by Dejvid Ahmetović and Gregor Prosen
Introduction
C-spine x-ray interpretation is one of the fundamental skills of emergency physicians. Although current guidelines lead us to use CT scan for a suspected c-spine injury, c-spine x-rays are still valuable in some low resource settings and patient groups who are susceptible to radiation. Therefore, this chapter will summarize the basics of c-spine x-ray interpretation.
Interpretation of radiographs has its limitations, which more or less depending on the individual’s knowledge of anatomy and clinical experience.
Because anatomical landmarks for measurements can sometimes be difficult to find or identify. A more systematic approach to reading cervical radiographs can significantly reduce the chances of missing an important injury.
Visualisation
Plain radiographs, when they show the lateral projection of the cervical spine and include an open mouth view, are fairly sensitive in identifying c-spine fractures. The risk of missing a significant fracture is, according to statistics, less than 1%. Addition of the anteroposterior (AP) projection increases sensitivity to approximately 100%. All of the three essential above mentioned projections can be seen in Figure 1.
Figure 1: Lateral view with normal slight lordosis (A), Odontoid or open mouth view of the atlas and axis (B), Standard anteroposterior or AP view with open mouth, it can also be taken with closed mouth (C).
- Before analyzing cervical radiographs, some additional facts need to be presented.
- Most spinal injuries occur at the junctions of the spine: craniocervical, cervicothoracic, thoracolumbar and lumbosacral.
- Only c-spine radiograph one should be satisfied with is the one showing all of the 7 cervical vertebrae (C1-Th1).
- The C7-Th1 vertebrae may be obscured in muscular or obese patients (Figure2), or in patients with spinal cord lesions that affect the muscles which normally depress shoulders. Such lesions that leave the trapezius muscle unopposed occur in the lower cervical region. Shoulders can be depressed by pulling the arms down slowly and steadily, or if the patient is capable, asking them to depress one shoulder and lift the other hand above his head to achieve the swimmer’s position, which better visualizes the lower vertebrae.
Figure 2: Two examples of a cervical x-ray that is not good enough for the evaluation of the possible injury of the neck.
There are 3 basic views of c-spine
- Cross-Table Lateral View
- Odontoid – Open Mouth View
- Anteroposterior View
Cross-Table Lateral View
The lateral (cross-table) view is the most helpful x-ray study in diagnosing c-spine injuries. Inspection of the x-ray should be thorough, methodical and complete. At this point it is not easy to differentiate ‘ABCs’, because of all the acronyms across the field of medicine, but the ‘ABCs’ in this case stands for: A – alignment and adequacy, B – bone abnormalities, C – cartilage space assessment and S for soft tissues.
A – Alignment and adequacy: First, visualize the spine from the base of the skull to the C7-Th1 junction. Next, check if the x-ray is a real lateral view, or if it is slightly rotated. Facet joints are best visualized when we have a proper lateral projection. (see Figure 3).
Figure 3: Example of a slightly rotated not ideal lateral projection of the cervical spine in (A) and an x-ray of an ideal lateral projection in (B).
To check for proper alignment, look for a normal smooth lordotic curve and imagine two lines, each running along the anterior and posterior margins of vertebral bodies. Additionally, a third line (spino-laminar line), running along the base of spinous processes and up to the posterior aspect of the foramen magnum, must be visualized (Figure 4).
Figure 4: Always assess (AV) anterior vertebral, (PV) posterior vertebral and (SL) spinolaminar lines, they should run smooth, without any disruptions, and should form a slight lordotic shape.
All three lines should form a smooth and lordotic curve of the cervical spine. Any disruption in the flow of these lines suggests either a bony or a ligamentous injury (Figure 5).
Figure 5: Disruption in the shape of the AV line, that indicates injury, and in this case a fracture of the body of C7.
An exception to this rule is a pseudo-subluxation of C2 and C3 in the pediatric population, which can cause confusion. In these cases inspect the spino-laminar line from C1-C3 and be suspicious of injury if the C2 spinous process base lies more than 2 mm from this line. Also correlate with the soft tissue findings (see below, under “S”). Furthermore, on the lateral view, inspect the predental space, which is the distance between the anterior surface of the odontoid process and the posterior aspect of the anterior ring of C1. It should not exceed 3 mm in adults or 5 mm in children. (Figure 6).
Figure 6: Predental space, the distance between the anterior surface of the odontoid process and posterior aspect of the anterior ring of C1, in adult, it should not exceed 3 mm, or 5 mm in children.
B – Bone: Watch for a normal bony outline of the vertebras and bone density. Subtle changes in bone density should be noted, as it may indicate a compression fracture. Areas with decreased bone density which may be found in patients with rheumatoid arthritis, osteoporosis or metastatic osteolytic lesions, are more prone to breaking under stress. Acute compression fractures of the above-mentioned changes show as areas of increased bone density (Figure 7).
Figure 7: Watch for a non-disrupted bony outline. Disruption, as in the above examples means fracture of the bone structure. Also search for any hypo- or hyper-dense areas in the bone, as it may be the only indication of the compression fracture. In (A) slight widening of the soft tissue is visible just in front of the fracture, under the white arrow, which may indicate that this is an acute injury.
C – Cartilage space assessment: Inspection of a good quality lateral view x-ray in a healthy person should show uniform intervertebral spaces. (Figure 8).
