Longissimus

The longissimus is the intermediate and largest of the three longitudinal muscle columns that form the erector spinae. It lies between iliocostalis laterally and spinalis medially and extends through much of the length of the back, from the lumbosacral region to the skull.

Longissimus is divided into three main parts: longissimus thoracis, longissimus cervicis, and longissimus capitis. Together, these parts form a continuous longitudinal system that extends and laterally flexes the vertebral column. The superior portion also acts directly on the head and neck.

Location

Longissimus occupies the central column of the erector spinae on each side of the vertebral column. Its position is particularly useful for understanding the organization of the intrinsic back muscles: iliocostalis lies lateral to it, while spinalis lies medial to it.

The muscle extends from the lumbosacral region through the thoracic and cervical regions. Its most superior fibers reach the mastoid process of the temporal bone. This extensive vertical course makes longissimus the longest of the erector spinae columns.

Like the other erector spinae muscles, longissimus belongs to the intermediate layer of the intrinsic back muscles. It lies deep to more superficial back and neck muscles and superficial to much of the transversospinalis group.

Structure

The longissimus is not a single uninterrupted muscle belly. It consists of numerous overlapping fascicles arranged into regional parts according to their attachments. These are longissimus thoracis, longissimus cervicis, and longissimus capitis.^[1]

Longissimus thoracis

Longissimus thoracis is the largest and most inferior part. Despite its name, it extends through both the lumbar and thoracic regions. Its fibers arise from the common erector spinae origin and related lumbosacral attachments and ascend to the lumbar and thoracic transverse processes and the ribs.

Detailed anatomical descriptions may distinguish lumbar and thoracic portions within longissimus thoracis. The lumbar fascicles are associated particularly with the accessory and transverse processes of the lumbar vertebrae, while the thoracic fascicles extend to the thoracic transverse processes and adjacent ribs.

Longissimus cervicis

Longissimus cervicis continues the column into the neck. It consists of muscular and tendinous fascicles extending from the upper thoracic transverse processes to the transverse processes of the cervical vertebrae.

Its position between the thoracic spine and cervical transverse processes allows it to contribute directly to extension and lateral flexion of the cervical vertebral column.

Longissimus capitis

Longissimus capitis is the most superior part of the longissimus. It arises from the upper thoracic and lower cervical region and ascends toward the skull, passing along the lateral side of semispinalis capitis before attaching to the mastoid process.

Unlike the thoracis and cervicis portions, longissimus capitis acts directly on the head because of its cranial attachment. Its mastoid insertion also places it near the insertions of splenius capitis and sternocleidomastoid.

Origin and Insertion

The attachments of longissimus follow its longitudinal organization. Inferior fibers connect the lumbosacral region with the lumbar and thoracic vertebrae and ribs, while progressively superior parts connect the thorax with the cervical spine and skull.

The precise vertebral levels assigned to individual fascicles vary somewhat among anatomical descriptions. The important arrangement is the progressive continuation of the longissimus column from the lumbosacral region to the thoracic spine, from the thorax into the cervical spine, and finally from the upper thoracic and cervical region to the mastoid process.^[1][2]

Innervation

Longissimus is supplied segmentally by the posterior rami of spinal nerves, predominantly through their lateral branches at the corresponding spinal levels. This innervation pattern is characteristic of the intrinsic muscles of the back.

Rather than receiving its motor supply from a single named peripheral nerve, the long muscle column receives branches at multiple levels along its course. Longissimus thoracis receives thoracic and lumbar segmental supply, while the cervical and cranial portions receive branches from cervical posterior rami.^[1]

Blood Supply

The extensive length of longissimus is matched by a segmental arterial supply. In the thoracic region, dorsal branches of the posterior intercostal arteries contribute to the muscle. The lumbar portion receives branches of the lumbar arteries, while the cervical and cranial portions receive branches from arteries supplying the deep posterior neck, including the deep cervical and occipital arterial territories.

This distributed blood supply allows different regions of the muscle to receive vessels locally rather than depending on a single artery running along its entire length.

Relations

The most important relationship of longissimus is its position within the erector spinae. It forms the intermediate column between iliocostalis laterally and spinalis medially.

• Laterally: Iliocostalis.
• Medially: Spinalis and structures closer to the vertebral spinous processes.
• Superficially: Thoracolumbar fascia and overlying extrinsic back muscles at lower levels, with splenius and other superficial posterior neck muscles covering its superior portions.
• Deeply: Transversospinalis muscles and the posterior elements of the vertebral column, depending on the level.

Near the skull, longissimus capitis approaches the mastoid process deep to splenius capitis and near the attachment of sternocleidomastoid. Its position lateral to semispinalis capitis is useful when distinguishing these muscles in the posterior neck.^[1]

Function

The longissimus is a major extensor and lateral flexor of the vertebral column. Because it spans several regions, its effects depend partly on which portions are active.

• Bilateral contraction: Extends the vertebral column and contributes to maintaining the trunk in an upright position.
• Unilateral contraction: Produces lateral flexion of the vertebral column toward the same side.
• Longissimus cervicis: Contributes particularly to extension and ipsilateral lateral flexion of the cervical spine.
• Longissimus capitis: Extends the head when acting bilaterally and contributes to ipsilateral lateral flexion and rotation when acting unilaterally.

The longissimus also contributes to postural control by generating and resisting movement across multiple vertebral levels. Its long fascicular arrangement is suited to producing movement across broader regions of the vertebral column rather than acting only between adjacent vertebrae.^[2]

Anatomical Variations

Variation occurs in the number, size and exact attachments of individual longissimus fascicles. Differences are especially common in the vertebral levels assigned to longissimus cervicis and capitis, which explains why anatomical references may give slightly different cervical and thoracic attachment ranges.

The organization of longissimus thoracis also varies in description. Some anatomical accounts distinguish a lumbar component, sometimes called longissimus lumborum, while others include these fascicles within longissimus thoracis. These differences reflect the overlapping architecture of the erector spinae rather than completely separate muscular systems.

Clinical Significance

Longissimus is readily recognized on cross-sectional imaging as a substantial component of the paraspinal muscle mass. Its intermediate position between iliocostalis and the more medial intrinsic back muscles provides an important landmark on CT and MRI.

Posterior spinal anatomy

Longissimus forms part of the muscular layers encountered during posterior approaches to the thoracic and lumbar vertebral column. Its relationship to iliocostalis, spinalis and the deeper transversospinalis muscles helps define the organization of the paraspinal musculature during dissection and surgical exposure.

Longissimus capitis and the posterior neck

The mastoid attachment of longissimus capitis is particularly useful for understanding posterior neck anatomy. Near its insertion, the muscle lies deep to more superficial muscles attaching around the mastoid region and lateral to semispinalis capitis. These relationships can also be identified with high-resolution ultrasound and cross-sectional imaging.

Muscle injury and paraspinal assessment

Longissimus can be affected by strain, direct trauma, disuse and other processes involving the paraspinal musculature. Because its fibers blend functionally with the other erector spinae columns, symptoms arising from the region cannot always be assigned to longissimus alone on clinical examination.

Atrophy, asymmetry or structural change in the erector spinae may be visible on imaging. Identifying longissimus separately from iliocostalis and the deeper multifidus is therefore useful when evaluating the morphology of the posterior spinal muscles.