C8 myotome tests which actions?

C8 myotome tests which actions?

• A. Shoulder elevation
• B. Finger flexion and thumb extension
• C. Great toe extension and hip abduction
• D. Elbow flexion and wrist extension

Answer: (C)

The key idea is that the C8 myotome governs hand and finger movements, not leg movements. The C8 nerve root supplies the intrinsic hand muscles and the finger flexors, so testing this myotome focuses on finger flexion and thumb control. Clinicians assess C8 by asking the patient to flex the fingers (for example, making a strong fist or resisting finger flexion) and by testing thumb movements against resistance. Great toe extension and hip abduction are controlled by lower-limb myotomes (toe extension by a lumbar level, typically L5, and hip abduction by L4–L5/S1), so those actions do not reflect C8 function. If C8 is impaired, weakness would appear in finger flexion and thumb movements rather than in toe or hip actions.

The key idea is that the C8 myotome governs hand and finger movements, not leg movements. The C8 nerve root supplies the intrinsic hand muscles and the finger flexors, so testing this myotome focuses on finger flexion and thumb control. Clinicians assess C8 by asking the patient to flex the fingers (for example, making a strong fist or resisting finger flexion) and by testing thumb movements against resistance. Great toe extension and hip abduction are controlled by lower-limb myotomes (toe extension by a lumbar level, typically L5, and hip abduction by L4–L5/S1), so those actions do not reflect C8 function. If C8 is impaired, weakness would appear in finger flexion and thumb movements rather than in toe or hip actions.