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Femoral Triangle - Complete Anatomy

Overview

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Boundaries

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Contents (Lateral to Medial: NAVY or NAVeL)

• N - Femoral Nerve
• A - Femoral Artery
• V - Femoral Vein
• eL - Empty space (femoral canal) + Lymphatics

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1. Femoral Nerve

• Largest branch of the lumbar plexus (L2, L3, L4)
• Descends through the muscular compartment (lacuna musculorum), lateral to the iliopectineal arch
• Lies lateral to the femoral artery in the femoral triangle
• NOT enclosed within the femoral sheath (this is a key exam point)
• Divides into multiple branches within the femoral triangle:
  • Motor branches to quadriceps, sartorius, pectineus
  • Cutaneous branches (intermediate and medial cutaneous nerves of the thigh)
  • Gives rise to the saphenous nerve - the longest branch, which follows the femoral artery into the adductor canal

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2. Femoral Artery

• Continuation of the external iliac artery, which becomes the femoral artery as it passes under the inguinal ligament
• Palpable just inferior to the inguinal ligament, midway between the ASIS and pubic symphysis (midpoint of the inguinal ligament)
• Passes vertically through the femoral triangle, then continues into the adductor canal
• Exits through the adductor hiatus to become the popliteal artery behind the knee

Branches in the Femoral Triangle

• Medial circumflex femoral artery - main blood supply to the femoral head/neck
• Lateral circumflex femoral artery - ascending, descending, and transverse branches
• 3 perforating arteries - supply the posterior thigh muscles

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3. Femoral Vein

• Continuation of the popliteal vein superiorly
• Lies medial to the femoral artery in the femoral triangle
• Receives the great saphenous vein through the saphenous opening (cribriform fascia) just inferior to the inguinal ligament
• Together with the femoral artery and lymphatics, it is enclosed in the femoral sheath

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4. Lymphatics

• Lie in the most medial compartment of the femoral sheath - the femoral canal
• The Cloquet's node (or Rosenmüller node) is a deep inguinal lymph node lying at the femoral ring
• Drain lymph from the lower limb upward to the external iliac nodes

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The Femoral Sheath

• Superiorly continuous with: transversalis fascia (anteriorly) and iliac fascia (posteriorly)
• Merges inferiorly with vessel adventitia about 4 cm below the inguinal ligament
• Divided into 3 compartments:

Femoral Canal and Femoral Hernia

• Anteriorly: inguinal ligament
• Posteriorly: pectineus muscle + its fascia
• Medially: lacunar ligament (Gimbernat's ligament)
• Laterally: femoral vein

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Iliopectineal Arch - The Compartment Divider

• Lacuna musculorum (lateral, muscular compartment): contains iliopsoas, femoral nerve, lateral femoral cutaneous nerve
• Lacuna vasorum (medial, vascular compartment): contains femoral artery, vein, lymphatics (all within femoral sheath), and femoral branch of genitofemoral nerve

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Adductor Canal (Hunter's Canal) - Continuation from Apex

• Bounded by: vastus medialis (anterolateral), adductor longus then adductor magnus (posterior), sartorius (roof)
• Contains: femoral artery, femoral vein, saphenous nerve, nerve to vastus medialis, and medial femoral cutaneous nerve
• Ends at the adductor hiatus in adductor magnus → femoral vessels become popliteal vessels

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Clinical Relevance

1. Femoral Pulse and Vascular Access

• Cardiac catheterization (coronary angiography, angioplasty)
• Peripheral vascular access (aortography, renal/gonadal vein cannulation)
• Femoral vein access: allows catheterization up to the right heart, pulmonary artery, superior vena cava, and renal veins

2. Femoral Hernia

• Passes through the femoral ring into the femoral canal
• More common in women
• Presents as a mass below and lateral to the pubic tubercle
• Risk of strangulation is high because the femoral ring has rigid bony/ligamentous boundaries

3. Femoral Nerve Block

4. Deep Vein Thrombosis (DVT)

5. Femoral Nerve Injury

• Caused by trauma, pelvic surgery, or psoas hematoma
• Results in: weakness of knee extension (quadriceps), loss of knee jerk reflex (L3/L4), sensory loss over anterior thigh and medial leg (saphenous nerve territory)

6. Cruciate Anastomosis

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Summary Table

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KNEE JOINT - Long Answer Question (LAQ)

1. Introduction

1. Medial tibiofemoral joint - between medial femoral condyle and medial tibial condyle
2. Lateral tibiofemoral joint - between lateral femoral condyle and lateral tibial condyle
3. Patellofemoral joint - between the patella and the anterior patellar surface of the femur

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2. Bones and Articular Surfaces

Femur (lower end)

• Two large condyles (medial and lateral) project posteriorly and inferiorly
• The articular surfaces on the posterior femoral condyles (curved and rounded) articulate with the tibia in flexion
• The surfaces on the inferior femoral condyles (broad and flat) articulate in full extension - this makes the joint more stable in extension
• The anterior patellar surface (V-shaped trochlear groove) articulates with the patella
• The intercondylar fossa (notch) separates the two condyles posteriorly and houses the cruciate ligaments

