Medial Arcuate Ligament of the Diaphragm

ligamentum arcuatum mediale

The medial arcuate ligament is a thickened band of the thoracolumbar fascia arching over the psoas major muscle, connecting the body of L1 medially to the transverse process of L1 or L2 laterally. The psoas major passes posterior to it. It forms part of the posterior attachment of the diaphragm and is one of the boundaries of the lumbar triangle through which the lumbar sympathetic chain passes.

Region: Abdomen

Biomechanics

Function & Actions

Provides a fibrous arch over the psoas major through which the diaphragm attaches posteriorly, allowing the psoas to pass from the thorax to the lumbar spine without penetrating the diaphragm.

Clinical Relevance

Clinical Notes

The medial arcuate ligament is a landmark in retroperitoneal surgery and in lumbar sympathectomy procedures, where the sympathetic chain runs beneath it at the L1-L2 level. In the Lumbocostal trigone (Bochdalek foramen) area, variations in diaphragmatic muscle development near the arcuate ligaments produce the most common site for posterior diaphragmatic herniation. In laparoscopic adrenalectomy on the left, the medial arcuate ligament defines the medial extent of safe dissection.

Pathology

Common Injuries & Conditions

Bochdalek Hernia in Adults

Incomplete diaphragmatic closure near the medial and lateral arcuate ligament junctions produces a posterior diaphragmatic hernia that can be incidentally discovered on adult imaging with herniation of retroperitoneal fat or abdominal viscera into the chest, occasionally requiring surgical repair.