What is the anatomy of the lower limb?

Anatomy of the Lower Limb

The lower limb consists of several key anatomical structures organized in a functional hierarchy that enables weight-bearing, locomotion, and stability. The lower limb includes the hip, thigh, knee, leg, ankle, and foot regions, each containing specific bones, joints, muscles, blood vessels, and nerves that work together to provide mobility and support.

Bony Structure

Hip and Pelvis

• Pelvic girdle (innominate bone) consisting of:
  • Ilium
  • Ischium
  • Pubis
• Femoral head articulates with the acetabulum forming the hip joint

Thigh

• Femur (longest bone in the body)
  • Femoral head
  • Greater and lesser trochanters
  • Femoral shaft
  • Medial and lateral condyles

Knee

• Patella (sesamoid bone)
• Distal femur
• Proximal tibia with tibial plateau
• Proximal fibula

Leg

• Tibia (medial, weight-bearing)
• Fibula (lateral, non-weight-bearing)

Ankle and Foot

• Tarsal bones (7):
  • Talus
  • Calcaneus
  • Navicular
  • Cuboid
  • Three cuneiform bones
• Metatarsals (5)
• Phalanges (14)

Joints

Hip Joint

• Ball-and-socket synovial joint
• Allows flexion/extension, abduction/adduction, and rotation

Knee Joint

• Complex hinge joint
• Components:
  • Tibiofemoral joint
  • Patellofemoral joint
• Stabilized by:
  • Anterior and posterior cruciate ligaments
  • Medial and lateral collateral ligaments
  • Menisci (medial and lateral)

Ankle Joint

• Talocrural joint (mortise joint)
• Allows dorsiflexion and plantarflexion

Subtalar Joint

• Between talus and calcaneus
• Allows inversion and eversion

Muscular System

Hip and Thigh Muscles

• Anterior compartment:
  • Iliopsoas (hip flexion)
  • Quadriceps femoris (knee extension)
  • Sartorius
• Posterior compartment:
  • Hamstrings (biceps femoris, semitendinosus, semimembranosus)
  • Gluteal muscles (gluteus maximus, medius, minimus)
• Medial compartment:
  • Adductor group (adductor magnus, longus, brevis)
  • Gracilis

Leg Muscles

• Anterior compartment:
  • Tibialis anterior
  • Extensor digitorum longus
  • Extensor hallucis longus
• Lateral compartment:
  • Peroneus longus and brevis
• Posterior compartment:
  • Superficial: Gastrocnemius, soleus (Achilles tendon)
  • Deep: Tibialis posterior, flexor digitorum longus, flexor hallucis longus

Foot Muscles

• Intrinsic muscles:
  • Dorsal: Extensor digitorum brevis
  • Plantar: Four layers of muscles for toe movement and arch support

Vascular Supply

Arterial Supply

• Common iliac artery divides into:

  • Internal iliac artery (supplies pelvic structures)
  • External iliac artery (continues as femoral artery)

• Femoral artery:

  • Supplies anterior thigh
  • Continues as popliteal artery behind knee

• Popliteal artery divides into:

  • Anterior tibial artery (continues as dorsalis pedis artery)
  • Posterior tibial artery (gives off peroneal artery)

• Foot arterial supply:

  • Dorsalis pedis artery (dorsum of foot)
  • Plantar arteries (from posterior tibial artery)

According to the International Working Group on the Diabetic Foot, detailed visualization of below-the-knee and pedal arteries is critical when evaluating vascular disease 1.

Venous Drainage

• Superficial veins:
  • Great saphenous vein (medial)
  • Small saphenous vein (posterior)
• Deep veins:
  • Follow arterial pathways (tibial, popliteal, femoral veins)
• Perforating veins connect superficial and deep systems

Nervous System

Lumbar and Sacral Plexuses

• Lumbar plexus (L1-L4):
  • Femoral nerve (anterior thigh)
  • Obturator nerve (medial thigh)
• Sacral plexus (L4-S3):
  • Sciatic nerve (posterior thigh)
    • Divides into tibial and common peroneal nerves

Lower Leg and Foot Innervation

• Tibial nerve:
  • Posterior leg muscles
  • Plantar foot surface
• Common peroneal nerve:
  • Divides into superficial and deep peroneal nerves
  • Anterior and lateral leg compartments
  • Dorsum of foot

Functional Considerations

The American College of Cardiology/American Heart Association guidelines emphasize understanding the anatomical distribution of arterial disease when evaluating peripheral artery disease (PAD) 1:

• Inflow disease: Affects suprainguinal vessels (infrarenal aorta and iliac arteries)
• Outflow disease: Affects vessels below the inguinal ligament to the trifurcation
• Runoff disease: Affects trifurcation vessels (anterior tibial, posterior tibial, and peroneal arteries)

Understanding these anatomical patterns is crucial for appropriate diagnosis and management of vascular pathologies 1.

Clinical Relevance

The 2024 ACC/AHA guidelines define anatomic levels of the lower extremity as 1:

1. Aortoiliac: Includes infrarenal abdominal aorta, common iliac, external and internal iliac arteries
2. Femoropopliteal: Includes common femoral, profunda femoris, superficial femoral, and popliteal arteries
3. Infrapopliteal: Includes tibial-peroneal trunk, anterior tibial artery, posterior tibial artery, peroneal artery, plantar pedal loop, and pedal vessels

These anatomical distinctions are important for proper diagnosis, classification, and treatment of lower extremity vascular disease 1.

Angiosome Concept

The angiosome concept divides the lower limb into three-dimensional tissue blocks, each with its own feeding artery 1. This concept is particularly important in:

• Understanding vascular territories
• Planning revascularization procedures
• Managing diabetic foot ulcers

The goal of revascularization is to restore direct flow to at least one foot artery, preferably the one supplying the anatomical region of a wound 1.

Understanding the complex anatomy of the lower limb is essential for proper diagnosis and management of various conditions affecting mobility, stability, and vascular health.