venerdì 5 giugno 2009
Bilateral jumped facets with spinal cord transection
Axial CT scan of the cervical spine demonstrates the naked facet sign, with uncovered articulating processes. A fracture is noted anteriorly on the left.
Sagittal image shows marked subluxation of C6 on C7 with marked narrowing of the spinal canal.
Sagittal images of the right facets. The facets are jumped.
Sagittal T2 and STIR show marked anterior subluxation of C6 on C7, transection of the spinal cord, edema and hemorrhage in the prevertebral soft tissues and spinal cord edema extending from C4 to T1.
Diagnosis: Bilateral jumped facets with spinal cord transection
Bilateral facet joint dislocation is a severe unstable cervical flexion injury. Flexion- rotation injuries can cause dislocation of the vertebral bodies with jumped/locked facets which can be unilateral or bilateral. If the dislocation is not complete, the facets may appear “perched” upon one another. Unilateral facet dislocation more characteristically has a rotatory component and carries a better prognosis.
With complete dislocation, the facets are said to be jumped and/or locked. The integrity of all the spinal ligaments including the posterior longitudinal ligament, the posterior portions of the annulus fibrosus, and the capsular, interspinous and supraspinous ligaments is disrupted. Destabilization of the ligamentous support of the cervical spine allows for the charactersitic >50% anterolisthesis observed. Unfortunately, severe narrowing of the spinal canal and intervertebral foramen occurs with subsequent severe neurologic deficits (in approximately 75% of cases), as seen in this case with spinal cord transection.
The naked facet sign, also referred to as the, “Hamburger Sign” refers to the CT appearance of uncovered articulating processes. Normally, on axial CT, the vertebral facet joint looks like a hamburger with the superior articular process of the vertebra below forming the, “bun” on top of the “meat patty,” and the inferior articular process of the vertebra above forms the bun beneath the patty. When the joint is dislocated, the superior articular facet (top bun of the Hamburger) now lies posteriorly. This is the Hamburger Sign, which can be unilateral or bilateral.
Associated osseous injuries include avulsion of the spinous process above the locked level and small triangular fractures of the anterosuperior corner of the inferior involved vertebral body.