Musculoskeletal Imaging

Clasp-knife deformity

a constellation of findings in degenerative disease of the spine characterized by hypertrophy of the spinous process of the fifth lumbar vertebra, which extends through a spina bifida defect into the spinal canal on hyperextension of the back (Fig.1). This deformity is well seen with radiography, CT scanning and MR imaging.

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Fig.1

AP radiograph of the lumbosacral junction demonstrates hypertrophy of the spinous process of the fifth lumbar vertebral body (arrow) with incomplete ossification of the posterior elements of the adjacent S1 vertebra (arrowheads).
Clasp-knife deformity, Fig.1