Spondylolisthesis: AI-Powered Imaging Analysis

The Meyerding classification quantifies the degree of vertebral slip as a percentage of the inferior endplate of the superior vertebra. Grade I is 0–25% slip, grade II is 26–50%, grade III is 51–75%, grade IV is 76–100%, and spondyloptosis (grade V) is greater than 100% where the upper vertebra has completely fallen off the lower. Grades I–II are typically managed conservatively with physical therapy and activity modification, with surgery reserved for persistent neurological deficits or intractable pain. Grades III–IV generally require surgical reduction and instrumented posterolateral fusion, often combined with interbody reconstruction. High-grade slips in skeletally immature patients carry risk of progression and may require prophylactic fusion.

Standing lateral radiographs remain the primary tool for measuring slip percentage and assessing dynamic instability on flexion-extension views — a greater than 4 mm change in slip or greater than 10° of angular change on dynamic films confirms segmental instability. MRI best evaluates the neural consequences: foraminal stenosis compressing the exiting root, central canal narrowing, disc degeneration (Pfirrmann grading), and Modic endplate changes at the slipped level. CT with or without myelography delineates the pars interarticularis defect in isthmic spondylolisthesis (spondylolysis) and helps characterize the bony anatomy for pre-surgical planning. SPECT bone scanning is useful in adolescents to detect metabolically active stress reactions before frank pars fracture occurs.

Isthmic spondylolisthesis results from a pars interarticularis defect (spondylolysis), typically occurring at L5–S1, and is common in adolescent athletes involved in hyperextension sports such as gymnastics and football. The slip can occur in young patients without disc degeneration. Degenerative spondylolisthesis occurs most often at L4–L5 in adults over 50, predominantly in women, and results from facet joint degeneration and disc incompetence without a pars defect — meaning the posterior elements remain intact, limiting slip to grade I–II but causing more pronounced spinal stenosis. Dysplastic spondylolisthesis is congenital and associated with sacral or L5 arch deficiency. Treatment strategy differs because degenerative cases more often require decompression for stenotic symptoms, while isthmic cases may require repair of the pars defect in younger patients.