Expansion
Petit's inferior triangle and Grynfeltt's superior triangle
Expansion
Inferior lumbar triangle (of Petit)
- Base - iliac crest
- Medially - latissimus dorsi
- Laterally - external oblique
- Floor - internal oblique
Superior lumbar triangle (of Grynfeltt-Lesshaft)
- Superiorly - twelfth rib and serratus posterior inferior
- Medially - quadratus lumborum
- Laterally - internal oblique
- Floor - transversalis fascia
These are natural weak points in the posterior abdominal wall where a lumbar hernia can occur, either spontaneously or after flank surgery such as nephrectomy. The superior triangle is the larger and the commoner site.
Petit’s triangle is also a recognised approach for draining a retroperitoneal or psoas abscess, since it gives access without entering the peritoneal cavity.