Surgery, in this setting, is truly exploratory. As helpful as the tests done before surgery are, they are not 100 percent reliable in telling us what to expect at surgery, and they are certainly not reliable enough to decide that a child will not be helped by surgery. Initially, the plexus is exposed by first finding the phrenic nerve, which supplies the breathing muscle, the diaphragm, and following it back to the point it branches off the nerve roots as they leave the spine.
The space through which the C5, C6, C7 and sometimes the C8 nerve roots leave the spine are then surgically exposed and the respective nerve roots are looked for and evaluated. This evaluation includes electrical stimulation to see if they can transmit a signal down to the muscles of the arm. Abnormally appearing roots, coupled with poor response to stimulation, typically labels a root as having been partially or completely avulsed (pulled from the spinal cord). Once the nerve roots have been identified and tested, they are followed out into the shoulder and further areas of injury are looked for.
Several types of injuries can be encountered. The simplest, a local conduction block, is a focal area of abnormal nerve function without evidence of breakage of the nerve or its contents. An example is a constrictive neuropathy due to scar tissue investing the nerve as it travels through the shoulder, constricting it to such a degree as to interfere with its blood supply. Here, simple cutting away of the investing scar tissue will allow for the reestablishment of the blood supply to the nerve and restoration of its function. Also, there can be breakage of some of the nerve’s fibers (axonotmesis) without breakage of the nerve’s outer coverings. There is some dieback in the portion of the nerve where the breakage has occurred, with new growth coming down from the spinal cord to replace that which has died back. This new growth can successfully cross the area of breakage and grow out to the targeted muscle reestablishing that muscle’s nerve supply. Conversely, the new growth may grow out through the breakage and randomly grow in the area of injury, causing a neuroma to form. Finally, the most severe type of injury encountered is a complete breaking of the nerve (neurotmesis). Here there is complete dieback of the nerve to the spinal cord. New growth then starts out down the former nerve’s sheath. When this growth reaches the breakpoint, it randomly grows out into the tissues surrounding the nerve, causing a large neuroma to form.
Specific treatments are indicated for the various injuries encountered. Frank nerve root avulsions where the nerve root has been completely pulled from the spinal cord can only be dealt with by running a graft from a donor site to the part of the nerve downstream from the point of avulsion. There can be difficulty finding an acceptable proximal graft site for such an arrangement, so, not uncommonly, this injury is not dealt with out of a desire not to worsen the child’s clinical deficits. Constrictive neuropathy, while rare, is straightforward to deal with, requiring only surgical cutting away of the invading scar tissue. Axonotmesic injuries can require either no treatment, cutting away of some of the neuroma, or cutting away all the neuroma and placing a graft to bridge the defect in the nerve. The exact procedure done is determined at the time of surgery based on the clinical findings and electrical testing. Neurotmesis is dealt with by cutting away the neuroma and then placing a graft to bridge the defect.
After the repair is complete, the child’s wound is closed and dressings applied. The child is then stabilized in a papoose to prevent lateral flexion of the head away from the shoulder just operated upon so as to avoid ripping apart any grafts that have been placed. Recovery of muscle function is measured in months since nerves must grow from the spinal cord and only grow at a rate of one inch per month. Once the nerve reaches the muscle, the muscle must strengthen and the child must learn to use the muscle again. Improvements can span several years after one of these procedures, and it is not uncommon for additional, augmenting procedures to be required.