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.