Tibialis Posterior muscle, originating from the proximal tibia and fibula, passes distally with a broad insertion on the plantar aspect of the navicular, cuneiform, cuboid, and metatarsal bases and normally functions to invert the subtalar joint and to adduct the forefoot. Its principal antagonist is the peroneus brevis, which normally everts the subtalar joint and abducts the forefoot. Posterior tibial tendon dysfunction is a condition, as its name suggests, that is characterized by the loss of function of the posterior tibial tendon.
Anatomy of Tibialis Posterior
The tibialis posterior muscle originates on the inner posterior borders of the tibia and fibula. It is also attached to the interosseous membrane, which attaches to the tibia and fibula.
The tendon of the tibialis posterior muscle (sometimes called the posterior tibial tendon) descends posterior to the medial malleolus and terminates by dividing into plantar, main, and recurrent components. The main portion inserts into the tuberosity of the navicular and the plantar surface of the medial cuneiform. The plantar portion inserts into the bases of the second, third and fourth metatarsals, the intermediate and lateral cuneiforms and the cuboid. The recurrent portion inserts into the sustentaculum tali of the calcaneus.
- Origin: The superior two-thirds of the medial posterior surface of the tibia
- Insertion: The tendon courses distally, splitting into two at the calcaneonavicular ligament, to insert on the tuberosity of the navicular bone (superficial slip) and the plantar surfaces of the metatarsals two to four (deep slip)
- Action: The posterior tibialis is the primary inverter of the foot but also adducts, plantar flexes, and aides in supination of the foot
- Blood Supply: Sural, peroneal, and posterior tibial arteries
- Innervation: Tibial nerve
Nerve Supply of Tibialis Posterior
- 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 of Tibialis Posterior
- 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.
The Function of Tibialis Posterior
As well as being a key muscle and tendon for stabilization, the tibialis posterior also contracts to produce inversion and assists in the plantar flexion of the foot at the ankle. The tibialis posterior has a major role in supporting the medial arch of the foot. Dysfunction of the tibialis posterior, including rupture of the tibialis posterior tendon, can lead to flat feet in adults, as well as a valgus deformity due to unopposed eversion when inversion is lost.
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, the 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, the contraction of the 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. The inversion of the foot also has several important functions. Through this action, the 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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