Diagnosis and Recognition
A careful history regarding nerve injury provides important information aiding in treatment and in predicting outcome. Patient age and mechanism of injury are well-known to affect outcome after nerve repair. As part of the medical history, a careful assessment of comorbid conditions that detrimentally affect the peripheral nervous system is important.
A careful motor examination should indicate whether a specific muscle is functioning and, if so, how well. Specific muscles are useful in identifying selected peripheral nerve injuries. Since cross innervation and joint motion aided by several muscles are a source of potential confusion, a working knowledge of the specific muscles that correlate to specific peripheral nerve function is essential ( Table 2 ).
Sensory evaluation in the clinical setting requires patient cooperation and interpretation of various stimuli. There are only three objective tests of sensation: the triketohydrindene hydrate (Ninhydrin) sweat test, the O'Riain skin wrinkle test, and electrophysiologic testing. None of these is particularly practical in the initial patient evaluation; therefore, tests that require patient interpretation are most commonly used.
The most commonly used clinical tools are two-point discrimination (2-PD) (both moving and static), Semmes-Weinstein monofilaments, and vibrometer testing. Initial evaluation of the nerve-injured patient should at least include assessment of static 2-PD in the digits and touch sensation in the cutaneous distribution of potentially injured nerves. Crossover in sensory territories is normal, and only selected areas will provide accurate information concerning specific nerve injury ( Table 3 ). The available methods of sensory evaluation provide different and specific information regarding reinnervation.
Electrodiagnostic testing is a useful adjunct to evaluation in patients with nerve injury. It is rarely needed for initial diagnosis but may be helpful in evaluation after repair and especially in assessing nerve lesions in continuity. Electrodiagnostic testing includes somatosensory-evoked potentials, intraoperative nerve-to-nerve stimulation, nerve conduction studies, and electromyography. Nerve conduction studies provide a measure of the speed with which a nerve carries information over a known distance. The time from which the stimulus is initiated until it is recorded is called the latency period. Since time and distance are known, conduction velocity can be calculated. Normal values have been established for both latency and nerve conduction velocity (NCV) for specific nerves and specific locations. In evaluating nerve injury, as opposed to compression neuropathy, determining the presence or absence of response is frequently more important than learning the latency or NCV.
Electromyography is distinctly different from nerve conduction studies and provides different information. A needle electrode is placed into a specific muscle, and electrical activity is recorded both at rest and with attempts at muscle contraction. Normal muscle will show a short burst of insertional activity related to the local trauma of needle insertion. This burst of activity is brief, and normal muscle at rest will rapidly become electrically silent. Abnormal insertional activity is seen in denervated muscle or in muscle that is being reinnervated. Spontaneous depolarization in denervated muscle produces fibrillation potentials and positive sharp waves. These are descriptive terms identifying recognizable patterns of electrical activity, as recorded on an oscilloscope.
Electrical activity can also be recorded during active muscle contraction. Contraction of fibers produces an M wave, indicating electrical potential change in the muscle. As the force of contraction continues, multiple M waves are progressively created; these result in a recognizable sequence called a recruitment pattern. Changes in M-wave amplitude or recruitment pattern are present with neuropathy and can be helpful in identifying denervated muscle or in following recovery.
J South Orthop Assoc. 2001;10(2) © 2001 Southern Medical Association
Cite this: Nerve Repair and Grafting in the Upper Extremity - Medscape - Nov 01, 2001.