Femoral Triangle: Boundaries, NAVEL and the Femoral Hernia

The femoral triangle is a shallow depression below the inguinal ligament that carries the entire neurovascular supply of the lower limb across a very small area. Almost every practical procedure at the groin depends on knowing the order of its contents.

At a glance

Contents: NAVEL, lateral to medial

• N — femoral nerve (L2, L3, L4), the most lateral structure
• A — femoral artery, continuation of the external iliac artery below the inguinal ligament
• V — femoral vein
• E — empty space, the femoral canal
• L — lymphatics, including the deep inguinal node of Cloquet

The femoral artery lies at the mid-inguinal point — halfway between the anterior superior iliac spine and the pubic symphysis. Do not confuse this with the midpoint of the inguinal ligament, which is halfway between the anterior superior iliac spine and the pubic tubercle and marks the deep inguinal ring. Examiners ask this constantly and the two points are genuinely different.

The femoral sheath

A funnel of fascia continuous above with the transversalis fascia in front and the iliac fascia behind. It contains three compartments: the artery laterally, the vein in the middle, and the femoral canal medially. The femoral nerve lies outside the sheath — a small fact with two large consequences. It explains why a femoral nerve block is placed lateral to the palpable arterial pulsation, and why the nerve is comparatively protected during femoral vascular access.

The femoral canal and the femoral ring

The femoral canal is the medial compartment, about 1.25 cm long. It exists as dead space so the femoral vein can distend during exercise or a Valsalva. Its upper opening is the femoral ring, closed by a condensation of extraperitoneal fat called the femoral septum, and bounded by:

• Anteriorly: inguinal ligament
• Posteriorly: pectineal (Astley Cooper’s) ligament on the superior pubic ramus
• Medially: lacunar (Gimbernat’s) ligament
• Laterally: femoral vein

Femoral hernia

A femoral hernia descends through the femoral ring into the femoral canal, then out through the saphenous opening. Three points make it clinically dangerous.

• The ring is narrow and bounded on three sides by unyielding ligament and bone, so a hernia that enters cannot easily reduce. Strangulation and Richter’s hernia are correspondingly common, and the presentation is frequently obstruction rather than a lump.
• It is commoner in women, because the female pelvis is wider and the ring larger — though inguinal hernia remains the commonest hernia in both sexes.
• It lies below and lateral to the pubic tubercle, whereas an inguinal hernia lies above and medial to it. This is the single most reliable bedside discriminator between the two.

Clinical applications

• Vascular access: the femoral artery and vein are punctured here for angiography, cardiac catheterisation and central venous access. Puncture below the inguinal ligament so bleeding can be compressed against the femoral head; a puncture above it can bleed retroperitoneally without any external sign.
• Femoral nerve block: needle inserted lateral to the arterial pulsation, outside the sheath.
• Saphenous opening: the great saphenous vein pierces the cribriform fascia here to join the femoral vein, roughly 3–4 cm below and lateral to the pubic tubercle. This is the saphenofemoral junction ligated in varicose vein surgery.
• Lymph nodes: the inguinal nodes drain the lower limb, perineum, anal canal below the pectinate line, and the abdominal wall below the umbilicus — which is why an inguinal lump can be a signpost to disease well away from the groin.

Last-minute checklist

• Inguinal ligament, sartorius, adductor longus.
• NAVEL from lateral to medial; nerve outside the sheath.
• Mid-inguinal point is the artery; midpoint of the inguinal ligament is the deep ring.
• Femoral ring: inguinal, pectineal, lacunar, femoral vein.
• Femoral hernia below and lateral to the pubic tubercle; inguinal above and medial.

Frequently asked questions

Why is the femoral nerve outside the femoral sheath?

The sheath is derived from the transversalis and iliac fasciae carried down around the vessels as they leave the abdomen. The nerve runs behind the iliac fascia rather than with the vessels, so it is never enclosed.

Why do femoral hernias strangulate more often than inguinal ones?

The femoral ring is small and bounded anteriorly, posteriorly and medially by rigid ligament, so once bowel enters there is no room for it to swell or slip back.

How do you distinguish a femoral from an inguinal hernia at the bedside?

Locate the pubic tubercle. An inguinal hernia emerges above and medial to it; a femoral hernia lies below and lateral to it.

References

• B. D. Chaurasia’s Human Anatomy, Volume 2 — lower limb.
• Gray’s Anatomy for Students — the femoral triangle.
• Bailey & Love’s Short Practice of Surgery — groin hernias.