The Pain Source

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?

• Continue Reading

Related Content:

• Finkelstein’s Test
• De Quervain’s Tenosynovitis Injection – Technique and Tips
• Setup – Median Motor NCS

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.

Continue Reading

Related Content:

• Carpal Tunnel Syndrome – Electrodiagnostics
• Tinel’s Sign at the Wrist
• Phalen’s Test
• Are EMG Findings Related to Epidural Steroid Injection Relief?
• Ultrasound – Carpal Tunnel Injection

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

Continue Reading

Related Content:

• Setup – P8 Median-Ulnar Sensory NCS
• Setup – Split Ring Median-Ulnar Sensory NCS
• Carpal Tunnel Syndrome – Electrodiagnostics
• Setup – Numb Thumb Median-Radial Sensory NCS
• Carpal Tunnel Syndrome: A Review

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)

Continue Reading

Related Content:

• Ultrasound – Axilla Nerve Blocks
• Carpal Tunnel Syndrome: A Review
• Setup – Ulnar Motor NCS
• Setup – P8 Median-Ulnar Sensory NCS
• Setup – Split Ring Median-Ulnar Sensory NCS