Femoral Triangle & Femoral Sheath
Anatomy · Lower Limb · lean revision notes
Femoral Triangle & Femoral Sheath
A small wedge of the upper antero-medial thigh that carries an enormous exam yield: it packages the femoral vessels and nerve, the femoral sheath with its three compartments, the femoral canal, Cloquet's node, and the anatomical basis of femoral hernia versus inguinal hernia and femoral arterial puncture. Master the boundaries, the VAN order, and the relations of the hernia neck — these are the lines that decide a question.
Definition & surface anatomy
The femoral triangle (of Scarpa) is a triangular hollow in the upper one-third of the antero-medial thigh, formed when the muscles of the front and medial compartments diverge below the inguinal ligament. It is the proximal gateway through which the chief neurovascular structures pass from the abdomen/pelvis into the lower limb. It is continuous distally with the adductor (subsartorial / Hunter's) canal, which conveys the vessels onward to the popliteal fossa.
High-yield: The femoral triangle is described as an inverted triangle — base above (inguinal ligament), apex below (where sartorius crosses adductor longus).
Boundaries — base, sides, floor & roof
| Boundary | Structure |
|---|---|
| Base (superior) | Inguinal ligament (Poupart's ligament) |
| Lateral side | Medial border of sartorius |
| Medial side | Medial border of adductor longus (classical) |
| Apex | Point where lateral and medial borders meet (sartorius crosses adductor longus) |
| Roof | Skin, superficial fascia (with superficial inguinal lymph nodes, great saphenous vein, superficial branches of femoral artery), fascia lata pierced by cribriform fascia over the saphenous opening |
| Floor (medial → lateral) | Adductor longus, pectineus, iliopsoas (psoas major + iliacus) — gutter-shaped |
High-yield: Floor of the femoral triangle from medial to lateral = adductor longus → pectineus → iliopsoas. The iliopsoas forms the lateral part of the floor and the floor is gutter-/groove-shaped.
A common point of confusion: some texts give the medial boundary as the medial border of adductor longus, while older descriptions used the medial border of the thigh / gracilis. For NEET PG, take medial border of adductor longus as the answer.
Mnemonic for the floor — "PAIL": Pectineus, Adductor longus, Iliopsoas — the three muscles you would step on if you fell into the triangle (think of a "pail" lying in the gutter).
Contents of the femoral triangle
From lateral to medial, remember the order NAVeL (or its reverse VAN):
Femoral nerve → Femoral artery → Femoral vein → (femoral canal/Lymphatics)
| Lateral → Medial | Structure | Relation to femoral sheath |
|---|---|---|
| 1 | Femoral nerve | OUTSIDE the sheath (lies on iliopsoas, lateral to sheath) |
| 2 | Femoral artery | Inside sheath — lateral compartment |
| 3 | Femoral vein | Inside sheath — intermediate compartment |
| 4 | Femoral canal (lymph node + fat) | Inside sheath — medial compartment |
High-yield: The femoral nerve lies OUTSIDE the femoral sheath (about 1 cm lateral), on the iliopsoas. Only the artery, vein and canal lie within the sheath. This is the single most repeated MCQ from this region.
Order under the inguinal ligament from lateral to medial — "NAVY" is a trap; the correct clinical mnemonic is NAVEL (Nerve, Artery, Vein, Empty space [canal], Lymphatics). Reading medially: the femoral vein lies medial to the artery in the triangle.
Other contents: femoral branch of genitofemoral nerve, nerve to pectineus, lateral cutaneous nerve of thigh near the apex, and the termination of the great saphenous vein into the femoral vein (at the saphenous opening, ~3.5 cm below and lateral to the pubic tubercle).
Femoral sheath
The femoral sheath is a funnel-shaped, downward (caudal) prolongation of the abdominal extraperitoneal fascia (transversalis fascia) into the thigh. It surrounds the proximal 3–4 cm of the femoral vessels.
- Anterior wall = downward continuation of transversalis fascia.
- Posterior wall = downward continuation of iliac/iliopsoas fascia.
- It ends ~3–4 cm below the inguinal ligament by fusing with the tunica adventitia of the femoral vessels.
High-yield: Anterior wall of femoral sheath = transversalis fascia; posterior wall = iliopsoas (iliac) fascia. The sheath does not contain the femoral nerve.
Three compartments of the sheath
The sheath is divided by vertical fibrous septa into three compartments (lateral → medial):
| Compartment | Contents |
|---|---|
| Lateral | Femoral artery + femoral branch of genitofemoral nerve |
| Intermediate | Femoral vein |
| Medial | Femoral canal — loose areolar tissue, fat, lymphatics, and the deep inguinal lymph node of Cloquet (Rosenmüller) |
Femoral canal & femoral ring
The femoral canal is the smallest, most medial compartment of the femoral sheath. It is a potential space (~1.25–2 cm long) that allows the femoral vein to expand (e.g., with increased venous return on standing/Valsalva).
Functions / significance:
- Accommodates expansion of the femoral vein.
