Multifidus Thoracis

Origin, Insertion, Action & Nerve

Attachments explained

The Multifidus Thoracis is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.

Action & function

When the Multifidus Thoracis contracts, it produces the following movements: Stabilizes the vertebrae; extends and rotates the thoracic spine to the opposite side.

As part of the Back group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Multifidus Thoracis receives its nerve supply from the Posterior (dorsal) rami of thoracic spinal nerves.

Because a muscle can only contract when its nerve is intact, injury to the Posterior can weaken or paralyse the Multifidus Thoracis, impairing the movements it normally produces (stabilizes the vertebrae). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Multifidus Thoracis (the OIANS method)

Learn thoracic multifidus by the same rule that governs the whole muscle: transverse process below to spinous process two to four levels above, with short fibres that make segmental stabilisation the priority over movement. The thoracic version simply applies this pattern along the chest region of the spine, so its extension and contralateral rotation are modest supporting actions.

Use it to bridge your understanding between the lumbar and cervical multifidus. It is thinner than the powerful lumbar part yet follows the identical fascicle geometry, which makes it a good reminder that multifidus is one continuous system spanning the column. Keep it layered above rotatores and below semispinalis thoracis so the transversospinales depth order stays clear.

Frequently asked questions

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