A thoracic spine translation injury with lateral facet dislocation.

20-year-old motorcyclist sustained a complete T3–T4 fracture–dislo-cation 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). 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 paraverte-bral 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 dis-location have been described [1]: anterior subluxation with anterior facet dislocation, lateral subluxation with lateral facet disloca-tion, and acute kyphosis with superior sub-luxation of the facets. Axial CT signs include the " empty " or " naked " facet and the " double vertebra " signs. A small fracture of the an-terosuperior or anteroinferior margin of a ver-tebral 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 verte-bral 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 angula-tions, 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 scolio-sis. 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 …