Multifidus

The multifidus muscle (Latin: musculus multifidus) is a group of relatively short and small triangular-shaped back muscles located on either side of the spine in the groove between the spinous and transverse processes of the vertebrae. Together with the semispinalis and rotatores, the multifidus muscles belong to the transversospinal group of the deep back muscles. All transversospinal muscles lie in the deep layer of the deep back muscles. The multifidus muscles are shorter than the semispinalis but longer than the rotatores. Moreover, they are the thickest muscles in the group.

Each multifidus muscle stretches between the transverse and spinous processes of vertebrae, and they span over three to six vertebral levels. The multifidus muscles extend from the cervical to the lumbar spine. Therefore, the multifidus muscles are subdivided into three portions based on the spine regions they occupy. These portions are named the cervical multifidus, thoracic multifidus and lumbar multifidus.

Cervical multifidus

Origin

The cervical multifidus muscles originate from the superior articular processes of the fourth to seventh cervical vertebrae (C4 - C7).

Insertion

The fibers of the cervical multifidus extend superomedially and insert on the spinous processes of the second to fifth cervical vertebrae (C2 - C5).

Action

Muscle contractions on both sides (bilateral contractions) extend the cervical spine, while contractions on one side (unilateral contractions) provide lateral flexion (ipsilateral) and rotation of the cervical spine (contralateral). Also, these muscles participate in stabilizing the cervical spine.

Innervation

The cervical multifidus muscles are innervated by the medial branches of the dorsal rami of the spinal nerves.

Blood supply

The multifidus muscles in the cervical region receive arterial blood supply mainly via the vertebral and deep cervical arteries, which arise from the subclavian artery and costocervical trunk, and the occipital artery - a branch of the external carotid.

Thoracic multifidus

Origin

The thoracic multifidus muscles arise from the transverse processes of the thoracic vertebrae.

Insertion

The muscle fibers of the thoracic multifidus extend superomedially and insert on the spinous processes of the vertebrae two to four, sometimes five levels above their origin.

Action

Muscle contractions on both sides (bilateral contractions) extend the thoracic spine, while contractions on one side (unilateral contractions) provide lateral flexion (ipsilateral) and rotation of the thoracic spine (contralateral). Also, these muscles participate in stabilizing the thoracic spine.

Innervation

The thoracic multifidus muscles are innervated by the medial branches of the dorsal rami of the spinal nerves.

Blood supply

The thoracic multifidus muscles are mainly supplied by the dorsal branches of the posterior intercostal and subcostal arteries, which are branches of the thoracic aorta.

Lumbar multifidus

Origin

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

Insertion

The fibers of the lumbar multifidus extend superiorly and insert on the spinous processes of the vertebrae that are two to four, sometimes five levels above the origin sites.

Action

Muscle contractions on both sides (bilateral contractions) extend the lumbar spine, while contractions on one side (unilateral contractions) provide lateral flexion (ipsilateral) and rotation of the lumbar spine (contralateral). Also, these muscles participate in stabilizing the lumbar spine.

Innervation

The multifidus muscles are innervated by the medial branches of the dorsal rami of the spinal nerves.

Blood supply

The lumbar multifidus muscles are mainly supplied by the lumbar and lateral sacral arteries - branches of the abdominal aorta and internal iliac artery, respectively.