Related Experiment Video
Updated: Oct 18, 2026

Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies
Published on: January 11, 2019
The influence of wrist thickness on amplitudes of sensory nerve action potentials
W Chira-Adisai1, K Yan, B Turan
1Department of Rehabilitation Medicine, Ramathibodi Hospital, Bangkok, Thailand.
Abstract:
Normal values of sensory nerve action potential (SNAP) amplitudes vary widely. There are many factors which can influence the amplitude of the SNAP, such as the type of recording techniques, temperature, distance between recording electrodes, skin impedance, etc. In this study, we investigated the correlation between wrist thickness (palmar to dorsum diameter) and amplitudes of the SNAP of median and ulnar nerves of 20 healthy subjects. Ring electrodes were placed on the second and the fifth fingers and a surface block electrode was placed at the wrist between the flexor carpi radialis and the palmaris longus tendon and just radial to the flexor carpi ulnaris tendon, for testing the median and ulnar nerves, respectively. Both orthodromic and antidromic techniques were used. Depending on the technique, either ring or surface block electrodes could be the stimulating or the recording electrodes. By supramaximal intensity stimulation, the amplitude of the SNAP was measured from peak to peak. The results revealed that SNAP amplitudes and wrist thickness are reversely correlated, with statistical significance (p < or = 0.005) by using the antidromic technique. The influence of wrist thickness on SNAP amplitudes should be recognized when performing an electrodiagnostic study to determine axonal degeneration by using the SNAP amplitude parameter.
Related Concept Videos
Local Anesthetics: Differential Sensitivity of Nerve Fibers
Spinal Nerves: Plexus I
The Cervical Plexus
The cervical plexus, formed by the anterior rami of the first four...
Muscle Stimulation Frequency
Wave summation
At low firing rates, motor neurons induce individual twitch contractions in muscle fibers. These twitches...
Action Potential
Membrane potential in neurons
Neurons typically have a resting membrane potential of about -70 millivolts (mV). When they receive...
Action Potential
Membrane potential in neurons
Neurons typically have a resting membrane potential of about -70 millivolts (mV). When they receive...
Pulse amplitude and quality
A weak or absent pulse may indicate reduced cardiac output or poor left ventricular contraction, which can be signs of cardiovascular dysfunction or...