The erector spinae muscles are a group of three long, powerful muscles that run longitudinally along the back, forming the primary extensor muscles of the spine. This group consists of the iliocostalis, longissimus, and spinalis muscles, which are further divided into regional components based on their attachments. The erector spinae muscles are essential for supporting the spine and maintaining posture.
Location
The erector spinae muscles are located on either side of the vertebral column, extending from the sacrum and pelvis to the base of the skull.
- They lie deep to the thoracolumbar fascia, trapezius, latissimus dorsi, and rhomboids.
- The iliocostalis is the most lateral, longissimus is intermediate, and spinalis is the most medial. These muscles span the lumbar, thoracic, and cervical regions of the back.[7]
Anatomy
The erector spinae muscles are a group of three vertically oriented muscles that span the length of the vertebral column. These muscles are positioned in the intermediate layer of the intrinsic back muscles and are vital for maintaining spinal structure and mobility.
Components
Iliocostalis Muscle (Lateral Column)
Subdivisions:
- Iliocostalis lumborum: Originates from the sacrum, iliac crest, and thoracolumbar fascia and inserts onto the angles of the lower ribs.[5]
- Iliocostalis thoracis: Originates from the angles of the lower ribs and inserts onto the angles of the upper ribs and C7 transverse process.
- Iliocostalis cervicis: Originates from the angles of the upper ribs and inserts onto the transverse processes of C4–C6.
Location: Lateral-most component, running along the ribcage and lumbar region.
Longissimus Muscle (Intermediate Column)
Subdivisions:
- Longissimus thoracis: Originates from the lumbar transverse processes and thoracolumbar fascia and inserts onto the thoracic transverse processes and adjacent ribs.
- Longissimus cervicis: Originates from the thoracic transverse processes and inserts onto the cervical transverse processes.
- Longissimus capitis: Originates from the upper thoracic and lower cervical transverse processes and inserts onto the mastoid process of the temporal bone.
Location: Medial to the iliocostalis, running along the spine and extending to the skull.
Spinalis Muscle (Medial Column)
Subdivisions:
- Spinalis thoracis: Originates from the spinous processes of the lower thoracic and upper lumbar vertebrae and inserts onto the spinous processes of the upper thoracic vertebrae.[3]
- Spinalis cervicis: Originates from the spinous processes of the cervical and upper thoracic vertebrae and inserts onto the spinous processes of higher cervical vertebrae.
- Spinalis capitis: Often poorly defined, blending with the semispinalis capitis and inserting onto the occipital bone.
Location: Most medial component, adjacent to the vertebral spinous processes.
Attachments
Origin
Common tendinous origin from the sacrum, iliac crest, spinous processes of the lumbar and lower thoracic vertebrae, and thoracolumbar fascia.
Insertion
Varies across the three columns, attaching to the ribs, transverse processes, spinous processes, and the skull.
Structure
- The erector spinae muscles are long, powerful, and segmented, with tendinous intersections along their lengths.
- They run vertically, forming a muscular ridge visible on either side of the spinous processes.
Relations
- Superficial:
- Covered by the trapezius, rhomboids, latissimus dorsi, serratus posterior inferior, and thoracolumbar fascia.
- Deep:
- Lies superficial to the transversospinalis group (e.g., multifidus, semispinalis, rotatores) and vertebral laminae.[1]
- Medial:
- Adjacent to the vertebral spinous processes.
- Lateral:
- Extends to the ribs and is bordered by the costal muscles.
Innervation
- Innervated by the posterior rami of the spinal nerves, corresponding to their segmental levels.
Vascular Supply
Segmentally supplied by:
- Posterior intercostal arteries in the thoracic region.
- Lumbar arteries in the lumbar region.
- Deep cervical arteries in the cervical region.
Associated Structures
- Thoracolumbar Fascia:
- Provides structural support and serves as an attachment site for the iliocostalis and longissimus in the lumbar region.
- Vertebral Column:
- Serves as the central framework for these muscles, with numerous attachment points.
