Where does the nerve:
• Come from--i.e. what are the spinal cord root levels?
• Where does it go?--i.e. what are the distal end organs?
• How does it get there?--i.e. what are the structures it travels through and with?
What is the location of the nerve in relation to other structures such as:
• Overlying structures--these might cause compressive neuropathy.
• Nearby non-nerve structures--look for associated trauma patterns. For example:
• A humerus fracture might be associated with radial nerve injury.
• A brachial artery laceration in the antecubital area is likely associated with a median nerve laceration as well.
• Nearby nerves because:
• A pattern of injury might tell you the nerves or roots that are injured.
• It may also help determine the course of treatment by defining the nerves nearby that are functioning and can be used for a therapeutic nerve transfer procedure.
The anatomy from the spinal cord to the distal end organ can be approached in two ways:
• You can look at the nerve longitudinally and dissect it out trying to separate the fascicles to each distal end organ.
• You can look at the nerve in cross section and try to identify which fascicles go to each distal end organ and where they sit at that one point.
• Both pieces of information are important to diagnosing and treating patients
In addition, basic anatomic information about the deficits seen helps determine the location of the injury. Examples:
• An injury that affects all of hand function with loss of extrinsic and intrinsic hand function at the thumb, index, long, ring and small fingers as well as sensation of the entire hand is more likely an injury of the C6, C7 and C8 roots at the lower brachial plexus rather than an injury of the median, ulnar and radial nerves more distally.
• An injury that causes loss of hand function including loss of function of the hypothenar, interossei, and ring and small finger lumbrical muscles as well as dimished sensation at the ulnar half of the ring finger and small finger but preserved distal interphalangeal joint flexion of the ring and small finger and preserved sensation over the dorsal ulnar hand is more likely an injury of the ulnar nerve at the wrist level rather than a partial more proximal ulnar nerve injury or a spinal cord root level injury.