Dr. Strother and Dr. Day are in the Department of Radiology and Radiological Sciences, and Dr. McGirt is in the Department of Neurological Surgery at Vanderbilt Medical Center, Nashville, TN.
craniocervical junction functions as one joint with complex mechanics,
and because half of the rotational motion in the cervical spine occurs
at the atlantoaxial junction, the joint relies disproportionately on
ligamentous integrity.1 Ligamentous injury may be inferred
from computed tomography (CT) and radiograph findings, or demonstrated
with flexion-extension radiographs. Increasingly, however, ligamentous
integrity is evaluated with magnetic resonance imaging (MRI). The
radiologic examination is critical for diagnosing and treating cervical
spine injuries and in preventing neurologic injury. In this article, the
implications of radiologic findings for spinal stability are discussed
in the context of surgical treatment planning.
stabilizing the atlantoaxial junction (C1-C2 joint), which are shown in
Figure 1, include the tectorial membrane, the cranial extension of the
posterior longitudinal ligament that limits axial distraction; the alar
ligaments, which transfix the dens to the occipital condyles to restrain
rotational motion; and the transverse atlantal ligament (TAL), which
restricts the dens from impacting the cord in flexion.The TAL is the
most important ligament, stabilizing the atlantoaxial joint against
translational forces.2 The TAL runs posterior to the dens and
anterior to the spinal column. Most surgeons define C1 stability based
on the integrity of the TAL ligament.2 A combined lateral
displacement of the C1 lateral masses > 6.9 mm in relation to the
lateral border of the axis body indicates enough displacement to cause
(C1) is the most “fragile” vertebra. Atlas ring fractures with > 3
parts are characterized as burst fractures, as described byJefferson.4 Stable
Jefferson fractures with intact TAL (Figure 2) usually heal with
immobilization for 8 to 12 weeks in a rigid cervical brace or halo. When
spine trauma is treated in this fashion, serial radiographs starting
within 3 weeks of the initial injury are recommended to confirm
stability.5 Transverse atlantal rupture with C1 tubercle
avulsion (Figure 3) is more likely to heal with nonoperative treatment
than is a purely ligamentous TAL injury.6 In adults, the
atlantodental interval should be within 3 mm. Anterior widening of > 5
mm in flexion suggests an incompetent TAL requiring posterior surgical
instrumented fixation.5 When an atlas fracture is associated
with an axis fracture, patients may undergo external immobilization to
allow C1 to heal prior to surgical repair of C2. Surgical stabilization
of the C1-C2 motion segment is usually achieved through posterior
fixation (Figure 4), but can be achieved via a single anterior odontoid
screw if the dens fracture is isolated (Figure 5). Regardless of the
surgical approach, postoperative assessment of stability with
radiographs is required.Vertebral artery injury during posterior
craniocervical fusion, which complicates 1.3% to 4.1% of cases, is most
common in cases of high-riding vertebral arteries.7
Rotary subluxation of C1 on C2
rotary subluxation in adults is rare and typically presents following
MVA. The presence and extent of anterior displacement of C1 is important
for treatment planning.8 However, dynamic CT for traumatic rotary subluxation of C1 on C2 is rarely indicated.9
Cervical traction in rigid cervical bracing is successful in most
cases. Atlantoaxial rotary subluxation in children, an atraumatic
injury, which typically occurs following upper pharyngeal infections, is
a different entity.
C2 fractures and epidemiology
C2 fractures represented 18.7% of cervical spine fractures in a series of 340 axis fractures.10 Automobile collisions are the most frequent mechanism of injury, followed by falls.10,11 Together these two mechanisms account for 85% of all C2 fractures.10 Overall 34% of patients with C2 fractures have an additional spinal fracture, with C1 fractures the most common.10,12 The distribution of C2 fracture consists of odontoid 59%, hangman’s 22%, and nonodontoid, nonhangman’s fractures 20%.10 Other series have shown similar incidence of the various types of C2 fractures.11,13 Odontoid fractures have increased incidence relative to other C2 fractures with advancing age.10,12 Nonodontoid,nonhangman’s
fractures, which encompass fractures of the vertebrae inferior to the
dens and anterior to the pedicle, represent an important subset of
fractures and differing classification systems exist.14-17
Treatment (surgery versus bracing) and surgical approach (anterior
versus posterior) vary greatly depending on the anatomical location of
the C2 fracture and degree of fracture displacement or ligamentous
disruption. Isolated lamina and spinous process fractures at C2 are
The dens fracture
classification scheme, which was devised by Anderson and D’Alonzo in
1974, divides dens fractures into types I,II, and III. This system
assists in determining prognosis and making treatment decisions.18 The
type I fracture is rare, seen in only 2 of 49 cases in the original
series and 2 of 340 in the largest series published to date.10,18
The proposed etiology is avulsion of the insertion of the alar ligament
on the dens resulting in an oblique fracture of the dens tip as shown
in Figure 6.18 Type I fractures heal without operative intervention.10,18 Six weeks of a rigid cervical collar is often utilized.
