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Abductor hallucis false motor points: electrophysiologic mapping and cadaveric dissection
1Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin, Milwaukee, USA.
Muscle & Nerve
|September 1, 1996
Summary
False motor points (FMPs) are common in the abductor hallucis muscle, affecting nerve conduction studies. Identifying the true motor point is crucial for accurate electrophysiologic assessments.
Area of Science:
- Neurology
- Clinical Electrophysiology
- Anatomy
Background:
- False motor points (FMPs) can inaccurately prolong distal motor latencies in electrodiagnostic studies.
- Accurate identification of the true motor point (MP) is essential for reliable nerve conduction assessments.
Purpose of the Study:
- To investigate the presence and characteristics of FMPs in the abductor hallucis (AH) muscle.
- To compare the location and stimulation characteristics of FMPs with the true anatomical MP of the AH muscle.
Main Methods:
- Electrophysiologic mapping of compound muscle action potential (CMAP) onset using a grid of stimulation sites over the AH.
- Percutaneous threshold stimulation mapping of the AH muscle.
- Cadaveric dissection to identify the anatomical MP of the AH.
Main Results:
- FMPs were identified in 19 out of 20 feet (2.7 FMPs per foot), prolonging CMAP onset latency by 0.5-2.3 ms.
- The true anatomical MP of the AH was located inferior and posterior to the navicular tuberosity.
- The posterior MP site required significantly lower stimulus intensity compared to FMPs and other sites.
Conclusions:
- FMPs are prevalent in the abductor hallucis muscle and can be identified in nearly all individuals.
- These FMPs do not represent the true anatomical motor point.
- FMPs likely result from superimposed potentials of adjacent muscles or nerves, impacting electrodiagnostic accuracy.