Posterior Inferior Serratus

Description

Posterior trunk anatomy is presented with the serratus posterior inferior muscle lying deep to the latissimus dorsi and inferior to the lower fibers of trapezius, spanning from the lower thoracic and upper lumbar midline toward the inferior borders of ribs 9 through 12. Medially, its aponeurotic origin blends with the thoracolumbar fascia and spinous processes, then the fibers run superolaterally to their serrated costal insertions. Superficial gluteal contouring is visible inferiorly, while the paraspinal mass sits just lateral to the implied midline. Fiber direction is unambiguous. Clinically, the serratus posterior inferior matters less for gross power than for understanding the deep dorsal plane: it forms part of the layered relationship between latissimus dorsi, thoracolumbar fascia, and the rib cage, a junction often explored when teaching posterior thoracolumbar anatomy and segmental mechanics. Pain generators in this region are frequently attributed to thoracolumbar fascia strain, myofascial trigger points near the rib angles, or costovertebral irritation, and a clear view of the muscle’s rib attachments helps differentiate these patterns from latissimus dorsi tendinous pain or lower thoracic radiculopathy. Small muscle, common confusion. Use this artwork for gross anatomy lab orientation (back dissection and fascia removal), for radiology teaching that correlates muscular layers with ultrasound-guided thoracolumbar fascia plane injections, and for surgical education on posterior approaches where recognizing the latissimus dorsi and deep fascia planes reduces dissection error. Anatomical accuracy verified by SciePro's Medical Advisory Board.