Tibia (upper end)

• Medial and lateral tibial condyles form the tibial plateau
• Medial plateau is oval, slightly concave
• Lateral plateau is more circular
• Between them: the intercondylar area where the cruciate ligaments and menisci attach
• The tibial tuberosity on the anterior surface is the attachment point for the patellar ligament

Patella

• Largest sesamoid bone in the body
• Embedded in the quadriceps femoris tendon
• Posterior surface articulates with the femoral trochlear groove
• Increases the mechanical advantage of the quadriceps by ~30%

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3. Menisci

• Deepen the articular surfaces (act as "shock absorbers")
• Distribute compressive load across a wider area
• Improve joint stability and lubrication
• Guide the rolling and gliding movements of the femoral condyles

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4. Joint Capsule

• Anteriorly: thin; attached to margins of the patella; reinforced by expansions from vastus medialis and lateralis (medial and lateral patellar retinacula), and the iliotibial tract anterolaterally
• Posteriorly: reinforced by the oblique popliteal ligament (expansion of semimembranosus tendon, running superolaterally) and the arcuate popliteal ligament
• The tendon of popliteus passes through an aperture in the posterolateral capsule

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5. Ligaments

A. Patellar Ligament

• Continuation of the quadriceps femoris tendon below the patella
• Attached: apex of patella → tibial tuberosity
• Very strong; tested by the knee-jerk reflex (L3, L4)

B. Collateral Ligaments

C. Cruciate Ligaments

Key fact: ACL injury causes immediate hemarthrosis because the ligament is intracapsular with a rich blood supply.

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6. Synovial Membrane

• Suprapatellar bursa (pouch): extends 3-4 cm above the patella between the femur and quadriceps tendon - this is continuous with the main joint cavity and is the largest recess. Effusion here produces the "horseshoe swelling" above and around the patella
• Infrarapatellar fat pad: lies between the patellar ligament and the synovial membrane; contains the infrapatellar fold (ligamentum mucosum) which extends to the intercondylar fossa
• Alar folds flank the infrapatellar fat pad on each side

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7. Bursae Around the Knee

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8. Movements of the Knee Joint

Rotation is only possible when the knee is flexed (collateral ligaments become lax). It is completely prevented in full extension.

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9. Locking and Unlocking Mechanism

Locking (Extension → Full Extension)

1. The medial femoral condyle has a larger articular surface than the lateral; after the lateral condyle exhausts its articular surface, the medial condyle continues to roll
2. This causes medial rotation of the femur on the tibia (or lateral rotation of tibia if foot is free), "screwing" the joint tight
3. All ligaments become taut
4. The body's center of gravity falls anterior to the axis of the knee joint, passively maintaining extension
5. Result: the joint is "locked" - requiring minimal muscular effort to stand

Unlocking

• Initiated by the popliteus muscle (the "key to unlock the knee")
• Popliteus laterally rotates the femur on the fixed tibia (or medially rotates tibia on fixed femur)
• This "unscrews" the joint, freeing the collateral ligaments and allowing flexion

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10. Vascular Supply

• Descending genicular branch of the femoral artery
• 5 genicular branches of the popliteal artery (medial/lateral superior and inferior genicular + middle genicular)
• Circumflex fibular artery
• Anterior and posterior recurrent branches of the anterior tibial artery
• Descending branch of the lateral circumflex femoral artery

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11. Nerve Supply

• Femoral nerve (and its branches - nerve to vastus medialis, saphenous nerve) - anterior and medial
• Obturator nerve - medial aspect
• Common peroneal nerve - lateral aspect (via its articular branch)
• Tibial nerve - posterior aspect

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12. Relations

Anterior

• Quadriceps femoris tendon, patella, patellar ligament
• Prepatellar and infrapatellar bursae

Posterior (Popliteal Fossa)

• Popliteal artery (most anterior - closely related to posterior capsule, vulnerable in posterior dislocations)
• Popliteal vein (posterior to artery)
• Tibial nerve (most superficial)
• Common peroneal nerve
• Popliteal lymph nodes
• Small saphenous vein terminal part

Medial

• Tibial collateral ligament, sartorius, gracilis, semitendinosus (pes anserinus), semimembranosus

Lateral

• Fibular collateral ligament, biceps femoris, iliotibial tract, common peroneal nerve

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13. Clinical Anatomy

Unhappy Triad (O'Donoghue's Triad)

1. Medial (tibial) collateral ligament tear
2. Anterior cruciate ligament tear
3. Medial meniscus tear

Clinical Tests

Joint Aspiration (Arthrocentesis)

Patellofemoral Pain Syndrome

Osteoarthritis of the Knee

• Most common joint affected in the body
• Loss of medial compartment cartilage → genu varum (bow leg)
• Loss of lateral compartment cartilage → genu valgum (knock knee)
• Findings: reduced joint space, subchondral sclerosis, osteophytes, cyst formation

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14. Summary Table

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