Although any paraspinal muscle innervated by the dorsi rami can be considered an erector spinae, this section only considers the iliocostalis and longissimus muscles, while other erector spinae muscles are dealt with in other articles. The deep division originates from the lumbar vertebrae and the superficial division originates from the thoracic vertebrae [1].

Origins and Insertions

The following attachments, unless otherwise quoted, are from Bogduk [2]

Longissimus Thoracis pars Thoracis: Nutation

Origin: Transverse processes of T1 or T2 to T12, and adjacent ribs from T4 to T12

Insertion: Spinous processes of L3 to S3 and sacrum lateral to S3. Fibers from T12 insert into the posterior superior iliac spine (PSIS)

• Forms the medial half of erector spinae aponeurosis
• Tendons blend with the supraspinous ligament of the lumbar spinous processes

Functions:

• Creates a bowstring effect to increase lumbar lordosis [1]p37 [2]
• Extends the thorax (decreases the thoracic kyphosis) [1] [3]p180-183
• Acting eccentrically, it controls descent of the spine during flexion [4]p70.
• Laterally flexes the thoracic spine and, indirectly, the lumbar spine [2]p107

Longissimus Thoracis pars Lumborum: Counternutation

Origins: Transverse process of L5 and the accessory processes of L1 to L4.

Insertions: Fibers from L5 insert into the posterior superior iliac spine (PSIS) and blend with the iliocostalis lumborum while fibers from L1 to L4 form a common tendon, the lumbar intermuscular aponeurosis, which inserts lateral and superior to the PSIS.

Functions:

• Draws the lumbar vertebrae backward into flexion
• Creates ipsilateral axial rotation with simultaneous posterior translation of the lower lumbar vertebrae
• Pulls the ilium anteriorly and superiorly
• Acting unilaterally, it will cause lateral flexion

Iliocostalis Lumborum pars Thoracis: Nutation

In erect posture, it provides little ipsilateral rotation but, during contralateral rotation, it de-rotates the trunk [2]p108

Origin: Angles of the lower 8 ribs

Insertion: Iliac crest at the PSIS and 5 cm laterally, forming the lateral part of the erector spinae aponeurosis [2]p107-109

    Functions:

• Creates a bowstring effect to increase lumbar lordosis [1]p37
• Extends the thorax (decreases the thoracic kyphosis) [1] [3]p180-183
• Directly laterally flexes the thoracic spine, and indirectly laterally flexes the lumbar spine [2]p108
• Fibers run from the ribs, inferiorly and anteriorly, to attach to the iliac crest so that it will pull the crest posteriorly [4]p73
• Acting eccentrically, it controls descent of the spine during flexion [4]p70

Iliocostalis Lumborum Pars Lumborum: Counternutation

Origin: Transverse processes of L1 to L4 and the middle layer of thoracolumbar fascia, which attaches to the transverse processes

Insertion: Iliac crest lateral to the PSIS. A fiber from L5 appears to form the posterior band of the iliolumbar ligament [2]p105-107

Functions:

• Draws the lumbar vertebrae backward into flexion
• Creates ipsilateral axial rotation with simultaneous posterior translation of the lower lumbar vertebrae [2]p106
• Pulls the iliac crest anteriorly and superiorly
• Acting unilaterally, it acts to control lateral flexion [2]p106

The Erector Spinae as Grouped Functionally into Superficial and Deep Divisions – Both Porterfield [4]p70-75 and Levangie [3]p180 base this grouping on Bogduk and Adams [1, 2, 5]. They discuss the separate actions of the superficial and deep erector spinae. This major muscle group acts to create both nutation and counternutation, depending on whether the superficial or deep divisions are activated.

Superficial Erector Spinae: Nutation

This muscle group consists of the longissimus thoracis pars thoracis and iliocostalis lumborum pars thoracis with additional fibers attaching to the sacrum [4]p73-74. The Iliocostalis lumborum pars thoracis forms the lateral part of erector spinae aponeurosis and inserts into the ilium [2]p108.

Functions:

• Due to the line of pull from the rib cage, inferiorly and anteriorly to the ilium, it rotates the ilium posteriorly, inducing nutation
• The sacral fibers rotate the sacrum anteriorly, also inducing nutation
• Spans the lumbar spine, without attaching to it, and acts like a bowstring to create lumbar extension
• Because it traverses the posterior aspect of the thoracic curve, it will extend (flatten) the thoracic spine.
• By decreasing the ipsilateral thoracic kyphosis, it rotates the bodies of the thoracics contralaterally, into the concavity of the spine, in alignment with the lumbar rotation. From this, we can see that decreasing the thoracic kyphosis is a function of ipsilateral nutation.
• May laterally flex the thoracic spine, and thereby the lumbar spine
• Eccentrically, it acts to control forward flexion of the trunk

Acting as a group, the superficial erector spinae spans the lumbar spine, without attaching to it, and acts like a bowstring to increase lumbar lordosis [1]p37 [2]. Because it traverses the posterior aspect of the thoracic spine, it will extend the thoracic spine (decrease the thoracic kyphosis) [1] [3]p180-183. By decreasing the ipsilateral thoracic kyphosis, it rotates the bodies of the thoracics contralaterally into the concavity of the spine in alignment with the lumbar and sacral rotation, with the exception of L5 and, possibly, L4. It directly laterally flexes the thoracic spine, and indirectly laterally flexes the lumbar spine [2]p108. Its fibers run from the ribs, inferiorly and anteriorly, to attach to the iliac crest with a vector that will pull the crest posteriorly and superiorly [4]p73. Because of their attachment below S3, the sacral fibers pull the sacrum into nutation [4]p73.

