Two measurement methods of motor ulnar nerve conduction velocity at the elbow: A comparative study

Background: Electrodiagnostically, localization of ulnar nerve lesions, which commonly occurs at the elbow, is sometimes problematic. Measurement of motor ulnar nerve conduction velocity (NCV) at the elbow is amongst the most popular techniques to diagnose ulnar neuropathy. In this method, recording from the first dorsal interosseous muscle (FDI) is suggested to be more sensitive than the abductor digiti minimi (ADM). However, the criterion for abnormality is based on the normal values recorded from ADM.
Aims: To determine the normal values of Ulnar motor NCV using FDI and ADM and the difference between the values obtained from FDI and ADM. Additionally, to measure the amount of reduction of NCV across the elbow for each recording site.
Materials and Methods: This was a cross-sectional study performed on 50 healthy volunteers (100 nerves).All subjects were in the same condition regarding joint position and surface hand temperature. We recorded ulnar NCV at forearm and across the elbow with recording electrode on both FDI and ADM, simultaneously.
Results and Conclusions: The mean NCV at the elbow recorded from ADM and FDI were 62.65 ± 7.62 m/s and 60.49 ± 7.42 m/s respectively, showing significant difference. The ulnar minimum normal NCVs recorded from ADM and FDI were 47.4 m/s and 45.6 m/s, respectively. If the normal values of ADM are used as the basis for recording from FDI, it could lead to false-positive diagnosis of cases suspicious of ulnar neuropathy. Therefore it is preferred to use the normal values of FDI itself while recording.

Keywords
Abductor digiti minimi muscle, conduction velocity, first dorsal interosseous muscle, ulnar nerve damage