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Internal and External Obliques Anatomy: Origin, Insertion, Action and Innervation

internal-oblique

Internal Oblique

  • Origin: Lumbar fascia, anterior two-thirds of the iliac crest, and the lateral two-thirds of the inguinal ligament.
  • Insertion: Costal margin, aponeurosis of the rectus sheath, conjoined tendon to the pubic crest and pectineal line, 10-12 rib.
  • Actions: Bilaterally flexes the spine. Unilaterally assists in lateral flexion and rotation of the spine.
  • Innervation: Ventral primary rami of T7 to T12; conjoined tendon supplied by L1.
  • Vascular Supply: Branches from the musculophrenic artery, the lower two or three posterior intercostal arteries, the subcostal artery and branches from the superficial epigastric artery.

 

Primary Actions of the Internal Oblique:

 1. Lateral flexion of the thoracic spine when acting unilaterally

  Agonists: Muscles located on the same side of movement 

  1. Iliocostalis cervicis
  2. Iliocostalis thoracis
  3. Iliocostalis lumborum
  4. Longissimus cervicis
  5. Longissimus thoracis
  6. External oblique

  Antagonists: The same muscles listed above but on the opposite side of movement

Note: Semispinalis cervicis, semispinalis thoracis, and the intertransversarii assist with lateral flexion of the thoracic spine.

2. Lateral flexion of the lumbar spine when acting unilaterally

  Agonists: Muscles located on the same side of movement 

  1. Iliocostalis lumborum
  2. Longissimus thoracis
  3. Psoas Major
  4. Quadratus lumborum,
  5. External Oblique

  Antagonists: The same muscles listed above but on the opposite side of movement

Note: The intertransversarii assist with lateral flexion of the lumbar spine.

3. Ipsilateral rotation of the trunk when acting unilaterally


 

Secondary Actions of the Internal Oblique:

1. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists: Rectus abdominis

  Antagonists: 

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Spinalis thoracis
  • Semispinalis cervicis
  • Semispinalis thoracis

2. Assists with flexion of the lumbar spine when acting bilaterally

  Agonists: Rectus Abdominis

  Antagonists: 

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Spinalis thoracis

Note: External oblique and psoas major also assist with thoracic and lumbar spine flexion

3. Assists with forced expiration

  Agonists: 

  • Serratus posterior inferior
  • Transversus abdominis

  Antagonists: 

  • Serratus posterior superior
  • Levatores costarum breves
  • Levatores costarum longi

Note: Rectus abdominis and external oblique assist with forced expiration. 

 

 

exterior-oblique

External Oblique

External Oblique

  • Origin: Anterior fibers: external surfaces of ribs 5 to 8, interdigitating with serratus anterior. 
    Lateral fibers: external surfaces of 9th rib, interdigitating serratus anterior, and those ribs 10 to 12, interdigitating with lattissimus dorsi.
  • Insertion: Anterior Fibers: into a broad flat aponeurosis, terminating at the linea alba.
    Lateral fibers: into the anterior iliac spine and pubic tubercle, and into the external lip of the anterior half of the iliac crest.
  • Actions: Bilaterally flexes the spine. Unilaterally assists in lateral flexion and rotation of the spine.
  • Innervation: Ventral primary rami of T7 to T12; conjoined tendon supplied by L1.
  • Vascular Supply: Branches from the musculophrenic artery, the lower two or three posterior intercostal arteries, the subcostal artery and branches from the superficial epigastric artery.

 

Primary Actions of the External Oblique:

 1. Lateral flexion of the thoracic spine when acting unilaterally

  Agonists: Muscles located on the same side of movement 

  1. Iliocostalis cervicis
  2. Iliocostalis thoracis
  3. Iliocostalis lumborum
  4. Longissimus cervicis
  5. Longissimus thoracis
  6. Internal oblique

  Antagonists: The same muscles listed above but on the opposite side of movement

Note: Semispinalis cervicis, semispinalis thoracis, and the intertransversarii assist with lateral flexion of the thoracic spine.

2. Contralateral rotation of the trunk when acting unilaterally

  Agonists: Muscles located on the same side of movement 

  1. Semispinalis cervicis
  2. Semispinalis thoracis
  3. Multifidus

Antagonists: The same muscles listed above but on the opposite side of movement

Note: The rotatores assist with contralateral rotation of the trunk.

3. Lateral flexion of the lumbar spine when acting unilaterally

  Agonists: Muscles located on the same side of movement 

  1. Iliocostalis lumborum
  2. Longissimus thoracis
  3. Psoas major
  4. Quadratus lumborum
  5. Internal oblique

  Antagonists: The same muscles listed above but on the opposite side of movement

Note: The intertransversarii assist with lateral flexion of the lumbar spine.


 

Secondary Actions of the External Oblique:

1. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists: Rectus abdominis

  Antagonists: 

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Spinalis thoracis
  • Semispinalis cervicis
  • Semispinalis thoracis

2. Assists with flexion of the lumbar spine when acting bilaterally

  Agonists: Rectus Abdominis

  Antagonists: 

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Spinalis thoracis

Note: Internal oblique and psoas major also assist with thoracic and lumbar spine flexion

3. Assists with forced expiration

  Agonists: 

  • Serratus posterior inferior
  • Transversus abdominis

  Antagonists: 

  • Serratus posterior superior
  • Levatores costarum breves
  • Levatores costarum longi

Note: Rectus abdominis and internal oblique assist with forced expiration. 

4. Supports the abdominal wall

Agonists: 

  • Rectus abdominis
  • Transversus abdominis
  • Internal oblique

  Antagonists: 

  • None
oblique_feat

Information about cause and effect of oblique pain:

External Internal Oblique Muscles: Abdomen, Groin, Testicular Pain