Peroneal & Tibial Nerves - Advanced

Peroneal and Tibial Nerves: Advanced Innervation

Motor innervation of the leg and foot

Anterior Leg

Deep peroneal nerve

Innervates:

• Tibialis anterior (L4, L5)
  • Provides foot dorsiflexion and to a lesser extent foot inversion.
• Extensor digitorum longus, extensor hallucis longus, and peroneus tertius (all supplied by L5, S1)
  • Extensor digitorum longus extends the toes (except the great toe)
  • Extensor hallucis longus extends the great toe, only
  • Peroneus tertius assists in foot eversion.
  • To a lesser extent, all three of these muscles also provide foot dorsiflexion.

Lateral Leg

Superficial peroneal nerve (lateral leg)

Innervates:

• Peroneus longus and peroneus brevis (both L5, S1).
  • Provide foot eversion and to a lesser extent foot plantar flexion.

Foot

Deep peroneal nerve

Innervates:

• The short extensor muscles of the foot: extensor digitorum brevis and extensor hallucis brevis (both L5, S1).
• Extensor digitorum brevis extends the middle three toes.
• Extensor hallucis brevis extends only the great toe and only at the proximal phalanx.

Posterior Compartment Muscles

Tibial nerve

Superficial:

• Gastrocnemius and Soleus (both S1, S2)
  • Both muscles provide foot plantar flexion: we test gastrocnemius with the knee extended and soleus with the knee flexed.

Deep:

• Tibialis posterior and flexor digitorum longus and flexor hallucis longus (all L5, S1).
  • Note that some texts indicate that L4 also innervates tibialis posterior and some texts indicate that S2 also innervates the flexor digitorum and hallucis muscles.
  • Tibialis posterior provides foot inversion.
  • Flexor digitorum longus flexes the toes (except the great toe).
  • Flexor hallucis longus flexes the great toe.

Lesser muscles

• Popliteus & Plantaris.
  • Popliteus unlocks the knee at the beginning of knee flexion.
  • Plantaris acts in concert with gastrocnemius.

Foot

• The plantar nerves innervate the plantar intrinsic foot muscles (S1 – S3).

sensory innervation of the leg and foot

• The common peroneal nerve derives a common sensory trunk that produces both the lateral sural cutaneous nerve and also the sural communicating branch.
• The tibial nerve produces the medial sural cutaneous nerve, which joins the sural communicating branch to form the sural nerve.
• When the sural nerve passes through the ankle, it produces both the lateral calcaneal nerve branch and also the lateral dorsal cutaneous nerve.
  • The lateral calcaneal branch is the lateral corollary of the medial calcaneal branch (see below).
• Within the tarsal tunnel, the tibial nerve divides into the plantar nerves (medial and lateral) and also the medial calcaneal sensory nerve.
• The plantar nerves and medial calcaneal nerve provide sensory coverage to the sole of the foot.