Interspinales muscles

The interspinales muscles are a group of paired muscle fascicles found in the paraspinal portion of the deepest layer of the intrinsic back muscles.

Gross anatomy

The interspinales muscles extend between the spinous processes of two neighboring vertebrae. They are present throughout the entire length of the spine, with one pair of fascicles on each side of the interspinous ligament ¹. They consist of three different muscle categories, each named after their location in the vertebral column. The primary function of the interspinales muscles is to stabilize the spine during movement and maintain body posture ^2,5.

Often a source of contention, most authors consider the interspinales as incapable of generating enough force to produce significant movement. Even though they span the entire length of the vertebral column, they are only properly developed in the cervical and lumbar spine; assisting with extension in those vertebral regions ^1,2,4,5.

Interspinales cervicis 

The interspinales cervicis are paired muscles found deep within the posterior part of the neck and consist of six pairs of muscles.

 Summary

• origin: superior aspects of spinous processes of C3 - T1 vertebrae

• insertion: inferior aspects of spinous processes of C2 - C7 vertebrae

• blood supply: vertebral, deep cervical, transverse cervical and occipital arteries

• innervation: dorsal rami of cervical spinal nerves

• action: extension of cervical spine, stabilization of cervical spine, maintenance of body posture

Origin

The interspinales cervicis muscles originate from the superior aspects of the spinous processes of the 3^rd cervical to 1^st thoracic vertebrae (C3 - T1).

Insertion

The interspinales cervicis are located on either side of the interspinous ligaments. These muscles insert one level above the origin sites on the inferior aspects of the spinous processes of the 2^nd to 7^th cervical vertebrae (C2 - C7).

Arterial supply

The interspinales cervicis receive blood supply from branches of the vertebral, deep cervical, occipital, and transverse cervical arteries. These arteries arise from the subclavian artery, costocervical trunk, external carotid artery, and thyrocervical trunk, respectively ¹.

Innervation

The nerve supply to the interspinales cervicis muscles is provided by the dorsal rami of the cervical spinal nerves.

Action

The interspinales cervicis muscles aid in the extension of the cervical spine and, more importantly, stabilize the cervical spine and maintain a body posture.

Interspinales thoracis

The interspinales thoracis muscles are located deep within the thoracic region of the back. These muscles are typically found in pairs of three, which are usually underdeveloped or even absent ^2,4.

Summary

• origin: superior aspects of spinous processes of T2, T11 and T12 vertebrae

• insertion: inferior aspects of spinous processes of T1, T10 and T11 vertebrae

• blood supply: superior and posterior intercostal arteries, subcostal artery

• innervation: dorsal rami of thoracic spinal nerves

• action: aids in extension of thoracic spine

Origin

The three pairs of the interspinales thoracis muscles originate from the superior aspects of the spinous processes of the 2^nd (T2), 11^th (T11) and 12^th thoracic vertebrae (T12). However, the origin sites of these muscles may vary between individuals ².

Insertion

Each interspinales thoracis muscle insert on the 1^st (T1), 10^th (T10) and 11^th thoracic vertebrae (T11), attaching to the inferior aspects of the spinous processes of the vertebra one level above the respective site of origin.

Blood supply

The muscles are supplied by of the superior and posterior intercostal arteries and subcostal artery. The superior intercostal artery arises from the costocervical trunk while the posterior intercostal artery branches of the superior intercostal artery and, alongside the subcostal artery, the thoracic aorta ^1,3.

Innervation

The interspinales thoracis muscles are innervated by the dorsal rami of the thoracic spinal nerves.

Action

While the interspinales thoracis tend to be underdeveloped muscles, they provide support in extending the thoracic spine ⁵.

Interspinales lumborum

The interspinales lumborum is a group of four paired muscles located deep within the lumbar region of the back.

Summary

• origin: superior aspects of spinous processes of L2 - L5 vertebrae

• insertion: inferior aspects of spinous processes of L1 - L4 vertebrae

• blood supply: lumbar arteries

• innervation: dorsal rami of lumbar spinal nerves

• action: extension of lumbar spine, stabilization of lumbar spine, maintenance of body posture

Origin

The fibers of the interspinales lumborum muscles originate from the superior aspects of the spinous processes of the 2^nd to 5^th lumbar vertebrae (L2 - L5).

Insertion

The interspinales lumborum muscles insert on the inferior aspects of the spinous processes of the adjacent vertebrae one level above the origin site - on the 1^st to 4^th lumbar vertebrae (L1 - L4), accordingly.

Blood supply

The arterial blood supply to the interspinales lumborum muscles is delivered primarily by the lumbar arteries, which are branches of the abdominal aorta.

Innervation

The nerve supply to the interspinales lumborum muscles is provided by the dorsal rami of the lumbar spinal nerves.

Action

The interspinales lumborum muscles maintain body posture by stabilizing the lumbar spine in addition to playing a role in the extension of the lumbar spine.