In cervical spondylolisthesis, which vertebral component is defective?

• A. Lamina
• B. Vertebral body
• C. Pars interarticularis
• D. Pedicle

Answer: (D)

Spondylolisthesis arises when the pars interarticularis develops a defect, allowing one vertebra to slip forward relative to the one below. In the cervical spine, this is classically seen with a pars interarticularis fracture of C2 (Hangman’s fracture), which permits anterior displacement of C2 on C3. The lamina forms the posterior arch and its injury would affect the posterior elements or the canal roof rather than permit slippage. The vertebral body would have to fracture or collapse to cause different problems, not the characteristic slippage from a pars defect. The pedicle, while important for stability, is not the typical site allowing vertebral slippage. Thus, the defect is in the pars interarticularis.