Pitfalls

• Clean ends of nerve must be sewn together to avoid a neuroma in continuity.

• Missed diagnosis with a devas-cularized finger may lead to amputation

• Range of motion must be controlled with splinting.

Weber Static Two Point Discrimination

Figure 20—1. Weber static two-point sensory discrimina tion test.

Figure 20—1. Weber static two-point sensory discrimina tion test.

Diagnosis

Acute Laceration, Radial Nerve, of the Index Finger

Neurapraxia is the mildest form of nerve injury. This usually involves demyelination without axon disruption and degeneration. This type of injury has a relatively short recovery time, and full function is expected without intervention.

Axonotmesis occurs when axons, myelin, and associated internal nerve structures are disrupted. These injuries often result from situations in which traction overcomes the inelastic internal structures but leaves the elastic epineurium intact. When axons are disrupted and the endoneurium and the rest of the nerve are intact, degeneration and regeneration occur. This is the first stage of injury that shows an advancing Tinel's sign. Because the endoneurium is intact, regeneration should be full with complete sensory and motor function regained.

Another type of injury occurs when the axons and the endoneurium are damaged and the perineurium and epineurium are intact. This leaves the blood—nerve barrier intact but provides a disorganized bed through which the axons can travel. Nerve regeneration may be slowed due to infiltration of scar tissue or a smaller number of axons capable of survival and regeneration. An advancing Tinel's sign, though somewhat slowed, should be present.

The worst form of closed nerve damage is when all structures are damaged except the epineurial covering. This disables the intact axons and no conduction down the nerve is possible. Surgical intervention is required to restore function. ATinel sign is present at the level of injury and does not move distally because the regenerating nerve is kept from advancing by large amounts of scar tissue or debris.

Neurotmesis is the most severe type of injury. This class of injury is easy to diagnose because it usually involves an open wound with nerve deficits. Surgical repair is a requirement for any return in function to occur. Results following the surgical repair of digital nerves are inconsistent. Among the factors that could impact on outcomes are the amount of direct trauma to the nerve, the length of nerve that has been traumatized, and the age of the patient. Increased tension on the repair has also been shown to effect the final results.

Nerve repair never results in the return of full sensibility. However, reasonable protective sensibility to light touch and pin pricks can be obtained. Two-point discrimination can approach normal in as many as one patient in three (33%).

Surgical Management

After usual draping and prepping of the patient, the skin is marked. The patient is supine and a regional anesthetic is administered. If multiple structures need to be repaired, then general anesthesia is used and the arm is exsanguinated using a tourniquet on the forearm or arm.

Incision use for this procedure is a midaxial incision because it offers the best extensile exposure to the palm and finger. Some surgeons use a Bruner zigzag to expose the nerve, but we feel excessive scarring results with this type of incision. Gross exploration is accomplished under loupe magnification using tenotomy or other scissors.

After initial exploration, using a microscope for high-power magnification, identify the nerve and trim any necrotic or bruised tissue until normal fascicles are

Nerve High Magnification

found (Fig. 20—2A). Then transect the nerves perpendicular to the main axis and carefully examine them to ensure that they are healthy and uninjured fascicles are found (Figs. 20—2B,C). Several sequential transections may be indicated before finding appropriate endings for repair.

Use a systematic approach consisting of a simple suture first being placed on either side of the nerve anteriorly. and this is followed by another in the midline posteriorly. The intervening epineurium is then sutured (Fig. 20-3).

Many surgeons suggest the use of 9-0 or 10-0 nylon or Prolene sutures. If the nerve is under too much tension, the sutures will not hold. If there is any question about increased tension on the digital nerve repair, grafting should be considered because holding a digit in flexion to oppose nerve endings often leads to contracture.

Closure of the wound is accomplished with simple sutures. A bulky bandage is wound circumferentially around the digit to help diminish swelling. A dorsal and palmar splint may be applied.

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