Nerves act as ‘electric cables’ or ‘wires’ of the body carrying information (impulses) to and from the brain. Motor nerves carry messages from the brain to muscles and make the body move. Sensory nerves carry messages to the brain from different parts of the body and transmit impulses related to pain, temperature and pressure. The nerves in the body can be either only motor or sensory, or most commonly, are made of both type of ‘cables’.
A single nerve contains millions of individual fibers (fascicles), which are grouped in bundles and wrapped in a fine sheath (coat) called the epineurium. Nerve anatomy is incredibly delicate requiring microsurgical skills and finesse during surgery with mandatory use of surgical loops and powerful microscopes.
Nerve pathologies vary greatly, but in my practice the commonest surgical abnormalities affecting the nerves of the forearm and hand are:
- injuries (crushes, stretching and cuts (lacerations)
- nerve defects requiring nerve grafting
- painful nerve scars called neuromas
- scarring around the nerve requiring release of adhesions (procedure called neurolysis)
- nerve tumours requiring resections
Trauma is by far the commonest cause of nerve dysfunction in the hand and as such is described in more detail illustrating some basic principle of nerve surgery.
Nerves are fragile and can be damaged by pressure, stretching or cutting. Constant exposure of the hand in various daily activities and relative superficial position of nerves within the tissue layers makes them particularly vulnerable. Injury to a nerve can stop the transmission of signals to and from the brain, preventing muscles from working, causing loss of feeling in the area supplied by that nerve and leading to frustrating disabilities. Pressure or stretching can cause the nerve fibres to break and stop transmitting impulses, without disrupting the surrounding nerve sheath. When a nerve is cut, both the nerve and the epineurium are disrupted.
To fix a cut nerve, the sheath around both ends of the nerve needs to be sewn together. The goal is to repair the outer cover so that nerve fibers can grow down the empty tubes and reconnect. As there are millions of fibers in the nerve, not all of the original connections can be re-established, but if the majority of cables are realigned reasonably well, chemical signals of healing are likely to lead to spontaneous reconnections too. Needless to say, that sooner the nerve is repaired after injury (within the first 5-7 days), better the recovery and vice versa. Potential for healing decreases as the time elapses and several months after the injury, repair attempts should be judged very carefully.
A nerve in a finger for example, is only 2mm thick so the stitches have to be very fine and thin. Since repairs are so delicate, splint might need to be worn for the first 2-3 weeks to protect it from stretching. If there is a gap between the ends of the nerve, a piece of nerve from another part of the body (nerve graft) might need to be taken in order to ‘bridge’ the defect. This may cause permanent loss of feeling in the area where the nerve graft was taken – the logic behind such ‘lending’ is that less important nerve is used for re-innervations of important hand muscle or skin patch. Smaller gaps can sometimes be bridged with “conduits” made from a vein or special synthetic materials.
Approximately 2-3 weeks after the nerve cover is fixed surgically, the nerve fibers begin to grow across the repair. The nerve fibers usually grow down the empty nerve tubes up to 0.5-1mm per day. This is why following an injury to a nerve in the arm, it may take up to 12-14 months before feeling returns to the fingertips. The feeling of pins and needles in the fingertips is common during the recovery process.
As the nerve recovery is slow, it is important to remain patient, optimistic and compliant with the physiotherapy. If the joints become stiff, they will not work even after muscles begin to work again. When a sensory nerve has been injured, the patient must be extra careful not to burn or cut their fingers since there is no feeling in the affected area. After the nerve has recovered, the brain gets “lazy,” and a procedure called sensory re-education may be needed to improve feeling to the hand or finger.
Factors that affect results after nerve repair include age, location of the injury, the type of wound and type of the nerve transected.
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