Dr Jeremy Jones et al.

The diaphragm is the dome-shaped muscle that separates the thoracic cavity from the abdominal cavity, enclosing the inferior thoracic aperture.

The diaphragm's muscular fibres originate around the circumference of the inferior thorax and converge to a common insertion point of the central tendon.

The muscle slips can be grouped according to their origins:

  • sternal: arises from two strips under the xiphoid process
  • costal: arise from the inner surfaces of the costal cartilages of the 6th ribs on either side which interdigitates with the transversus abdominus muscles
  • lumbar: arise from the aponeurotic arches (lumbocostal arches) and from the lumbar vertebrae (crura)

There are two paired tendinous lumbocostal arches:

  • medial lumbocostal arch (medial arcuate ligament): a tendinous arch that covers psoas major; continuous medially with the ipsilateral crura; attached to the L2 vertebral body and in the front of the transverse process of L1 and L2
  • lateral lumbocostal arch (lateral arcuate ligament): covers quadratus lumborum; attached medially to the L1 transverse process and attached laterally to the tip of the 12th rib. This may be discontinuous on CT in up to 11% of people and hence may mimic diaphragmatic rupture 8.

The crura are tendinous structures that blend with the anterior longitudinal ligament of the vertebral column:

  • right crus is longer than the left, and arises from the anterior surfaces of the bodies of L1-3
  • left crus arises from the corresponding portions of L1-2

The medial margins of the two crura pass forwards and medially. They meet in the midline to form an arch in front of the aorta called the median arcuate ligament

All these muscles insert into the central tendon, a thin but strong aponeurosis. It is situated immediately below and is fused to the pericardium. It is within this central tendon that vena caval hiatus is located, with the tendon allowing the IVC to remain patent during respiration.

Through the diaphragm are a series of 3 major and some minor apertures that permit the passage of structures between the thoracic and abdominal cavities:

The vertebral levels of the 3 main diaphragmatic apertures can be remembered by this mnemonic.

  • each phrenic nerve (C3-5) supplies the ipsilateral hemidiaphragm with motor fibres
  • lower intercostal nerves supply proprioceptive fibres to the margins 4

Thoracic anatomy
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Article Information

rID: 5764
Section: Anatomy
Tag: cases
Synonyms or Alternate Spellings:
  • Hemidiaphragm
  • Diaphragm - anatomy
  • Hemi-diaphragm

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Cases and Figures

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    Figure 1: under surface of diaphragm
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