Ch03: Lower Limb II — Anterior & Medial Thigh（股前内侧区）

# Ch03: Lower Limb II — Anterior & Medial Thigh (Femoral Triangle, Adductor Canal)

Preparatory Mindset

The anterior thigh is clinically the most important region of the lower limb — it contains the femoral triangle (arterial access, femoral vein puncture), the femoral sheath & canal (femoral hernias), and the adductor canal (Hunter's canal).

Exam mindset: "Boundaries of the femoral triangle", "contents of the femoral sheath from lateral to medial", "what is in the femoral canal (and why femoral hernias are more common in women)", "what passes through the adductor canal" — these are the classic 局解 questions. Femoral hernia questions also appear in the 100-Concepts deck (concept 18).

Core Concepts

1. Femoral triangle

- Superior: inguinal ligament - Lateral: medial border of sartorius - Medial: medial border of adductor longus - Floor (posterior): iliopsoas & pectineus - Roof (anterior): fascia lata + cribriform fascia (pierced by great saphenous vein through the saphenous opening)

• Boundaries:
• Contents (lateral → medial): femoral nerve, femoral artery, femoral vein, femoral canal (lymphatics & deep inguinal nodes) — mnemonic "NAVY" (Nerve, Artery, Vein, lymphatics-Y)

2. Femoral sheath & femoral canal (concept 18 — MUST KNOW)

• Femoral sheath: funnel-shaped extension of transversalis fascia (anterior) and iliacus fascia (posterior) into the thigh, deep to the inguinal ligament; encloses the femoral artery (lateral), femoral vein (middle), and femoral canal (medial)
• Femoral canal: the most medial compartment of the sheath; contains lymphatic vessels and the deep inguinal (Cloquet's) node; normally occupied by loose connective tissue
• Femoral ring: the abdominal opening of the canal, bounded medially by the lacunar ligament (clinically important — this is the sharp edge that strangulates a femoral hernia)
• Femoral hernia: herniation through the femoral ring into the canal → more common in women (wider pelvis) → presents below the inguinal ligament, lateral to the pubic tubercle → high strangulation risk because of the rigid lacunar ligament
• Clinical: femoral hernia lies inferior & lateral to the pubic tubercle; inguinal hernia lies superior & medial to it — key exam distinction

3. Femoral artery & its branches

• Continues from the external iliac artery behind the inguinal ligament, at the midpoint of the inguinal ligament (surface landmark: midway between ASIS & pubic tubercle)
• Pulse: felt just below the inguinal ligament, lateral to the femoral vein (used for femoral artery puncture/cannulation)
• Branches: superficial epigastric, superficial circumflex iliac, superficial & deep external pudendal; deep femoral (profunda femoris) artery — the main branch, giving medial & lateral circumflex femoral arteries and 3 perforating arteries (supply posterior thigh/hamstrings)
• Clinical: femoral artery is the second most common site for atherosclerotic occlusion; used for angiography, cardiac catheterization access

4. Adductor canal (Hunter's / subsartorial canal)

• Position: middle third of the thigh, deep to sartorius; from the apex of the femoral triangle to the adductor hiatus (~15 cm long)
• Boundaries: anterior = sartorius + vastus medialis; posterior = adductor longus & adductor magnus
• Contents: femoral artery & vein, saphenous nerve, nerve to vastus medialis (femoral n. branch); the saphenous nerve leaves the canal to accompany the great saphenous vein
• Clinical: the adductor hiatus is where the femoral vessels become the popliteal vessels

5. Medial (adductor) compartment of thigh

• Muscles: pectineus, adductor longus, adductor brevis, adductor magnus, gracilis
• Innervation: obturator nerve (L2-L4) — except pectineus (femoral n.) and part of adductor magnus (sciatic n./tibial portion)
• Obturator artery & vein: pass through the obturator canal with the obturator nerve
• Clinical: obturator nerve injury → weak thigh adduction; obturator hernia (rare, Richter type) → pain down medial thigh (Howship–Romberg sign)

High-Yield Points

• Mnemonic "NAVY": femoral sheath contents lateral→medial = Nerve, Artery, Vein, Y (lymphatics in femoral canal)
• Femoral ring boundaries: "LIPV" — Lateral: femoral vein; Inferior: inguinal ligament; Posterior (P): pectineus/iliopectineal; Medial: lacunar ligament (the stricture that strangulates)
• Femoral vs inguinal hernia: femoral = below & lateral to pubic tubercle, more common in women, high strangulation; inguinal = above & medial, more common in men
• Adductor canal contents: "SAVES the nerve" — Saphenous nerve, Artery, Vein, (nerve to) vastus medialis... (use: Femoral A/V + saphenous n. + nerve to vastus medialis)
• Deep femoral artery: main supply of the posterior thigh via perforating branches — ligation of femoral artery below deep femoral origin preserves limb perfusion
• Obturator nerve: only motor to adductors (except pectineus & hamstring part of magnus) — obturator neuropathy → weak adduction, "scissoring" gait

Topic Summary

The anterior & medial thigh is anchored by the femoral triangle (inguinal ligament / sartorius / adductor longus; NAVY contents), the femoral sheath & canal (medial compartment with lymphatics — the site of femoral hernia, strangulated by the lacunar ligament, more common in women, below & lateral to the pubic tubercle), the femoral artery (mid-inguinal point, giving the deep femoral artery with medial/lateral circumflex & perforating branches), the adductor canal (sartorius/adductor magnus/adductor longus; femoral A&V + saphenous nerve + nerve to vastus medialis; ends at the adductor hiatus), and the obturator nerve supplying the adductors.