Superficial Back Muscles Anatomy Guide

Trapezius

• Proximal Attachment (Origin):

  • Upper fibers: Medial 1/3 of the superior nuchal line, external occipital protuberance, ligamentum nuchae, and spinous process of C7.
  • Middle fibers: Spinous processes of T1–T6.
  • Lower fibers: Spinous processes of T7–T12.

• Distal Attachment (Insertion):

  • Upper fibers: Lateral 1/3 of the posterior surface of the clavicle.
  • Middle fibers: Medial border of the acromion and superior lip of the scapular spine.
  • Lower fibers: Triangular area medial to the base of the spine of the scapula.

• Innervation:

  • Somatic Motor and Sensory:
  • Spinal accessory nerve (CN XI)
  • Ventral rami (C3, C4)

• Blood Supply:

  • Variation #1: Superficial cervical artery (a branch off the thyrocervical trunk)
  • Variation #2: Superficial branch of the transverse cervical artery (a branch off the thyrocervical trunk)

• Actions:

  • Open Chain – Distal (insertion) to Proximal (origin) (Unilateral):
  • Upper fibers: Scapular elevation (upward slide with upward rotation); assists with retraction.
  • Middle fibers: Scapular retraction (medial slide with external rotation); may assist with upward rotation.
  • Lower fibers: Downward slide with upward rotation of the scapula; assists with retraction.
  • Open Chain – Proximal (origin) to Distal (insertion) (Unilateral):
  • Upper fibers: Ipsilateral side-bend (lateral flexion) of the head and neck; contralateral rotation of the head and neck.
  • Middle fibers: Not clinically significant.
  • Lower fibers: Not clinically significant.
  • Additional Actions (Bilaterally):
  • Assists in extending head and neck.

Latissimus Dorsi

• Proximal Attachment (Origin):

  • Spinous processes of T7–L5
  • Median sacral crest
  • External lip of the posterior iliac crest (via the thoracolumbar fascia)
  • Muscular slips to ribs 9–12

• Distal Attachment (Insertion):

  • Floor of the bicipital (intertubercular) groove (sulcus) on the humerus
  • May have a small attachment to the posterior (dorsal) surface of the inferior angle of the scapula

• Innervation:

  • Somatic Motor and Sensory: Thoracodorsal (middle or long subscapular) nerve (C6, C7, C8) (a branch off the posterior cord of the brachial plexus)

• Blood Supply:

  • Thoracodorsal artery (off of the 3rd part of the axillary artery)

• Actions:

  • Open Chain (Unilateral):
  • Shoulder or glenohumeral joint: Humeral adduction, humeral extension, humeral internal (medial) rotation.
  • Scapulothoracic articulation: Assists with scapular depression (downward slide with downward rotation).
  • Closed Chain (Unilateral):
  • Not clinically significant.

Rhomboid Major

• Proximal Attachment (Origin):

  • Spinous processes of T2–T5

• Distal Attachment (Insertion):

  • Medial border of the scapula, between the root (base) of the scapular spine and the inferior angle

• Innervation:

  • Somatic Motor and Sensory: Dorsal Scapular nerve (C4, C5) (a branch off the superior root of the brachial plexus)

• Blood Supply:

  • Variation #1: Dorsal scapular artery (a branch off the subclavian artery)
  • Variation #2: Deep branch of the transverse cervical artery (a branch off the thyrocervical trunk)

• Actions:

  • Open Chain (Unilateral):
  • Scapular retraction (medial slide with external rotation)
  • Downward rotation of the scapula
  • May assist with upward slide of the scapula
  • Closed Chain (Unilateral):
  • Not clinically significant

Rhomboid Minor

• Proximal Attachment (Origin):

  • Lower portion of the ligamentum nuchae
  • Spinous processes of C7 and T1

• Distal Attachment (Insertion):

  • Medial border of the scapulae at the level of the root (base) of the scapular spine

• Innervation:

  • Somatic Motor and Sensory: Dorsal Scapular nerve (C4, C5) (a branch off the superior root of the brachial plexus)

• Blood Supply:

  • Variation #1: Dorsal scapular artery (a branch off the subclavian artery)
  • Variation #2: Deep branch of the transverse cervical artery (a branch off the subclavian's thyrocervical trunk)

• Actions:

  • Open Chain (Unilateral):
  • Scapular retraction (medial slide with external rotation)
  • Downward rotation of the scapula
  • May assist with upward slide of the scapula
  • Closed Chain (Unilateral):
  • Not clinically significant

Levator Scapulae

• Proximal Attachment (Origin):

  • Transverse processes of C1–C4
  • Posterior tubercles of the transverse processes of C3, C4

• Distal Attachment (Insertion):

  • Medial border of the scapula, between the superior angle and the root (base) of the scapular spine

• Innervation:

  • Somatic Motor and Sensory:
  • Dorsal Scapular nerve (C4, C5) (a branch off the superior root of the brachial plexus)
  • Ventral Rami (C3, C4)

• Blood Supply:

  • Variation #1: Dorsal scapular artery (a branch off the subclavian artery)
  • Variation #2: Deep branch of the transverse cervical artery (a branch off the subclavian's thyrocervical trunk)

• Actions:

  • Open Chain – Distal (insertion) to Proximal (origin) (Unilateral):
  • Upward slide of the scapula
  • Downward rotation of the scapula
  • Open Chain – Proximal (origin) to Distal (insertion) (Unilateral):
  • Ipsilateral side bend (lateral flexion) of the neck
  • Ipsilateral rotation of the neck