Myotomes

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A myotome is the group of muscles that a single spinal nerve innervates. Most muscles are innervated by more than one spinal nerve root, and therefore consist of multiple myotomes. Understanding the myotomes is integral for performing an accurate motor system examination.

Simplified Examination

Simplified myotomes^[1]
Spinal Level	Movement
Upper Limb
C5	Shoulder abduction
C6	Elbow flexion
C7	Elbow extension
C8	Finger flexion
T1	Finger abduction
Lower Limb
L2	Hip flexion
L3	Hip adduction
L4	Knee extension
L5	Ankle dorsiflexion
S1	Ankle plantarflexion

Commonly Tested Movements

Commonly tested movements. UMN column are movements that are preferentially weak in UMN lesions^[2]
Movement	UMN	Root	Reflex	Nerve	Muscle
Upper Limb
Shoulder abduction	++	C5		Axillary	Deltoid
Elbow flexion		C5/6 C6	+ +	Musculocutaneous Radial	Biceps Brachioradialis
Elbow extension	+	C7	+	Radial	Triceps
Radial wrist extension	+	C6		Radial	Extensor carpi radialis longus
Finger extension	+	C7		Posterior interosseous nerve	Extensor digitorum communis
Finger flexion		C8	+	Anterior interosseous nerve Ulnar	Flexor pollicis longus and flexor digitorum profundus (index) Flexor digitorum profundus (ring and little)
Finger abduction	++	T1 T1		Ulnar Median	First dorsal interosseous Abductor pollicis brevis
Lower Limb
Hip flexion	++	L1/2			Iliopsoas
Hip adduction		L2/3	+	Obturator	Adductors
Hip extension		L5/S1		Sciatic	Gluteus Maximus
Knee flexion	+	S1		Sciatic	Hamstrings
Knee extension		L3/4	+	Femoral	Quadriceps
Ankle dorsiflexion	++	L4		Deep peroneal	Tibialis anterior
Ankle eversion		L5/S1		Superficial peroneal	Peronei
Ankle plantarflexion		S1/S2	+	Tibial	Gastrocnemius, soleus
Big toe extension		L5		Deep peroneal	Extensor hallucis longus

Complete Myotome Chart

Complete Myotome Chart
Muscle	Nerve	Spinal Roots
Upper Limb ^[3]^[2]^[4]
		C3	C4	C5	C6	C7	C8	T1
Trapezius	Spinal accessory nerve	🔲	🔲
Supraspinatus, infraspinatus	Suprascapular nerve			🔳	🔲
Pectoralis major	Lateral and medial pectoral nerves			🔲	🔲	🔲	🔲
Latissimus dorsi	Thoracodorsal nerve				🔲	🔳	🔲
Teres major	Lower subscapular nerve			🔲	🔲	🔲
Serratus anterior	Long thoracic nerve			🔲	🔲	🔲
Rhomboids	Dorsal scapular nerve		🔲	🔲
Deltoid	Axillary nerve			🔲	🔲
Biceps and brachialis	Musculocutaneous nerve			🔲	🔲
Triceps	Radial nerve				🔲	🔳	🔲
Brachioradialis				🔲	🔳
ECRL				🔲	🔳	🔲
ECU						🔳	🔲
Finger extensors						🔲	🔲
FCR, pronator teres	Median nerve				🔲	🔲
FDS							🔲	🔳
APB							🔲	🔲
FPL, FDP, PQ	Anterior interosseous nerve					🔲	🔳	🔲
EDC, EPL	Posterior interosseous nerve					🔳	🔲	🔲
FCU	Ulnar nerve					🔲	🔳	🔲
FDP radial digits							🔳	🔲
FDP ulnar digits						🔲	🔳	🔲
Interossei						🔲	🔲	🔳
Lower Limb ^[2]^[4]
		L1	L2	L3	L4	L5	S1	S2
Iliopsoas	Femoral nerve	🔳	🔳	🔲
Quadriceps femoris	Femoral nerve		🔲	🔳	🔳
Adductor longus and magnus	Obturator nerve		🔳	🔳	🔲
Gluteus medius, minimis, tensor fascia lata	Superior gluteal nerve				🔳	🔳	🔲
Gluteus maximus	Inferior gluteal nerve					🔳	🔳	🔲
Semitendinosus, biceps femoris, semimembranosus	Sciatic nerve trunk†					🔲	🔳	🔲
Tibialis posterior	Tibial nerve†				🔲	🔲
Gastrocnemius and soleus							🔲	🔲
Flexor digitorum longus						🔲	🔳	🔳
Tibialis anterior	Peroneal nerve†				🔳	🔲
Extensor digitorum longus, extensor hallucis longus						🔳	🔲
Abductor hallucis, abductor digiti minimi, interossei							🔲	🔲
Extensor digitorum brevis, peroneus longus, peroneus brevis						🔲	🔲
🔲 segmental contribution, 🔳 significant segmental contribution. † The sciatic nerve trunk divides above the knee into the peroneal and tibial nerves, therefore lesions of the sciatic nerve trunk affect the muscles of all three branches.

