Which movement is tested by the C5 myotome?

Which movement is tested by the C5 myotome?

• A. Ankle dorsiflexion
• B. Elbow extension and wrist flexion
• C. Shoulder abduction and external rotation
• D. Shoulder elevation

Answer: (C)

C5 myotome mainly assesses movements powered by the shoulder muscles, especially the deltoid for lifting the arm away from the body. Shoulder abduction is the classic test for C5 because the deltoid’s primary action is to abduct the arm, making this movement the clearest indicator of C5 function. External rotation involves the infraspinatus, which also receives C5-C6 input, so testing that motion can reflect C5 integrity as well. The other movements map to different nerve roots: ankle dorsiflexion (L4-L5), elbow extension and wrist flexion (primarily C7–C8), and shoulder elevation (more C4). Thus, shoulder abduction and external rotation best represent the C5 myotome.

C5 myotome mainly assesses movements powered by the shoulder muscles, especially the deltoid for lifting the arm away from the body. Shoulder abduction is the classic test for C5 because the deltoid’s primary action is to abduct the arm, making this movement the clearest indicator of C5 function. External rotation involves the infraspinatus, which also receives C5-C6 input, so testing that motion can reflect C5 integrity as well. The other movements map to different nerve roots: ankle dorsiflexion (L4-L5), elbow extension and wrist flexion (primarily C7–C8), and shoulder elevation (more C4). Thus, shoulder abduction and external rotation best represent the C5 myotome.