Figure 8: Uniform intervertebral cartilage spaces, also facet joints must be inspected, for any unusual alignment or increased space.
An emergency physician may diagnose subluxations and dislocations of the facet joints through the assessment of cartilage space between corpora of vertebrae, facet joints, and space between spinous processes. Increased interspinous distance by more than 50% suggests a ligamentous injury and the protective muscle spasm may make the interpretation difficult.
S – Soft tissues: The prevertebral soft tissues can be used as an indicator of an acute swelling or hemorrhage resulting from an injury, and may sometimes be the only indicator of an acute injury on an x-ray. The normal width of the prevertebral tissue decreases down from C1 to C4 and increases from C4 downwards. Normal measurements from C1 to C4 are less than 7 mm (less than half of the vertebral body at this level), and less than 22 mm below the C5 (less than the vertebral body at this level) see Figure 9. Air within soft tissue could suggest rupture of the esophagus or trachea.
Figure 9: Retro-pharyngeal soft tissue, narrows down from C1 to C4, and should not exceed more than 7mm (less than third of the vertebral body). Bellow the C4 soft tissue starts widening, but should not exceed 22mm (for easier thinking, should not exceed the width of the body of the vertebrae.
Odontoid – Open Mouth View
This is usually the second standard view obtained in the emergency department. The main goal is to picture the odontoid process of the C2 and the C1. It can be done with the mouth either open or closed. Two things are assessed when inspecting the odontoid x-ray: the distance between the odontoid process and the lateral masses of the C1 should be equal. If not, the inequality may be due to a slight rotation of the head. Secondly, and considering the previous point, the margins of C1 and C2 should remain aligned (Figure 10).
Figure 10: The distance between the odontoid process and the lateral masses of the C1 should be equal, if not inequality may be due to the slight rotation of the head. (If the patient has the upper central incisor teeth, we can check if the space between those two teeth aligns with the middle of the odontoid process, this might give the slight idea about rotation in case process itself is not broken and misaligned). Even with the slight rotation of the head we can still check alignment by looking at the lateral margins of the C1 and C2, which should remain aligned.
Anteroposterior View
Images taken in this projection are usually much less clear than the two mentioned above. The tips of the spinous processes should lie in a straight line in the mid-line and distances between the spinous processes should also be checked. Anomalies, such as bifid spinous processes, can make interpretation difficult. The laryngeal and tracheal shadows should align down the middle. The alignment of the lateral masses of the vertebra should also be checked (Figure 11).
Figure 11: Blue line connects the spinous processes, they should lie mid-line and have an equal amount of space between. Red-line should smoothly connect the lateral masses of the vertebrae. Always check the edges of the picture, in most cases, apexes of the lungs are visible, check for pneumothorax.
Other Views
Oblique and flexion/extension views are useful only to an experienced physician. Flexion and extension are often either contraindicated because of the suspected unstable trauma or impossible to accomplish because of the spastic musculature post-injury. (Figure 12). Unsupervised or even forced flexion or extension in a patient with ligamentous injury may also lead to neurologic injury.
Figure 12: Straightened normal lordotic curvature of the c-spine, may be due to the muscle spasm as a protective mechanism, what also makes flexion and extension views hard to capture.
Figure 13: Suspected fracture of the odontoid process, but with closed mouth teeth might affect the view.
Figure 14: Same patient as in Figure 13, but with open mouth view, and the fracture through the body of C2 is visible, also note misalignment of lateral borders of C1 and C2 and difference in space between odontoid process and lateral masses of C2 on both sides.
Figure 15: Lateral view of a type 2 odontoid process fracture seen in A. Fracture of spinous processes of C7 and Th1 vertebrae named Clay – shoveler fracture in B.
SCIWoRA (Spinal Cord Injury Without Radiographic Abnormality)
Plain radiographs are negative in 25% of pediatric patients with an injury to the spinal cord. Tenderness of the neck and careful neurologic examination must stay the main way of diagnosing a patient, especially in the pediatric population. Even in adults, a normal cross-table lateral x-ray does not exclude a spinal cord injury. If in doubt, treat as if there is spinal cord injury until proven otherwise. It is also worthwhile to memorize a short mnemonic for children: SCIWoRA (Spinal Cord Injury Without Radiographic Abnormality).
References and Further Reading
- Court-Brown CM, Heckman JD, McQueen MM, Ricci WM, Tornetta P, McKee MD. Rockwood and Green’s fractures in adults. 8th ed. Philadelphia [etc.]: Wolters Kluwer; 2015.
- Eastman AL, Rosenbaum DH, Thal ER, Parkland Memorial Hospital (Dallas Tex.). Parkland trauma handbook. Third edition. ed. Philadelphia, Pa.: Mosby/Elsevier,; 2009.
- Holmes EJ, Misra RR, ebrary Inc. A-Z of emergency radiology. A-Z series. Cambridge, UK: Greenwich Medical Media,; 2004.
- Rosen P, Marx JA, Hockberger RS, et al. Rosen’s emergency medicine : concepts and clinical practice. Vol Volume I. Eighth edition. ed. Philadelphia: Elsevier/Saunders; 2014.
- Tintinalli JE, Stapczynski JS, Ma OJ, Cline D, Meckler GD, Yealy DM. Tintinalli’s emergency medicine : a comprehensive study guide. Eight edition. ed. New York: McGraw-Hill Education; 2016.