Function
The erector spinae muscles are the primary extensors of the vertebral column and play a critical role in maintaining posture and facilitating movement. Composed of the iliocostalis, longissimus, and spinalis muscles, this group functions synergistically to control the spine and head.
Primary Functions
Extension of the Spine and Head
Bilateral Contraction:
- When both sides of the erector spinae muscles contract simultaneously, they extend the vertebral column, returning the back to an upright position from flexion.[8]
- The iliocostalis lumborum and longissimus thoracis extend the lumbar and thoracic spine.
- The longissimus capitis and spinalis capitis extend the head and neck, enabling upward gaze.
Lateral Flexion of the Spine
Unilateral Contraction:
- When one side of the erector spinae muscles contracts, it produces ipsilateral lateral flexion, bending the spine toward the side of the contraction.
- This function is particularly prominent in the iliocostalis and longissimus components, which are located laterally.
Postural Support
- The erector spinae muscles are essential for maintaining an upright posture. By counteracting the pull of gravity, they stabilize the spine and allow the torso to remain aligned during static positions such as standing or sitting.[6]
- The iliocostalis lumborum and longissimus thoracis play a significant role in lumbar and thoracic stabilization, particularly during weight-bearing activities.
Dynamic Stability of the Spine
- During activities such as walking, running, or lifting, the erector spinae muscles provide segmental stabilization of the spine.
- This stabilization ensures that the vertebrae remain aligned and prevents excessive motion that could lead to injury.
Secondary Functions
Head and Neck Movements
- The longissimus capitis and spinalis capitis contribute to head extension and slight rotation.
- They also help maintain head alignment during dynamic movements, such as looking up or side to side.
Assistance in Rib Movement
The iliocostalis thoracis and longissimus thoracis, which attach to the ribs, assist in stabilizing and moving the ribcage during respiration, contributing to rib elevation and depression as needed.
Regional Contributions
Iliocostalis:
- Provides powerful extension and lateral flexion, especially in the lumbar and thoracic regions.
- Assists in stabilizing the lower back and maintaining spinal curvature.
Longissimus:
- Contributes to extension, lateral flexion, and stabilization throughout the spine and head.
- The longissimus capitis enables head extension and slight ipsilateral rotation.
Spinalis:
- Primarily supports spinal extension and stabilization in the thoracic and cervical regions.
Its contributions are more focused on maintaining the alignment of the vertebral column.[4]
Proprioception
The erector spinae muscles contain muscle spindles, providing proprioceptive feedback about the position and movement of the spine. This feedback helps coordinate posture and dynamic spinal adjustments during activities such as walking or balancing.
Synergistic Actions
The erector spinae muscles work synergistically with:
- Transversospinalis Group (e.g., multifidus): To stabilize the vertebrae and fine-tune movements.
- Abdominal Muscles: To balance trunk movements and maintain core stability.
- Quadratus Lumborum: To assist in lateral flexion and stabilization of the lumbar spine.
Clinical Significance
The erector spinae muscles are crucial for spinal support, and their dysfunction can contribute to various clinical issues:
Back Pain
Strain, overuse, or spasm of the erector spinae muscles, especially in the lumbar region, is a common cause of acute or chronic back pain. This can result from poor posture, improper lifting, or repetitive stress.
Postural Disorders
Weakness or imbalance in the erector spinae muscles can lead to postural issues such as kyphosis, lordosis, or scoliosis, causing chronic pain and impaired mobility.
Trigger Points
Trigger points in the erector spinae, particularly in the thoracic and lumbar regions, can refer pain to other areas of the back and ribs, mimicking conditions such as intercostal neuralgia or herniated discs.[2]
Rehabilitation
The erector spinae muscles are commonly targeted in physical therapy for spinal rehabilitation, postural correction, and recovery from injuries such as lumbar strain or disc herniation.
Surgical and Diagnostic Considerations
During spinal surgeries or imaging, understanding the anatomy and function of the erector spinae is critical for avoiding complications and diagnosing musculoskeletal pathologies.
