Erector Spinae Muscle

Introduction

The erector spinae is a series of muscles that extend from the sacrum to the neck and is located within the back, which is the largest muscle group in the body. The muscles of this specific group are divided into three different sections, which are the iliocostalis, longissimus and spinalis, which all have different functions.

The erector spinae muscle, also known as sacrospinalis and extensor spinae in some texts is from the deep muscles of the back.

It lies superficial to the transversospinales muscle group and deep to the intermediate group of back muscles (serratus posterior superior and inferior).

The erector spinae muscle extends the vertebreal column.

It is formed of 3 muscles and its fibers run more or less vertically throughout the lumbar, thoracic and cervical regions.

It lies in the groove to the side of the vertebral column.

In cervical region it is covered by nuchal ligament and in thoracic and lumber region by thoracolumbar fascia.

The erector spinae are divided into three groups, from medial to lateral:

• Spinalis muscles
• Longissimus muscles
• Iliocostalis muscles

The function of the spinal erectors is to move the vertebral column. Bilateral contraction of these muscles extends the spine, while unilateral contraction causes lateral flexion (ipsilateral).

They also help to maintain posture by steadying the spine on the pelvis during walking.

Anatomy of Erector Spinae Muscle

Spinalis:

• Is the most medial part just next to the spine. It connects the spinous process of the adjacent vertebrae to each other.
• The spinalis muscles are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves.
• The blood supply to the spinalis muscles comes from the vertebral, deep cervical, occipital, intercostal, and lumbar arteries.
• The function of the spinalis muscles is to extend and laterally flex the cervical and thoracic regions of the spine.

It is divided into 3 parts:

Muscle	Origin	Insertion
Spinalis capitis	Usually blends with semispinalis capitis	With semispinalis capitis
Spinalis cervicis	Spinous process of C7 (sometimes T1 to T2) and ligmentum nuchae	Spinous process of C2 and C3-C4
Spinalis thoracis	Spinous process of T11 to L2	Spinous process of upper thoracic vertebrae

Longissimus:

• It forms the middle part of the erector spinae muscles, lateral to the spinalis.
• The longissimus muscle forms the main meat of the erector group. It attaches along the transverse process of the vertebrae.
• The longissimus muscles have an identical innervation to the spinalis muscles; from the lateral branches of the posterior rami of the adjacent spinal nerves.
• They receive arterial blood from branches of the vertebral, deep cervical, occipital, transverse cervical, intercostal, and sacral arteries.

• The function of the longissimus muscles is to extend and laterally flex (ipsilateral) the spine. Longissimus capitis also helps to rotate the head ipsilaterally.

It is divided into 3 parts:

Muscle	Origin	Insertion
Longissimus capitis	C4-T4 transverse process	Posterior edge of the mastoid process
Longissimus cervicis	T1-T4 transverse process	C2 to C6 transverse process
Longissimus thoraci	Transverse process of lumbar vertebra and blends with iliocostalis in the lumbar region	Transverse process of all thoracic vertebrae

Iliocostalis:

• It is the most lateral part of the erector spinae muscles. It attaches to the ribs.
• Because of it’s lateral position, a tight iliocostalis can bring a hip up, or bring the ribcage down toward the hip.
• Similar to the other erector spinae groups, iliocostalis muscles are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves.
• Arterial supply is via branches of the occipital, deep cervical, vertebral, posterior intercostal, subcostal, lumbar and lateral sacral arteries.
• The function of the iliocostalis muscle is to extend and laterally flex (ipsilateral) the spine.

It is divided into 3 parts:

Muscle	Origin	Insertion
Iliocostalis cervicis	Angle of ribs 3-6	Transverse process of C4-C6
Iliocostalis thoracis	Angle of lower six ribs	Angles of upper six ribs and transverse process of c7
Iliocostalis lumborum	Iliac crest	L1-L4 lumbar transverse processes, angle of 4-12 ribs and thoracolumbar fascia

STRUCTURE OF ERECTOR SPINAE:

• The erector spinae is not just one muscle, but a group of muscles and tendons which run more or less the length of the spine on the left and the right, from the sacrum or sacral region (the bony structure beneath the lower back [lumbar] vertebrae and between your hips/glutes) and hips to the base of the skull.
• They are also known as the sacrospinalis group of muscles. These muscles lie on either side of the vertebral column spinous processes (the bony points up and down the middle of the back) and extend throughout the lumbar, thoracic, and cervical regions (lower, middle, and upper back and the neck).
• The erector spinae is covered in the lumbar and thoracic regions (lower back and lower middle back) by the thoracolumbar fascia, and in the cervical region (neck) by the nuchal ligament.
• This large muscular and tendinous mass varies in size and structure at different parts of the vertebral column. In the sacral region, it is narrow and pointed, and at its origin chiefly tendinous in structure.
• In the lumbar region, it is larger, and forms a thick fleshy mass. Further up, it is subdivided into three columns. They gradually diminish in size as they ascend to be inserted into the vertebrae and ribs.
• Picture a tree trunk branching out left and right.
• The erector spinae is attached to the medial crest of the sacrum to the spinous processes of the lumbar (bony points along your lower back) and the eleventh and twelfth thoracic vertebrae and the supraspinous ligament, to the back part of the inner lip of the iliac crests (the top border of your hips), and to the lateral crests of the sacrum, where it blends with the sacrotuberous and posterior sacroiliac ligaments.
• Some of its fibers are continuous with the fibers of origin of the gluteus maximus muscle.

ACTION:

• Bilateral contractions straighten the back and pull the head posteriorly and are involved in the control of the flexion of the vertebral column.
• Unilateral contraction bends the vertebral column laterally and turns the head towards the contracting side.

Nerve Supply:

• Doral rami of spinal nerves

Blood Supply:

• Branches of the vertebral, deep cervical, occipital, transverse cervical, posterior intercostal, subcostal, lumbar and lateral sacral arteries.

Clinical Importance:

• The ESP block is a newer regional anesthetic that can provide thoracic, abdominal, and even some lower extremity analgesia.
• A versatile block, ESP blocking has been used by anesthesiologists to provide analgesia for a myriad of conditions from chronic shoulder pain to pain following hip surgery.
• Much of the information on the efficacy of ESP blocking is from case reports and anecdotal experiences, so formal research is underway to determine if ESP blocks lead to a statistically significant reduction in opioid consumption, lower pain scores, and potential length of hospital stay.

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