Longissimus Thoracis, Gross Anatomy

Description

Running longitudinally along the posterior thoracic wall, the longissimus thoracis is presented as the lateral column of the erector spinae, lying lateral to spinalis and medial to iliocostalis, with its muscle belly thickest in the mid to lower thorax. Segmental slips extend superiorly and laterally from the lumbar region toward the thoracic transverse processes and adjacent rib angles, while the fibers maintain a predominantly craniocaudal orientation that clarifies its line of pull in trunk extension. Superficial landmarks include trapezius over the upper thorax and posterior deltoid at the shoulder, with the erector spinae mass continuing inferiorly toward the iliac crest and blending visually with the superior gluteal region. Clear separation of longissimus from the transversospinalis group (semispinalis, multifidus, rotatores) matters because these layers are approached and retracted differently in posterior spine surgery and in posterior paraspinal exposure for instrumentation. Persistent low back pain is often linked to paraspinal muscle dysfunction, and longissimus thoracis is a frequent target in electromyography and rehabilitation discussions when examining extensor endurance and lumbar stabilization. This is the muscle that fatigues. Use this posterior back plate for gross anatomy labs, kinesiology instruction on spinal extension and lateral flexion, or as a figure in orthopedic and neurosurgical education materials describing midline versus paramedian posterior approaches and the paraspinal plane. It also suits patient-facing spine care brochures where accurate labeling of deep back muscles prevents the common trapezius-only oversimplification. Anatomical accuracy verified by SciePro's Medical Advisory Board.