Hand Nerve Injury Repair Workup

Updated: Apr 30, 2019
  • Author: Subhas Gupta, MD, PhD, CM, FRCSC, FACS; Chief Editor: Joseph A Molnar, MD, PhD, FACS  more...
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Workup

Laboratory Studies

Serum albumin test

  • The reason for ordering this test is to determine if the nutritional status of the patient is adequate to allow reconstructive surgery. If the values returned are less than normal, healing may be impaired and surgical repair compromised.

  • Generally, proceeding is acceptable when albumin levels are greater than or equal to 2.5 g/dL.

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Imaging Studies

Short tau inversion recovery MRI

  • This is a unique form of MRI that returns pictures that can highlight nerve trauma, although it is less sensitive than other diagnostic tests for determining the degree and location of injury.

  • The short tau inversion recovery MRI works by placing a phased array of surface coils on the body, thus allowing imaging of a smaller area with a more precise picture.

  • Both T1- and T2-weighted images can be used to view nerve pathology, which alters the nerve signal from its normally isodense state. T2-weighted images allow the hyperintense signal of nerve injury to be more apparent because of the ability to suppress the fat signal.

  • This type of test is indicated in patients with nonclassic symptoms, in those with ambiguous findings such as occur in patients with diabetes, for scar and nerve inflammation imaging after the addition of gadolinium, to visualize neuromas, and to determine the length of damaged nerve present.

  • This technology is not yet consistent enough to play a major role in diagnosis, but it can serve as a useful adjunct to other tests. [67, 13, 53]

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Other Tests

Sensory tests [4, 68, 69, 70]

  • Tinel test: The patient should feel a sensation when the tip of the severed nerve is tapped.

  • Two-point discrimination: Both moving (M2PD) and static (S2PD) are performed with the patient's eyes closed. Results should be consistent enough to exclude the patient guessing. This examination should be very thorough if a partial injury is suggested. S2PD is excellent if less than or equal to 6 mm, and M2PD is considered excellent if less than or equal to 3 mm. A lack of 2PD is poor.

  • Semmes-Weinstein test: This uses monofilaments, which allow the application of stimuli using constant force so that administration error is reduced. Findings should be similar to those from S2PD and M2PD.

Motor tests [4, 69, 70]

  • Grip and pinch strength: This is usually tested by having the patient squeeze a measuring device that can determine the amount of force the patient produces. Results may be compared to the unaffected hand to grade the deficiency. Testing intrinsic and extrinsic muscles separately can be helpful.

  • Muscle bulk: This test looks for atrophy of large muscles such as the first interosseous muscle.

Williams test: Denervated skin responds differently to stimuli. This allows clear demarcation of the affected area in the hand when the injured hand is placed in water. Innervated skin wrinkles when submerged, but denervated skin does not.

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Diagnostic Procedures

Electrodiagnostic techniques have been refined and help a great deal in testing and diagnosing neuromuscular lesions. The 2 most common tests are the nerve conduction study (NCS) or nerve conduction velocity test and electromyography (EMG). EMG is often understood to refer to both tests. [71, 13]

Table 4. Electrodiagnostic Characteristics of Nerve Injury (Open Table in a new window)

 

Electromyography

Nerve Conduction Study/Nerve Conduction Velocity

 

Fibrillations

Voluntary Muscle Unit Action Potential

Sensory and Motor Latency

Compound Motor Action Potential/Sensory Nerve Action Potential

Normal

None

Present

Normal

Normal

Nerve block/neurapraxia

None

None

None across the block, normal above and below

Normal above and below the block

Complete lesion/ axonotmesis, neurotmesis

Present

None

Absent

Absent

Incomplete

Present

Decreased in distribution of injury

Normal or slightly prolonged (spread out)

Reduced

 

NCSs use a percutaneous current to stimulate muscle and sensory nerves. This can result in a compound motor action potential or sensory nerve action potential, respectively. An active pickup generates the current that travels along the nerve and is read by another pickup a set distance away in either the efferent or afferent directions. This measures how fast the nerve conducted the stimulus (v = d/t). The current is gradually increased until a maximum response is obtained. This provides the basis for comparison of results over time. The distal ends of transected nerves have an NCS result that gradually falls over 7-9 days postinjury. This test can also help detect complete and partial nerve blocks. [71, 72, 13]

EMG tests record the depolarization potentials of active and spontaneous muscle movement. This is recorded as a muscle unit action potential. Resting muscle is normally electrically silent. Muscle distal to an injury may appear normal for several days after the injury until wallerian degeneration has advanced far enough for the muscle to become denervated and fibrillations to start. This often requires 14-21 days; thus, the best time for EMG diagnosis is 3-4 weeks after injury. Denervated muscle displays positive sharp waves and fibrillations, in that order. [71, 72, 73, 12]

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