When starting to think about nerve injuries one needs to understand the differences between the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord. The peripheral nervous system includes the branches coming off the spinal cord or from the brain (called the cranial nerves). Injuries to the central nervous system are treated by neurosurgeons (brain and spinal cord) or by orthopedic surgeons (spinal cord). The peripheral nervous system injuries are treated by surgeons trained in those areas through which the peripheral nerves travel. For example, a plastic surgeon or an ear, nose and throat surgeon (ENT) may be asked to repair a laceration of the face which may also involve a laceration of a nerve controlling the muscles of the face. Where there is a lacerated nerve in the arm or forearm from glass breakage, this may be repaired by a plastic surgeon or an orthopedic surgeon. These are just a few examples of peripheral nerve injuries.
Peripheral nerves can be injured in any number of ways. Lacerations and crushing injuries are some of the more common injuries, especially on fingers and hands. Like all injuries, the mechanism of the injury must be understood. This is usually determined at the time of the history and physical examination.
The mechanism of injury relates to the prognosis in many cases. For example, someone who is cleaning dishes in the sink cuts a finger on a knife while reaching into a sink full of soapy water and losses sensation in the tip of the finger is expected to have a better prognosis for return of sensation than someone who cuts the same finger with a skill saw while working in a wood shop building cabinets. The reason is the mechanism of injury. The knife injury is a “clean” cut of the digital nerve whereas the skill saw injury is the result of a tearing action of the skill saw blade. The tearing action creates more damage. The knife injury is repaired using a technique of nerve repair called an epineural repair and the skill saw injury may require a nerve graft which takes a nerve from somewhere else in the body and interposes the nerve graft between the edges of the injured nerve that remains.
When speaking about nerve repairs one usually distinguishes between primary versus secondary repair. The primary repair includes immediate repair (within a few hours of the injury) and what is called a “delayed primary” repair (within the first week). If the repair is more than a week out from the injury, it is a secondary repair.
Patients have asked why not do immediate repair on every nerve injury? This is a good question and the answer is: Conditions at the time of the injury may prevent immediate repair.
Imagine a war related injury in which the injured nerve is located in a wound which has been open for half a day as the combatant is transported to a hospital. The wound is contaminated with soil from the site of the battle. The risk of infection is high and delaying the repair for several days is a better choice. Or imagine a patient has multiple injuries from a high speed motor vehicle accident with additional injuries including a cardiac contusion, fractured lower legs and arms and a ruptured spleen along with lacerations from glass from the wind shield cutting a nerve in the forearm. This patient is better served with a delayed repair. The clinical situation determines what the surgeon will do in most cases.
Fortunately, surgical training provides the resident with the broad experience to help make the judgment call. It is this experience obtained working under attending physicians while in residency and the experience obtained in the practice of surgery and the clinical and basic science research done that allows surgeons to provide the care to injured patients.