Repair of peripheral nerve defects in the upper extremity.

Repair of peripheral nerve defects in the upper extremity using end-to-end coaptation is accomplished by one of four techniques: in situ mobilization, rerouting and transposition, joint positioning, and bone shortening. A key concern is the amount of tension generated when nerves are elongated to overcome a gap defect. The evidence indicates that elongation should be limited to 8% to 10% of the original length to avoid neural ischemia. It should be noted, however, that when repairs are delayed, the vascularity of nerves is increased. As a result, compared with acute injuries, chronic injuries will tolerate the same degree of elongation with less neural ischemia despite increased stiffness. The mesoneural attachments along each end of the nerve may be safely stripped to a distance of 8 to 12 cm when mobilizing the nerve. Larger nerves tolerate greater lengths of mobilization than smaller nerves. The maximum amount of mobilization that does not produce ischemia can be expressed as a ratio of the diameter of the nerve to the length mobilized and its value is 1:45. The amount of nerve mobilization required for a secondary repair may be reduced by the initial application of tension to unrepaired nerves, thereby reducing the amount of retraction. As the interval to repair increases, nerve retraction results in up to a six-fold increase in the gap defect that must be overcome. Finally recommendations exist for the repair of peripheral nerve segmental defects in the acute setting.