Posterior Perspective of the Fourth Lumbar Vertebra

Description

Centered in the lower lumbar spine, the fourth lumbar vertebra (L4) is highlighted from a posterior perspective, with its spinous process projecting posteriorly in the midline between the laminae and flanked laterally by the transverse processes. Superior and inferior to L4, adjacent lumbar vertebrae frame the interspinous spaces and align toward the lumbosacral junction. Inferiorly, the sacrum forms the posterior wall of the pelvic inlet, its median sacral crest continuing the line of spinous processes. Facet (zygapophysial) joints sit posterolaterally, where the inferior articular processes of L4 meet the superior articular processes of L5. Posterior anatomy at L4 matters because it is where palpation, imaging localization, and posterior approaches intersect. The L4 spinous process and the L4 to L5 interspace are common surface landmarks used to count levels on radiographs and to target procedures under fluoroscopy, while the facet orientation at this level influences patterns of lumbar spondylosis and contributes to degenerative spondylolisthesis at L4 to L5. Radicular pain from an L4 to L5 disc herniation often tracks to the L5 nerve root, but posterior element hypertrophy (facet arthropathy and ligamentum flavum thickening) can also narrow the lateral recess and central canal. Small details decide diagnoses. Use this illustration in gross anatomy and musculoskeletal modules when teaching lumbar vertebral morphology, facet joints, and the transition to the sacrum, or in radiology and spine surgery content that explains level identification, posterior decompression, and facet-mediated low back pain. It also fits patient education materials for L4 to L5 stenosis and targeted injections. Anatomical accuracy verified by SciePro's Medical Advisory Board.