Iliocostalis muscles

Origin: Sacrum/Illiac Crest/Spinous Processes of lower lumbar/thoracic vertebrae

Insertion: Ribs

Artery: Lateral sacral artery

Function: extending and laterally flexing the lumbar spine.

Description:

The iliocostalis muscle is part of the erector spinae muscle group, which is crucial for maintaining posture and facilitating movements of the vertebral column, with its intricate innervation and segmental structure allowing for coordinated spinal movements. It is divided into three parts: iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum.

1. Iliocostalis cervicis: This portion originates from the angles of the upper ribs and inserts into the transverse processes of the cervical vertebrae. It functions to extend and laterally flex the cervical spine.

2. Iliocostalis thoracis: This segment originates from the lower ribs and inserts into the upper ribs and transverse processes of the lower cervical vertebrae. It plays a role in extending and laterally flexing the thoracic spine.

3. Iliocostalis lumborum: This part originates from the iliac crest, sacrum, and lumbar vertebrae, and inserts into the lower ribs. It is involved in extending and laterally flexing the lumbar spine.

The innervation of the iliocostalis muscle is segmental, with nerves arising from the dorsal rami of the spinal nerves at each corresponding level. The nerves to the iliocostalis muscles (NICs) run caudally and enter the muscle at points shifted inferiorly by one segment level compared to their origin.[1-2] This segmental innervation pattern is consistent across different regions of the spine, although the complexity and overlap of muscle segments can vary.[2]