Femoral Triangle

Boundaries

Floor

• Iliopsoas (laterally) - descending from the abdomen
• Pectineus (medially)
• Adductor longus completes the medial floor

Roof

Contents (lateral to medial)

Femoral Sheath

• Continuous superiorly with transversalis fascia (anterior) and iliac fascia (posterior) of the abdomen
• Divided into 3 compartments:
  1. Lateral - femoral artery
  2. Intermediate - femoral vein
  3. Medial (femoral canal) - lymphatics + Cloquet's (Rosenmüller) node

• Anteriorly: inguinal ligament
• Posteriorly: pectineus muscle/pectineal ligament
• Medially: lacunar ligament
• Laterally: femoral vein

Iliopectineal Arch (Muscular vs. Vascular Compartments)

• Vascular compartment (medial to arch): femoral artery, femoral vein, femoral branch of genitofemoral nerve, deep inguinal lymphatics
• Muscular compartment (lateral to arch): iliopsoas muscle, femoral nerve, lateral femoral cutaneous nerve

Key Relations and Clinical Points

Femoral Pulse

Vascular Access

• Arterial catheterization - coronary angiography, angioplasty, peripheral vascular interventions
• Venous access - right heart catheterization, pulmonary artery access, renal/gonadal vein sampling

Femoral Hernia

• More common in women (due to wider pelvis/femoral ring)
• Passes through the femoral canal, inferior and lateral to the pubic tubercle (distinguishes it from an inguinal hernia, which lies superior and medial to the pubic tubercle)
• High risk of strangulation due to the rigid boundaries of the femoral ring

Femoral Nerve Injury

• The femoral nerve (L2-L4) lies lateral to the femoral sheath and artery
• Injury causes weakness of hip flexion and knee extension, loss of knee jerk, and sensory loss over the anteromedial thigh and medial leg (via saphenous nerve)

Adductor Canal (Subsartorial/Hunter's Canal)

Summary Table

Lumbar Plexus

Formation and Location

• The plexus forms within the substance of the psoas major muscle, anterior to the transverse processes of the lumbar vertebrae.
• It receives a contribution from T12 (subcostal nerve).
• L4 is called the nervus furcalis because it splits - part goes to the lumbar plexus and part (with L5) forms the lumbosacral trunk, which continues into the sacral plexus.
• The L2, L3, L4 roots each divide into anterior and posterior divisions:
  • Anterior divisions → Obturator nerve
  • Posterior divisions → Femoral nerve + lateral femoral cutaneous nerve

Branches

Complete Branch Table

Individual Branches in Detail

1. Iliohypogastric Nerve (L1)

• Arises from the anterior ramus of L1 (together with ilioinguinal as a single trunk initially).
• Crosses anterior to quadratus lumborum, posterior to the kidney.
• Pierces transversus abdominis, then runs between it and internal oblique.
• Lateral cutaneous branch: supplies posterolateral gluteal skin.
• Anterior cutaneous branch: pierces external oblique above the superficial inguinal ring; supplies skin just above the pubis.

2. Ilioinguinal Nerve (L1)

• Travels parallel to and just below the iliohypogastric nerve.
• Enters the inguinal canal through the deep inguinal ring, exits through the superficial inguinal ring.
• Supplies skin of upper medial thigh, root/dorsal penis and upper scrotum (male), or mons pubis and labium majus (female).
• Surgical note: can be injured in herniorrhaphy, causing persistent groin neuralgia.

3. Genitofemoral Nerve (L1, L2)

• Pierces psoas major anteriorly and descends on its anterior surface.
• Divides into:
  • Genital branch: enters the inguinal canal, supplies cremaster muscle and scrotal/labial skin.
  • Femoral branch: passes under the inguinal ligament in the vascular compartment, supplies upper anterior thigh skin.

4. Lateral Femoral Cutaneous Nerve / LCNT (L2, L3)

• Formed from posterior divisions of L2 and L3.
• Exits the lateral border of psoas, crosses iliacus, passes under the inguinal ligament near the ASIS.
• Purely sensory: anterior and lateral thigh to the knee.
• Compression near the ASIS causes meralgia paresthetica - burning/numbness/dysesthesia over the lateral thigh. Associated with tight belts, obesity, pregnancy, or lumbar disc protrusion.

5. Obturator Nerve (L2, L3, L4) - Anterior Divisions

• Descends through psoas, exits medially, runs posterior to common iliac vessels.
• Exits the pelvis through the obturator foramen to enter the medial thigh.
• Divides into:
  • Anterior division: adductor longus, gracilis, adductor brevis, pectineus; articular branch to hip.
  • Posterior division: obturator externus, adductor magnus; articular branch to knee.
• Sensory: medial thigh, occasionally medial knee.
• Can be compressed by pelvic masses (tumor, gravid uterus) or injured in pelvic fractures.

6. Femoral Nerve (L2, L3, L4) - Posterior Divisions

• The largest branch of the lumbar plexus.
• Descends through psoas, exits at the lower lateral border, runs between psoas and iliacus under the iliacus fascia.
• Passes posterior to the inguinal ligament and enters the femoral triangle (lateral to femoral artery, outside the femoral sheath).
• Immediately divides into multiple branches in the thigh:
  • Motor: iliacus, pectineus, sartorius, all four quadriceps muscles.
  • Sensory (cutaneous): medial and intermediate cutaneous nerves of thigh (anterior thigh).
  • Saphenous nerve (longest cutaneous branch): descends through the adductor canal, supplies medial leg and foot down to the medial malleolus.
  • Articular: hip joint, knee joint.

Lumbosacral Trunk

Clinical Correlates

Key Memory Aid (Branches of Lumbar Plexus)

• Iliohypogastric (L1)
• Ilioinguinal (L1)
• Genitofemoral (L1, L2)
• Lateral cutaneous nerve of thigh (L2, L3)
• Obturator (L2-L4)
• Femoral (L2-L4)