlay of bones and soft tissues from other planes. Just as with the lateral x-ray view, the midsagittal CT image allows assessment of alignment, using the curves of the anterior and posterior longitudinal ligaments and the spinolaminar line. In this view, the spinal canal can be seen in detail and inspected for any fracture fragments or subluxation of vertebral bodies that could impinge on the spinal cord. Remember that you are only looking at a single plane—you need to scroll laterally to the patient’s right and then left to perform these same steps in planes moving away from the patient’s midline. In the midsagittal plane, notice how large the dens is—perhaps you did not appreciate this on x-ray, but look now at the lateral x-ray for comparison. Check the contour of the dens for fracture lines, and if fracture is present, inspect for retropulsion of the dens into the spinal canal. Inspect the predental space for widening. Look at prevertebral soft tissues for increased thickness suggesting soft-tissue injury. Inspect each vertebral body for fracture lines. Check the spinal lamina and posterior spinous processes for fracture. Notice that in the midsagittal plane, the facet joints are not visible. These are lateral structures and are seen in the far lateral parasagittal images ( Figure 3-20 ). Inspect these joints for unilateral or bilateral dislocation (jumped facets, shown in a later figure). At the cephalad limit of the cervical spine, inspect the articulation of the occipital condyles with C1 (see Figure 3-20 ). It may take you some time to become accustomed to imagining the cervical spine in three dimensions as you scroll through it in this plane.

Normal mid-sagittal computed tomography (CT) image, compared with normal lateral cervical spine x-ray.

This 24-year-old female hydroplaned on a wet road at 45 mph and complained of midline cervical spine tenderness. Her CT is reviewed to demonstrate normal findings.

A, When reviewing CT sagittal images, follow the paradigm of the lateral x-ray. First, select bone windows. Next, select the midsagittal CT image and note the alignment of vertebral bodies, using the same four lines used for evaluating alignment on the lateral x-ray (see Figure 3-10 ). Then, inspect each vertebra for fractures (shown in subsequent figures). Notice how the facet joints are not visible in the midsagittal plane. Also notice how large the dens is and how small the ring of C1 is. Prevertebral soft tissues can be evaluated using the same criteria as for x-ray. B, Lateral x-ray for comparison.

Normal parasagittal computed tomography (CT) image, compared with lateral cervical spine x-ray.

A, In this far lateral parasagittal CT image, the facet joints can be seen articulating normally, like shingles on a roof. The vertebral bodies are not seen in this plane, as we are far from the midline. The occipital condyles are seen articulating with C1. B, Lateral x-ray for comparison. Notice how much clearer the occipital–cervical junction is on CT.

Step 2: Inspect the Coronal Images

Use the coronal CT images ( Figure 3-21 ) to simulate the open-mouth odontoid and AP cervical x-rays. Scroll through the “stack” of coronal images until you see the odontoid process projecting between the lateral masses of C1. Check for the same features you would expect on the open-mouth odontoid view. The lateral masses of C1 and C2 should align along their lateral borders. The spaces between the odontoid process and the lateral masses of C1 should be symmetrical. The odontoid process itself should have a smooth contour, with no fracture lines present. Once you have completed this evaluation, scroll in anterior and posterior directions through the stack of images, inspecting for fractures of the vertebral bodies, facets, and transverse processes. Fractures in the sagittal plane are visible on coronal images, and may be missed on the sagittal images reviewed first. Look for lateral displacement of vertebral bodies with respect to one another. Spend some time reviewing the figures in this chapter to familiarize yourself with the most common fracture patterns.

Normal coronal computed tomography image, compared with odontoid view x-ray.

A, Same patient as Figures 3-19 and 3-20 . A coronal image centered on the odontoid (dens) and C1, simulating the open-mouth odontoid x-ray. CT findings of a normal dens are the same as those seen on open-mouth odontoid x-ray, and deviation from normal should heighten suspicion for injury, even when a fracture line is not seen. Subluxation without fracture may be present. The lateral borders of the C1 and C2 vertebral bodies should align. Fractures of the ring of C1 (Jefferson fractures) commonly result in radial spread of C1 fragments, disturbing this normal alignment. The spaces between the lateral masses of C1 and the odontoid process should be bilaterally symmetrical. C1 fractures can result in asymmetrical spread of fragments, and subluxation of the transverse ligament can also result in asymmetry. The odontoid process should be smoothly contoured with no visible fracture lines. A slight notched appearance on each side of the base of the dens is normal. B, Open-mouth odontoid x-ray for comparison.

Step 3: Inspect the Axial Computed Tomography Images

The axial CT images ( Figure 3-22 ) have no immediate analogue in the normal three-view x-ray series. They can provide additional information not readily seen on the sagittal and coronal views. Particularly, they demonstrate fractures of the canals housing the vertebral arteries (foramen transversarium), which are more difficult to assess on other views. They also provide good views of fractures in the sagittal and coronal planes, which may not be seen well on those image series as they lie parallel to the plane of the image. From the sagittal images, you should already have a good idea of the alignment of the cervical spine, although the axial images can also demonstrate jumped facet joints. The axial images provide an en face view of the spinal canal. As you scroll from the level of C1 to T1, imagine yourself traveling down the spinal canal, and watch for fracture fragments that narrow the canal and may impinge on the spinal cord. Check the body, pedicles, lamina, and transverse and posterior spinous processes for fractures. We review many abnormal findings on the axial images in the figures throughout this chapter (see list, Table 3-1 ).

Normal axial computed tomography image.

Same patient as Figures 3-19 through 3-21 . An axial image shows a cervical vertebra in cross section. The vertebral body, spinal canal, pedicles, lamina, and base of the posterior spinous process are visible. It takes some practice to become accustomed to the normal appearance of vertebrae in axial section. They are irregular structures and never lie completely within a single axial plane. Apparent discontinuities in the ring may be visible on some slices but may not represent fractures—instead, they simply reflect the irregular contour of the vertebrae passing in and out of the image plane. A, B, Two sequential slices.