Median Anastamosis

·     Martin Gruber-median to ulnar anastamosis

Median to ulnar nerve crossover in forearm.o      Motor fibers usually

o      Rare sensory cross over described.

·       1st described by Martin in 1763, and later by Gruber in 1870.

·       ? Autosomal dominant inheritance.

·       Reported incidence of 10-40% of median nerves.

·       Usually cross over fibers originate from the distal anterior interosseous nerve but other patterns described

o      Branch from proximal anterior interosseous nerve

o      Branch directly from median nv.

o      Branch from AIN to ulnar FDP.

o      Branch from AIN to join ulnar nerve at more than one site.

·       Type I-crossover fibers terminate in hypothenar muscles.

o      Ulnar NCS- may observe ulnar pseudo-conduction block in the forearm-more fibers stimulated at wrist with higher CMAP than proximal forearm or above elbow stim.

·       Type II-crossover fibers terminate in first dorsal interossei innervation.

o      Most common.

o      Again-ulnar NCS result in higher CMAP with wrist stim than proximal to crossover.

·       Type III-crossover fibers terminate in thenar muscles.

o      Least common.

o      Median NCS-larger CMAP with elbow stim than wrist stim.

·       Martin-gruber anastamosis with carpal tunnel syndrome

o      Initial positive deflection CMAP with elbow stim-always indicative of carpal tunnel syndrome (Guttman)

o      May have erroneous high NCV-very short latency with elbow stim-these fibers not impeded at carpal tunnel.

Marinacci Anastamosis

·       Ulnar to median motor cross over in forearm or wrist.

Riche Cannieu anastamosis

·       Ulnar deep motor crossover to median nerve in palm.

·       Incidence

o      6/16 hands in one dissection

o      27/35 hands in another.

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