2025 Workshop Handout Bundle-W102RFA NCS in the foot

W102RFA NCS in the foot - Del Toro

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This document provides a comprehensive overview and analysis of nerve conduction studies (NCS) for diagnosing entrapment neuropathies in the lower extremity, with emphasis on the foot's nerve anatomy, pathophysiology, and electrodiagnostic evaluation techniques.<br /><br />Entrapment neuropathies occur when peripheral nerves are compressed mechanically at vulnerable anatomical sites, causing focal demyelination and sometimes secondary axonal degeneration. Symptoms vary based on affected fiber types and may include sensory, motor, or autonomic deficits.<br /><br />The common peroneal nerve, vulnerable at the fibular head and as it passes under the peroneus longus muscle, is frequently affected. Electrodiagnostic evaluation includes motor NCS over muscles like the extensor digitorum brevis (EDB) and anterior tibialis, with findings indicating conduction block or axonal loss. Sensory NCS of superficial and deep peroneal nerves aid diagnosis, especially in rare entrapments such as anterior tarsal tunnel syndrome.<br /><br />The superficial peroneal nerve, branching from the common peroneal nerve, can be entrapped near the fibular head or ankle, producing sensory deficits diagnosable via sensory NCS of its branches—the medial dorsal cutaneous (MDC) and intermediate dorsal cutaneous (IDC) nerves. Oh’s antidromic and orthodromic techniques enable precise assessment of these branches.<br /><br />Posterior tibial nerve entrapments, though rarer, include tarsal tunnel syndrome (TTS), where the nerve is compressed beneath the flexor retinaculum at the ankle. Diagnosis is supported by motor and mixed nerve conduction studies of plantar nerves and needle EMG of intrinsic foot muscles. Medial and lateral plantar neuropathies and disorders like inferior calcaneal neuropathy and interdigital neuropathy (Morton’s neuroma) are detailed with their electrodiagnostic profiles.<br /><br />Saphenous and lateral femoral cutaneous nerve neuropathies are described, with sensory NCS techniques aiding in diagnosis, often in association with surgical complications or entrapment.<br /><br />Additionally, a 2017 update compares four NCS techniques for the superficial fibular sensory nerve (SFSN): the Spartan, Izzo medial and intermediate dorsal cutaneous branches, and Daube methods. In a study of 108 subjects, all techniques reliably elicited sensory nerve action potentials (SNAPs) in 95%, differing statistically but not clinically in latency, amplitude, and required stimulation intensity. The Spartan technique had the longest latency but lowest stimulation threshold, whereas the Daube method yielded the largest amplitudes.<br /><br />Overall, this work underscores the importance of detailed anatomical knowledge and precise electrodiagnostic techniques for accurately diagnosing lower extremity entrapment neuropathies, facilitating appropriate clinical management.

Keywords

nerve conduction studies

ncs

entrapment neuropathies

lower extremity

common peroneal nerve

superficial peroneal nerve

posterior tibial nerve

tarsal tunnel syndrome

sensory nerve conduction studies

electrodiagnostic evaluation

foot nerve anatomy