AJR 2001; 176:978
© American Roentgen Ray Society
Trauma Cases from Harborview Medical Center |
A Complex Atlantoaxial Fracture with Craniocervical Instability
A Case with Bilateral Type 1 Dens Fractures
Y. Marc Bellis1,
Ken F. Linnau2 and
F. A. Mann2
1
Department of Emergency Medicine, University of Washington/Madigan Army
Medical Center, 9040 Reid St., Fort Lewis, Tacoma, WA 98431-1100.
2
Department of Radiology, Harborview Medical Center, 325 Ninth Ave., Box
359728, Seattle, WA 98104-2499.
Received August 29, 2000;
accepted after revision August 29, 2000.
This is another in the continuing series on radiology in trauma cases from
the Harborview Medical Center. Editors: Fred A. Mann, Eric J. Stern, and Lee
B. Talner.
Address correspondence to F. A. Mann.
Introduction
A 17-year-old girl presented with right upper extremity weakness after
being ejected during a high-speed motor vehicle collision. She sustained a
complex atlantoaxial injury, consisting of an unstable C1 burst fracture,
bilateral type I dens fractures, and distraction between the occiput and C2
(Fig.
1A,1B,1C).
She developed quadriplegia, bradycardia, and respiratory failure requiring
endotracheal intubation that improved after emergent C1 laminectomy and
occiput to C3 fusion.
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Fig. 1A. —17-year-old girl who sustained complex atlantoaxial injury
with bilateral type I dens fractures in high-speed motor vehicle collision.
Axial CT scan through C1 shows bilateral type I dens fractures as flake
avulsions of alar ligament insertions (arrows) and anterior component
of unstable Jefferson's burst fracture.
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Fig. 1B. —17-year-old girl who sustained complex atlantoaxial injury
with bilateral type I dens fractures in high-speed motor vehicle collision.
Coronal reformations from CT scans of craniocervical junction show bilateral
type I dens fractures (arrows) and asymmetric widening of C0-C1 and
C1-C2 joint spaces associated with atlantooccipital dissociation.
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Fig. 1C. —17-year-old girl who sustained complex atlantoaxial injury
with bilateral type I dens fractures in high-speed motor vehicle collision.
Coronal reformations from CT scans of craniocervical junction show bilateral
type I dens fractures (arrows) and asymmetric widening of C0-C1 and
C1-C2 joint spaces associated with atlantooccipital dissociation.
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Discussion
Injuries involving the occipitocervical junction are often unstable and
rapid diagnosis facilitates early stabilization and reduces the risk of
subsequent iatrogenic neurological injury
[1]. More than one third of
high-energy C1 fractures are associated with contiguous craniocervical
injuries. Combined C1-C2 injuries more frequently sustain neurological
deficits than isolated C1 or C2 fractures. Treatment of complex atlantoaxial
fractures is also different from isolated atlas or axis fractures
[2]. Thus, recognition of one
fracture must trigger a careful search for contiguous injuries, including
those to the craniocervical junction.
The paired alar ligaments prevent translation of the occiput from the upper
cervical vertebrae and inhibit excessive lateroflexion and rotation of the
atlantoaxial joint. A type I dens fracture represents an avulsion fracture of
the alar ligament from its insertion site on the dens and occurs by
distraction, rotation, or a combined mechanism
[3]. Although type I fractures
are uncommon and their clinical significance is commonly dismissed
[4], they may not be
inconsequential. Avulsion of one or both of the alar ligaments is well
recognized in fatal atlantooccipital dislocation in the setting of high-energy
forces, such as a high-speed motor vehicle collision or a fall
[5]. Survival after traumatic
atlantooccipital dislocation with a unilateral type I dens fracture has also
been reported [6].
Adjunctive imaging may be necessary to examine atlantooccipital instability
due to type I dens fractures with or without other concomitant cervical
vertebral fractures. Findings on CT include distraction or subluxation at
either or both of the atlantooccipital or atlantoaxial joints (Figs.
1B and
1C). MR imaging findings
suggestive of biomechanical instability include loss of preclival fat on
T1-weighted sagittal sequences and fluid-sensitive sequences, showing
precervical edema and hemorrhage, epidural hematoma, abnormal joint-space
signal, and abnormal signal of the brainstem and spinal cord
[1]. For patients without
clinical instability, integrity of the craniocervical junction may be assessed
by the "stretch" test, which is graded incremental axial traction.
A stretch test that detects pathologic dynamic diastasis (an increase of
dens—basion distance of 
1.7 mm) between the basion and intact tip of
the dens provides evidence of craniocervical instability
[7].
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Introduction
Discussion
