ABSTRACT
SCHWANN CELL n Surrounds individual myelinated axons (produces myelin), or surrounds several unmyelinated
axons
NODE OF RANVIER Gap at junction between Schwann cells n Allows rapid nerve conduction: Action potential depolarization jumps from one node of Ranvier
to the next (3-150 m/sec versus 2-2.5 m/sec for unmyelinated axons)
FASCICLES Grouped arrangement of axons with endoneurium surrounding each axon and perineurium surrounding each fascicle n Invested by internal (inner) epineurium n Logistically the smallest unit that can be treated surgically n Interconnect and branch proximally2
• Makes matching fascicles more difficult proximally, but fibers can be adjacent in a fascicular group
PERINEURIUM Connective tissue encircling each fascicle n Selective permeability (tight junctions that create a blood-nerve barrier, similar to the blood-
brain barrier) n Thin but dense; high tensile strength n Encircled by internal (inner) epineurium
• Sutured in fascicular repair
OUTER EPINEURIUM Outer sheath of peripheral nerve n Sutured in epineurial repair n Contains collagen and elastin fibers n Surrounded by loose areolar tissue (mesoneurium)
MESONEURIUM Outer adventitial layer of nerve n Incorporated in epineurial repair n Critical for nerve excursion and gliding
BLOOD SUPPLY n Arteriae nervosum (vaso nervosus)
• Enter nerve segmentally • Divide into longitudinal superficial branches in epineurium • Help guide proper orientation of nerve ends during repair
n Extrinsic vessels supply intrinsic longitudinal vessels in epineurium, which communicate with capillary plexus in perineurium
n Capillary plexus • Enters the endoneurium obliquely • Becomes occluded if endoneurial pressure rises because of injury (crush, edema)
MARTIN-GRUBER ANASTOMOSIS n Motor connections between median and ulnar nerves in forearm, or distally between anterior
interosseous nerve and ulnar branches n Present in up to 17% of the population n May mask the actual site of nerve injury (e.g., a median nerve injury at elbow level with loss of
all intrinsic muscle function, even though the ulnar nerve is intact)
RICHE-CANNIEU ANASTOMOSIS n Motor connections between median and ulnar nerves in palm n Present in up to 70% of the population3
n Can mask injury pattern
FROMENT-RAUBER ANASTOMOSIS n From radial nerve (either posterior interosseous nerve or superficial radial nerve) to ulnar
motor branches innervating the first, second, or third dorsal interosseous muscles n Rare n Can mask injury pattern
BERRETTINI CONNECTION n Sensory connections between the ulnar and median nerves in the palm n Usually travels deep to the superficial volar arch or immediately distal to the carpal tunnel n Present in approximately 80% of all cadaver specimens n Can produce confusing findings in physical examination for nerve injury
WALLERIAN DEGENERATION n Nerve stump undergoes degeneration distal to axonotomy. n Cytoplasmic calcium increases. n Macrophages proliferate; myelin phagocytosis. n Schwann cells proliferate and myelin breaks down. n Schwann cells and macrophages replace neural tube and organize into bands of Bunger,
providing a scaffold for regenerating axons.
