Thigh, knee, and popliteal fossa

The lower extremity consists of the hip, thigh, knee, popliteal fossa, leg (crus), ankle, and foot. The thigh is the portion of the lower limb extending from the hip to the knee. The knee is the joint that connects the thigh and the leg (crus). The space posterior to the knee is referred to as the popliteal fossa. The femur is the long bone of the thigh, which articulates proximally with the acetabulum of the pelvis to form the hip joint and distally with the tibial condyles and the patella to form the knee joint. The muscles of the thigh are separated by intermuscular septa into the anterior, posterior, and medial (adductor) compartments, all of which are enclosed by the fascia lata. The anterior compartment, which is innervated by the femoral nerve, contains muscles involved in knee extension and hip flexion. The posterior compartment (hamstrings), which is innervated by the tibial part of the sciatic nerve, contains muscles involved in hip extension and knee flexion. The medial (adductor) compartment, which is innervated by the obturator nerve, contains muscles involved in hip adduction, flexion, and external rotation. The femoral triangle is a triangular intermuscular space in the anterior thigh through which pass major neurovascular structures (femoral artery, femoral vein, femoral nerve). Additional noteworthy anatomic regions in the thigh include the femoral canal, femoral ring, and adductor canal. The thigh is perfused by the femoral and obturator arteries and drained by the long saphenous vein (superficial) and the femoral vein (deep). The knee joint consists of the tibiofemoral and patellofemoral joints. Soft-tissue structures of the knee include the menisci (medial and lateral), the cruciate ligaments (anterior and posterior), the collateral ligaments (medial and lateral), and the bursae (prepatellar bursa, anserine bursa). The knee joint allows for flexion and extension of the leg as well as a certain degree of internal rotation and external rotation. The knee joint is perfused by branches of the femoral and popliteal vessels and innervated by the genicular branches of the femoral, obturator, tibial, and common peroneal nerves. The popliteal fossa is a diamond-shaped region on the posterior aspect of the knee, which contains the popliteal artery and vein and the tibial and common peroneal nerve.

Overview

• The femur is the longest and strongest bone of the body.
• It articulates with:
  • Acetabulum of the pelvis to form the hip joint
  • Tibial condyles to form the knee joint

Important landmarks

• Head
  • A nearly spherical structure that articulates with the acetabulum of the pelvis.
  • Has a notch, known as the fovea capitis, to which the round ligament of the hip is attached
  • Vascular supply
    • Branch of the obturator artery (travels through the round ligament of the femur)
    • Arterial ring around the femoral neck: formed by the medial and lateral femoral circumflex arteries
  • Clinical significance
    • Osteonecrosis of the femoral head
    • Femoral head fracture
• Neck
  • Connects the head to the shaft of the femur
  • Clinical significance: femoral neck fracture
• Greater trochanter: lies on the lateral aspect of the junction between the neck and shaft of the femur
• Lesser trochanter: lies on the posteromedial aspect of the junction between the neck and shaft of the femur
• Shaft
  • Linea aspera: ridge seen on the posterior aspect of the shaft
  • Pectineal line: medial border of the linea aspera to which the pectineus muscle is attached
  • Adductor tubercle: a prominence above the medial femoral condyle to which the adductor magnus muscle is attached
• Distal end
  • Medial and lateral condyles
    • The inferior surface articulates with the tibial condyles to form the knee joint.
    • The anterior surface articulates with the patella to form the patellofemoral joint.
  • Intercondylar fossa: groove between the condyles to which the anterior and posterior cruciate ligaments are attached

Overview

The deep fascia of the thigh separates the muscles into three compartments:

• Anterior compartment
  • Common nerve supply: femoral nerve
  • Common function: knee extension
• Posterior compartment
  • Common origin: the ischial tuberosity
  • Common nerve supply: tibial part of the sciatic nerve
  • Common function: hip extension and knee flexion
• Medial compartment
  • Common nerve supply: obturator nerve
  • Common function: hip adduction

Anterior compartment of the thigh

Posterior compartment of the thigh

Medial compartment of the thigh

Femoral triangle

• Definition: a triangular intermuscular space in the superomedial aspect of the anterior thigh through which the major neurovascular structures of the lower limb pass
• Boundaries
  • Superior: inguinal ligament
  • Lateral: medial border of the sartorius
  • Medial: medial border of the adductor longus
• Floor: adductor longus, iliopsoas, and pectineus muscles
• Roof: fascia lata
• Contents (lateral to medial)
  • Femoral nerve
  • Femoral branch of the genitofemoral nerve
  • Femoral artery
  • Femoral vein
  • Femoral canal
  • Lymphatics
• Clinical significance
  • Easy access into the arterial system via the femoral artery (e.g., coronary angiography)
  • Easy access into the central venous system via the femoral vein
  • Femoral hernia: herniation of intra-abdominal contents through the femoral canal

Venous close to penis. Nerves close to hip curves.

