Anatomy of Lower Limb Extremity

The Foot

• The foot consists of three regions: the tarsus (proximal region), metatarsus (intermediate region), and phalanges (distal region).
• The tarsus consists of seven tarsal bones, including the calcaneus, talus, navicular, three cuneiform bones, and the cuboid.
• The calcaneus is the largest and strongest tarsal bone.
• The talus is the only bone of the foot that articulates with the fibula and tibia.
• The talus transmits about half the weight of the body to the calcaneus during walking.

Functions of the Foot

• The foot serves two main functions: to support body weight and to act as a lever to propel the body forward during walking or running.

Arches of the Foot

• The foot has three arches: the medial longitudinal arch, lateral longitudinal arch, and transverse arch.
• The medial longitudinal arch consists of the calcaneum, talus, navicular, three cuneiform bones, and the first three metatarsal bones.
• The lateral longitudinal arch consists of the calcaneum, cuboid, and the 4th and 5th metatarsal bones.
• The transverse arch consists of the bases of the metatarsal bones, cuboid, and three cuneiform bones.

Mechanics of Arch Support

• The arches of the foot are supported by the shape of the bones, the presence of wedge-shaped "keystones", strong plantar ligaments, and the tie beams formed by the plantar aponeurosis and long flexor muscles' tendons.
• The talus is the "keystone" of the medial longitudinal arch, while the cuboid is the "keystone" of the lateral longitudinal arch.
• The cuneiform bones are the "keystones" of the transverse arch.

Ankle Joint

• The ankle joint is a synovial hinge joint that articulates the lower end of the tibia (medial malleolus), the lower end of the fibula (lateral malleolus), and the talus.
• The ankle joint is stabilized by the shape of the close-fitting bones, strong ligaments, and surrounding tendons of muscles.

Movements of the Ankle Joint

• The ankle joint allows for two movements: dorsiflexion (toes pointing upward) and plantarflexion (toes pointing downward).
• The ankle joint is less stable when plantarflexed, making it more susceptible to sprains.

Blood Supply of the Lower Limb

• The lower limb receives blood supply from the femoral artery, popliteal artery, posterior tibial artery, and dorsalis pedis artery.
• The pulses of these arteries can be felt at specific locations.
• Absence of pulses indicates arterial occlusion.

Venous Drainage of the Lower Limb

• The lower limb has a saphenous system of veins, which includes the long (great) saphenous vein and the short saphenous vein.
• Varicose veins are veins with larger diameters and are elongated than normal veins.
• Great saphenous vein grafts may be used in heart surgery (coronary bypass surgery).

Nerve Injuries of the Lower Limb

• Sciatic nerve injuries can occur due to badly placed intramuscular injections in the gluteal region.
• Sciatica is caused by pressure on one of the sciatic nerve roots (L4, L5, S1, S2, S3) as a result of a slipped intervertebral disc at the lumbar area.
• Common peroneal nerve injury can occur when the neck of the fibula is fractured, leading to foot drop.

Muscles of the Foot

• The foot has 12 muscles, which can be divided into four layers: the first layer (abductor hallucis, flexor digitorum brevis, and abductor digiti minimi), the second layer (quadratus plantae and lumbricals), the third layer (flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis), and the fourth layer (plantar interossei, dorsal interossei, extensor digitorum brevis, and extensor hallucis brevis).