What is the anatomy of the posterior tibial nerve (L4-S3) in nerve entrapment syndromes of the lower extremity?

Updated: Oct 15, 2019
  • Author: Minoo Hadjari Hollis, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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Answer

The posterior tibial nerve (L4-S3) is a branch of the sciatic nerve. After entering the lower leg between the two heads of the gastrocnemius, it runs deep to the soleus in the deep posterior compartment of the leg. In the upper leg, the nerve lies between the posterior tibial muscle and the flexor digitorum longus; in the lower leg, it is between the flexor digitorum longus and the flexor hallucis longus.

The posterior tibial nerve then travels behind the medial malleolus, through the proximal tarsal tunnel, where it divides into its terminal branches, the medial and lateral plantar nerves. Havel et al have shown that in 93% of cases, this bifurcation occurs within 2 cm of an imaginary line drawn between the middle of the medial malleolus and the mid calcaneus. [10] Calcaneal branches, which have a highly variable anatomy, are present.

Most individuals (79%) have a single calcaneal nerve, usually arising from the posterior tibial nerve but sometimes arising from the lateral plantar nerve. About 21% have multiple calcaneal branches originating from the posterior tibial nerve, the lateral plantar nerve, the medial plantar nerve, or some combination of these. The calcaneal branches travel over the abductor hallucis and supply sensation to the medial heel pad. The medial calcaneal nerve or nerves penetrate the flexor retinaculum and innervate the skin over the medial and posterior heel.

The tarsal tunnel is formed by the medial surface of the talus, the inferomedial navicular, the sustentaculum tali, and the curved medial surface of the calcaneus. The fibrous portion of the canal is the flexor retinaculum, also called the laciniate ligament. The retinaculum is formed by the deep and superficial aponeurosis of the leg and is attached closely to the sheaths of the posterior tibial, flexor digitorum longus, and flexor hallucis tendons.

Typically, a fibrous septum courses between the calcaneus and the deep fascia of the abductor hallucis and separates the medial and lateral plantar nerves just beyond their division from the posterior tibial nerve.

The first branch of the lateral plantar nerve travels between the deep fascia of the abductor hallucis and the medial fascia of the quadratus plantae, then continues deep to the flexor digitorum brevis. Although the anatomy is somewhat variable, this branch typically provides a sensory branch to the medial calcaneal tuberosity, motor branches to the flexor digitorum brevis, and sometimes a motor branch to the quadratus plantae. It then provides a sensory branch to the lateral heel and a motor branch to the abductor digiti quinti.

Various anomalies have been reported, including the direct origination of all branches of the medial and lateral plantar nerves from the posterior tibial nerve.

The medial plantar nerve provides sensation to the medial half of the foot and the medial three and one half digits. The nerve provides motor branches to the abductor hallucis, the flexor digitorum brevis, and the flexor hallucis brevis, as well as to the first lumbrical.


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