Imaging of upper cervical spine injuries – Part III: C2 below the dens

Applied Radiology — Vol. 33 , Issue 7 , pp. 9 -21

DOI: 10.37549/AR1266

Published: July 1, 2004

Amanda Mignon Jarolimek, MD, El Centro C. Coffey, MD, Carl M. Sandler, MD, O. Clark West, MD

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[Editor’s note: The first article in this series was: West OC. Imaging of upper cervical spine injuries—Part I: C0–C1. Appl Radiol. 2002; 31(2):23-32. The second article in this series was: West OC, Bilow RM, Jarolimek AM. Imaging of upper cervical spine injuries—Part II: The dens. Appl Radiol. 2003;32(2):30-38.]

This is the third in a series of articles that review the radiography and computed tomography of upper cervical spine injuries. The intent of this series of pictorial essays is to illustrate the array of spinal injuries in wide breadth, with a heavy emphasis on images under the motto, “few words, many pictures.” Part I of this series covered fractures of C0–C1, and Part II of this series covered fractures of the dens.1,2 This article concludes this series by focusing on fractures of the C2 neural arch, body, and lateral mass. It will attempt to clarify the anatomy of the axis vertebra, address the Effendi classification scheme, differentiate the classical “hangman’s fracture” from true traumatic spondylolisthesis (TS), and discuss classification schemes for both TS and other C2 body fractures. The article will end with examples of C2 lateral mass fractures and other C2 fractures not previously addressed.

Anatomy

In order to accurately describe C2 injuries, the anatomy of C2 must first be accurately defined. Over the years, there has been much discussion and discord regarding the location of the pedicle versus the pars interarticularis. The question is relevant because the terms have been used interchangeably in describing hangman’s fractures. After a thorough literature search, we were unable to find any embryological text describing the origins of these two segments. Therefore, we have chosen to rely on observational anatomic surveys. We concur with Ebraheim and colleagues3 who define the pedicle of C2 as the slip of bone posterolateral to the vertebral body and anteromedial to the transverse foramen, while the pars interarticularis is the slip of bone between the superior and inferior articular surfaces (Figure 1). We use the pleural form, partes interarticulares, where appropriate.

FIGURE 1.
FIGURE 1. Illustration of the C2 vertebra showing the locations of the pedicle and pars interarticularis. (A) Superior view. Note the illustration of the right showing the hemitubular pedicle after removal of the superior facet. (B) Lateral (left) and inferior (right) views. (Reprinted with permission from Ebraheim NA, Fow J, Xu R, Yeasting RA. The location of the pedicle and pars interarticularis in the axis. Spine. 2001;26:E34-E37.)

Fractures of the C2 neural arch (ring)

In 1981, Effendi and colleagues4 published a classification scheme inclusive of all fractures of the axis neural arch. Effendi I injuries are “isolated hairline fractures of the ring of the axis with minimal displacement of the body of C2. The fracture line is then oblique, usually involving one or, rarely, both posteroinferior corners of the body”4 (Figure 2). There is no disruption of the C2/C3 intervertebral disc (Figure 3). Effendi II injuries have similar fractures of the C2 ring but are distinguished from type I injuries by “an abnormal disc below the axis.”4 Type II injuries have “3 mm or more of anterior translation and significant angulation at the C2–C3 intervertebral disc space.”5 “The body of the axis may be displaced in fiexion (Figure 4), extension, or obvious forward listhesis”4 (Figure 5). Effendi III injuries were originally defined as “displacement of the anterior fragment, with the body of the axis in the fiexed position; but in addition, the facet joints at C2–C3 are dislocated and locked”4 (Figure 6). Currently, the definition has been broadened to include unilateral or bilateral subluxation or dislocation of the C2–C3 facet joints6 (Figure 7).

