Original Editor - Aarti Sareen
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.
It is made up of 3 muscles:
- Medially by Spinalis
- Centerally by Longissimus
- Laterally by Illiocostalis
Each of these have 3 parts further.
| spinalis capitis
|| longissimus capitis
|| illiocostalis cervicis|
| spinalis cervicis
|| longissimus cervicis
|| illiocostalis thoracis|
| spinalis thoracis
|| longissimus thoracis
|| illiocostalis lumborum|
Is the most medial part just next to the spine. It connects the spinous process of the adjacent vertebrae to each other.
It is divided into 3 parts:
|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|
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.
|Longissimus capitis||C4-T4 transverse process||Posterior edge of the mastoid process|
|Longissimus cervicis||T1-T4 transverse process||C2 to C6 transverse process|
|Longissimus thoracis||Transverse process of lumbar vertebra and blends with iliocostalis in the lumbar region||Transverse process of all thoracic vertebrae|
Is 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.
It is divided into 3 parts:
|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|
Bilateral contraction they straighten the back and pull the head posteriorly and they are involved in the control the flexion of the vertebral coloumn.
Unilateral contraction bends the the vertbral column laterally and turns the head towards the contracting side.
Doral rami of spinal nerves.
Branches of the vertebral, deep cervical, occipital, transverse cervical, posterior intercostal, subcostal, lumbar and lateral sacral arteries.
Erector Spinae Muscle and Low Back Pain
The erector spinae muscle plays an important role in the spinal stability.
In patients with low back pain there is decreased activity and atrophy of the multifidus muscle which compromises the spinal stability. The spinal control is compensated for by the increased activity of the erector spinae muscle to stabilize the lumbar spine.
The increased activity of erector spinae increases the compression load on the vertebral column, stimulating the nociceptors of the spinal structures continuously which may increases the risk of injury.
The relationship between Erector spinae muscle cross section area and low back pain is inconclusive, some studies found decrease in the erector spinae muscle mass with low back pain while others found no relation.
Function and Training
Erector Spinae Flexion-Relaxation Phenomenon
The flexion-relaxation phenomenon is defined as silencing of the erector spinae myoelectric activity during full trunk flexion.
In healthy individuals with no low back pain, the erector spinae muscle relaxes in the range from upright position to full-flexion lumbar, due to the deep back muscles (multifidus) acting to stabilize the lumbar spine.
While in individuals with low back pain the erector spinae flexion-relaxation phenomenon is absent as the erector spinae functions to stabilize the lumbar spine due to laxity of the passive structures and changes in the neuromuscular activation pattern.
Lumbar stabilization exercise can restore the erector spinae flexion-relaxation phenomenon by strengthening the multifidus muscle.
However, even in individuals with no low back pain there can be asymmetric trunk flexion (combined with rotation or side bending) leading to asymmetric Flexion relaxation phenomenon in the right and left erector spinae due to factors like repeated asymmetric posture and activities.
Asymmetry in the flexion relaxation phenomenon increases the risk of low back pain. Which could also be corrected by lumbar stabilization exercise.
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