Key Myotomes
Introduction
Accurate motor testing is a high‑value clinical skill in the ED. Motor findings, interpreted with reflexes and dermatomal sensory loss, help localise lesions to a spinal root, plexus or peripheral nerve and guide decisions about imaging and referral.
New or progressive motor weakness, or bilateral lower‑limb weakness with saddle anaesthesia or bladder/bowel disturbance, requires urgent investigation (usually MRI) and neurosurgical/spinal referral (NICE NG59, NG127; RCEM Cauda Equina position statement).
This section gives a concise myotome map, practical testing technique, interpretation principles, ED priorities and common pitfalls.
Quick myotome map (for immediate bedside use)
- C5 - Deltoid: shoulder abduction.
- C6 - Wrist extensors (extensor carpi radialis).
- C7 - Elbow extensors (triceps).
- C8 - Finger flexors to middle finger (flexor digitorum profundus).
- T1 - Small‑finger abductors (abductor digiti minimi).
- L2 - Hip flexors (iliopsoas).
- L3, L4 - Knee extensors (quadriceps).
- L4, L5, S1 - Knee flexion (hamstrings).
- L5 - Ankle and big‑toe dorsiflexors (tibialis anterior, extensor hallucis longus).
- S1 - Ankle plantarflexors (gastrocnemius / soleus).