Acute Nerve Injury Treatment & Management

The goal of treatment is to return function to the damaged nerve and, at minimum, to improve the quality of life of patients. Not only is the nerve treated, but exogenous sources of nerve injury also are treated. Bone dislocation with neurological deficit requires prompt anatomical reduction to prevent irreversible nerve necrosis. ^[26]

Imaging workup of developmental lesions that involves the axial skeleton most frequently involves plain radiographs, followed by CT for assessment of bony matrix and MRI for evaluation of intrinsic spinal cord parenchymal changes and potential neural compression. With some lesions, bony scintigraphy or PET scanning may be helpful to assess for metabolic injury. ^[39]

The use of analgesics can help patients control pain from nerve injuries. ^[10]  Anticonvulsant drugs (AEDs) that have shown promise in several include oxcarbazepine, zonisamide, topiramate, levetiracetam, and lamotrigine. These results may be due to their GABA effects. These agents are most helpful clinically in the signs and symptoms of radiculopathic and neuropathic pains and paresthesias.

Antivirals and steroids help to decrease endoneurial edema, an etiology of nerve injury. ^[35] Hyperbaric oxygen (HBO) is an approved adjunctive treatment for acute traumatic ischemic reperfusion injury. ^[35] HBO decreases endoneurial edema and pressure and vascular compromise of the vasa nervorum. ^[35] Ciliary neurotrophic factor (CNTF) enhances motor neuron survival both in vivo and in vitro. ^[40]

Primary repair is direct reconnection of the nerve immediately after injury. In an epineurial repair, the epineuriums of the separated nerve endings are sutured together using a microsuture (usually 8-0 or 10-0 Ethicon). ^[15] Best results occur when the nerves are either purely sensory or purely motor and when the intraneural connective tissue component is small (this can vary from 22 to 80% ^{[5, 15]} ) and the fascicles have been clearly aligned.

Sharp lacerations without loss of nerve substance or partial lacerations with proper alignment are good examples of injuries that benefit from epineurial repair. In a crushing or delayed repair requiring trimming of the nerve ends, group fascicular repair improves fascicular alignment without an excessive number of sutures. Excessive sutures add to scar tissue production. Individual fascicle repair is not practiced widely because it requires numerous sutures and because it is technically difficult. ^[5]

Secondary repairs are delayed repairs that may entail different strategies. Bones can be shortened to add length to a nerve. Nerve transposition across a flexed joint (eg, the ulnar nerve in the elbow) is another strategy for gauging nerve length in secondary repairs. ^[5] These techniques can gain as much as an approximate 10% increase in available nerve length. ^[5] However, within 3 weeks after injury, a nerve may lose as much as 8% of its length. ^[5] Many surgeons prefer delayed suture to primary suture because this allows the wound to heal and it decreases the risk of infection. In addition, during a delayed repair, scarred ends of the nerve can be defined more accurately and trimmed back to normal fasciculi. The epineurial suture is more secure because the sheath has toughened. ^[4] The suture of a severed nerve should not be delayed beyond 1 month. ^[4]

Neurolysis is performed on intraneural and extraneural scar tissue to release regenerating nerve fibers in the hope of improving functional recovery. ^[2] Contaminated wounds, such as gunshot wounds and avulsions with severe tissue disruption, benefit from a secondary repair. ^[2] Severely damaged nerves may require a nerve graft. For example, a graft would be necessary if, after resection of injured nerve ends (including neuroma), the defect could not be closed without tension. ^[15]

Studies show that sensation can return after nerve grafting. ^[41] The sural nerve is the criterion standard for nerve autografts because of a favorable ratio of axons to epineuriums. ^[5] Loss of the sural nerve produces only a well-tolerated sensory loss on the lateral foot. Extensive research has focused on the use of allograft nerves to replace peripheral nerves that require a long nerve graft. Allografts can survive if the patient is immunosuppressed and if the nerve allograft is preserved to maintain cell viability. Immunosuppression can be discontinued when the nerve graft has been incorporated with an ingrowth of Schwann cells from the host nerve ends. Nevertheless, results from autograft use are slightly more favorable than allograft use. ^[5]

Artificial conduits have not proven to be as successful as conventional nerve autografts. ^[5] Brain-derived neurotrophic factor (BDNF) and collagen tubulization have been used in an attempt to create a reliable artificial conduit for axonal regeneration. ^{[42, 43]}