Type II fractures, the most common dens fracture subtype, extend through the base of the dens (Figure 6).10,11,13,18,19 Type II fractures are the most prone to nonunion with conservative management.13 Odontoid displacement > 6 mm correlates with failure of nonoperative management.10,11,13 The degree of angulation of the odontoid has also been shown to contribute to nonunion.19 Patient age > 60 years and active smoking have shown variable correlation with incidence of nonunion.10,11,13,19 Nondisplaced
type II fractures are usually managed with a trial of HALO
stabilization. Type II fractures with anterior or posterior translation
or angulation that do not reduce in closed traction is an indication for
surgical stabilization via posterior occiput-C2, posterior C1-C2
fusion, or anterior odontoid screws. Transverse atlantal-ligament injury
may coexist with dens fracture and is associated with nonunion and
instability.20 In the setting of TAL injury, posterior C1-C2
fusion is indicated. Anterior odontoid screw fixation does not
immobilize the C1-C2 joint and is considered poorly effective for C1-C2
instability arising from TAL injury.21 Some studies have questioned this, however.22
type III fractures, the fracture orientation is transverse through the
superior aspect of the body (Figure 6). Type III fractures have a better
outcome with nonoperative management than type II fractures, perhaps
due to the large contact area at the fracture line with cancellous bone.10,11,13,18 First-line treatment remains 8 to 12 weeks of cervical hard collar or HALO immobilization.
type IIA fracture subtype consists of a small bony fragment or
fragments at the base of a dens fracture, as shown in Figure 6. This
subtype may not heal with nonoperative management.23
Axis ring fractures
ring fractures have been referred to as “hangman’s fractures” due to
the similarities with fractures seen in persons executed by judicial
hanging.24 However, C2 ring fractures caused by hanging also
have a distraction component, which is not a major component of typical
traumatic etiology of C2 ring fractures.25 Some authors
reserve the term hangman’s fracture for those involving the pars
interarticularis, referred to more precisely as traumatic
spondylolisthesis.16 C2 ring fractures, which can be due to
flexion and extension mechanisms, typically widen the central canal at
the C2 level and thus rarely cause permanent paralysis.25-27 Fractures of the C2 ring are nearly always bilateral and frequently asymmetric.26
Effendi was the first to categorize these fractures using the broader definition of the C2 ring.26 This
system is still in use with little modification. Francis et al have
also proposed a classification system of traumatic spondylolisthesis.25 The
systems are similar in that both evaluate angulation and displacement
of the C2 body as a way of evaluating the competence of the supporting
ligamentous structures and the stability of the fracture. The Effendi
classification divides lesions into 3 types:
Type I: “hairline” fractures of the C2 ring with minimal C2 body displacement (Figure 7).
II: C2 fracture with displacement of the fragment anterior to the ring
fracture with flexion, extension, or anterolisthesis (Figure 8).
III: C2 fracture with displacement of the anterior fragment with the C2
body in flexion as well as locked C2-C3 facet joints (Figure9).
Levine and Edwards subsequently modified the Effendi classification by dividing the type II fractures into type II and type IIA.27 Type
II fractures are characterized by both angulation and displacement of
the C2 body; and were thought to be caused by initial
hyperextension-axial load followed by flexion and compression. The
flexion and compression forces resulted in the frequent (22 of 29
cases)coexistence of C3 anterosuperior body fractures.27 Type
IIA injuries, which are thought to be due to flexion and distraction,
have minimal displacement, but marked angulation, as shown in Figure 10.
