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EMG - General Discussion:
- conduction velocity in the ulnar nerve across the elbow is slowed compared with the velocity in the forearm segment;
- as noted by Kaempffe et al 1998, abnormal EMG results are associated w/ poor surgical outcome;
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position of elbow during EMG/NCS:
- remember that elbow flexion may cause greater than a 10% ulnar nerve strain in upto 25% of patients;
- it is important to keep elbow flexed 70 to 90 deg during conduction measurements because in this position nerve is optimally stretched;
- during extension nerve buckles upon itself & is redundant, factor that may lead to spuriously low computed values of conduction velocity;
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amplitude of motor response in abductor digiti minimi is decreased and duration of response is
prolonged w/ stimulation above elbow compared w/ stimulation below the elbow;
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motor conduction velocity:
- look for slowing of more than 10 m/sec;
- velocity less than 41 m / sec across the elbos is abnormal;
- motor latency from above the elbow more than 10.2 sec;
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sensory latency is prolonged;
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motor latency:
- when axonal degeneration of the ulnar nerve occurs,
positive waves and
fibrillation may be observed;
