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Micro Anatomy

OVERVIEW
 
Knowledge of the micro anatomy or internal topography of the nerve is critical to performance of nerve transfer procedures.
It is also helpful in general for the proper treatment of transection and other types of nerve injuries.
Knowledge of the concept of internal topography is a critical first step to performing nerve transfer procedures. 
• However, most surgeons do not routinely learn this in medical school, residency or beyond.
• With this website, we hope to provide some information in the forms of:
• Anatomic dissections that will help train the user to recognize the longitudinal path of the nerve fiber to the motor and sensory end organ. 
• Video of the surgeries that show stimulation of the fascicles within a nerve at different points in the extremity will also provide some information. 
• Also, wide exposure during surgical treatment, use of intraoperative nerve stimulation of the donor nerves as well as a combination of physical and visual neurolysis of the fascicles from the end organ to the site of surgical repair will provide additional critical information.
Nerves are made up of nerve fibers--of different types:
• The fibers can be motor, sensory or sympathetic.
• The fibers can be myelinated or unmyelinated.
• The individual fibers are microscopic and cannot be seen under loupe or operating room microscope magnification.
These fibers are grouped into fascicles.  Fascicle characteristics:
• Fascicles can be monofascicular (one fascicle), oligofascicular (a few fascicles), polyfascicular (several fascicles which may or may not be grouped themselves).
• The fascicles are organized within the nerve and certain fascicles generally go to one end target--thus for example:
• The ulnar nerve deep motor branch, which supplies the hand intrinsic muscles, fascicles can be dissected off of the ulnar nerve sensory fibers at a level well proximal to the hand.  This allows targeted reinnervation at the forearm level by transfer of the anterior interosseous nerve branch to the pronator quadratus to this ulnar nerve deep motor branch. 
• Also, the lateral antebrachial cutaneous nerve from the musculocutaneous nerve could be transferred to the ulnar nerve sensory portion.
• In another example, the median to musculocutaneous nerve branch transfer (which can be combined with use of redundant fascicles from the ulnar nerve in the ‘double fascicular transfer’), the flexor carpi radialis and flexor digitorum superficialis fascicles can be dissected free of the remaining portions of the median nerve at a level well proximal to the elbow.  This allow targeted reinnervation of the biceps and brachialis branches of the musculocutaneous nerve by nerve transfer procedure of these functionally redundant expendable median nerve fibers.
Note, that there some interconnections between the various fascicles:
• Historically, it was thought that there was a lot of plexus formation along the course of the peripheral nerve--this holds true for the very proximal portion of the nerve.  But even at a proximal level nerve fibers destined for a particular distal function remain grouped together.
• However, distally, by and large these interconnections are not critical and may be cut to allow for nerve transfer and other procedures.
• Overall, the fibers to a specific end organ are grouped within the nerve and occupy the same microanatomic cross-sectional position.