A broad and variable lumbosacral myotome map uncovered by foraminal nerve root stimulation

Area of Science:

• Neurology
• Anatomy
• Electrophysiology

Background:

• The human myotome map is essential for diagnosing neurological disorders but is outdated and poorly described.
• Existing myotome maps lack detail on variability and reliability, limiting clinical application.

Purpose of the Study:

• To reconstruct and analyze the human myotome map using a novel electrophysiological method.
• To investigate the variability and breadth of muscle innervation by lumbosacral nerve roots.

Main Methods:

• Electrical stimulation of spinal nerve roots (T12-S1) in 42 patients undergoing dorsal root ganglion electrode placement.
• Measurement of triggered electromyography responses in muscles to map myotome innervation.

Main Results:

• Lumbosacral nerve root stimulation revealed variable muscle activation patterns, deviating from the classic myotome.
• Significant overlap and coactivation of muscles were observed, indicating broader innervation than previously assumed.
• Specific examples include L4/L5 activating quadriceps and tibialis anterior (TA), and S1 activating gastrocnemius and abductor hallucis (AH).

Conclusions:

• The muscular innervation of lumbosacral nerve roots exhibits substantial inter-individual variability and differs from established myotome charts.
• Each nerve root may innervate a wider array of muscles than commonly recognized.
• These findings are critical for improving the accuracy of diagnosing radicular pathologies and neurological conditions.