Tibialis posterior muscleTibialis posterior is the most central and deepest muscle located in the posterior aspect of the leg. Together with popliteus, flexor hallucis longus and flexor digitorum longus, it forms the deep group of muscles of the posterior compartment of leg.
These muscles are located posterior to the tibia, fibula and interosseous membrane. Tibialis posterior is hidden from view by the large, superficial muscles of the leg; gastrocnemius and soleus. This muscle crosses the ankle joint to insert on the plantar surface of the foot. As a result, it helps with plantar flexion of the foot at the ankle joint. It is also a synergist of tibialis anterior in inversion of the foot.
|Origin||Posterior surface of tibia, posterior surface of fibula and interosseous membrane|
|Insertion||Tuberosity of navicular bone, all cuneiform bones, cuboid bone, bases of metatarsal bones 2-4|
|Actions||Talocrural joint: Foot plantarflexion
Subtalar joint: Foot inversion
Supports medial longitudinal arch of foot
|Innervation||Tibial nerve (L4, L5)|
|Blood supply||Branches of the posterior tibial artery|
This article will discuss the anatomy and function of the tibialis posterior (tib post) muscle.
Origin and insertion
Tibialis posterior is attached between the bones of the leg and the foot. The muscle consists of two parts close to its origin; medial and lateral. The medial portion arises from the upper two-thirds of the posterior surface of tibia, inferior to the soleal line, and from the posterior surface of interosseous membrane of leg. The lateral part originates from the upper two-thirds of the posterior surface of fibula. The two parts become one muscle, which travels towards the foot. At the ankle, the tendon of tibialis posterior passes posteriorly to the medial malleolus of the tibia. It continues into the medial part of the foot by passing through the tarsal tunnel, deep to the flexor retinaculum of ankle.
Here, the tendon of tibialis anterior divides into two divisions; superficial and lateral. The superficial, and larger division, inserts onto the plantar surface of the tarsal bones of the foot, mainly onto the tuberosity of navicular bone and the medial cuneiform bone. The deeper, and smaller division, inserts onto the middle and lateral cuneiform bones, the cuboid bone and the bases of the second, third and fourth metatarsal bones.
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Tibialis posterior is the deepest and most central muscle in the posterior compartment of leg. It is located posterior to the tibia, fibula and interosseous membrane of leg. The latter separates tibialis posterior from the anterior leg muscles. The belly of the muscle is overlapped by the flexor hallucis longus and flexor digitorum longus muscles. In addition, gastrocnemius, soleus and the tendon of plantaris are superficial to tibialis posterior. Towards the ankle, the tendon of tibialis posterior is crossed by the tendon of flexor digitorum longus and lies medial to it as they pass through the tarsal tunnel. In the sole of the foot, the tendon lies deep to all of the intrinsic muscles of the foot.
Tibialis posterior is also related to some important neurovascular structures. For example, it lies anterior to the posterior tibial artery, which gives off a branch called the fibular artery. The fibular artery descends between the fibula and tibialis posterior. The anterior tibial artery travels between the medial and lateral parts of the muscle, close to its origin points. The tibial nerve travels over tibialis posterior for most of its course.
Blood supply to the tibialis posterior muscle is through branches of the posterior tibial artery, which stems the popliteal artery. These branches include the fibular and medial plantar arteries. The medial malleolar arterial network also contributes to the blood supply of the tendon. Tibialis posterior is drained by the posterior tibial veins, which empty into the popliteal vein.
Tibialis posterior is involved in movements at two different joints, as follows:
- Plantar flexion of the foot at the talocrural (ankle) joint.
- Inversion of the foot at the subtalar joint.
Through its action on the ankle joint, tibialis posterior helps the other, more powerful foot flexors to elevate the heel when the foot is planted on the ground. This facilitates walking, running and various fitness exercises, such as calf raises. In addition, contraction of tibialis posterior approximates the tibia and fibula. This brings the malleoli together during plantar flexion, improving their grip on the talus and supporting the ankle. Inversion of the foot also has several important functions. Through this action, tibialis posterior resists the tendency of the body to sway laterally when standing on one leg, thus facilitating balance.
This muscle also plays a support role by elevating, tensing and reinforcing the medial longitudinal arch of the foot. This action helps to distribute the body weight when the foot is planted on the ground.