Lumbar Triangle, Anatomy

Description

Centered over the posterolateral lower back, the inferior lumbar triangle (triangle of Petit) is defined by the posterior border of the external oblique muscle anterolaterally and the anterior border of the latissimus dorsi posteromedially, with the iliac crest forming the inferior boundary. Deep to these margins, the internal oblique constitutes the floor, and superficial fascia and skin overlie the interval. From a posterior perspective, the triangle sits inferior to the 12th rib, lateral to the erector spinae mass, and proximal to the gluteal region. Clinically, Petit’s triangle matters because it represents a relative weak point in the posterolateral abdominal wall where acquired lumbar hernias can protrude, often after flank surgery, trauma, or marked weight loss, and the bulge may become more evident with coughing or Valsalva. Small. Distinguishing this inferior triangle from the superior lumbar triangle (Grynfeltt-Lesshaft), which lies more cranial and deep to the latissimus dorsi near the 12th rib, helps when correlating physical examination with CT findings or planning a repair. The iliac crest border is also a dependable surface landmark when mapping incisions for retroperitoneal access and when orienting trainees to muscle fiber direction in the flank. Educators will find this view suited to gross anatomy labs covering the posterior abdominal wall and to course materials that integrate surface anatomy with abdominal wall layers (external oblique, internal oblique, transversus abdominis, thoracolumbar fascia). It also fits surgical atlases and hernia references discussing lumbar hernia anatomy, mesh placement planes, and the relationship of the defect to the latissimus dorsi and iliac crest. Anatomical accuracy verified by SciePro's Medical Advisory Board.