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What is a dermatome?
An area of skin that is mainly supplied by a single spinal nerve.
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How is the sensory distribution of dermatomes tested?
Tested with a pinwheel, acupuncture guide tube, or cotton swab.
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What are some key landmarks for dermatomes?
- C5: Clavicle,
- C6: Thumb,
- T4: Level of Nipples,
- T10: Level of Umbilicus,
- T12: Level of Inguinal Region,
- L2: Anterior Mid-Thigh,
- L4: Medial side of Great Toe.
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What are myotomes?
A group of muscles innervated by the same nerve root.
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What is the clinical significance of testing myotomes?
If there is weakness apparent in a group of muscles innervated by the same nerve root, the issue is likely at the nerve root level.
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What are the upper myotomes and their associated movements?
- C1-C2: Cervical Flexion,
- C3: Cervical Lateral Flexion,
- C4: Shoulder Elevation,
- C5: Shoulder Abduction,
- C6: Elbow Flexion/Wrist Extension,
- C7: Elbow Extension/Wrist Flexion,
- C8: Thumb Extension,
- T1: Finger Abduction/Adduction.
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What are the lower myotomes and their associated movements?
- L2: Hip Flexion,
- L3: Knee Extension,
- L4: Ankle Dorsiflexion,
- L5: Big Toe Extension,
- S1: Ankle Plantarflexion,
- S2: Knee Flexion.
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What are the typical etiologies for peripheral nerve injuries in the upper extremity?
- Axillary: humeral head fracture, anterior dislocation of the shoulder. Musculocutaneous: fracture of the clavicle.
- Radial: compression of the nerve in the radial tunnel, humerus fracture. Median: compression of carpal tunnel, pronator teres entrapment. Ulnar: compression in the cubital tunnel, entrapment in Guyon’s canal.
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What are the typical etiologies for peripheral nerve injuries in the lower extremity?
- Femoral: THR, displaced acetabular fracture, anterior dislocation of femur, hysterectomy, appendectomy.
- Sciatic: blunt force trauma to the buttock, THR, accidental injection to the nerve.
- Obturator: fixation of femur fracture, THR.
- Peroneal: femur, tibia or fibula fracture, positioning during surgical procedures.
- Tibial: tarsal tunnel entrapment, popliteal fossa compression. Sural: fracture of the calcaneus or lateral malleolus.
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What are the procedures used to assess nerve and muscle function?
Electroencephalography (EEG): Non-invasive, measures electrical activity of the brain. Electromyography (EMG): Invasive, assesses nerve and muscle dysfunction or spinal cord disease. Nerve Conduction Velocity (NCV): Non-invasive, determines nerve action potentials and the nerve’s ability to send a signal.
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