Which imaging finding is most characteristic of a pars interarticularis defect?

Which imaging finding is most characteristic of a pars interarticularis defect?

• A. Scotty dog fracture sign on oblique views
• B. Spondylolysis of the pars interarticularis seen on lateral views
• C. Schmorl node on MRI
• D. Facet arthrosis on AP view

Answer: (A)

On oblique lumbar radiographs, the pars interarticularis forms the neck of a “Scottie dog” in the classic appearance. A fracture through the pars shows up as a break or collar around the neck, known as the Scotty dog fracture sign, which is the most characteristic and widely recognized clue for a pars interarticularis defect (spondylolysis). Other findings point to different problems: a Schmorl node is endplate herniation of disc material seen best on MRI, not the pars; facet arthrosis reflects degenerative changes of the facet joints visible on various views, not a pars defect. While a pars defect can be seen on lateral views, the oblique view’s Scotty dog sign is the hallmark imaging feature.

On oblique lumbar radiographs, the pars interarticularis forms the neck of a “Scottie dog” in the classic appearance. A fracture through the pars shows up as a break or collar around the neck, known as the Scotty dog fracture sign, which is the most characteristic and widely recognized clue for a pars interarticularis defect (spondylolysis). Other findings point to different problems: a Schmorl node is endplate herniation of disc material seen best on MRI, not the pars; facet arthrosis reflects degenerative changes of the facet joints visible on various views, not a pars defect. While a pars defect can be seen on lateral views, the oblique view’s Scotty dog sign is the hallmark imaging feature.