Myotomes
Key myotome levels allow rapid clinical testing of spinal cord integrity. Each level has a specific movement that is reliably tested at the bedside.
✦ The Mnemonic
"Shoulders Elevate, Elbows Extend, Wrists Flex, Hand Grips; Hips Kick, Knees Dip, Ankles Pop"
C5→C6→C7→C8→T1 in the upper limb; L1–2→L3–4→L5→S1 in the lower limb
Clinical Breakdown
Myotomes are the muscle groups supplied by a single spinal nerve root. Unlike dermatomes (which are relatively discrete), myotomes significantly overlap — most muscles receive innervation from two consecutive roots. Testing the index movement for each root provides a rapid clinical screen.
The most clinically tested myotomes: C5 (shoulder abduction — deltoid); C7 (elbow extension — triceps); L3–L4 (knee extension — quadriceps, knee jerk); S1 (ankle plantarflexion — gastrocnemius/soleus, ankle jerk). These four cover the most common disc protrusion levels.
Upper limb myotome testing: C5 — arm raise. C6 — forearm curl. C7 — arm push-down. C8 — grip. T1 — finger spread. This 'five-step' sequence can be performed quickly during trauma assessment.
⭐ Clinical Pearl
Root vs peripheral nerve lesion: a dermatomal or myotomal pattern (following spinal segments) suggests root compression (disc, tumour, fracture). A peripheral nerve pattern (following a named nerve distribution) suggests mononeuropathy. Nerve conduction studies and EMG can distinguish them electrophysiologically.