Primary Repair and Nerve Grafting following Complete Nerve Transection in the Hand, Wrist, and Forearm



Primary Repair and Nerve Grafting following Complete Nerve Transection in the Hand, Wrist, and Forearm


Matthew E. Hiro

Randy R. Bindra





DEFINITION



  • Complete transection of a peripheral nerve is defined as interruption of all of the axons within the nerve.


  • Primary nerve repair is the tension-free reapproximation of severed nerve ends performed within a week of injury.


  • Delayed primary repair is performed up to 3 weeks from injury when local soft tissue injuries do not permit primary wound closure.


  • The healing of an injured peripheral nerve is different from the healing of other tissue types.


  • Injury is followed by an immediate degeneration, followed by incomplete recovery.


  • Irreversible changes in the motor and sensory end organs make timing of repair critical to achieve useful recovery.


ANATOMY



  • The anatomy of the peripheral nerve can be simplified by examining its component parts (FIG 1).


  • Axon. The basic unit of a nerve is composed of a cell body, dendrites, and longer axons.



    • All axons are surrounded by Schwann cells, which produce the myelin sheath surrounding the axon.


    • Interruptions in the myelin sheath are referred to as nodes of Ranvier. Impulse propagation is faster in myelinated axons using a process called saltatory conduction, as the depolarization potential “jumps” between nodes.


    • Myelinated fibers are between 2 and 22 µm in diameter. The larger the fiber, the faster the conduction speeds.


    • Axonal transport of cytoskeletal elements and neuronal factors is oxygen-dependent. Antegrade transport along the axon occurs at roughly 1 to 4 mm per day. The transport is the rate-limiting step in nerve regeneration.






    FIG 1 • Schematic of ultrastructure of the nerve. The smallest nerve unit visible to the naked eye is the nerve fascicle.


  • Endoneurium. Delicate connective tissue that supports and surrounds each axonal fiber and associated Schwann cells



    • Consists of longitudinally arranged collagen fibrils and intrinsic blood vessels


  • Perineurium. The connective tissue that surrounds groups of axons, creating bundles referred to as fascicles. The fascicle is the smallest visible unit of the nerve at surgery.



    • The fascicle is several layers thick and acts as a protective membrane and a barrier to diffusion.


  • Epineurium. Surrounds groups of fascicles to form the superstructure of a peripheral nerve



    • Forms a sheath about the entire nerve and also supports the fascicular structure by passing between all the fascicles


    • Forms 60% to 85% of the cross-sectional area of a peripheral nerve


    • Composed on longitudinally oriented collagen fibers, fibroblasts, and intrinsic vessels


  • Paraneurium or mesoneurium. Loose areolar tissue surrounding the epineurium



    • Limited to the outer surface of the nerve


    • Location for the extrinsic vascular supply of the nerve


    • Makes up the gliding apparatus of a peripheral nerve


  • Fascicles have a definite topographic arrangement within a peripheral nerve.



    • Fascicular segregation into motor and sensory components is important when aligning a sectioned nerve before primary repair or nerve grafting.


    • This concept of functional segregation allows for use of part of a donor healthy nerve for nerve transfer with minimal functional deficit.


PATHOGENESIS



  • Injuries involving peripheral nerves can be simply classified as tidy or untidy.


  • Tidy wounds involve sharp transections with minimal to no tissue loss:



    • Sharp lacerations from glass or knife wounds


    • Most iatrogenic nerve injuries


  • Untidy wounds involve crushing or avulsion of tissues in the area:



    • Bony injury may be present.


    • Surrounding soft tissue may have been lost or rendered nonviable and is expected to heal with significant scarring. This corresponds to the zone of injury.







FIG 2 • Comparison of a normal neuron cell body (A) with that of a nerve after transection (B). Note cellular swelling, dissolution of Nissl granules in the cytoplasm, and retraction of the dendritic processes.


NATURAL HISTORY



  • Complete transection of a nerve results in retraction of the nerve ends. The nerve will not heal without surgical intervention to approximate the nerve ends.


  • Wallerian degeneration occurs in the nerve segment distal to the level of transection.



    • The axon distal to the injury degenerates and does not directly contribute to repair. The axonal and myelin debris are cleared by macrophages. Schwann cells proliferate, releasing nerve growth factors or neurotrophic factors. The distal stump does produce a complex protein, neurotropic factor, that attracts regenerating axons from the proximal stump.


    • The cell body swells, Nissl granules in the cytoplasm diminish, and its dendritic processes retract. Several cells rupture and die, especially with more proximal nerve injuries (FIG 2).


  • Regenerating axons sprout from the surviving axons and migrate toward the empty tubules in the degenerate distal stump at a rate of 1 to 3 mm per day.



    • Proliferating Schwann cells myelinate the newly regenerated axons.


    • In an unrepaired nerve, the random proliferation of axons from the proximal stump forms a tender mass of disorganized axons and fibrosis termed a neuroma.


PATIENT HISTORY AND PHYSICAL FINDINGS



  • History of trauma



    • Penetrating, ballistic, burn, stretch, blunt, fracture, or previous surgery


    • Timing of onset of symptoms: at initial presentation; after procedure, for example, manipulation and casting or internal fixation of a fracture


    • Depth and location of the injury


    • Severity of bleeding-associated blood vessel injury


  • Patient reports



    • Paresthesias (pins and needles) or absent sensation (numbness) in fingers


    • Weakness


    • Paralysis due to nerve or associated tendon injury


    • Pain: neurogenic type; can be constant and severe


    • Rarely, a sensation of warmth or anhydrosis


  • Physical examination



    • Note the distribution of sensory loss. The area of sensory loss varies with the nerve that is injured (FIG 3).


