The Pain Source

Electrode placement (use the ring electrodes)

14-cm distance (black to black)

• E1 (black):  Proximal phalanx of the index finger — want to keep away from the metacarpophalangeal (MCP) joint skin, as this may pick up motor conduction artifact.
• E2 (red):  3-4cm distally from E1.
• Ground:  Dorsum of hand

Stimulation site

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Electrode placement (use the ring electrodes)

14-cm distance (black to black)

• E1 (black):  Proximal interphalangeal joint (PIP) of the little finger — want to keep away from the metacarpophalangeal (MCP) joint skin, as this will likely pick up motor artifact from the abductor digiti minimi (ADM).
• E2 (red):  3-4cm distally from E1.  Usually almost hanging off the distal phalanx.
• Ground:  Dorsum of hand

Stimulation site

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By Chris Faubel, MD –

Photo from medicalacupuncture.org

EMG disease is a rare condition in which increased insertional activity (positive sharp waves and sometimes fibrillations) is seen in all muscles, in the absence of any known neuropathic, myopathic, or metabolic disorder.

• Normal nerve conduction study
• Short runs of positive sharp waves
• NO waxing and waning, early recruitment, sustained grip, or contractions with thenar muscle tapping  (classic signs of myotonia)

Insertional activity is caused by local muscle damage from the passage of the needle.

Positive sharp waves (PSWs) and fibrillations are the result of single muscle fiber action potentials that have a destabilized membrane (such as after denervation of a muscle).

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By Chris Faubel, MD –

The posterior interosseous nerve (PIN) is one of those nerves learned best by knowing the exceptions.

Source: Clinically Oriented Anatomy, 4th edition

In this case, the PIN innervates all the muscles on the dorsal side of the forearm, EXCEPT the brachioradialis, extensor carpi radialis longus (ECRL), and anconeus.

• It may help to remember these 3 exceptions by remembering they are the only muscles in the dorsal forearm that cross the elbow joint
• So that means, ALL dorsal forearm muscles that do NOT cross the elbow joint are innervated by the deep radial nerve/PIN (see below)

When does the radial nerve become the PIN?

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By Chris Faubel, MD –

Understanding nerve injury classification is essential for prognostic value clinically.

Some basic anatomy, along with the two classification systems, and their corresponding EMG findings need to be learned and remembered.

Two classification systems exist (and are frequently tested in various exams):

1. Seddon’s classification (neuropraxia, axonotmesis, neurotmesis)
2. Sunderland’s classification (types 1-5)

To understand the systems, you must first review some basic nerve anatomy.

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By Chris Faubel, MD –

I’ve  made it the “A-OK” sign, instead of just the “OK” sign, because the “A” will help to remind you about its innervation…the Anterior interosseous nerve (AIN)

• the AIN is a pure motor branch of the median nerve; just like the posterior interosseous nerve is a pure motor continuation of the deep branch of the radial nerve.

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By Chris Faubel, MD –

A 50 year old male was referred to us for evaluation of his right lower extremity.  Pt had a gunshot injury to the abdomen about two months ago, with a resultant right-sided retroperitoneal abscess that was subsequently drained.  He presented today with significantly weakened right hip flexors (3-/5) and knee extensors (2/5), with numbness over the anterior thigh and medial leg.  **note that the knee extension was more affected than the hip flexion
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By Chris Faubel, MD –

If the median sensory latency or median motor latencies are prolonged, this index is not needed.  But, if they are both normal, then perform the CSI.

The CSI is a summation of three latency differences:
1) Split thumb: median and radial antidromic conduction at 10cm; reference = 0.5 or less
2) Split ring: median and ulnar antidromic conduction at 14cm; reference = 0.4 or less
3) P8: median and ulnar orthodromic conduction at 8cm; reference = 0.3 or less

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By Chris Faubel, MD –

A patient presents to your clinic with a very clear presentation of ulnar neuropathy at the elbow:

• numbness in the medial hand (palmar and dorsal surfaces and medial 1.5 digits), that is worse when talking on the phone and reading a book – basically all activities when his elbows are flexed 90 degrees or more
  • note: if it was only the palmar surface, then the lesion would be more likely at the wrist, b/c the dorsal ulnar cutaneous nerve supplies the dorsal medial hand and branches off before the wrist — thus not involved in Guyon’s canal lesions
• NO paresthesias in medial forearm (b/c that would be from the medial antebrachial cutaneous nerve, and therefore a lower brachial plexus lesion)

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