The posterior compartment of the lower leg contains seven muscles, organised into two layers – superficial and deep. The two layers are separated by a band of fascia.
The posterior leg is the largest of the three compartments. Collectively, the muscles in this area plantar-flex and invert the foot. They are innervated by the tibial nerve, a terminal branch of the sciatic nerve.
The Tibialis Posterior is a spindle shaped long muscle of the calf group, present deep on the posterior aspect of the lower leg, in the posterior compartment (one of the four compartments of the lower leg)
Its main role is to It move the ankle downwards (plantar-flexion) and twists it inwards (inversion). It also plays an important role in stabilising the medial longitudinal arch. Tibialis posterior dysfunction can lead to flat feet.
The tendon of Tibialis posterior supports the arch of the foot. The dysfunction of Tibialis posterior tendon, results in a condition called acquired flat foot deformity, which results in pain and dysfunction of involved foot. It helps with the function of other muscles in the posterior compartment of leg.