FIGURE 2.
FIGURE 2. A 32-year-old woman with mildly asymmetric traumatic spondylolisthesis, Effendi I. (A) Radiograph shows a 2- to 3-mm wide fracture through the partes interarticulares. There is mild anterior translation of the C2 vertebral body relative to C3 with a normal disk space. Also note the anterior translation of the posterior arch of C1 relative to C2. (B and C) Sequential axial images through the fracture show involvement of the pars interarticularis. (D) Right, (E) mid-, and (F) left sagittal images show slightly asymmetric fractures through the partes interarticulares. Note the anterior translation of the C2 vertebral body without widening of the disk. The facet joints at C2–C3 are norm
FIGURE 3.
FIGURE 3. A 16-year-old adolescent with asymmetric traumatic spondylolisthesis, Effendi I. (A) Lateral radiograph reveals a minimally displaced fracture through the pars interarticularis (arrows). The fracture is partially obscured by the superimposed inferior articular facet. (B) Axial CT image shows a pars interarticularis fracture on the right and a fracture involving the posterior aspect of the vertebral body and the transverse process on the left. Asymmetric fractures are frequently encountered. (C) Right sagittal image shows an oblique fracture through the pars interarticularis. (D) Fracture through the anterior aspect of the left pars interarticularis. The fracture extends into the vertebral body and transverse process on other images, not shown
FIGURE 4.
FIGURE 4. A 21-year-old woman with asymmetric atypical traumatic spondylolisthesis, Effendi II. (A) Radiograph shows a posteriorly located fracture involving the lamina superiorly and extending to the inferior articular facet. Fracture on the opposite side involves a small fragment of the posterior vertebral body. The C2 vertebral body and the dens are tilted in flexion. Prevertebral soft-tissue swelling is present. (B and C) Axial images illustrate the right pars interarticularis fracture. The left fracture extends from the vertebral body, to the left pars, and then to left transverse process. (D) Right sagittal image shows the right pars fracture extending to the margin of the facet joint. (E) Midsagittal image illustrates flexion of the C2 vertebral body and dens relative to C3. The posteroinferior vertebral body fragment is characteristic of the “atypical” pattern.
FIGURE 5.
FIGURE 5. A 61-year-old man with traumatic spondylolisthesis characterized by anterior translation and extension. Radiograph shows marked anterior translation of C2 vertebral body relative to C3. Note fracture lines through the anterior portion of the partes interarticulares extending into the posteroinferior aspects of the vertebral body bilaterally
FIGURE 6.
FIGURE 6. A male patient with traumatic spondylolisthesis and bilateral facet joint dislocation, Effendi III. The partes interarticulares are fractured with anterior translation and flexion of the vertebral body. The facet joints at C2–C3 are dislocated bilaterally. The anteroinferior corner of the C2 vertebral body has been avulsed. Note severe prevertebral soft-tissue swelling with resultant compromise of the pharyngeal airway. (Image courtesy of the John H. Harris, Jr., MD, DSc, collection
FIGURE 7.
FIGURE 7. A 6-year-old with traumatic spondylolisthesis and bilateral facet joint subluxation, Effendi III. (A) Conventional radiograph obtained after cervical halo placement reveals severe subluxation of the C2–C3 facets bilaterally. Hairline fracture through the pars interarticularis (arrow) is noted. (B and C) Two axial images show the minimally displaced fracture through the partes interarticulares. (D) Right sagittal image shows perched C2–C3 facets (arrow) and hairline pars fracture. (E) Midsagittal image reveals kyphotic angulation of C2 relative to C3. (F) Left sagittal image shows severe facet subluxation (arrow) and hairline pars fracture

The strength of Effendi’s classification system is that it includes all fractures of the C2 neural arch (or ring). Effendi recognized that fractures of the C2 ring are almost always bilateral but are frequently asymmetrical.4 Indeed, fractures involving the laminae are easily classified using the Effendi system (Figure 8).

FIGURE 8.
FIGURE 8. A 47-year-old man with multiple cervical spine fractures, including bilateral lamina fractures of C2, Effendi II. (A) Postoperative plain film focusing on C2 shows bilateral overlapping fractures of the lamina (arrow). (B) Axial image through the neural arch of C2 shows minimally displaced fractures at the right spinolaminar junction, and in the midportion of the left lamina. Minimally displaced laminar fractures are classified as Effendi I.

Because the Effendi system is simple and inclusive, it necessarily describes injuries resulting from differing force vectors. As a result, fractures with differing positions and orientations all fall within this system.

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Traumatic spondylolisthesis

In order to create more homogenous injury patterns, a subset of C2 neural arch fractures are known as traumatic spondylolisthesis, which is defined as bilateral fracture of the pars interarticularis of C2 or of the adjacent portion of either the superior or inferior articular facet7 (Figure 9). The mechanisms causing TS vary but most frequently are hyperextension combined with axial loading, or fiexion combined with axial load-ing.5,8

