The posterior compartment of the leg has two layers of muscles, a superficial and a deep layer. The superficial layer is made up of three muscles namely: gastrocnemius, soleus and plantaris. The first two muscles provide for strong plantar flexion of the foot at the ankle joint. The two heads of the gastrocnemius attach proximally to their respective condyles of the femur. The deep layer is made up of flexor hallucis longus laterally, and flexor digitorum longus medially. In between these muscles is the tibialis posterior. These muscles also account for some weak plantar flexion of the foot at the ankle joint, but individually they provide for powerful flexion of the great toe, flexion of the lateral four toes and also inversion of the foot respectively. FDL is attached distally to the terminal phalanges of the lateral four toes and FHL is attached to the terminal phalanges of the great toe. The nerve supply to this compartment is by the tibial nerve which is a terminal branch of the sciatic nerve. The blood supply is from the posterior tibial artery (the larger branch of the two) which arises from the popliteal artery.

Popliteus Muscle

The popliteus muscle is innervated by the tibial nerve and acts to unlock the knee at the beginning of flexion by laterally rotating the femur.

Posterior Tibial Artery

The popliteal artery splits into the anterior and posterior tibial arteries just beneath the popliteus muscle. The anterior branch goes on to supply the anterior compartment of the leg. The posterior tibial artery further gives off a branch known as the common peroneal artery and this supplies the lateral compartment of the leg. The posterior tibial artery transcends downwards between the flexor hallucis longus and flexor digitorum longus muscles, overlying the fascia of tibialis posterior muscle. It reaches the ankle where it passes deep to the flexor retinaculum but before gives off superficial branches before dividing into the medial and lateral plantar arteries.

The lesser branch, common peroneal artery, transcends deep to the flexor hallucis longus laterally and upon the fascia of the tibialis posterior. This supplies the lateral compartment of the leg.

Category: Anatomy Notes