Muscle Above, Aponeurosis Anterior, Ligament below, Transversalis fascia behind, 2 Ms, 2 As, 2 Ls, 2 Ts
Mnemonic
MALT, taking 2 M’s, 2 A’s, 2 L’s and 2 T’s and reading them into the four walls:
- M - Muscles: internal oblique and transversus abdominis form the roof
- A - Aponeuroses: external and internal oblique form the anterior wall
- L - Ligaments: inguinal and lacunar form the floor
- T - Transversalis fascia and conjoint Tendon form the posterior wall
The posterior wall is the weak point, which is why direct hernias push through it medial to the inferior epigastric vessels, while indirect hernias enter the deep ring lateral to them and follow the canal.
“Medial to the vessels is direct, lateral is indirect”, and the deep ring lies at the mid-point of the inguinal ligament, half an inch above the femoral pulse.
Expansion
M, Muscles superiorly (roof)
- Internal oblique and transversus abdominis (arching fibres, forming the conjoint tendon medially)
A, Aponeurosis anteriorly
- External oblique aponeurosis, reinforced laterally by internal oblique
L, Ligaments inferiorly (floor)
- Inguinal ligament and lacunar ligament
T, Transversalis fascia posteriorly
- Transversalis fascia, reinforced medially by the conjoint tendon
The canal is about 4 cm long, running from the deep ring (an opening in transversalis fascia, at the mid-point of the inguinal ligament) to the superficial ring (a defect in the external oblique aponeurosis, above and medial to the pubic tubercle).
Its oblique course means that raised intra-abdominal pressure presses the anterior and posterior walls together, a flap-valve mechanism that resists herniation.