Nerve roots: L4-S3
Sensory: Innervates the skin of the posterolateral side of the leg, lateral side of the foot, and the sole of the foot.
Motor: Innervates the posterior compartment of the leg.
The tibial nerve is a branch of the sciatic nerve, and arises at the apex of the popliteal fossa. It travels through the popliteal fossa, giving off branches to muscles in the superficial posterior compartment of the leg. Here, the tibial nerve also gives rise to branches that contribute towards the sural nerve, which innervates the posterolateral aspect of the leg.
The tibial nerve continues its course down the leg, posterior to the tibia. During its descent, it supplies the deep muscles of the posterior leg.
At the foot, the nerve passes posteriorly and inferiorly to the medial malleolus, through a structure known as the tarsal tunnel. This tunnel is covered superiorly by the flexor retinaculum. Within this tunnel, branches arise from the tibial nerve to supply cutaneous innervation to the heel
Immediately distal to the tarsal tunnel, the tibial nerve terminates by dividing into sensory branches, which innervate the sole of the foot.
Clinical Relevance: Tarsal Tunnel Syndrome
This is a condition where the tibial nerve is compressed within the tarsal tunnel (posterior to the medial malleolus). There are varying causes, of which the main three are:
- Rheumatoid arthritis
- Post-trauma ankle deformities
Patients complain of paraesthesia in the ankle and sole of the foot, which can radiate up the leg slightly. It is aggravated by activity and relieved by rest.
Tarsal tunnel symptoms can be treated conservatively by anti-inflammatory drugs and changes in footwear. If these interventions are not successful, the flexor retinaculum can be cut surgically, which releases the pressure.
The tibial nerve innervates all the muscles in the posterior compartment of the leg. They are divided into a deep and superficial compartment:
- Popliteus – Laterally rotates the femur on the tibia to unlock the knee.
- Flexor Hallucis Longus – Flexes the big toe and plantar flexes the ankle.
- Flexor digitorum Longus – Flexes the other digits and plantar flexes the ankle.
- Tibialis Posterior – Inverts the foot and plantar flexes the ankle.
- Plantaris – Plantar flexes the ankle.
- Soleus – Plantar flexes the ankle.
- Gastrocnemius – Plantar flexes the ankle and flexes the knee.
In the popliteal fossa, the tibial nerve gives off cutaneous branches. These combine with branches from the common fibular nerve to form the sural nerve. This sensory nerve innervates the skin of the posterolateral side of the leg and the lateral side of the foot.
The tibial nerve also supplies all the sole of the foot via three branches:
- Medial calcaneal branches: These arise within the tarsal tunnel, and innervate the skin over the heel.
- Medial Plantar Nerve: Innervates the plantar surface of the medial three and a half digits, and the associated sole area.
- Lateral Plantar Nerve: Innervates the plantar surface of the lateral one and a half digits, and the associated sole area.
Clinical Relevance: Damage to the Tibial Nerve
Damage to the tibial nerve is rare, and is often a result of direct trauma, entrapment through narrow space or compression for long period of time. Damage results in loss of plantar flexion, loss of flexion of toes and weakened inversion (The tibialis anterior can still invert the foot).