Dermatomes and Myotomes

Dr Edrish Contractor

Introduction

• Spinal nerves have motor fibres and sensory fibres. • The motor fibres innervate certain muscles, while the

sensory fibres innervate certain areas of skin. • A skin area innervated by the sensory fibres of a single

nerve root is known as a dermatome• A group of muscles primarily innervated by the motor

fibres of a single nerve root is known as a myotome.• Although slight variations do exist, dermatome and

myotome patterns of distribution are relatively consistent from person to person.

 Test Dermatomes at dots 

Upper Body Test Ponits

C2 - Occipital Protuberance

C3 - Supraclavicular Fossa

C4 - Acromioclavicular Joint

C5 - Lateral Antecubital Fossa

C6 – Thumb

C7 - Middle Finger

C8 - Little Finger

T1 - Medial Antecubital Fossa

T2 - Apex of Axilla

Lower Body Test Points

L1 - Upper Anterior Thigh

L2 - Mid Anterior Thigh

L3 - Medial Femoral Condyle

L4 - Medial Malleolus

L5 - Dorsum 3rd MTP Joint

S1 - Lateral Heel

S2 - Popliteal Fossa

S3 - Ischial Tuberosity

S4,S5 - Perianal Area

Clinical significance

• Dermatomes are useful to help localize neurologic levels, particularly in radiculopathy.

• American Spinal Injury Association classification• Dermatomes are clinically important and

necessary for assessing and diagnosing the level of spinal cord injury in the American Spinal Injury Association (ASIA) Impairment scale.[2]

Example

• Pain radiating down the back of leg to the small toes in the general pattern of the S1 dermatome suggests that a herniated disk may be pinching the S1 nerve root in the spine.