Isthmic Spondylolisthesis is defined by a defect in which spinal structure?

Prepare for the Neuromusculoskeletal II Lecture Exam with detailed study guides, flashcards, and multiple choice questions. Unlock comprehensive insights and enhance your knowledge for success.

Isthmic spondylolisthesis occurs because of a defect in the pars interarticularis, the narrow bridge between the superior and inferior articular processes of a vertebra. When this pars is fractured or defective (often bilaterally), the vertebral body can slip forward over the bone below, producing listhesis. This condition is classically seen in young athletes due to repetitive hyperextension and loading of the lumbar spine, and is often identified on oblique X-rays where a pars fracture can create the “scotty dog” sign with a collar. Other structures—the intervertebral disc or facet joints—can contribute to different forms of spondylolisthesis (degenerative or facet-related instability), but the defining feature of isthmic spondylolisthesis is a defect in the pars interarticularis. Spinous process fractures do not cause anterior slippage.