In isthmic spondylolisthesis, the defect causing forward slip of one vertebral body on the next is located at the:
- A Pedicle (bilateral pedicle fractures)
- B Pars interarticularis (spondylolysis) ✓
- C Facet joint articular surface (facet fracture)
- D Posterior annulus fibrosus with disc herniation
Explanation
Isthmic spondylolisthesis (most common type in young adults and adolescents, particularly L5–S1) results from a fatigue stress fracture of the pars interarticularis (the isthmus connecting the superior and inferior articular processes of the vertebra). This defect — called spondylolysis — allows the vertebral body, disc, and superior articular processes to slip forward relative to the inferior articular processes and the posterior elements below. The oblique view X-ray classically shows the 'Scottie dog' sign with a collar around the dog's neck representing the pars defect. Meyerding grades I–IV (and V/spondyloptosis) quantify the slip.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.