Double spinous process sign | Radiology Signs

Answer:

The double spinous process sign is the appearance of two spinous process shadows at one level on the frontal cervical radiograph, produced when an avulsed spinous process fragment displaces caudally and is projected below the intact base. It indicates a clay-shoveler fracture, an avulsion of the spinous process of a lower cervical or upper thoracic vertebra, most often C7 and next most often C6 and T1. The injury is classically an avulsion from sudden forced flexion against contracted paraspinal muscles or from repetitive traction in manual work and in sports such as rowing, golf and weightlifting, and it also occurs with direct trauma. It is a stable injury of the posterior elements alone, without neurological risk, and is treated symptomatically, but the label should only be applied once flexion-distraction and other unstable injuries have been excluded, since interspinous widening, facet joint incongruity, anterolisthesis and vertebral body compression all indicate a different and unstable pattern. The fragment is often better seen on the lateral view, and the frontal sign is useful because the lower cervical spine is frequently obscured by the shoulders on that projection. CT is the definitive study in trauma and shows the fracture and any additional injury, and multiple contiguous levels may be involved.

Why is it called so?

The displaced fragment and the residual base of the spinous process appear as two separate shadows on the same frontal image.

Pathophysiology

The spinous processes of the lower cervical vertebrae are the attachment of the ligamentum nuchae and of the trapezius and rhomboid muscles. Sudden or repetitive flexion of the neck while these muscles contract transmits a tensile force through the ligament and muscle insertion. The cortical bone at the tip of the process fails before the ligament does, and the avulsed fragment is pulled inferiorly by the ligamentum nuchae, coming to lie below its original position. Because the fracture involves only the posterior spinous element and leaves the facet joints, laminae and vertebral body intact, the spinal canal and the three columns of stability are unaffected, which is why the injury is stable despite its dramatic appearance.

Alternative names: Clay-shoveler fracture sign; ghost sign of the spinous process

Other associated named signs: Fat C2 sign, the naked facet sign and interspinous widening of flexion-distraction injury