Myotome Dance

Myotome Dance
Spinal Levels	Memory Aid	Action
Upper Limb
C1, 2	I nod to you	Neck flexion/extension
C3	Don’t tickle me	Neck lateral flexion
C4	I’m not sure	Shoulder elevation
C5	Feel alive	Shoulder flexion, abduction, & lateral rotation
C6, 7, 8	Close the gate	Shoulder extension, adduction & medial rotation
C5, 6	Pick up sticks	Elbow flexion
C7, 8	Lay them straight	Elbow extension
C5, 6	Flick my wrists	Forearm supination
C7, 8	The time is late	Forearm pronation
C6, 7	Fly up to heaven	Wrist flexion & extension
C7	Paper	Finger extension
C8	Rock	Finger flexion (though some sources say C7, 8 does both finger extension and flexion)
T1	Scissors	Finger abduction & adduction
Lower Limb
L2, 3	Lift my knee	Hip flexion
L3, 4	Kick the door	Knee extension (& knee-jerk reaction)
L4, 5	Foot points to the sky	Ankle dorsiflexion
L4, 5	Extend my thigh	Hip extension
L5, S1, (S2)	Kick my bum (Run to poo)	Knee flexion
S1, 2	Stand on my shoes	Ankle plantarflexion (& ankle jerk)
L2, 3, 4	Modestly close the door	Hip adduction & internal/medial rotation
L4 - S2	The opposite is true	Hip abduction & external/lateral rotation
C3, 4, 5	Keeps the diaphragm alive	Innervates the diaphragm
S2, 3, 4	Keeps poo off the floor	Innervates bowel, bladder, sex organs, anal sphincter, pelvic muscles. (& anal wink reflex)

Note

T1-12 Supplies chest wall and abdominal muscles
L1 Contributes to hip flexion & adduction
L5, S1, S2 Babinski plantar reflex/extensor response in UMN lesion

References

↑ The Noted Anatomist. Myotomes. Feb 29, 2020. Available on youtube
↑ ^2.0 ^2.1 ^2.2 Brain. Aids to the Examination of the Peripheral Nervous System, 4th edition. 2000
↑ Bell et al.. Refinement of myotome values in the upper limb: Evidence from brachial plexus injuries. The surgeon : journal of the Royal Colleges of Surgeons of Edinburgh and Ireland 2017. 15:1-6. PMID: 26409623. DOI.
↑ ^4.0 ^4.1 McGee, Steven R. Evidence-based physical diagnosis. Philadelphia, PA: Elsevier, 2018.

[1] The Noted Anatomist. Myotomes. Feb 29, 2020. Available on youtube

[brain-2] 2.0 ^2.1 ^2.2 Brain. Aids to the Examination of the Peripheral Nervous System, 4th edition. 2000

[3] Bell et al.. Refinement of myotome values in the upper limb: Evidence from brachial plexus injuries. The surgeon : journal of the Royal Colleges of Surgeons of Edinburgh and Ireland 2017. 15:1-6. PMID: 26409623. DOI.

[:0-4] 4.0 ^4.1 McGee, Steven R. Evidence-based physical diagnosis. Philadelphia, PA: Elsevier, 2018.

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