The tibial nerve is one of two main muscular branches of the sciatic nerve that innervates the triceps surae, plantaris, popliteus, tibialis posterior, flexor digitorum longus and flexor hallucis longus muscles.
Once the tibial nerve divides into the medial and lateral plantar nerves, it will innervate the muscles below:
- Medial plantar nerve: abductor hallucis, flexor digitorum brevis, flexor hallucis brevis (medial head), and first lumbrical
- Lateral plantar nerve: flexor hallucis brevis (lateral head), quadratus plantae, abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi, second, third and fourth lumbricals, first through third plantar interossei, first through fourth dorsal interossei, and adductor hallucis.
The sciatic nerve descends along the posterior thigh, and divides in the lower third of the thigh into the tibial nerve and common fibular nerve as it travels towards the popliteal fossa. Next, the tibial nerve divides at the foot into the medial and lateral plantar nerves.
Before it divides, the tibial nerve gives off cutaneous branches to the medial sural cutaneous nerve (which is continuous with the sural nerve), lateral calcaneal branches, medial calcaneal branches, and lateral dorsal cutaneous nerve. The tibial nerve continues on and passes through the center of the popliteal fossa and runs below the tedinous arch of the soleus muscle to the superficial and deep plantar flexors. More specifically, in the deep posterior compartment, the tibial nerve continues distally in a neurovascular bundle and passes through the tarsal tunnel, accompanied by deep flexor tendons. Once it has passed through the tunnel, the tibial nerve then divides into the lateral and medial plantar nerves, which supplies all of the muscles on the plantar side of the foot.
Tibial nerve divisions in the foot
- The medial plantar nerve supplies: the abductor hallucis, the flexor digitorum brevis, the flexor hallucis brevis, and the first lumbrical. Cutaneous distribution of the medial plantar nerve is to the medial sole and medial three and one half toes, including the nail beds on the dorsum (similar to the cutaneous distribution of the median nerve in the hand). A good mnemonic is “LAFF muscles”:
LAFF muscles (pronounced "laugh")
A- Abductor Hallucis
F- Flexor digitorum brevis
F- flexor hallucis brevis
- The lateral plantar nerve supplies: the quadratus plantae, the flexor digiti minimi, the adductor hallucis, the interossei, three lumbricals, and abductor digiti minimi. Cutaneous innervation is to the lateral sole and lateral one and one half toes (similar to the cutaneous distribution of the ulnar nerve in the hand).
Compression of the tibial nerve or its terminal branches will lead to an entrapment syndrome known as tarsal tunnel syndrome. This syndrome results in pain and sensory disturbances that affects the sole of the foot, and can cause palsies of the intrinsic foot muscles. This can also result from severe nerve trauma connected to fractures of the tibial shaft or medial malleolus.