FIGURE 9.
FIGURE 9. A 49-year-old woman with symmetric traumatic spondylolisthesis, Effendi I, with associated hyperextension teardrop fracture. (A) Conventional radiograph exhibits prevertebral soft-tissue swelling and a large triangular fragment avulsed from the anteroinferior corner of the C2 vertebral body (white arrow). Fractures of the partes interarticulares are difficult to appreciate. The most apparent manifestation is disruption of Harris’ ring posteriorly (black arrows). (B) Axial CT image shows mildly displaced fractures through the partes interarticulares. (C) Right sagittal image shows extension of the fracture from the pars interarticularis into the inferolateral portion of the vertebral body. (D) Midsagittal image illustrates the triangular hyperextension teardrop fracture. (E) Left sagittal image shows a fracture of the left pars interarticularis that is nearly a mirror image of the opposite side. The mild displacement with normal C2–C3 disk space indicates an Effendi I injury

Many authors use the term hangman’s fracture interchangeably with TS, which is incorrect. While the fractures produced by judicial hanging are similar to those seen in TS, judicial hanging is caused by “hyperextension combined with sudden violent distraction,”9 and the differing injury mechanisms distinguish the two.8 At Memorial Hermann Hospital in Houston, TX, our colleagues in Emergency Medicine and Trauma Surgery often order C-spine radiographs and CT scans in victims of suicidal hanging, presumably to identify hangman’s fractures. We have never encountered an actual cervical spine fracture in this setting. Others report a similar lack of clinical utility when imaging victims of suicidal hanging.10,11 To avoid confusion regarding the mechanism of injury in suicidal hanging, we recommend abandoning use of the colorful term hangman’s fracture when referring to TS and other nonjudicial fractures of the C2 neural arch.

Special categories of traumatic spondylolisthesis

Review of the literature reveals inconsistent use of the terms atypical and type A as subcategories of TS. In 1985, Levine and Edwards5 expanded upon the Effendi classification scheme by including a subclass of injuries that they referred to as Type IIa. These injuries had the features of an Effendi Type II with severe angulation, but minimal or no anterior translation. They found that the addition of therapeutic traction to patients with this injury resulted in distraction at the C2–C3 intervertebral disc space (Figure 10).

FIGURE 10.
FIGURE 10. A 38-year-old man with traumatic spondylolisthesis, Effendi IIA, with wide distraction of the C2–C3 disk. (A) Conventional lateral radiograph shows fractures through both partes interarticulares. The C2–C3 intervertebral disk space is 3 times normal width. One of the two C2–C3 facet joints is also widened and subluxed. A fragment of the left lateral mass, which could be mistaken for a dislocated inferior articular facet, projects through the widened C2–C3 disk space. (B) Axial CT shows fractures through the partes interarticulares. (C) Right sagittal image shows the typical fracture line of traumatic spondylolisthesis. (D) Midsagittal image emphasizes the severe widening of the C2–C3 intervertebral disk. (E) Left sagittal image shows a mirror image fracture line, but also illustrates facet joint widening and subluxation at C2–C3

Atypical traumatic spondylolisthesis (ATS) is another variant of TS in which fracture lines extend from the pars interarticularis into the posterior portion of the body of C2.7 These obliquely oriented fractures create fragments of the inferoposterior vertebral body. If the neural arch displaces posteriorly, as occurs with type II injuries, this posterior body fragment may narrow the spinal canal and cause spinal cord injury (Figure 11).12 In contrast, typical TS usually results in expansion of the vertebral canal and has low propensity for spinal cord injury.13,14 In our opinion, the atypical type I (or Ia) classification is not particularly important because there is no translation, and therefore no therapeutic implication (Figure 12). The terms Ia, IIa, and atypical have been used interchangeably in the literature, but in our interpretation they actually represent distinct patterns of injury.

FIGURE 11.
FIGURE 11. A 38-year-old woman with atypical traumatic spondylolisthesis, Effendi II. (A) Conventional lateral radiograph shows oblique fracture through both partes interarticulares. On one side, the fracture involves a large fragment of the posterior vertebral body that impinges upon the spinal canal (arrow). The remainder of the C2 vertebral body has translated anteriorly. (B) Axial CT shows a displaced fragment on the left side of the C2 vertebral body impinging upon the spinal canal, the defining feature of the “atypical” pattern
FIGURE 12.
FIGURE 12. A 57-year-old woman with asymmetric atypical traumatic spondylolisthesis, Effendi I. (A) Fracture through the right pars interarticularis is shown on this axial image. (B) More caudally, the fracture on the right extends into the posteroinferior vertebral body with minimal posterior displacement of the fracture fragment. A minimally displaced fracture is present in the left lamina. (C and D) Two sequential sagittal images show the fracture through the pars interarticularis extending into the posterior vertebral body. The lack of displacement of the body fragment makes the atypical fracture pattern less clinically significant. (E) Left sagittal image shows a fracture line through the left lamina extending to the pars inferiorly.

