Diaphragm

Introduction:

The diaphragm is a curved musculotendinous sheet attached to the thoracic outlet and the upper lumbar vertebrae. It is domed peripherally and rises higher on the right side than on the left. On a properly inspired posteroinferior chest radiograph, the right hemidiaphragm is located at the anterior end of the sixth rib, whereas the left hemidiaphragm is 1.5-2.5 cm lower.  Diaphragmatic excursion is around 2 cm during peaceful respiration in the erect position, increasing to approximately 7 cm during active respiration. The diaphragm is at the lowest position while sitting posture, allowing maximum lung excursion and explaining why asthma patients feel most comfortable in this position. The diaphragm is higher in the supine (compared to the erect) position, and the dependent half of the diaphragm is significantly higher than the uppermost one in the decubitus position.

Projections of the diaphragm on the chest wall

• Central tendon: Directly posterior to the xiphisternal joint
• Right dome: Upper border of rib 5 in the midclavicular line (in forced expiration: fourth costal cartilage)
• Left dome: Lower border of rib 5 in the midclavicular line
  
  

Attachments: 

The diaphragm has three parts: sternal, costal, and vertebral. The sternal part is made up of two fleshy slips that emerge from the posterior surface of the xiphoid process.  Each side's costal part is made up of six fleshy slips that emerge from the inner surface of the lower six ribs near their costal cartilages. The lumbar region is formed by the right and left crura of the diaphragm, as well as five arcuate ligaments. 

Insertion is into the diaphragm's central tendon.

The diaphragm, the main muscle of inspiration, descends when it contracts, increasing thoracic volume by increasing the vertical diameter of the thoracic cavity.

Crus of diaphragm:

The right crus attaches to the anterior aspects of the upper three lumbar vertebrae and the intervertebral discs.  The left crus (which is shorter in length) connects to the anterior aspects of the upper two lumbar vertebrae and intervertebral discs. The right crus' medial fibres embrace the oesophagus where it passes through the diaphragm, the more superficial fibres ascend on the left, and deeper fibres cover the right margin. A superficial muscular bundle from the left crus contributes to the formation of the right margin of the hiatus in 30% of the population.

Arcuate ligaments:

The medial arcuate ligament is a fibrous band that connects the upper ends of two crura. The thickened upper margin of the psoas sheath is known as the medial arcuate ligament (Medial Lumbocostal Arch). It runs from the side of the L2 vertebra's body to the tip of the L1 vertebra's transverse process. Lateral arcuate ligament (Lateral Lumbocostal Arch) is the thickened upper margin of fascia covering the anterior surface of the quadratus lumborum. It runs from the tip of the L1 vertebra's transverse process to the 12th rib.

Diaphragmatic openings:

Minor Openings: 

There is a space called the Larry's space between the muscle slips that originate from the xiphoid process and the seventh costal cartilage. It is traversed by superior epigastric veins.

The musculophrenic artery travels through the space between the origin slips on the seventh and eighth ribs. Greater, lesser, and least splanchnic nerves pass by piercing the crus of the diaphragm to enter the abdomen; sympathetic chain passes deep to the medial arcuate ligament; subcostal nerves and vessels pass deep to the lateral arcuate ligament; azygous vein pierces the right crus of the diaphragm to enter the thorax; and hemiazygos vein pierces the left crus.

Neurovascular structures of diaphragm:

Hernia:

90% of cases of sliding hernias, which affect more than 50% of individuals with gastro-oesophageal reflux, are frequently acquired. The stomach and the GE junction are able to herniate through the diaphragm and into the thorax because to the laxity of the phreno-oesophageal ligament. Only the stomach herniates through the diaphragm and into the thorax in the case of a para-oesophageal (type II) hiatus hernia. Gastric contents do not reflux, although obstruction or strangulation could happen. The paralyzed dome of the diaphragm is pulled upward as a result of increased abdominal pressure in the case of a phrenic nerve injury, which can cause paralysis and paradoxical movement of the diaphragm.