Type II fractures can be successfully reduced with traction. Type I and
Type II fractures can be successfully managed in the vast majority of
cases with 8 to 12 weeks of cervical bracing. Type IIA and Type III
fractures are indications for surgical stabilization of the C2-C3 motion
segment. When the fracture dislocation, angulation, or translation can
be reduced in traction, a C2-C3 anterior cervical discectomy and fusion
can be performed. Alternatively, posterior cervical fusion with C3
lateral mass screws and lag screws placed through the pars fracture into
the C2 body can be utilized to achieve C2-C3 segment stability.
However, the application of traction in type IIA injuries results in
increased distraction and thus is to be avoided.27
Axis body fractures
less common than dens and C2 ring fractures, C2 body fractures are not
uncommon. Benzel described C2 body fractures from a variety of
mechanisms. Type 1 and 2 are both vertically oriented fractures in the
coronal and sagittal planes respectively.14 In type 1
fractures(Figure 11), the fracture extends through the posterior C2
vertebral body rather than the pars interarticularis extension of the
hangman’s fracture.14,16 Type 2 fractures (Figure 11), which
extend through the junction of the body and the pedicle with variable
comminution of theC2 body, are due to axial loading, commonly following a
blow to the skull vertex.14
Teardrop fractures of C2
“Teardrop” fractures are uncommon injuries of C2.28-30
All result in a triangular fracture fragment at the anteroinferior
corner of the vertebral body. The 3 types of C2 teardrop fractures are
the extension teardrop fracture, the hyperextension dislocation, and the
flexion teardrop. Flexion teardrop injuries are more common in the
lower cervical spine and are unstable injuries. They are associated with
splaying of the spinous processes and posterior ligamentous injury. The
hyperextension teardrop is differentiated from the hyperextension
dislocation by the morphology of the avulsed fracture fragment.31 Both
fragments avulse from the anteroinferior corner of the vertebral body.
In the extension teardrop fracture the craniocaudal length of the
fragment is greater or equal to the transverse length.The fracture
fragment may be fairly large.30 Conversely, hyperextension
dislocations are greater in transverse length. Flexion teardrop injuries
almost always represent 3-column ligamentous injury with C2-C3
instability, requiring operative intervention. Either an anterior or
posterior approach as described above can be utilized. The extension
teardrop fracture of C2 is typically without cord injury and heals with
nonoperative management.29,30 Conversely, hyperextension dislocation often causes central cord syndrome.31,32
Of note, the alignment of the vertebral bodies is often normal in
hyperextension dislocation in spite of the injury’s seriousness and lack
stabilizing structures fail in the cervical region, devastating
neurologic sequelae can occur, including high-level tetraplegia.
Tetraplegia occurs in 1:10 spinal cord injuries, but results in 80% of
direct medical costs of spinal cord injury. The incidence of
trauma-induced spinal injury has not changed significantly over the past
3 decades, and the cervical region is the most commonly injured.33
Given the importance of the atlantoaxial joint and the frequency of
cervical region injury, it is essential to recognize subtle differences
in fracture patterns which convey critical information regarding spine
- Jacobson ME, Khan SN, An HS. C1-C2 posterior fixation: Indications, technique, and results. Orthop Clin North Am. 2012;43:11-18.
- Koller H, Resch H, Tauber M, et al. A biomechanical rationale for
C1-ring osteosynthesis as treatment for displaced Jefferson burst
fractures with incompetency of the transverse atlantal ligament. Eur Spine J. 2010;19:1288-1298.
- Spence KF Jr, Decker S, Sell KW. Bursting atlantal fracture associated with rupture of the transverse ligament. J Bone Joint Surg Am.1970;52:543-549.
- Jefferson G. Fracture of the atlas vertebra: Report of four cases and a review of those previously recorded. Br J Surg. 1919;7:407-422.
- Canale ST, Beaty JH eds. Campbell’s Operative Orthopaedics, 11th
ed. Chapter 35: Fractures, dislocations, and fracture-dislocations of
the spine. Maryland Heights, MO: Mosby; 2007:1761-1830.
CA, Greene KA, Sonntag VK. Injuries involving the transverse atlantal
ligament: Classification and treatment guidelines based upon experience
with 39 injuries. Neurosurgery. 1996;38:44-50.
