Lower Extremity Nerves
Study techniques for leg and foot nerves
The Lumbo-Sacral Plexus
The major branches of the sacral plexus are routinely studied. In performing nerve conduction studies in the legs, we normally examine the peroneal and posterior tibial nerves for motor nerve function and the sural and superficial peroneal nerves for sensory nerve function.
The Brachial Plexus
The brachial plexus is formed by the ventral rami of the fifth through eighth cervical and first thoracic spinal nerves. These nerves combine to form three trunks:
- Upper trunk: C5 and C6
- Middle trunk: C7
- Lower trunk: C8 and T1
Each trunk divides into anterior and posterior divisions. The divisions then combine to form three cords:
- Lateral cord: anterior divisions of upper and middle trunks
- Posterior cord: posterior divisions of all three trunks
- Medial cord: anterior division of lower trunk
The Femoral And Sciatic Nerves
The femoral nerve arises from the lumbar plexus (L2, L3, L4) and innervates the quadriceps muscles. The sciatic nerve is the largest nerve in the body, arising from L4-S3, and divides into the tibial and common peroneal nerves.
The Peroneal Nerve
The common peroneal nerve winds around the fibular head where it is vulnerable to compression. It divides into:
- Deep peroneal nerve: innervates ankle dorsiflexors and toe extensors
- Superficial peroneal nerve: innervates foot evertors and provides sensory innervation to the dorsum of the foot
The Posterior Tibial Nerve
The posterior tibial nerve courses behind the medial malleolus through the tarsal tunnel. It innervates the intrinsic foot muscles and provides sensory innervation to the sole of the foot.
The Sural, Superficial Peroneal, And Saphenous Nerves
These are the primary sensory nerves studied in the lower extremity:
- Sural nerve: sensory to lateral foot and ankle
- Superficial peroneal nerve: sensory to dorsum of foot
- Saphenous nerve: sensory to medial leg and foot