Key Wordsperipheral nerve, nerve repair, nerve injury, nerve graft, nerve allograft
Nerve injuries can occur anywhere in the body. Reconstructive surgeons most commonly encounter them in the extremities or on the face. The management of nerve injuries requires a methodical pre-operative examination. Adjunct studies such as electrodiagnostic tests can be very helpful in confirming the diagnosis. The most important components of successful nerve repair are the debridement of injured fascicles, coaptation with no tension at the repair site, and the appropriate use of nerve grafts and other modalities to bridge nerve gaps.
A nerve is a bundle of fibers that transmits messages from the brain and spinal cord to the muscles in the body. The smallest component of a nerve is the axon. The axon is surrounded by connective tissue called the endoneurium. Many axons comprise one fascicle. The fascicles are surrounded by connective tissue called the perineurium. Fascicles are grouped together to form a single nerve. The nerve is surrounded by connective tissue called the epineurium. The perineurium and the epineurium are important structures for nerve repair. Nerves can carry motor axons, sensory axons, or both. Motor axons power muscles, whereas sensory axons report sensation to the brain.
Nerve injuries can occur anywhere in the body, but reconstructive surgeons most commonly encounter them in the extremities or on the face. Injuries can be open (knife injury, gunshot wound) or closed (stretch injury, crush injury). Patients present with either loss of motor function, loss of sensation, or both. The deficit will be in the motor or sensory distribution of the affected nerve.
Nerve injuries are categorized according to the Seddon classification ( Table 2.2.1 ). Neurapraxia is caused by stretching or compression of a nerve. This type of injury typically resolves spontaneously within 3 months. Axonotmesis is caused by injury to the axon. Recovery will depend on the severity of the axonal injury and ranges from full recovery to no recovery. Neurotmesis is caused by complete transection of a nerve. This type of injury will not recover without surgical intervention.
|Neurapraxia||Degree I||Conduction block resolves spontaneously||Fast/excellent|
|Axonotmesis||Degree II||Axonal rupture without interruption of the basal lamina tubes||Slow/excellent|
|Degree III||Rupture of both axons and basal lamina tubes, some scar||Slow/incomplete|
|Degree IV||Complete scar block||None|
|Neurotmesis||Degree V||Complete transection||None|
|Degree VI (Mackinnon)||Combination of degree I–IV ± normal fascicles||Mixed|
Electrodiagnostic studies are very helpful in classifying nerve injuries. These include both nerve conduction studies and electromyography. Nerve conduction studies evaluate the speed of conduction of a nerve. Electromyography evaluates the viability of the motor endplates and muscle.
Typical scenarios that may be encountered by the reconstructive surgeon include facial nerve lacerations ( Fig. 2.2.1 ), radial nerve injuries associated with a humeral fracture, ulnar and median nerve injuries at the wrist, digital nerve injuries in the fingers, and peroneal nerve injuries at the fibular head.
Nerve injuries are often associated with injuries to nearby structures such as bones, tendons/muscles, and blood vessels. In facial nerve injury, the parotid duct is often injured. Care must be taken to assess all structures in the area of injury so that injury to surrounding structures is not missed.
The management of nerve injuries requires a methodical pre-operative examination. Adjunct studies such as electrodiagnostic tests can be very helpful in confirming the diagnosis. The physical examination will depend on the area of the nerve injury, but it should include all nearby muscles, blood vessels, and other important structures (i.e., parotid duct). The physical examination should determine the availability of nerve graft donor sites including the sural nerve in the leg and the medial antebrachial cutaneous nerve in the arm. Eliciting a Tinel’s sign can be helpful to localize the nerve injury.
Timing is critical in nerve repair. Nerve regenerates slowly at a rate of 1 mm/day. Motor endplates are irreversibly damaged about 18 months from the date of nerve injury. Thus it is important to repair the nerve as soon as the wound is clean and there is adequate soft tissue coverage.