Nerve Repair and Grafting in the Upper Extremity

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^[36]: the triketohydrindene hydrate (Ninhydrin) sweat test,^[37] the O'Riain skin wrinkle test,^[38] 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.^[39] 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.

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Table 1. Nerve Injury Classification ^[23]
Seddon	Sunderland	Pathophysiologic Basis
Neuropraxia	I	Local myelin damage. Axons preserved. No degeneration.
Axonotmesis	II	Endoneural tube preserved. Axon degeneration.
	III	Loss of endoneural tube continuity. Perineurium intact. Axon degeneration.
	IV	Endoneural tube and perineurium disrupted. Epineurium intact. Axon degeneration.
Neurotmesis	V	Complete loss of neural continuity.

Table 2. Selected Muscle Evaluation for Diagnosis of Motor Nerve Injury ^[35]
I.	Median nerve: intrinsic
	A. Thumb-palmar abduction (abductor pollicis brevis)
II.	Median nerve: extrinsic
	A. All flexor digitorum sublimi
	B. Flexor profundus digitorum to index
	C. Flexor pollicis longus
	D. Flexor carpi radialis
III.	Ulnar nerve: intrinsic
	A. First dorsal interosseous muscle
	B. Muscles of the hypothenar eminence
IV.	Ulnar nerve: extrinsic
	A. Flexor digitorum profundus, small finger
	B. Flexor carpi ulnaris
V.	Radial nerve: extrinsic
	A. Wrist extension (extensor carpi radialis brevis and longus, extensor carpi ulnaris)
	B. Extension of fingers at metacarpophalangeal joint (extensor digitorum communis, extensor indicis proprius, extensor digiti minimi)

Table 3. Sensory Evaluation for Specific Peripheral Nerve Injury ^[35]
I.	Median nerve -- Pulp of thumb and index finger
II.	Palmar cutaneous branch of median nerve -- Proximal palm over thenar eminence
III.	Ulnar nerve -- Pulp of small finger
IV.	Dorsal cutaneous branch of ulnar nerve -- Dorsal ulnar surface of hand
V.	Radial nerve -- Dorsal radial hand over first web space
VI.	Digital nerve -- Area of the distal phalangeal joint flexion crease

Table 4. Evaluation of Motor Recovery After Peripheral Nerve Injury
M0	No contraction
M1	Return of contraction in the proximal muscles
M2	Return of contraction in both proximal and distal muscles
M3	Return of function in both proximal and distal muscles of such a degree that all important muscles are sufficiently powerful to act against gravity
M4	Return of function as in M3; in addition, all synergistic and independent movements are possible
M5	Complete recovery

Table 5. Evaluation of Sensory Recovery After Peripheral Nerve Injury ^[40,54]
S0	Absence of sensibility in the autonomous area
S1	Recovery of deep cutaneous pain sensibility within the autonomous area of the nerve
S2	Return of some degree of superficial cutaneous pain and tactile sensibility within the autonomous area of the nerve
S3	Return of superficial cutaneous pain and tactile sensibility throughout the autonomous area, with disappearance of any previous overresponse
S3+	Return of sensibility as in S3; in addition, there is some recovery of 2-point discrimination within the autonomous area (7-15 mm)
S4	Complete recovery (2-point discrimination, 2-6 mm)

Table 6. Vascularized Nerve Grafts: Donor Nerves and Associated Vessels
Nerve	Vascular Supply
Superficial radial	Radial artery
Ulnar	Superior ulnar collateral artery
Sural	Superficial sural artery
Anterior tibial	Anterior tibial artery
Superficial peroneal	Superficial peroneal artery
Saphenous	Saphenous artery

Adapted from Breidenbach and Terzis. ^[70]

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Diagnosis and Recognition

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