Case clasp knife

Clasp-knife deformity is relatively common anomaly found at the lumbosacral junction and characterized by a large midline defect of the posterior arch of the sacrum (usually S1/S2 and occasionally S3) along with hypertrophy (or overgrowth) of the spinous process of the vertebra above (usually L5) 1-2.

When a clasp-knife deformity is accompanied by pain on extension secondary to protrusion of the enlarged spinous process (knife blade) into the sacral spinal canal, it is called clasp-knife syndrome 2.

History and etymology

The term of clasp-knife deformity was coined by G.W. Henry in 1958 as an analogy to the blade of a pocket (clasp) knife folding into its handle 3, 4.

• 1. Chew FS. Skeletal Radiology. Lippincott Williams & Wilkins. (2010) ISBN:. Read it at Google Books - Find it at Amazon
• 2. Goobar JE, Erickson F, Pate D et-al. Symptomatic clasp-knife deformity of the spinous processes. Spine. 1988;13 (8): 953-6. Pubmed citation
• 3. Yochum TR, Rowe LJ. Essentials of Skeletal Radiology. Lippincott Williams & Wilkins. (2005) ISBN:. Read it at Google Books - Find it at Amazon
• 4. Henry GW, Larsen IJ, Stewart SF. The roentgenologic criteria for appraising the human back as an economic asset or liability. The American journal of roentgenology, radium therapy, and nuclear medicine. 79 (4): 658-72. Pubmed