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C2 body fractures—The fat C2 sign

Obliquely oriented fractures through the body of C2 (dens type III, ATS, and comminuted fractures) can result in anterior and/or posterior displacement of the axis body fragments.15 On lateral radiographs, this produces an apparent increase in the distance between the anterior and posterior body margins of C2 compared with C3, which is called the “fat C2” sign (Figure 13). It is important to recognize a “fat C2” because the actual fracture line may not be visible on the lateral radiograph. The fat C2 sign indicates a potentially unstable injury and mandates further diagnostic imaging studies. Coronally oriented fractures through the posterior aspect of the C2 vertebral body occur through a zone of trabecular rarefaction, which contributes to C2 fractures in elderly individuals.

FIGURE 13.
FIGURE 13. An 89-year-old woman with Type III C2 vertebral body fracture illustrating the “fat C2” sign. (A) Lateral conventional radiograph shows a comminuted fracture of the C2 vertebral body with posterior displacement and fragmentation of the posterior cortex (arrows). Note the appearance of widening between the anterior and posterior cortical lines of C2—the “fat C2” sign. (B) Midsagittal CT image shows posterior displacement of the C2 vertebral body. (C) Axial image through the upper C2 vertebral body shows a comminuted fracture involving the body and superior articular facets. (D) Axial CT image through the inferior vertebral body shows coronally oriented fracture with posterior displacement of the posterior wall of the C2 body

C2 body fractures—Hyperextension teardrop fractures

Hyperextension teardrop fractures of the axis are the result of traction from the anterior longitudinal ligament on its insertion at the anteroinferior portion of the C2 body during sudden, violent extension.7 The resultant fracture produces a wedge-shaped piece of avulsed bone (Figures 9 and 14). In elderly patients with osteoporotic bones and inelastic soft tissues, even less violent forces can cause these fractures and may produce little or no prevertebral soft-tissue swelling.7 In younger patients, the presence of hyperextension teardrop fractures usually indicates that there has been tremendous force involved, and therefore, marked soft-tissue swelling is usually noted.7

FIGURE 14.
FIGURE 14. A 29-year-old man with hyperextension teardrop fracture of C2. (A) Lateral conventional radiograph shows a triangular fragment at the anteroinferior corner of the C2 vertebral body. There is marked prevertebral soft-tissue swelling. (B) Sagittal image clearly reveals the triangular fracture fragment. (C and D) Two sequential axial images illustrate the ease with which even large, substantially displaced hyperextension teardrop fractures may be overlooked in the axial plane

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C2 body fractures—Classification scheme

Compared with dens fractures and fractures of the C2 neural arch (TS and other types), fractures of the C2 body are uncommon. Fujimura and colleagues16 have devised a classification scheme based on 31 cases collected over a 26-year period. Type I is an avulsion fracture identical to the hyperextension teardrop fracture described above (Figures 9 and 14). Type II is a transverse fracture running horizontally through the C2 vertebral body caudal to the superior end of the atlantoaxial joint (Figure 15). The fracture line is caudal to that in the type III dens fracture. Type III is a burst fracture, or comminuted fracture of the C2 body with multiple fragments dislocated anteroposteriorly, often with retropulsion into the spinal canal. Traumatic spondylolisthesis is present in all cases (Figure 13). Type IV is a sagittal or parasagittal fracture extending from a point lateral to the dens vertically or diagonally to the inferior surface of C2 (Figure 16).

FIGURE 15.
FIGURE 15. A 36-year old woman with Type II C2 body fracture. (A and B) Axial images through the upper and midportions of the C2 vertebral body exhibit an obliquely oriented fracture involving the right C1–C2 joint and extending across the C2 body inferiorly. (C) Coronal image shows the oblique orientation of the fracture and involvement of the right superior articular facet
FIGURE 16.
FIGURE 16. A 74-year-old woman with Type IV C2 body fracture. (A) Lateral conventional radiograph shows fat C2 sign. Note the 6-mm posterior displacement of the posterior cortex of C2 vertebral body relative to the posterior cortex of the dens. Also note the absence of prevertebral soft-tissue swelling. (B) Coronal image shows an obliquely oriented, comminuted fracture extending from the left superior articular facet of C2 to the right side of the inferior endplate. (C, D, and E) Axial CT images through the (C) superior, (D) middle, and (E) inferior portions of the C2 vertebral body show the obliquely oriented, comminuted fracture.

