Posterior Tibialis Tendinitis
The tibialis posterior originates from the posterior medial aspect of the tibia and the interosseus membrane. It commences at the proximal third of the tibia The tendon of the posterior tibial muscle runs behind the medial malleolus and inserts into the navicular bone, with additional tendonous slips inserting into the second, third, and fourth metatarsal bases, the cuneiform bones and the cuboid. The primary function is to slow pronation after heel contact in gait. From the anatomical origin and insertion the nonweight bearing function of this muscle would be to invert and plantarflex the foot. The plantar flexion of the foot comes about because of its posterior relationship to the axis of the ankle joint. During gait it slows the forward motion of the tibia on the foot and slows internal rotation of the leg, concomitantly slowing the rate of pronation. In a foot that excessively pronates this tendon will be under excessive stress. A tear of this muscle will result in the unopposed action of the peroneal muscles and the gastrosoleus complex causing a progressive and severe loss of the medial arch of the foot.

The posterior tibial muscle is invested within a synovial lined tendon sheath. Inflammation occurring here may result in a true tenosynovitis (as opposed to tendinitis, occurring at the achilles tendon). Inflammation that occurs at the origin of this muscle may result in medial shin splints. Examination will reveal the posterior medial aspect of the tibia to be tender. The flexor hallucis longus is also frequently involved. This is the muscle that originates in the lower third of the tibia and the tendon also runs behind the medial malleolus to the bones of the great toe. Its functions at the ankle and subtalar joint are similar to that of the posterior tibial tendon.

Since the cause of many problems occurring in this area is pronation of the foot at the subtalar joint the remedy is control of pronation. Excessive pronation can be controlled by a custom orthotics.

Also see Compartment Syndromes, and Accessory Navicular