Nerve or tendon transfers may be necessary for unrestorable or unsuccessful nerve repair. Brachial plexus injuries are not always reparable. In such cases, neurotizations or nerve transfers may offer a better functional outcome. The spinal accessory or long thoracic nerve can be grafted onto distal arm nerve trunks, with some improvement in elbow flexion. ^{[4, 44]} When repair cannot or does not provide adequate results, planned tendon transfers can increase extremity function. ^[4] Tendon transfers, such as the posterior tibialis tendon passing through the interosseous membrane, can add power to a foot with a peroneal deficiency. ^[26] Do not perform tendon transfers before 3 months after injury, because early surgical exploration with nerve graft placement yields better results than primary tendon transfer. ^[3]

Preoperative details include determining the type of surgery to be performed and the time frame. For example, open injuries may require immediate surgery, and closed injuries may require reduction (in cases of dislocations or fractures) and monitoring. ^[1]

Sunderland suggests 2 criteria that must be present before fascicular repair or interfascicular grafting is considered. The fascicular bundle must be large enough for suturing and must be sharply localized or sufficiently well defined so that it can be identified and mobilized for repair. ^[4] Preoperative testing with SSEP, CT scan, EMG, and MRI has improved diagnostic accuracy. ^[44] The extent of surgical exploration is adapted to the reliability of the preoperative diagnosis. ^[44]

Intraoperative electrodiagnostic monitoring is important for assessing the functional integrity of motor and sensory peripheral nerves. The patient is draped to allow observation of the tested muscle groups. Intraoperative SSEPs and direct electrical stimulation can be used. Regional and local anesthetic blocks or tourniquets are avoided to facilitate intraoperative electrophysiologic testing. ^[1] Surgically resecting scar tissue may prevent pain and promote healing. ^[1] Keeping the nerve ends moist is important. ^[15] Ocular loupes are useful for lower magnification and wide-field dissections and are very helpful in preparing the ends of nerves and vessels for repair. ^[14] The nerve can be protected during surgery by reducing tension through joint and limb manipulation and shielding with a blunt retractor to prevent iatrogenic injury. ^[10]

Surgical exploration with intraoperative nerve stimulation helps determine if neurolysis is the only intervention necessary. ^[12] In a group of patients in whom treatment failed and who underwent operation for isolated and combined axillary nerve injuries, twice as many neurolyses as nerve grafts were performed compared with a group of patients who had successful treatment. ^[29]

Patients should undergo regular physical therapy to maintain a range of movement and to optimize the recovery of motor function as muscle reinnervation occurs. ^{[1, 2]} A short period to allow healing and adequate strength of the repair site is advised. ^[1] Protect repairs by relaxed joint posturing for approximately 3 weeks. ^[14] To prevent disruption of sutures at the repair site, the patient should avoid overzealous physical activity. ^[1] In nerve transfers, the extremity is immobilized for 4 weeks after surgery, at which time physical therapy is initiated. ^[44] Postoperative clinical and electrodiagnostic examinations are performed every 3 months for the first 2 years after surgery and every 6 months thereafter. ^[44]

Clinical outcome is documented by serial clinical examinations and electrodiagnostic studies. ^[1] Axillary injuries constitute an important clinical problem that requires close clinical and electrophysiologic evaluation during the months after the injury. ^[10] As a general rule, Grant et al suggested examining patients at 2 weeks, 6 weeks, 3 months, 6 months, 1 year, and then at yearly intervals if necessary and practical after surgery. ^[1] Test and document range of movement and recovery of strength and sensation at each visit. Electrodiagnostic studies can help reveal early signs of muscle reinnervation, several months before clinically evident muscle contractions appear. ^[1] After nerve transfer surgery, assess patients 3 years after surgery. ^[44] In most cases, maximal recovery requires as long as 24 months. ^[44] An advancing Tinel sign suggests, but does not prove, regeneration of the nerve. ^{[4, 16]}

