Femoral Triangle and Adductor Canal

Boundaries:

• Superior (base): Inguinal ligament.
• Medial: Medial border of adductor longus.
• Lateral: Medial border of sartorius.
• Apex: Where the medial borders of adductor longus and sartorius meet, continuous with the adductor canal.

Roof: Fascia lata, superficial fascia, skin; pierced by the saphenous opening (fossa ovalis), through which the great saphenous vein drains into the femoral vein, and by superficial inguinal lymph nodes/vessels.

Floor: Formed medially to laterally by adductor longus, pectineus, and iliopsoas (with a small contribution from adductor brevis, deep to pectineus).

Contents (lateral to medial): Femoral nerve → femoral sheath (containing femoral artery, femoral vein, femoral canal) → deep inguinal lymph nodes within the femoral canal.

Classic lateral-to-medial arrangement (mnemonic "NAVEL"): Nerve, Artery, Vein, Empty space (femoral canal), Lymphatics.

• Femoral nerve: lies lateral to the femoral sheath, outside it, on iliopsoas; divides into its terminal branches within the triangle.
• Femoral artery: enters the triangle at the midpoint of the inguinal ligament (midinguinal point, between the ASIS and pubic symphysis, key surface landmark and pulse point), gives off the profunda femoris artery within the triangle.
• Femoral vein: medial to the artery within the femoral sheath; receives the great saphenous vein via the saphenous opening.
• Femoral canal: medial-most compartment of the femoral sheath, containing fat and the deep inguinal lymph nodes.

• Formation: A funnel-shaped fascial extension of the abdominal transversalis fascia (anteriorly) and iliopsoas fascia (posteriorly), surrounding the femoral vessels for about 3–4 cm below the inguinal ligament.
• Compartments: Divided by two vertical septa into three compartments:
• Lateral compartment: femoral artery (and femoral branch of genitofemoral nerve).
• Intermediate compartment: femoral vein.
• Medial compartment: femoral canal (fat, lymphatics, occasionally a lymph node, the node of Cloquet/Rosenmüller).
• Contents: The femoral artery, femoral vein and femoral canal; the femoral nerve is not contained within the sheath, lying lateral to it.

• Boundaries:
• Anterior: inguinal ligament.
• Posterior: pectineal ligament (and pectineus fascia).
• Medial: lacunar ligament.
• Lateral: femoral vein (septum separating it from the intermediate compartment).
• Contents: Loose connective tissue, fat, lymphatic vessels, and the deep inguinal lymph nodes (typically 1–3 nodes, including the node of Cloquet at the femoral ring).
• Femoral ring: The proximal (superior) opening of the femoral canal, into the abdominal cavity; normally plugged by extraperitoneal fat and lymphatic tissue (femoral septum).
• Femoral hernia relevance: The femoral canal provides a potential space for abdominal/pelvic contents (typically bowel, or omentum) to herniate through the femoral ring, below the inguinal ligament and lateral to the pubic tubercle. Because the canal is bounded by rigid structures (inguinal ligament, lacunar ligament, pectineal ligament, femoral vein), a femoral hernia has a narrow, unforgiving neck, giving it a high risk of strangulation compared to the more common inguinal hernia. Femoral hernias are more common in women, related to a wider pelvis and femoral canal.

Boundaries:

• Anteromedial (roof): Sartorius, with the vastoadductor membrane deep to it.
• Lateral: Vastus medialis.
• Posterior: Adductor longus (proximally) and adductor magnus (distally).
• Extends from the apex of the femoral triangle to the adductor hiatus in adductor magnus, where it terminates and its contents enter the popliteal fossa.

Contents:

• Femoral artery and femoral vein: pass through the canal, exiting via the adductor hiatus to become the popliteal artery/vein.
• Saphenous nerve: branch of the femoral nerve; traverses the canal but does not pass through the adductor hiatus with the vessels, instead pierces the vastoadductor membrane/deep fascia between sartorius and gracilis lower down, continuing subcutaneously alongside the great saphenous vein down to the medial ankle/foot.
• Nerve to vastus medialis: branch of the femoral nerve, enters the canal briefly before supplying vastus medialis.

Clinical relevance: The adductor canal is a common site for regional anaesthetic nerve blocks (adductor canal block) for knee surgery, targeting the saphenous nerve and articular branches while largely sparing motor function to the quadriceps (unlike a femoral nerve block), preserving post-operative mobility.