Course
The tibial nerve runs in a straight line from the apex of the popliteal fossa to the space behind the medial malleolus, then turns forward into the sole.
In the popliteal fossa
It begins where the sciatic nerve divides, usually at the apex of the fossa, and descends vertically through the middle of it. It is the most superficial of the three main structures in the fossa: nerve, then popliteal vein, then popliteal artery deepest. As it descends it crosses the popliteal vessels from their lateral side to their medial side, passing behind them.
In the leg
The nerve leaves the fossa between the two heads of gastrocnemius and passes deep to the tendinous arch of soleus with the posterior tibial vessels. It descends in the deep posterior compartment, first on tibialis posterior and then on the back of the tibia, covered by soleus and gastrocnemius. At first the nerve lies medial to the posterior tibial artery; it then crosses behind the artery, so that for most of the leg the nerve is lateral to it.
At the ankle
The nerve passes behind the medial malleolus through the tarsal tunnel, deep to the flexor retinaculum, between the tendons of flexor digitorum longus and flexor hallucis longus. It lies posterior to the posterior tibial artery. Under the flexor retinaculum it divides into the medial and lateral plantar nerves.
Branches and distribution
The tibial nerve supplies the whole posterior compartment of the leg and, through the plantar nerves, all the intrinsic muscles of the sole.
| Level | Motor | Cutaneous and articular |
|---|---|---|
| Popliteal fossa | Both heads of gastrocnemius, plantaris, soleus, popliteus | Medial sural cutaneous nerve; genicular branches to the knee |
| Leg | Soleus (second branch), tibialis posterior, flexor digitorum longus, flexor hallucis longus | Ankle joint |
| Ankle | None | Medial calcaneal branches to the skin of the heel |
| Medial plantar nerve | Abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, first lumbrical | Medial sole and medial three and a half toes |
| Lateral plantar nerve | Quadratus plantae, abductor digiti minimi, flexor digiti minimi brevis, adductor hallucis, all interossei, second to fourth lumbricals | Lateral sole and lateral one and a half toes |
Sural nerve
The medial sural cutaneous nerve runs down between the heads of gastrocnemius and pierces the deep fascia in mid-calf. It usually joins the sural communicating branch of the common fibular nerve to form the sural nerve, which follows the small saphenous vein behind the lateral malleolus to the lateral border of the foot. The pattern of this union varies. The sural nerve is the standard donor for nerve grafts and the usual site for nerve biopsy.
The plantar nerves mirror the hand: the medial plantar nerve behaves like the median nerve and the lateral plantar nerve like the ulnar nerve.
Relations
The tibial nerve always travels with the popliteal and then the posterior tibial vessels, crossing them twice in its course.
- Popliteal fossa: superficial to the popliteal vein and artery, with the common fibular nerve diverging laterally along biceps femoris.
- Leg: deep to soleus and gastrocnemius, on tibialis posterior and the tibia, lateral to the posterior tibial artery.
- Tarsal tunnel: from front to back the structures behind the medial malleolus are tibialis posterior, flexor digitorum longus, the posterior tibial artery and its venae comitantes, the tibial nerve, and flexor hallucis longus.
The posterior tibial pulse is felt midway between the medial malleolus and the medial border of the calcaneal tendon, with the nerve just behind it.
Clinical relevance
Tibial nerve injury weakens plantarflexion and toe flexion and numbs the sole, but it is far less common than common fibular nerve injury because the tibial nerve lies deep and well protected.
Causes
- Knee dislocation and supracondylar femoral fractures, which also endanger the popliteal artery.
- Posterior compartment syndrome after tibial fracture or crush injury.
- Tarsal tunnel syndrome: compression under the flexor retinaculum by a ganglion, varicosities, bony spurs or a tight retinaculum. It causes burning pain and paraesthesia in the sole, often worse at night, with a positive Tinel sign behind the medial malleolus.
Signs
A high lesion leaves the patient unable to stand on tiptoe or push off, with loss of the ankle jerk (S1) and numbness of the sole. The unopposed dorsiflexors and evertors pull the foot into a dorsiflexed, everted position (calcaneovalgus). A lesion at the ankle spares the calf and affects only the intrinsic muscles and the skin of the sole, which is the more serious long-term problem because an insensate sole ulcerates.