Deep Erector Spinae: Counternutation

This muscle group consists of the longissimus thoracis pars lumborum and iliocostalis lumborum pars lumborum.

Functions:

• Pulls the lumbar spine and the lower thoracic cage posteriorly
• Pulls the iliac crest anteriorly
• Creates ipsilateral axial lumbar rotation and external flexion [4]p77

Acting as a group, the deep erector spinae draws the lumbar vertebrae posteriorly and creates ipsilateral axial rotation and lateral flexion [4]p73-75 [1] [2]p106. The vector of pull from origin to insertion indicates that it pulls the iliac crest anteriorly and superiorly [4]p77.

Porterfield & DeRosa [4]p73-75 discuss the role of the deep erector spinae as a common finding in low back muscle tension. They stated that anterior sheer stress to the lumbar segments (nutation) creates connective tissue injury, which causes a central nervous system reflex reaction (ligamento-muscular reflex). The reaction is to activate the deep erector spinae, which creates a posteriorly directed force on the lumbar spine while pulling the ilia forward through its attachment on the iliac crest (counternutation).”

Vleeming stated that “During counternutation, the long dorsal sacroiliac ligament tightens”. Loading of the erector spinae resulted in increased tension in the long dorsal SI ligaments, which demonstrated that a part of the erector spinae produced counternutation [6].

Erector Spinae Counternutation Pairing  (right Image in animation)

The deep group acts synergistically to decrease the lumbar curves while tilting the ilium anteriorly, creating counternutation.

Erector Spinae Nutation Pairing  (left Image in animation)

The superficial group acts to increase the lumbar curve and pull the sacral base forward, causing nutation.

Combined Action  (center Image in animation)

The center image shows bilateral contraction of both groups causing rightrotation of the thoracic and lumbar spine, with the exception of L4 & L5.

Side-to-Side Reciprocal Action

As the nutation muscles contract on one side of the body, the ipsilateral counternutation muscles are inhibited. Concurrently, the contralateral counternutation muscles contract, and the contralateral nutation muscles are inhibited. As shown in the animation, the deep muscles on the right decrease the lumbar lordosis, as the superficial muscles on the left increase the lumbar lordosis and decrease the upper thoracic kyphosis. Their combined action contributes to the cross-crawl patterning seen in gait. The reciprocating action of these two groups, between nutation and counternutation, provides oscillating motion from the sacrum superiorly to the cranium.

The Erector Spinae as Grouped non-functionally into Medial and Lateral Divisions

Anatomically, but not functionally, the intermuscular aponeurosis divides the lumbar erector spinae into medial and lateral divisions [5]. Each division includes segments from both the longissimus and iliocostalis muscles of the erector spinae.

• The medial group includes the longissimus thoracis pars lumborum (CN) and the longissimus thoracic pars thoracis (N).
• The lateral group includes the iliocostalis lumborum pars lumborum (CN) and the iliocostalis lumborum pars thoracis (N). Each division acts as a separate and continuous muscle. Additionally, each muscle is composed of individual strands that can act independently to affect different areas of the spine.

Bogduk [5] stated that “It is important to realize that the lumbar erector spinae does not simply span the lumbar region like a ‘bowstring’ between the sacrum and thorax. The concavity of the lumbar lordosis is filled by a laminated series of relatively short muscle fibers connecting the ilium to the lumbar transverse processes, with many acting through the lumbar intermuscular aponeurosis….An analysis must consider this muscle as a continuum of independent fibers, each with a unique orientation…If such action occurred at the L5 level, for example, it would tend to extend and retract the L5 vertebrae…and it is suggested that such segmental spasm of either the lumbar erector spinae or multifidus (or both) is the mechanism underlying the ‘loss of lordosis’ commonly seen in patients with low back pain.”

Bogduk[5] also stated that the lumbar intermuscular aponeurosis serves as the distal attachment of the longissimus thoracis pars lumborum muscles to the ilium. This brings all the force of this large muscle to a single, small point which he found to be a “…common site of tenderness in patients with low back strain.” He hypothesized that low back pain, rather than being due to a muscle strain, may actually be due to an avulsion of the lumbar intermuscular aponeurosis from the ilium, due to sudden longissimus spasm. This can happen in a nutation lesion with a strong counternutation muscular response.

References:

1. Adams, M.A., et al., The Biomechanics of Back Pain. 2002: Churchill Livingstone.
2. Bogduk, N., Clinical Anatomy of the Lumbar Spine and Sacrum. 2005: Elsevier Churchill Livingstone.
3. Levangie, P. and C. Norkin, Joint Structure and Function. A Comprehensive Analysis. 2005, Philadelphia, PA: F.A. Davis Company.
4. Porterfield, J. and C. DeRosa, Mechanical Low Back Pain: Perspectives in Functional Anatomy. 2nd ed. 1998: W B. Saunders Company.
5. Bogduk, N., A reappraisal of the anatomy of the human lumbar erector spinae. Journal of Anatomy, 1980. 131(Pt 3): p. 525-40.
6. Vleeming, A., et al., The function of the long dorsal sacroiliac ligament: its implication for understanding low back pain. Spine,