I was reading a paper investigating using MRI as a way to determine peripheral nerve regeneration: https://sci-hub.do/10.1016/j.expneurol.2009.10.012
They mention that
... nerve conduction studies are widely used but these studies are limited only to the distal parts of peripheral nerves and not suitable to measure regeneration early on and in response to proximal lesions (Kimura, 1999). Furthermore,after complete axonal injury, particularly as it relates to traumatic nerve injuries or proximal plexus lesions, the distal portions of nerves are often inexcitable, which limits electrodiagnostic testing's utility to assess the degree of regeneration in proximal nerve trunks.
I understand this because normal nerve conduction studies wrap an electrode on your finger (where current goes in) and reads it down stream at your wrist.
I totally get why this wouldn't work if the injury occurred very high up at say the elbow, because the signal could not travel from your finger upwards since it's all degenerated.
However, what if we instead stimulated the nerve a bit above the elbow (maybe using a needle) and measured the signal downstream. We could move closer and closer until a signal was detected. This is where the nerve has regenerated to - thus this method CAN detect peripheral nerve regeneration. What is wrong with my reasoning?