[Segmental (L4-S1) motor and sensory innervation of the lower extremity determined by electrical potentials]

Reliable knowledge of the segmental innervation of the muscles and skin of the lower extremity is required to evaluate the anatomical localization of the lumbosacral nerve root involvement. There exist a number of reports on the segmental innervation of the muscles and the area of skin supplied by the lumbosacral plexus. However, no universal acceptance on the lumbosacral nerve root innervation exists. In order to confirm the reliability of the information on myotomes and dermatomes that has been reported, muscle action potentials were recorded from 11 lower limb muscles of 10 subjects by electrical stimulation of the L4, L5 and S1 nerve roots. Sensory nerve potentials were also recorded from roots by stimulations of the sural nerve, superficial and deep peroneal nerve, and the 1st toe of 8 subjects. Under an image intensifier, the electrodes were inserted near the nerve root in the intervertebral foramen or the first sacral foramen. The medial and lateral head of gastrocnemius and the soleus were confirmed to be S1 innervation, but tibialis anterior had a dual innervation at L4 and L5. Extensor hallucis longus, extensor digitorum longus and brevis, and peroneus longus were supplied predominantly by L5. Abductor hallucis and the long head of biceps femoris were supplied by S1, and rectus femoris was supplied by the L4 root. The sural nerve and superficial peroneal nerve were supplied by S1 and L5 nerve root, respectively. The deep peroneal nerve was supplied by either L4 or L5. The 1st toe was supplied by L5.