Following acute nerve injury, various pain syndromes can develop. ^[4] Plexus or root avulsions may produce burning dysesthesias and paresthesias. ^[4] Painful neuromas and entrapment syndromes can arise at the site of injury and cause extreme local tenderness and pain. ^[4] Partial nerve injuries of mixed motor and sensory function can lead to causalgia. Symptoms include severe hyperesthesia, hypersensitivity to cold or muscle activity, and increased pain in stressful situations. ^[4] Paralysis can complicate nerve injury and sometimes cannot be repaired. If physical therapy is not instituted promptly after surgery, denervation can develop and result in muscle atrophy and fibrosis, joint stiffness, motor endplate atrophy, and trophic skin changes. ^[2]

The outcome and prognosis of acute nerve injury varies widely among the different types of injuries and the type and timing of therapy. Patient compliance and motivation for recovery also can have an important impact on the success of recovery. ^{[7, 14]} In traumatic hip dislocations and fracture dislocations, at least partial return of nerve function can be expected in approximately 60-70% of patients. ^[26] The extent of injury to neural tissue, contamination of the wound, and the age and medical status of the injured patient are important factors influencing the outcome and prognosis of recovery. ^[4] Surgical delays in excess of 5 months dramatically decrease the rate of functional return. ^[29] Therefore, schedule surgical repairs within 3 months following the injury. ^[29]

Neurapraxic injuries usually are reversible, and patients recover within days to weeks. ^{[1, 2]} In axonotmesis, although axons regenerate, functional recovery depends on the associated injuries, the amount of healthy proximal axon remaining after injury, and the age of the patient. ^[2]

In addition, recovery usually is complete unless the injury is so proximal that atrophy of the motor endplate or sensory receptor occurs before the axon can grow back to these organs. ^{[4, 5]} A loss of cross-sectional area without any loss in muscle fiber count begins within 1 week of denervation. ^[14] Recovery from axonotmetic injuries usually occurs over months. ^[1] In neurotmesis, regeneration occurs but function rarely returns to normal. ^[2] Intraoperative care with proper axial orientation of fascicles, proper coaptation, suture material, hemostasis, and suture line tension leads to better outcomes. ^[2] Tension of the suture line and inadequate preparation of the nerve stumps are 2 leading causes of regenerative failure across the suture site, resulting in poor recovery of nerve function. ^[1]

Spontaneous recovery (which occurs in two thirds of cases) may occur as late as 11 months after a gunshot wound. However, recovery after shotgun wounds is lower, with a 45% incidence rate of recovery. ^[4] Neural injuries associated with fractures have a greater than 80% incidence rate of spontaneous resolution. Recovery is less common with neural injuries secondary to dislocations. ^[4] Lesions resulting from shoulder dislocations recover within 12-45 weeks. ^[23] Prior radiation therapy impairs cell division. This may affect Schwann cell division after nerve injury. ^[30]

Decreasing the variability of injury and of functional recovery measurements will hopefully increase the sensitivity of the system to evaluate neuropathology and experimental interventions. ^[35]

Developing the ideal nerve injury model that can simulate acute hypoxic nerve injuries and can be evaluated by functional models for regeneration is important to obtaining a greater understanding of neuropathophysiology and potential therapeutic interventions. ^[35]

Experimental surgical techniques are being explored. In one repair technique, the injured nerves are frozen at the time of sectioning and repair and a protective solution is used to bathe the cut ends of the nerve during repair. Synthetic tubules have been used to encase the sectioned end of an injured nerve to allow regrowth. This technique seems to offer comparable or better results than suturing the nerve ends. ^[4]

Metabolic manipulations using pulsating electric fields across a nerve repair and administration of various biochemicals, including thyroid and adrenal hormones, anti-inflammatory agents, and other agents known to influence neurite growth in vitro, are being explored in experimental studies of nerve injury. ^[4] Clinical trials using trophic molecules to enhance axonal regeneration over time include insulinlike growth factors 1 and 2, NGF, BDNF, and neurotrophin 3 and 4/5. ^[1] Vascularized nerves can be useful to repair nerves longer than 8 cm and grafts placed in poor vascular beds that are heavily scarred. ^[15]

The use of MRI before surgery may be standardized in the future. Having a picture of the nerve anatomy before performing the surgery is valuable tool. ^[26]

The American Society of Anesthesiologists has released guidelines on patient positioning, protective padding and proper placement of equipment to reduce the risk and/or prevent perioperative peripheral nerve injury. ^[33] ​