lowerleg

The lower leg is the region of the leg between the knee and the ankle. It contains two long bones, the tibia and the fibula, connected by the interosseous membrane. The tibia bears most of the body's weight, while the fibula provides lateral stability and muscle attachments. The leg's soft tissues are organized into three fascial compartments—anterior, lateral, and posterior—separated by deep fascia.

The anterior compartment contains the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and fibularis (peroneus) tertius. These muscles primarily dorsiflex the ankle and extend the toes. Innervation is by the deep peroneal nerve, and the arterial supply is via the anterior tibial artery, which becomes the dorsalis pedis artery at the ankle.

The lateral compartment houses the fibularis longus and fibularis brevis, which ever and assist in plantarflexion of the foot. They are innervated by the superficial peroneal nerve and receive blood from perforating branches of the fibular artery.

The posterior compartment is subdivided into superficial and deep groups. The superficial group includes gastrocnemius, soleus, and plantaris, which perform plantarflexion. The deep group comprises popliteus, flexor hallucis longus, flexor digitorum longus, and tibialis posterior, contributing to plantarflexion and foot inversion. The posterior compartment is innervated by the tibial nerve, with blood supplied mainly by the posterior tibial artery; the gastrocnemius and soleus form the Achilles tendon, which inserts into the calcaneus.

Clinical relevance includes shin splints and tibial stress fractures, compartment syndrome, and Achilles tendon rupture. The lower leg also participates in complex locomotor movements, including knee mechanics and ankle stability.