    • Examine the skin for trophic changes or dry skin. Dry, warm skin implies sympathetic interruption.


    • Perform thumb abduction test to check for paralysis of the abductor pollicis brevis from median nerve injury.






      FIG 3 • Distribution of sensory loss with nerve injury. Yellow, median nerve; blue, ulnar nerve; pink, radial nerve.


    • Perform the Froment sign test. The test is positive if paper is held by flexing the thumb interphalangeal (IP) joint, indicating recruitment of the flexor pollicis longus, which implies paralysis of the adductor pollicis from ulnar nerve injury.


    • The thumb IP hyperextension test may indicate paralysis of the extensor pollicis longus due to posterior interosseous palsy.


    • Perform the Tinel sign test. The test is positive if the patient notes a tingling sensation in the sensory distribution of the nerve. Serial progression of Tinel sign distally is useful to monitor axon progression after repair.


  • When performing physical examinations, it is helpful to use motor function grading according to the Medical Research Council system. This grading allows for qualitative measurement of function and allows the clinician to chart recovery objectively:



    • M0: no contraction


    • M1: palpable contraction with only a flicker of motion


    • M2: movement of the part with gravity eliminated


    • M3: muscle contraction against gravity


    • M4: ability to contract against moderate resistance


    • M5: normal function


  • Quantitative measurements using grip and pinch strength dynamometers and comparing results to the contralateral normal side may also be useful.


  • Sensory grading is also useful in evaluation. Sensory function is evaluated within the anatomic distribution of the nerve in question. Sensation is quantified using two complementary tests—(1) Semmes-Weinstein monofilaments, which measure innervation threshold, and (2) two-point discrimination, which measures innervation density. Vibratory, pain, and temperature sensation should also be evaluated. Semmes-Weinstein filaments demonstrate subtle and early sensory loss and are more useful in evaluation of compressive neuropathy. Two-point discrimination measurements help gauge the severity of nerve injury, with two-point discrimination of less than 12 mm indicating neurapraxic injury and readings greater than 15 mm suggesting complete disruption. Used together, the various sensory tests allow for qualitative measurement of function and allow for the clinician to objectively chart recovery:



    • S0: lack of sensation


    • 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


    • S3: return of function (S2) without evidence of hypersensibility


    • S3+: return of function (S3) with some return of two-point discrimination


    • S4: normal function


  • Sensory recovery classification on two-point discrimination alone:



    • Normal: less than 6 mm


    • Fair: 6 to 10 mm


    • Poor: 11 to 15 mm


IMAGING AND OTHER DIAGNOSTIC STUDIES



  • Diagnosis in acute injuries is usually based on history and clinical examination alone without need for additional investigations.


  • Plain radiographs are of little use in evaluation of the nerves themselves but may be helpful in cases of injury from fracture or projectiles.


  • Computed tomography (CT) myelography is useful for evaluation of injuries to the brachial plexus. The formation of a pseudomeningocele is indicative of root avulsion.


  • Magnetic resonance imaging (MRI) is useful for evaluation of peripheral injury but is not routinely indicated for peripheral nerve injuries.



    • Short tau inversion recovery (STIR) MRI may show enhancement of the nerve near the site of injury or interruption of the nerve trunk on T1- and T2-weighted images.


    • MRI provides visualization of pseudomeningoceles at the spinal cord levels in root avulsion injuries.


  • Electrodiagnostic testing



    • Nerve conduction velocity (NCV) and electromyography (EMG) are useful in evaluation of closed nerve injuries, for example, after fracture or multiple nerve injuries such as brachial plexus injury.


    • If stimulation distal to the suspected injury elicits a motor response about 3 days after injury, then the lesion is likely a conduction block. However, muscle action may be present in the case of complete transection for up to 9 days.


    • Fibrillation potentials on EMG appear after 2 to 3 weeks and indicate muscle denervation and a severe grade nerve injury.


    • Recovery is best evaluated with serial examination of compound muscle action potentials. Early recovery of only a few motor units may indicate reinnervation from adjacent intact nerves and should not be used as an indicator of recovery of the repaired nerve.




DIFFERENTIAL DIAGNOSIS



  • Muscle or tendon injury in open lacerations


  • Parsonage-Turner syndrome (brachial plexus neuritis)


  • Peripheral nerve entrapment


  • Partial nerve injury (neuroma in continuity)


  • Neurapraxic injury (axonal dysfunction without discontinuity)


NONOPERATIVE MANAGEMENT



  • Nonoperative management of a completely transected nerve after an open injury is doomed to failure because cut ends retract and scar tissue forms in the gap.


  • Pending recovery of the nerve, splinting of the paralyzed joint maintains functional position and range-of-motion exercises prevent contractures.


  • Serial clinical examination and electrodiagnostic testing are helpful to evaluate recovery.


SURGICAL MANAGEMENT



  • Nerves that have been completely interrupted require surgical measures to restore continuity.


  • All open injuries with neurologic impairment must be explored expeditiously.


  • With closed injuries or delayed presentation, consider the overall functional capacity of the injured limb.


  • In a largely motor nerve, for example, the radial nerve, tendon transfers may restore function more reliably than nerve repair.


Preoperative Planning

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Jul 22, 2016 | Posted by in ORTHOPEDIC | Comments Off on Primary Repair and Nerve Grafting following Complete Nerve Transection in the Hand, Wrist, and Forearm

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