The Pain Source

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 –

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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