The multifidus muscles are a group of relatively short and small triangular-shaped deep back muscles located on either side of the spine in the groove between the spinous and transverse processes of the vertebrae. The multifidus muscles extend from the cervical to the lumbar spine.

Together with the semispinalis and rotatores muscles, they comprise the transversospinal muscle group. They are shorter than the semispinalis but longer than the rotatores. Moreover, the multifidus are the thickest muscles in the group.

Each multifidus muscle extends between the transverse and spinous processes of the vertebrae, bridging over two to five vertebral levels. These muscles provide several movements of the spine, including extension when they contract on both sides and lateral flexion and rotation when they contract only on one side.

This muscle group is subdivided into smaller portions based on the regions these muscles occupy - multifidus cervicis, multifidus thoracis and multifidus lumborum.

Multifidus cervicis

Origin: superior articular processes of the fourth to seventh cervical vertebrae (C4 - C7).

Insertion: fibers extend superomedially and insert into the spinous processes of the second to fifth cervical vertebrae (C2 - C5).

Action: bilateral contractions - extension of the cervical spine; unilateral contractions - lateral flexion of the cervical spine to the same side (ipsilateral), rotation of the cervical spine to the opposite side (contralateral). These muscles also stabilize the cervical spine.

Innervation: medial branches of the dorsal rami of the spinal nerves.

Blood supply: vertebral, deep cervical and occipital arteries.

Multifidus thoracis

Origin: transverse processes of the thoracic vertebrae.

Insertion: fibers extend superomedially and insert variably on the spinous processes of the vertebrae two to five levels above their origin.

Action: bilateral contractions - extension of the thoracic spine; unilateral contractions - lateral flexion of the thoracic spine to the same side (ipsilateral), rotation of the thoracic spine to the opposite side (contralateral). They also stabilize the thoracic spine.

Innervation: medial branches of the dorsal rami of the spinal nerves.

Blood supply: dorsal branches of the posterior intercostal and subcostal arteries, which are direct branches of the thoracic aorta.

Multifidus lumborum

Origin: mammillary and transverse processes of the lumbar vertebrae, dorsal surface of the sacrum. Additionally, some fibers also arise from the posterior superior iliac spine of the ilium and posterior sacroiliac ligament.

Insertion: fibers extend superiorly and insert on the spinous processes of the vertebrae that are two to five levels above the origin sites.

Action: bilateral contractions - extension of the lumbar spine; unilateral contractions - lateral flexion of the lumbar spine to the same side (ipsilateral), rotation of the lumbar spine to the opposite side (contralateral).

Innervation: medial branches of the dorsal rami of the spinal nerves.

Blood supply: lumbar and lateral sacral arteries that are direct branches of the abdominal aorta and internal iliac artery, respectively.

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Multifidus muscles