Multifidus thoracis muscle

At a glance

English

Multifidus thoracis muscle

Latin (TA2)

Musculus multifidus thoracis

System

Muscle

Region

Back

Side

Paired, left and right

About the multifidus thoracis muscle

Multifidus is a deep back muscle formed by many short bundles stacked along the spine from the sacrum to the axis. It belongs to the transversospinal group, the deep layer that fills the groove between the spinous and transverse processes. In the thoracic region it is thinner than in the lower back and lies under semispinalis thoracis and the erector spinae.

In this part each bundle arises from a thoracic transverse process. It runs upward and inward and attaches to the spinous process of a vertebra two to four levels higher. The deepest fibres are the shortest and the more superficial ones span more segments, so the muscle is layered from deep to superficial.

Because its bundles pass obliquely towards the midline, the muscle can extend the thoracic spine when both sides act and turn it towards the opposite side when one side acts. In practice its main job in the chest region is to control and steady each segment during movement of the trunk and limbs, rather than to produce large movements, since the ribs already limit thoracic motion.

Each segment is supplied by a medial branch of a thoracic dorsal ramus, and blood comes from the dorsal branches of the posterior intercostal arteries. The muscle is rich in muscle spindles and is thought to contribute to the sense of posture. It is lifted from the bone in surgical approaches to the thoracic spine.

Attachments, action and supply

Origin

Transverse processes of the thoracic vertebrae.

Insertion

Spinous processes two to four vertebrae higher.

Action

Steadies and extends the thoracic spine; on one side rotates it towards the opposite side.

Nerve supply

Medial branches of the dorsal rami of the thoracic spinal nerves.

Blood supply

Dorsal branches of the posterior intercostal arteries.