NAVEL: Nerve, Artery, Vein, Empty space (femoral canal), and Lymphatics (order of the femoral triangle contents, from lateral to medial).

Femoral canal

• Definition: a cylindrical space enclosed within the femoral sheath that contains loose areolar tissue and lymphatics
• Boundaries
  • Anterior: inguinal ligament
  • Posterior: pubic ramus and pectineal ligament
  • Medial: lacunar ligament
  • Lateral: femoral vein
• Clinical significance
  • Accommodates venous dilation of the femoral vein in response to increased venous return from the lower limbs
  • The femoral canal is wider in women, so women are more susceptible to developing femoral hernias.

Femoral sheath

• Definition: connective tissue formed by the iliac fascia and transversalis fasciae about 3–4 cm below the inguinal ligament
• Contents
  • Encloses most contents of the femoral triangle, including:
    • Femoral vein
    • Femoral artery
    • Femoral canal
    • Deep inguinal lymph nodes
  • Does not cover the femoral nerve
  • Vertical septae divide the sheath into compartments for the contents of the femoral triangle (see above).

Femoral ring

• Definition: the abdominal opening of the femoral canal
• Boundaries
  • Anterior: inguinal ligament
  • Posterior: pectineal ligament
  • Medial: lacunar ligament
  • Lateral: medial border of the femoral vein

Adductor canal

• Definition: a tunnel that extends from the apex of the femoral triangle to the adductor hiatus within the adductor magnus
• Boundaries
  • Anterior: sartorius
  • Posterior: adductor magnus and longus
  • Lateral: vastus medialis
• Contents
  • Femoral vessels
  • Saphenous nerve
  • Nerve to the vastus medialis
• Clinical significance: Regional anesthesia to the leg and distal thigh can be achieved by anesthetizing the saphenous nerve within the adductor canal.

Saphenous opening

• Definition: an opening in the fascia lata of the thigh located 4 cm below and lateral to the pubic tubercle (a palpable bony prominence on the superior ramus of the pubic bone)
• Clinical significance: site of the saphenofemoral junction
  • The great saphenous vein penetrates a fascia that covers the saphenous opening (known as the cribriform fascia) and drains into the femoral vein.
  • For open surgery of varicose veins, a skin incision and main dissection are performed in this region.

Arteries

Femoral artery

• Origin: continuation of the external iliac artery
• Course
  • Begins behind the inguinal ligament at the midinguinal point
  • Travels through the femoral triangle and the adductor canal (anterior thigh)
  • Enters the posterior compartment of the thigh through the adductor hiatus where it continues as the popliteal artery
• Supplies: all compartments of the thigh

Femoral artery branches

• Superficial branches (superficial femoral artery): supply the subcutaneous tissue of the lower abdomen and perineal region
  • Superficial epigastric artery
  • Superficial circumflex iliac artery
  • Superficial external pudendal artery
• Deep branches
  • Profunda femoris artery
    • Main branch of the femoral artery and the main artery of the thigh
    • Named branches: medial and lateral circumflex femoral arteries that supply the head and neck of femur (see “Osteonecrosis of the femoral head”)
    • Clinical significance: becomes the main collateral in femoropopliteal disease
  • Deep external pudendal artery: supplies the skin of the perineum

Obturator artery

• Origin: branch of the internal iliac artery
• Supplies: medial compartment of the thigh

Veins

• Superficial vein: long saphenous vein (see “Vascular supply” in “The leg, ankle, and foot” article for more details)
• Deep vein: femoral vein
  • Origin
    • Continuation of the popliteal vein
    • Begins at the adductor hiatus and accompanies the femoral artery throughout its course
  • Becomes the external iliac vein behind the inguinal ligament
  • Tributaries
    • Profunda femoris vein (deep vein of the thigh)
    • Lateral and medial circumflex femoral veins

Motor and sensory innervation

The motor and sensory nerve of the thigh arise from the lumbar plexus and sacral plexus.

