AJR 2002; 178:1450
© American Roentgen Ray Society
Trauma Cases from Harborview Medical Center |
A Thoracic Spine Translation Injury with Lateral Facet Dislocation
Ahmed Gharib1,
Gregory Postel1,
Sohail Mirza2 and
F. A. Mann3
1 Department of Radiology, University of Louisville, 530 S. Jackson St.,
Louisville, KY 40202-1675.
2 Department of Orthopaedic Surgery, Harborview Medical Center, University of
Washington School of Medicine, Seattle, WA 98104-2499.
3 Department of Radiology, Harborview Medical Center, 325 Ninth Ave., Box
359728, Seattle, WA 98104-2499.
Received June 26, 2001;
accepted after revision July 10, 2001.
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 20-year-old motorcyclist sustained a complete T3-T4 fracture-dislocation
that resulted in paraplegia. Radiographs of the thoracic spine showed 20% left
lateral translation at T3-T4 (Fig.
1A). CT showed an "empty" right facet and an avulsion
of the anteroinferior corner of the T3 vertebra
(Fig. 1B). Coronal CT
reformations showed a lateral dislocation at T3-T4
(Fig. 1C).
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Fig. 1B. —20-year-old man with T3-T4 lateral translation
fracture-dislocation. Axial CT scan obtained at T3 shows empty right facet
(arrowhead) and avulsion fracture (arrow) of anteroinferior
body.
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Traumatic lateral translation of adjacent thoracolumbar vertebrae results
in marked bio-mechanical instability
[1]. Translation injuries
completely disrupt structural elements of the vertebral column and the
adjacent paravertebral soft tissues
[2]. Associated soft-tissue
damage increases exponentially with the degree of translation, and neurologic
injury is almost certain at thoracic vertebral translations exceeding 20% of
the vertebra width.
Three patterns of thoracolumbar facet dislocation have been described
[1]: anterior subluxation with
anterior facet dislocation, lateral subluxation with lateral facet
dislocation, and acute kyphosis with superior subluxation of the facets. Axial
CT signs include the "empty" or "naked" facet and the
"double vertebra" signs. A small fracture of the anterosuperior or
anteroinferior margin of a vertebral body is often caused by avulsion of the
adjacent anterior longitudinal ligament
[1].
The structural components of the spine—vertebrae, ligaments, and
intervertebral disks—protect the spinal cord and nerve roots. Clinical
evaluation estimates the extent of the compromise in this protective capacity.
Severe injury to the structural elements creates the potential for further
compressive injury to neural tissue under physiologic loads (upright posture
and normal physical activity). Risk assessments for spinal instability are
based on the integrity of the vertebral structural components as visualized on
imaging studies [3,
4].
Conventional radiographs, including the initial chest radiograph, should be
searched for paraspinal hematomas (right or left paraspinal line
abnormalities), focal angulations, and translations of adjacent vertebral
bodies. In the absence of osteophytes, neither paraspinal line normally shows
focal bulging. Focal angulation, shown as two "straight" vertebral
segments intersecting at the injury site, contrasts with the continuous curves
of positional scoliosis or developmental scoliosis. Pathologic translation is
depicted as the loss of continuity of the spinal lines (anterior, posterior,
or lateral).
CT extends radiographic observations, including the detection of occult
fractures, and enables precise fracture characterization to guide surgical
planning. CT allows quantitative assessments of the spinal canal (width of
<10 mm predicts failure of neurologic recovery), the vertebrae (>50%
loss of height supports an anterior surgical procedure), and the integrity of
posterior elements. The latter is important in planning open
reduction-internal fixation techniques (e.g., "fuse short-rod
long"), which use lamina and transverse processes of the two to three
vertebral bodies above and below the injury level for bridging instrumentation
[3].
Soft-tissue injuries better predict outcome than do the associated osseous
disruptions. MR imaging best defines the extent and severity of soft-tissue
disruption. MR sequences should provide maximal information about cord injury
(hematoma, edema, continuity), disk and ligamentous integrity, facet injuries,
and paraspinal musculature.
Facet dislocations are unstable injuries requiring internal fixation and
fusion. Timely diagnosis and complete evaluation of the extent of bone,
ligament, disk, and spinal cord injury are important for therapeutic planning
and prognosis.
References
-
Manaster BJ, Osborn AG. CT patterns of facet fracture dislocations
in the thoracolumbar region. AJR
1987;148:335
-340[Abstract/Free Full Text]
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Lucas MJ, Berg EE. Unilateral thoracic facet dislocation.
Clin Orthop
1997;335:162
-165
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Gellad FE, Levine AM, Joslyn JN, Edwards CC, Bosse M. Pure
thoracolumbar facet dislocation: clinical features and CT appearance.
Radiology
1986;161:505
-508[Abstract/Free Full Text]
-
Berg EE, Gilpin AT. Unilateral jumped thoracic facet.
Spine
1991;16:590
-592[Medline]
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Introduction
References