- Contains fat, lymphatics, and Cloquet's (deep inguinal) lymph node — drains the glans/clitoris and deep lymphatics of the lower limb.
- Provides a weak point through which abdominal contents herniate → femoral hernia.
Femoral ring = the abdominal (upper) opening of the femoral canal; it is closed by extraperitoneal fat = the femoral septum (of Cloquet).
Boundaries of the femoral ring (must memorise)
| Border | Structure |
|---|---|
| Anterior | Inguinal ligament |
| Posterior | Pectineal ligament (of Cooper) + pectineus + superior pubic ramus |
| Medial | Lacunar ligament (of Gimbernat) |
| Lateral | Femoral vein (separated by a thin septum) |
High-yield: Medial boundary of the femoral ring = lacunar ligament (Gimbernat); lateral boundary = femoral vein. The sharp medial lacunar edge is what strangulates a femoral hernia.
Eponyms cluster — learn together: Lacunar ligament = Gimbernat; pectineal ligament = Cooper; deep inguinal node in the canal = Cloquet / Rosenmüller; canal of Scarpa = femoral triangle.
Femoral hernia
A femoral hernia is the protrusion of abdominal contents (usually omentum or small bowel) through the femoral ring → femoral canal → saphenous opening, emerging below and lateral to the pubic tubercle.
Pathway (flow): Femoral ring → femoral canal → saphenous opening (fossa ovalis) → turns upward over the inguinal ligament (acquires a characteristic "retort" shape).
Femoral vs inguinal hernia — the decisive table
| Feature | Femoral hernia | Inguinal hernia |
|---|---|---|
| Relation to pubic tubercle | Below & lateral | Above & medial |
| Relation to inguinal ligament | Below the ligament | Above the ligament |
| Sex predilection | More common in women (wider pelvis, larger ring) | More common in men |
| Neck of sac | Narrow, below inguinal ligament, medial to femoral vein | Above the ligament |
| Strangulation risk | High (narrow rigid ring) | Lower |
| Cough impulse | Often absent / poor | Usually present |
| Reducibility | Often irreducible | Usually reducible |
| Commonest hernia overall | No | Yes (inguinal is commonest) |
High-yield: Femoral hernia neck lies below and lateral to the pubic tubercle; inguinal hernia neck lies above and medial to the pubic tubercle. This pubic tubercle relationship is the classic clinical discriminator.
High-yield: Femoral hernia is more common in women, but the commonest hernia in women is still the inguinal hernia. A frequent trap! Femoral hernias have the highest risk of strangulation of all groin hernias because the lacunar ligament gives an unyielding sharp medial margin.
Surgical caveat — aberrant obturator artery ("corona mortis"): In ~25–30% of people the obturator artery arises from the inferior epigastric artery and crosses the lacunar ligament. Blind incision of the lacunar ligament to release a strangulated femoral hernia may lacerate this vessel → "crown of death" (corona mortis) haemorrhage. Mnemonic: corona mortis = the artery that can kill you when you cut the lacunar (Gimbernat's) ligament.
Surgical approaches to femoral hernia repair:
- Lockwood (low / infra-inguinal) approach.
- Lotheissen (trans-inguinal) approach.
- McEvedy (high) approach — preferred in strangulation/emergency (better bowel access).
Femoral artery — clinical access
The femoral artery is the continuation of the external iliac artery distal to the inguinal ligament. It enters the thigh at the mid-inguinal point = midpoint between the anterior superior iliac spine (ASIS) and the pubic symphysis.
High-yield: Femoral artery passes deep to the mid-inguinal point (ASIS ↔ pubic symphysis). Do not confuse with the midpoint of the inguinal ligament (ASIS ↔ pubic tubercle), which is the surface marking of the deep inguinal ring.
| Landmark | Definition | What lies there |
|---|---|---|
| Mid-inguinal point | Midpoint between ASIS and pubic symphysis | Femoral artery |
| Midpoint of inguinal ligament | Midpoint between ASIS and pubic tubercle | Deep inguinal ring |
Clinical use: The femoral artery is the standard site for arterial puncture/catheterisation (coronary angiography, cardiac catheterisation, femoral arterial blood gas, ECMO/IABP access). Because the vein is medial to the artery, the "NAVEL" order guides puncture — palpate the pulse, aim just medial for the vein and over the pulse for the artery.
High-yield: For arterial access, puncture over the femoral pulse below the inguinal ligament where the artery overlies the head of femur (which provides a firm backing for compression haemostasis). Puncturing above the inguinal ligament risks uncontrollable retroperitoneal haemorrhage.
Branches of femoral artery: superficial epigastric, superficial circumflex iliac, superficial external pudendal, deep external pudendal, and the large profunda femoris (deep femoral) — the chief artery of the thigh, which gives the medial and lateral circumflex femoral and perforating arteries. The femoral artery continues as the popliteal artery after passing through the adductor hiatus.
Femoral vein & femoral nerve — quick facts
- Femoral vein: lies medial to the artery at the inguinal ligament, but posterior to it at the apex of the triangle and in the adductor canal — i.e., the vein "spirals" posterolaterally as you descend. The great saphenous vein drains into it at the saphenous opening.