Dermatomal distribution of the thigh and knee

• Anterior thigh (craniocaudal): L2–L4
• Posterior thigh (lateromedial and caudocranial): S1–S4
• Anterior knee: L3, L4
• Popliteal fossa: S1, S2

Inguinal lymph node groups

• Superficial inguinal lymph nodes
  • A cluster of lymph nodes within the superficial fascia of the thigh in the region of the femoral triangle
  • The lymph nodes are arranged in the shape of “T”:
    • The horizontal group lies along the inguinal ligament: drain the inguinal region (inferior abdominal wall), gluteal region, perineum, scrotum, lower vagina, lower anal canal (below the dentate line).
    • The vertical group lies along the terminal part of the long saphenous vein: drain the lower extremity.
  • Drain into deep inguinal and external iliac lymph nodes
• Deep inguinal lymph nodes
  • A cluster of lymph nodes within the femoral sheath, medial to the femoral vein
  • Receive lymph from the popliteal lymph nodes (that drain the leg and foot), the glans penis or clitoris, and the superficial lymph nodes
  • Drain into the external iliac lymph nodes

Overview

• Type of joint: a complex hinge type of synovial joint made up of two components
  • The tibiofemoral articulation
    • Between the condyles of the tibia and femur
    • Weight-bearing
  • The patellofemoral articulation
    • Between the anterior surface of the femoral condyles and the posterior surface of the patella
    • Not weight-bearing
• Movements
  • Flexion: hamstrings, sartorius, gracilis, popliteus
  • Extension: quadriceps femoris
  • External rotation of the flexed knee: biceps femoris and sartorius
  • Internal rotation of the flexed knee: semimembranosus, semitendinosus, gracilis
• Blood supply: anastomosis around the knee joint between branches of the femoral and popliteal vessels (genicular anastomosis)
• Innervation: genicular branches of the femoral, obturator, tibial, and common peroneal nerves

Soft tissue structures of the knee

Ligaments and menisci

The unhappy triad: injury to the ACL, MCL, and medial meniscus caused by a lateral force to the knee.

To remember the orientation of the cruciate ligaments, cross your middle finger over the index finger of the same hand and hold your hand over the ipsilateral knee. The middle finger represents the ACL (from lateral femoral condyle to anterior tibia) and the index finger represents the PCL (from medial femoral condyle to posterior tibia).

Bursae

3-D model of the knee

References:^[4]

• Definition: a diamond-shaped region on the posterior aspect of the knee through which neurovascular structures pass from the thigh to the leg or vice versa
• Boundaries
  • Superomedial: semimembranosus and semitendinosus muscles
  • Superolateral: biceps femoris muscle
  • Inferomedial: medial head of the gastrocnemius muscle
  • Inferolateral: lateral head of the gastrocnemius muscle
• Floor
  • Posterior aspect of the knee joint and distal femur
  • Popliteus muscle
    • Origin: lateral femoral condyle
    • Insertion: posteriomedial surface of the proximal tibia, just below the medial tibial condyle
    • Innervation: tibial nerve
    • Action: internally rotates the tibia on the femur
• Roof: deep fascia and skin
• Contents (from superficial to deep)
  • Nerves: tibial nerve and common peroneal nerve (see “The leg, ankle, and foot” for more details)
  • Vein: popliteal vein
    • Origin: formed by the union of anterior tibial, posterior tibial, and the fibular veins at the inferior border of the popliteus
    • Becomes the femoral vein at the adductor hiatus
    • Main tributary: short saphenous vein
  • Artery: popliteal artery
    • Origin
      • Continuation of the femoral artery
      • Begins at the adductor hiatus
    • Ends at the inferior border of the popliteus by dividing into the anterior tibial artery and the tibioperoneal trunk
    • Branches
      • Genicular branches supply the anastomosis around the knee joint
      • Muscular branches to the surrounding muscles
• Clinical significance
  • Popliteal cyst (Baker cyst)
  • Popliteal artery aneurysm

References:^[5]

• Osteonecrosis of the femoral head
• Hip fractures
• Femoral shaft fracture
• Knee joint examination
• Knee ligament injuries
• Iliotibial band syndrome
• Meniscus tear
• Peripheral arterial disease
• Peripheral nerve injuries
• Femoral hernia
• Collection of orthopedic conditions