- Lall R, Patel NJ, Resnick DK. A review of complications associated with craniocervical fusion surgery. Neurosurgery. 2010;67:1396-1402; discussion 1402-1403.
- Fielding JW, Hawkins RJ. Atlanto-axial rotatory fixation: Fixed rotatory subluxation of the atlanto-axial joint. J Bone Joint Surg Am. 1977;59:37-44.
- Bono CM, Vaccaro AR, Fehlings M, et al. Measurement techniques for upper cervical spine injuries. Spine. 2007;32:593-600.
- Greene KA, Dickman CA, Marciano FF, et al. Acute axis fractures: Analysis of management and outcome in 340 consecutive cases. Spine.1997;22:1843-1852.
MN, Browner C, Sonntag VKH. Axis fractures: A comprehensive review of
management and treatment in 107 cases. Neurosurgery. 1985;17:281-290.
- Ryan MD, Henderson JJ. The epidemiology of fractures and fracture-dislocations of the cervical spine. Injury. 1992;21:38-40.
- Hadley MN, Dickman CA, Browner C, Sonntag VK. Acute axis fractures: A review of 229 cases. J Neurosurg. 1989;71:642-647.
- Benzel EC, Hart BL, Ball PA, et al. Fractures of the C-2 vertebral body. J. Neurosurg. 1994; 81:206-212.
- Fujimura Y, Nishi Y, Kobayashi K. Classification and treatment of axis body fractures. J Orthop Trauma. 1996;10:536-540.
- Burke JT, Harris JH. Acute injuries of the axis vertebra. Skeletal Radiol. 1989;18:335-346.
- Jakim I, Sweet MBE. Transverse fracture through the body of the axis. J Bone Joint Surg Br. 1988;70:728-729.
- Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974;56:1663-1674.
- Clark CR, White AA. Fractures of the dens. A multicenter study. J Bone Joint Surg Am. 1985;67:1340-1348.
- Greene KA, Dickman CA, Marciano FF, et al. Transverse atlantal ligament disruption associated with odontoid fractures. Spine. 1994;19:2307-2314.
- Pryputniewicz DM, Hadley MN. Axis fractures. Neurosurgery. 2010;66:68-82.
- Ebraheim HA, Fow J, Xu R, Yeasting RA. The location of the pedicle and pars interarticularis in the axis. Spine. 2001;26:E34-E37.
- Hadley MN, Browner CM, Liu SS. New subtype of acute odontoid fractures (type IIA). Neurosurgery. 1988;22(1 Pt 1):67-71.
- Schneider RC, Livingston KE, Cave AJE, et al. “Hangman’s fracture” of the cervical spine. J Neurosurgery. 1965;22:141-154.
- Francis WR, Fielding JW, Hawkins RJ, et al. Traumatic spondylolisthesis of the axis. J Bone Joint Surg. 1981;63-B:313-318.
- Effendi B, Roy D, Cornish B, et al. Fractures of the ring of the axis: A classification based on the analysis of 131 cases. J Bone Joint Surg Br. 1981;63-B:319-327.
- Levine AM, Edwards CC. The management of traumatic spondylolisthesis of the axis. J Bone Joint Surg Am. 1985;67:217-226.
- Boran S, Hurson C, Gul R, et al. Functional outcome following teardrop fracture of the axis. Eur J Orthop Surg Traumatol. 2005;15:229-232.
- Korres DS, Zoubos AB, Kavadias, GC, et al. The “tear drop” (or avulsed) fracture of the anterior interior angle of the axis. Eur Spine J. 1994;3:151-154.
- Watanabe M, Sakai D, Yamamoto Y, et al. Clinical features of the extension teardrop fracture of the axis: Review of 13 cases. J Neurosurg Spine. 2011;14:710-714.
- Edeiken-Monroe B, Wagner LK, Harris JH Jr. Hyperextension dislocation of the cervical spine. AJR Am J Roentgenol. 1986;146:803-808.
JS, Harris JH, Mueller CF. The significance of prevertebral soft tissue
swelling in extension teardrop fracture of the cervical spine. Emergency Radiology. 1997;4:132-139.
- Bucholz RW, Heckman JD, Court-Brown CM eds. Rockwood & Green’s Fractures in Adults. 6th edition. Philadelphia, PA: Lippincott, Williams and Wilkins; 2006.