- Femoral nerve (L2–L4): the largest branch of the lumbar plexus; lies lateral to the artery and OUTSIDE the sheath on iliopsoas. It divides into anterior and posterior divisions ~ below the inguinal ligament. Its longest branch is the saphenous nerve (purely sensory, accompanies the femoral/then great saphenous vein). The femoral nerve supplies the quadriceps, sartorius, pectineus and skin of the antero-medial thigh.
High-yield: Saphenous nerve is the longest cutaneous branch of the femoral nerve and the only branch reaching below the knee (supplies skin over the medial leg/ankle). It travels in the adductor canal but does not supply any muscle.
Adductor (subsartorial/Hunter's) canal — the continuation
Begins at the apex of the femoral triangle, ends at the adductor hiatus in adductor magnus. It is an intermuscular tunnel ~15 cm long.
| Boundary | Structure |
|---|---|
| Anterolateral | Vastus medialis |
| Posterior | Adductor longus (above) & adductor magnus (below) |
| Roof | Sartorius + fibrous (subsartorial) membrane |
Contents: femoral artery, femoral vein, saphenous nerve, nerve to vastus medialis. (The femoral vein lies posterior to the artery here.) Saphenous nerve and nerve to vastus medialis enter the canal but the saphenous nerve alone leaves the canal at its lower end without passing through the hiatus.
Complications & clinical correlates
- Strangulated femoral hernia — surgical emergency; bowel obstruction + ischaemia; corona mortis bleeding risk during release.
- Femoral artery catheterisation complications — haematoma, pseudoaneurysm, AV fistula, retroperitoneal bleed (high puncture), arterial thrombosis/limb ischaemia.
- Saphenous opening and varicose veins — incompetent saphenofemoral junction.
- Psoas abscess — tracks along iliopsoas (floor of triangle) and may point as a swelling below the inguinal ligament, mimicking a femoral hernia or femoral artery aneurysm.
- Enlarged Cloquet's node — can mimic a femoral hernia (lump in the femoral canal region).
Key differentials of a groin lump (below inguinal ligament)
- Femoral hernia (below & lateral to pubic tubercle, ± cough impulse).
- Saphena varix (compressible, disappears on lying down, fluid thrill on coughing).
- Enlarged inguinal/Cloquet lymph node.
- Femoral artery aneurysm / pseudoaneurysm (expansile pulsatile swelling).
- Psoas abscess / psoas bursa.
- Lipoma of the cord / ectopic testis (mainly inguinal region).
High-yield: Saphena varix classically shows a fluid thrill / Cruveilhier's sign on coughing and disappears on lying down — distinguishing it from a femoral hernia.
Recently asked / exam angle
- "Which structure does NOT lie within the femoral sheath?" → Femoral nerve (perennial favourite).
- "Medial boundary of the femoral ring?" → Lacunar ligament (Gimbernat).
- "Floor of femoral triangle from medial to lateral?" → Adductor longus, pectineus, iliopsoas.
- "Femoral artery is surface-marked at?" → Mid-inguinal point (ASIS to pubic symphysis).
- "Neck of femoral hernia is ___ to the pubic tubercle?" → Below and lateral.
- "Artery damaged when lacunar ligament is incised in femoral hernia surgery?" → Aberrant obturator artery (corona mortis).
- "Deep inguinal lymph node in the femoral canal?" → Node of Cloquet/Rosenmüller.
- "Commonest hernia in women?" → Inguinal (femoral is more common in women than in men, but inguinal still tops overall).
- "Approach for strangulated femoral hernia?" → McEvedy (high) approach.
- Image-based: identify VAN order on a cadaveric/diagram of the groin.
Rapid revision
- Femoral triangle base = inguinal ligament; lateral = sartorius; medial = adductor longus; apex distal.
- Floor (medial→lateral) = adductor longus → pectineus → iliopsoas ("PAIL").
- Contents lateral→medial = Nerve, Artery, Vein, Canal ("NAVEL").
- Femoral nerve is OUTSIDE the sheath; only artery + vein + canal are inside.
- Sheath = prolongation of transversalis fascia (anterior) + iliac fascia (posterior).
- Three sheath compartments: lateral = artery, intermediate = vein, medial = femoral canal.
- Femoral canal contains fat + lymphatics + Cloquet's node; closed above by femoral septum.
- Femoral ring medial border = lacunar ligament (Gimbernat); lateral = femoral vein; posterior = pectineal ligament (Cooper).
- Femoral hernia neck = below & lateral to pubic tubercle; inguinal = above & medial; femoral commoner in women, highest strangulation risk.
- Corona mortis = aberrant obturator artery crossing the lacunar ligament — beware during femoral hernia release.
- Femoral artery = mid-inguinal point (ASIS↔pubic symphysis); deep ring = midpoint of inguinal ligament (ASIS↔pubic tubercle).
- Adductor (Hunter's) canal carries femoral artery, vein, saphenous nerve, nerve to vastus medialis; ends at adductor hiatus → popliteal artery.