|· 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.
· Ulnar to median motor cross over in forearm or wrist.
Riche Cannieu anastamosis
· Ulnar deep motor crossover to median nerve in palm.
o 6/16 hands in one dissection
o 27/35 hands in another.