What is the anatomy of the lower limb?

Anatomy of the Lower Limb

The lower limb is a complex anatomical structure with interconnected bones, joints, muscles, blood vessels, and nerves that work together to provide support, mobility, and stability. The lower limb consists of the hip, thigh, knee, leg, ankle, and foot regions, each containing specific anatomical structures that contribute to locomotion and weight-bearing functions.

Bony Structures

• Hip and Pelvis

  • Pelvic girdle (ilium, ischium, pubis)
  • Acetabulum - socket for the femoral head
  • Femoral head - articulates with the acetabulum to form the hip joint

• Thigh

  • Femur - longest and strongest bone in the body
    • Femoral head
    • Greater and lesser trochanters
    • Femoral shaft
    • Medial and lateral condyles distally

• Knee

  • Distal femur (medial and lateral condyles)
  • Proximal tibia (medial and lateral tibial plateaus)
  • Patella (kneecap) - largest sesamoid bone in the body

• Leg

  • Tibia - medial weight-bearing bone
  • Fibula - lateral non-weight-bearing bone

• Ankle and Foot

  • Talus - articulates with tibia and fibula to form ankle joint
  • Calcaneus - heel bone
  • Tarsal bones (navicular, cuboid, three cuneiforms)
  • Metatarsals (5) - form the midfoot
  • Phalanges (14) - form the toes

Joints

• Hip Joint

  • Ball-and-socket joint between femoral head and acetabulum
  • Allows flexion/extension, abduction/adduction, and rotation

• Knee Joint

  • Complex hinge joint between femur, tibia, and patella
  • Includes tibiofemoral and patellofemoral articulations
  • Stabilized by cruciate ligaments (anterior and posterior) and collateral ligaments (medial and lateral)
  • Contains menisci (medial and lateral) for shock absorption

• Ankle Joint

  • Hinge joint between tibia, fibula, and talus
  • Allows dorsiflexion and plantarflexion

• Foot Joints

  • Subtalar joint - between talus and calcaneus (inversion/eversion)
  • Midtarsal joints - between tarsal bones
  • Tarsometatarsal joints
  • Metatarsophalangeal and interphalangeal joints

Muscular System

• Hip and Gluteal Region

  • Gluteal muscles (maximus, medius, minimus) - hip extension and abduction
  • Deep external rotators (piriformis, gemelli, obturator internus/externus, quadratus femoris)
  • Iliopsoas - primary hip flexor

• Thigh

  • Anterior compartment: Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) - knee extension
  • Medial compartment: Adductors (magnus, longus, brevis), gracilis, pectineus - hip adduction
  • Posterior compartment: Hamstrings (biceps femoris, semitendinosus, semimembranosus) - knee flexion and hip extension

• Leg

  • Anterior compartment: Tibialis anterior, extensor digitorum longus, extensor hallucis longus - ankle dorsiflexion and toe extension
  • Lateral compartment: Peroneus longus and brevis - foot eversion
  • Posterior compartment: Gastrocnemius, soleus (forming Achilles tendon), tibialis posterior, flexor digitorum longus, flexor hallucis longus - plantarflexion and toe flexion

• Foot

  • Intrinsic muscles - support arches and assist with fine movements of toes

Vascular Supply

• Arterial Supply 1

  • Common iliac artery bifurcates into internal and external iliac arteries
  • External iliac continues as femoral artery at the inguinal ligament
  • Femoral artery gives off deep femoral (profunda femoris) artery
  • Femoral artery becomes popliteal artery behind the knee
  • Popliteal artery divides into anterior and posterior tibial arteries
  • Posterior tibial artery gives off peroneal artery
  • Anterior tibial artery continues as dorsalis pedis artery in the foot
  • Plantar arteries form the plantar arch

• Venous Drainage

  • Superficial system: Great saphenous vein (medial) and small saphenous vein (posterior)
  • Deep system: Follows arterial pattern with paired veins (tibial, popliteal, femoral)
  • Perforating veins connect superficial and deep systems

Nervous Supply

• Lumbar Plexus (L1-L4)

  • Femoral nerve - innervates anterior thigh muscles
  • Obturator nerve - innervates medial thigh muscles
  • Lateral femoral cutaneous nerve - sensory to lateral thigh

• Sacral Plexus (L4-S3)

  • Sciatic nerve - largest nerve in the body
    • Divides into tibial and common peroneal nerves
  • Tibial nerve - innervates posterior leg muscles and plantar foot
  • Common peroneal nerve - divides into superficial and deep branches for lateral and anterior compartments
  • Sural nerve - sensory to lateral foot

Functional Considerations

• Weight-bearing

  • The lower limb is designed to support body weight
  • Bones progressively increase in size from foot to hip
  • Arches of the foot (medial longitudinal, lateral longitudinal, transverse) provide shock absorption

• Gait Cycle 2

  • Stance phase (60% of cycle) - foot in contact with ground
  • Swing phase (40% of cycle) - foot off ground
  • Requires coordination of multiple joints and muscle groups

• Vascular Considerations 1, 3

  • The lower limb arterial system can be divided into three major anatomic levels:
    • Aortoiliac (inflow) - includes infrarenal abdominal aorta and iliac arteries
    • Femoropopliteal (outflow) - includes common femoral, profunda femoris, superficial femoral, and popliteal arteries
    • Infrapopliteal (runoff) - includes tibial-peroneal trunk and tibial arteries

Clinical Relevance

• Peripheral Artery Disease 1, 3

  • Occlusive lesions at different anatomic levels produce characteristic symptoms
  • Aortoiliac disease often presents with buttock and thigh claudication
  • Superficial femoral artery occlusion typically causes calf claudication
  • Infrapopliteal disease more commonly associated with critical limb ischemia

• Angiosome Concept 1

  • The foot can be divided into three-dimensional blocks of tissue (angiosomes)
  • Each angiosome has its own feeding artery
  • Important consideration in revascularization procedures for foot ulcers

• Imaging Modalities for Vascular Assessment 1

  • Color duplex ultrasound
  • Computed tomography angiography
  • Magnetic resonance angiography
  • Intra-arterial digital subtraction angiography

Understanding the detailed anatomy of the lower limb is essential for proper diagnosis and treatment of various musculoskeletal and vascular conditions affecting this region.