Tibialis posterior 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 posterior 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.

Continuously re-reading and looking at your atlas won't help you remember the origins and insertions. Cement your knowledge and improve retention efficiently using Kenhub's muscle anatomy and reference charts! 

Relations

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. 

Learn everything you need to know about tibialis posterior and surrounding muscles of the leg using these interactive quizzes and videos:

There is a useful mnemonic to remember the order structures that pass through the tarsal tunnel (from anterior to posterior); 

Tom, Doug And Very Nervous Harry

• Tibialis posterior flexor
• Digitorum longus
• Artery (posterior tibial)
• Vein (posterior tibial)
• Nerve (tibial)
• flexor Hallucis longus

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.

Innervation

Tibialis posterior is innervated by the tibial nerve which arises from the L4 and L5 spinal nerves. The tibial nerve is the larger of the two branches of the sciatic nerve. 

Blood supply

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.

Function

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.

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