C2 lateral mass fractures

Fractures of the C2 lateral mass run the spectrum from small hairline fractures with no displacement (Figure 17), to grossly comminuted, depressed fractures with significant displacement (Figure 18).

FIGURE 17.
FIGURE 17. A 59-year old man with minimally displaced left lateral mass fracture of C2. (A and B) Two sequential axial CT images show a hairline fracture through the left superior articular facet
FIGURE 18.
FIGURE 18. An 18-year-old man with a depressed left lateral mass fracture. (A and B) Two sequential axial images reveal a comminuted fracture of the right lateral mass. A large fracture fragment is displaced anteriorly. (C) Coronal image shows depression of the right lateral mass. (D) Sagittal image shows a centrally depressed fracture fragment. Note abundant prevertebral soft-tissue gas

Conclusion

After studying cases of nonodontoid axis fractures in this pictorial essay, several important factors regarding fractures of the neural arch of C2 should be clear. The following are most important:

  1. 1)

    Traumatic spondylolisthesis involves the pars interarticularis. Fracture of the pedicle of C2 should be considered a separate entity.

  2. 2)

    Look for ≥3 mm of displacement at the C2–C3 interface, indicating an Effendi II fracture.

  3. 3)

    Identify distraction, subluxation, or dislocation of one or both the facet joints of C2–C3, as seen in an Effendi III fracture.

  4. 4)

    If a posterior fragment of the vertebral body is identified and compromises the spinal canal, the diagnosis of “atypical TS” is applicable and the spinal cord may be at risk.

  5. 5)

    Paradoxical widening of the C2–C3 intervertebral disc or increasing angulation of the C2 body fragment on images obtained after application of traction indicates a Type IIa fracture.

  6. 6)

    A triangular fragment of the vertebral body indicates a hyperextension teardrop fracture.

  7. 7)

    A “fat C2” sign indicates a comminuted fracture of the vertebral body.

References

  1. West O. Imaging of upper cervical spine injuries—Part I: C0–C1. Appl Radiol. 2002;31(2):23-32.
  2. West O, Bilow R, Jarolimek A. Imaging of upper cervical spine injuries—Part II: The dens. Appl Radiol. 2003;32(2):30-38.
  3. Ebraheim N, Fow J, Xu R, Yeasting R. The location of the pedicle and pars interarticularis in the axis. Spine. 2001;26.
  4. Effendi B, Roy D, Cornish B. Fractures of the ring of the axis. A classification based on the analy-sis of 131 cases. J Bone Joint Surg Br. 1981;63-B:319-327.
  5. Levine A, Edwards C. The management of traumatic spondylolisthesis of the axis. J Bone Joint Surg Am. 1985;67:217-226.
  6. Levine A, Clark C, Ducker T, Dvorak J. The Cervical Spine. 1998:429-449.
  7. Burke J, Harris J. Acute injuries of the axis vertebra. Skeletal Radiol. 1989;18:335-346.
  8. Francis W, Fielding J, Hawkins R. Traumatic spondylolisthesis of the axis. J Bone Joint Surg Br. 1981;63-B:313-318.
  9. Wood-Jones F. The ideal lesion produced by judicial hanging. Lancet. 1913;1:53.
  10. Kalita J, Mishra V, Misra U, Gupta R. Clinicoradiological observation in three patients with suicidal hanging. J Neurol Sci. 2002;198:21-24.
  11. Penney D, Stewart A, Parr M. Prognostic outcome indicators following hanging injuries. Resuscitation. 2002;54:27-29.
  12. Starr J, Eismont F. Atypical hangman’s fractures. Spine. 1993;18:1954-1957.
  13. Schneider R, Livingston K, Cave A, Hamilton G. “Hangman’s fracture” of the cervical spine. J Neurosurg. 1965;22:141-154.
  14. Hadley M, Browner C, Sonntag V. Axis fractures: A comprehensive review of management and treatment in 107 cases. Neurosurgery. 1985;17:281-290.
  15. Pellei D. The fat C2 sign. Radiology. 2000;217:359-360.
  16. Fujimura Y, Nishi Y, Kobayashi K. Classification and treatment of axis body fractures. J Orthop Trauma. 1996;10:536-540.

Citation

Jarolimek AM, Coffey ECC, Sandler CM, West OC. Imaging of upper cervical spine injuries – Part III: C2 below the dens. Applied Radiology. 2004;33(7):9-21. doi:10.37549/AR1266.