Femoral triangle

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Femoral Triangle

The femoral triangle is a wedge-shaped (pyramidal) depression in the upper anterior thigh, at the junction between the anterior abdominal wall and the lower limb. It is a key anatomical region because major neurovascular structures pass through it from the abdomen into the lower extremity.

Boundaries

Boundary	Structure
Base (superior)	Inguinal ligament
Lateral border	Medial margin of sartorius muscle
Medial border	Medial margin of adductor longus muscle
Apex (inferior)	Where the two borders meet; continuous with the adductor canal

Floor (from lateral to medial): iliopsoas muscle (lateral half) + pectineus and adductor longus muscles (medial half).

Roof: Fascia lata (deep fascia of the thigh) + skin and superficial fascia. The great saphenous vein pierces the roof through the saphenous opening (fossa ovalis) to drain into the femoral vein.

Contents (Lateral to Medial)

Contents of the Femoral Triangle - schematic diagram

The classic mnemonic is NAVEL (Nerve, Artery, Vein, Empty space [femoral canal], Lymphatics):

Structure	Notes
Femoral nerve	Most lateral; outside the femoral sheath
Femoral artery	Continuation of the external iliac artery
Femoral vein	Medial to the artery
Femoral canal	Most medial compartment; contains lymphatics (empty space = potential hernia site)

Femoral Sheath

Within the femoral triangle, the femoral artery, vein, and lymphatics are enclosed in a funnel-shaped fascial sleeve called the femoral sheath:

Continuous superiorly with transversalis fascia (anteriorly) and iliac fascia (posteriorly)
Divided internally into three compartments:
1. Lateral compartment - femoral artery
2. Intermediate compartment - femoral vein
3. Medial compartment (femoral canal) - lymphatics and areolar tissue

The femoral nerve is lateral to the sheath and is NOT enclosed within it.

Femoral Canal and Femoral Hernia

The femoral canal is the most medial, cone-shaped compartment of the femoral sheath. Its superior opening is the femoral ring, bounded by:

Anteriorly: inguinal ligament
Medially: lacunar ligament
Posteriorly: pectineal (Cooper's) ligament and the pectineus muscle
Laterally: femoral vein

The femoral ring is a potential weak point in the lower abdominal wall and is the site of femoral hernias. Femoral hernias are more common in women (wider pelvis) and emerge below and lateral to the pubic tubercle (distinguishing them from inguinal hernias, which emerge above and medial to the pubic tubercle).

The Femoral Artery

The femoral artery is the continuation of the external iliac artery below the inguinal ligament.
Its pulse is palpable just inferior to the inguinal ligament, midway between the anterior superior iliac spine (ASIS) and the pubic symphysis (the mid-inguinal point).
In the femoral triangle it gives off the profunda femoris (deep femoral artery) - the principal artery supplying the thigh muscles.
The femoral artery and vein exit the femoral triangle at its apex and pass into the adductor canal (subsartorial canal / Hunter's canal), emerging through the adductor hiatus to become the popliteal vessels behind the knee.

Vascular Compartment vs. Muscular Compartment (below the inguinal ligament)

THIEME Atlas - inguinal compartments, anterior view

The space below the inguinal ligament is divided by the iliopectineal arch into:

Muscular (lateral) compartment: iliopsoas, femoral nerve, lateral femoral cutaneous nerve
Vascular (medial) compartment: femoral artery, femoral vein, femoral branch of the genitofemoral nerve, deep inguinal lymphatics (Rosenmüller node is contained within the femoral canal here)

Apex and Continuation

The apex of the femoral triangle points inferiorly and leads into the adductor canal, which runs medially down the thigh between the vastus medialis anterolaterally and the adductor longus/magnus posteromedially, roofed by the sartorius. This continuation carries the femoral artery, femoral vein, and saphenous nerve (branch of femoral nerve) into the popliteal fossa.

Clinical Relevance

Femoral pulse - First choice site for pulse palpation in cardiac arrest; used for femoral artery catheterization in angiography, coronary angioplasty, and cardiac catheterization.
Femoral vein access - Provides access to the right heart, pulmonary vessels, renal veins, and superior vena cava via catheter.
Femoral hernia - Abdominal contents prolapse through the femoral ring into the femoral canal. The rigid lacunar ligament medially makes strangulation a serious risk. Treatment is surgical.
Femoral nerve block - Anesthesia of the femoral nerve in the femoral triangle provides analgesia for the anterior thigh and knee (used in hip/femur fractures and knee surgery).
Lymph node enlargement - Inguinal/femoral lymph nodes in the triangle are often palpable in lower limb or perineal infections.
Deep vein thrombosis - The femoral vein is a common site for DVT and is accessed for thrombolysis or filter placement.

Sources: Gray's Anatomy for Students (9780323934237, pp. 675-676, 771); THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System (9781626237186, p. 573)

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