Isthmic spondylolisthesis is most specifically due to which pathology?

• A. Pars interarticularis defect (stress fracture)
• B. Disc herniation
• C. Facet joint osteoarthritis
• D. Spinal stenosis due to hypertrophy

Answer: (B)

At the heart of isthmic spondylolisthesis is a defect in the pars interarticularis, usually a stress fracture from repetitive extension. When this defect is bilateral, the vertebral body can slip forward over the vertebra below, creating spondylolisthesis. This condition is most common in adolescents and young adults who engage in spine-hyperextension sports, where the pars may fatigue and fracture. Disc herniation involves herniation of the intervertebral disc material and can cause nerve compression, but it does not initiate the forward slippage seen in isthmic spondylolisthesis. Degenerative changes like facet joint osteoarthritis or spinal stenosis due to hypertrophy tend to occur with aging and contribute to symptoms differently, rather than being the primary cause in this condition. Imaging often shows the pars defect on oblique views (the “collar” on the Scotty dog) and the amount of slip is graded on lateral views using Meyerding.