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Digit distribution of proper digital nerve action potential
J C King1, D Dumitru, J J Wertsch
1Department of Rehabilitation Medicine, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA. kingj@uthscsa.edu
Muscle & Nerve
|December 18, 2001
Summary
Antidromic sensory nerve testing using ring electrodes is unreliable for assessing individual digital nerve branches. New techniques are proposed to accurately evaluate single terminal digital nerve responses, avoiding cross-talk interference.
Area of Science:
- Neuroscience
- Clinical Electrophysiology
Background:
- Antidromic sensory nerve action potential (SNAP) testing is standard for evaluating upper limb nerves.
- Proper digital nerves are the terminal branches of the median and ulnar nerves.
- Ring recording electrodes are typically used to capture antidromic responses.
Purpose of the Study:
- To evaluate the reliability of small surface electrodes for recording individual proper digital nerve responses.
- To identify limitations of current antidromic techniques in isolating single digital nerve function.
- To propose improved methods for accurately assessing single terminal digital nerve integrity.
Main Methods:
- Attempted recording of individual digital nerve contributions using small surface electrodes.
- Investigated cross-talk by measuring responses on non-stimulated branches.
- Utilized local anesthetic blockade on specific digital nerve branches for isolation.
Main Results:
- Small surface electrodes showed unreliable results, with 50-77% amplitude cross-talk from non-stimulated branches.
- Volume-conducted responses from opposite digital branches interfere with single-nerve assessment.
- Even with nerve blockade, recorded responses remained within reference ranges, indicating technique limitations.
Conclusions:
- Standard antidromic SNAP testing with ring electrodes is insufficient for reliably assessing individual proper digital nerve integrity.
- Volume conduction poses a significant challenge to isolating single digital nerve responses.
- Modified techniques are necessary to accurately diagnose injuries to specific terminal digital nerve branches.