Abdomen: Region between diaphragm and pelvis

Superiorly: Xiphoid process and costal cartilages of 7th-10th ribs

Inferiorly: Iliac crest, iliac spine, inguinal ligament, and pubis

Inguinal ligament is inferior edge of aponeurosis of external oblique muscle

Consist of 3 flat muscles (external oblique, internal oblique, and transverse abdominal), and 1 strap-like muscle (rectus)

Combination of muscles and aponeuroses (sheet-like tendons) act as corset to confine and protect abdominal viscera

Linea alba is fibrous raphe stretching from xiphoid to pubis

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  Forms central anterior attachment for abdominal wall muscles

  
  
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  Formed by interlacing fibers of aponeuroses of oblique and transverse abdominal muscles

  
  
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  Rectus sheath also formed by these aponeuroses as they surround rectus muscle

Linea semilunaris is vertical fibrous band at lateral edge of rectus sheath bilaterally

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  Aponeuroses of internal and transversus abdominis join in linea semilunaris before forming rectus sheath

External oblique muscle

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  Largest and most superficial of 3 flat abdominal muscles

  
  
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  Origin: External surfaces of ribs 5-12

  
  
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  Insertion: Linea alba, iliac crest, pubis via broad aponeurosis

Internal oblique muscle

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  Middle of 3 flat abdominal muscles

  
  
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  Runs at right angles to external oblique

  
  
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  Origin: Posterior layer of thoracolumbar fascia, iliac crest, and inguinal ligament

  
  
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  Insertion: Ribs 10-12 posteriorly, linea alba via broad aponeurosis, pubis

Transversus abdominis (transversalis) muscle

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  Innermost of 3 flat abdominal muscles

  
  
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  Origin: Lowest 6 costal cartilages, thoracolumbar fascia, iliac crest, inguinal ligament

  
  
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  Insertion: Linea alba via broad aponeurosis, pubis

Rectus abdominis muscle

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  Origin: Pubic symphysis and pubic crest

  
  
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  Insertion: Xiphoid process and costal cartilages 5-7

  
  
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  Rectus sheath: Strong, fibrous compartment that envelops each rectus muscle

  
  
  
  
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    Contains superior and inferior epigastric vessels

  
  

Actions of anterior abdominal wall muscles

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  Support and protect abdominal viscera

  
  
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  Help flex and twist trunk, maintain posture

  
  
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  Increase intraabdominal pressure for defecation, micturition, and childbirth

  
  
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  Stabilize pelvis during walking, sitting up

Transversalis fascia

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  Lies deep to abdominal wall muscles and lines entire abdominal wall

  
  
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  Separated from parietal peritoneum by layer of extraperitoneal fat

Consist of psoas (major and minor), iliacus, and quadratus lumborum

Psoas: Long, thick, fusiform muscle lying lateral to vertebral column

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  Origin: Transverse processes and bodies of vertebrae T12-L5

  
  
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  Insertion: Lesser trochanter of femur (passing behind inguinal ligament)

  
  
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  Action: Flexes thigh at hip joint; bends vertebral column laterally

Iliacus: Large triangular sheet of muscle lying along lateral side of psoas

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  Origin: Superior part of iliac fossa

  
  
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  Insertion: Lesser trochanter of femur (after joining with psoas tendon)

  
  
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  Action: “Iliopsoas muscle” flexes thigh

Quadratus lumborum: Thick sheet of muscle lying adjacent to transverse processes of lumbar vertebrae

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  Invested by lumbodorsal fascia

  
  
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  Origin: Iliac crest and transverse processes of lumbar vertebrae

  
  
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  Insertion: 12th rib

  
  
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  Actions: Stabilizes position of thorax and pelvis during respiration, walking; bends trunk to side

Also called erector spinae muscles

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  Invested by lumbodorsal fascia

Composed of 3 columns

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  Iliocostalis: Lateral

  
  
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  Longissimus: Intermediate

  
  
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  Spinalis: Medial

Origins: Sacrum, ilium, and spines of lumbar and 11th-12th thoracic vertebrae

Insertions: Ribs and vertebrae with additional muscle slips joining columns at successively higher levels

Action: Extends vertebral column

High-frequency (5-12 MHz) linear transducer for anterior abdominal wall and paraspinal muscles

3-5 MHz for posterior abdominal wall muscles

Supine position for examination of anterior and lateral abdominal wall

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  Image during Valsalva maneuver and in standing position to increase abdominal pressure and elicit hernias

  
  
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  Prone position for ultrasound of paraspinal muscles

Compare with contralateral side to check for symmetry

Panoramic/extended field-of-view techniques are very useful to demonstrate muscles and soft tissue