Timing in Traumatic Peripheral Nerve Lesions
Keywords: nerve injury, timing, microsurgery, trauma
Abstract
Surgical timing is one of the most important decisions to take in the operative management of traumatic injuries of peripheral nerves. It depends on a number of factors such as associated injuries, patient stability, level and degree of injury, medical comorbidities, and even the available operative resources. This chapter aims to demonstrate the proper timing for surgical intervention of the different types of traumatic injuries of peripheral nerves. Open wounds due to laceration mechanism deserve urgent attention, and sharp injuries are best treated within the first 72 hours after the trauma; blunt open injuries need a short delay of 3 to 4 weeks before exploration, aiming to avoid further nerve shortening and scar tissue formation into the suture site. Gunshot wounds should be treated conservatively for 4 to 6 months, as most of these injuries do not result in direct nerve hit. The majority of the closed injuries are explored from the third month after the trauma, and surgery is indicated for patients who do not demonstrate signs of spontaneous recovery of the critical muscles.
10.1 Introduction
Peripheral nerve injury is a dramatic event that significantly affects the daily-living activities of victims sustaining such type of trauma. Although the appropriate treatment is individually based, some general considerations may help in guiding the physician to optimize the proper therapy for a specific case. The main mechanisms that provoke injuries to the nerves of the neck or the limbs are very well known, i.e., traction, compression, laceration, and gunshot wounds. However, the clinical decision about when to operate can be, sometimes, difficult. For the cases of sharp and clean penetrating injuries, it seems logical that an immediate nerve repair shall be indicated. However, if the surgeon performs such acute repair in a penetrating injury associated with blunt trauma, the result may be disastrous. It is even worse for cases of traction injuries, because the decision about when to operate the patient may be one of the most important factors that will determine the final outcome. For these last cases, the surgeon faces a clinical dilemma: to operate early, aiming to decrease the time of muscle denervation, and at the same time taking the risk of operating (and occasionally transecting) a given nerve that would have a potential for spontaneous regeneration; or, otherwise, operate later in order to be completely sure about the lack of potential for spontaneous recovery, and assuming the risk that the mechanisms of muscle denervation and atrophy that follows a nerve injury may become so intense that the surgery may become useless.
Hence, determining the optimal surgical timing of each patient is one of the most important decisions to take in the operative management of traumatic injuries of peripheral nerves. The operative timing is variable and depends on a number of factors such as associated injuries, patient stability, level and degree of injury, medical comorbidities, and even the available operative resources. The knowledge about nerve regeneration, mechanism of injury, nerve injury classification, and neuropathology may be helpful in order to guide the surgeon in taking the appropriate decision. 1 This chapter aims to summarize the most available modern data from the medical literature about the proper timing for surgical intervention of the different possible types of traumatic injuries that affect peripheral nerves. Discussion about surgical timing for brachial plexus and facial nerve injuries has been excluded, because these issues will be further detailed in specific chapters.
10.2 Basic Science as an Aid for Taking an Important Decision
There are three critical temporal factors that may affect the decision of when to operate and also when to avoid surgery. Resolution of segmental demyelination requires 8 to 12 weeks, so deficits that persist beyond that period of time indicate that there has been axonal damage, not only neuropraxia (Grade I injury). Under ideal conditions, axon regrowth occurs at 1 to 3 mm/day, or 1 inch/month. The time after which irreversible muscle atrophy has occurred and operation cannot provide benefit ranges from 18 to 24 months, depending on: (1) the type of injury, (2) the injured nerve, and (3) the proposed technique for reconstruction. The Schwann cells and the endoneurial tubes remain viable for 18 to 24 months after injury. If they do not receive a regenerating axon within this time span, the tubes degenerate. Reinnervation must occur not only before the muscle undergoes irreversible changes, but also before the endoneurial tubes will no longer support the nerve regrowth. Hence, the time-distance equation has two primary variables: irreversible changes in critical target structures after 18 to 24 months, and axon regrowth rate at 1 to 3 mm/day from the site of injury or from the site of the surgical repair. 2
10.3 Initial Evaluation of a Peripheral Nerve Injury
The injuries that involve the nerves of the head, neck, and limbs are classified generally as closed (those caused by stretch or compression mechanisms) and open or penetrating (consequence of laceration or missile wounds). The most frequent type of injury observed in civilian practice are closed tractions injuries resulting from vehicular accidents; the injuries provoked by gunshot wounds and those that occurs secondary to blunt penetrating mechanism are less frequent, but still not uncommon; and lesions from sharp and clean divisions of peripheral nerves are usually very uncommon (in this last group, iatrogenic injuries may be very incidental). 3
The surgical timing and the management of closed and open injuries are different, and the type of the injury must always be determined at the moment of the initial evaluation. It is apparent in the majority of the cases, and specific details about the circumstances of the aggression or the trauma itself should be sought, as this kind of information may have prognostic value. For example, the severity of the trauma is usually roughly proportional to the degree of damage to the involved nerves.
Evaluating the postinjury neurological status following a peripheral nerve trauma—i.e., whether the deficit is improving, static, or worsening—has paramount importance for the decision-making process that finally will allow the surgeon to determine who are going to be operate or when one must be operated. Moreover, close attention to the progression of the neurological recovery in such cases will provide additional data about the severity of the lesion and will aid in establishing a working prognosis. Immediately following the injury, nearly all of the patients will show a specific neurological loss (it is very rare a progressive neurologic deficit following a peripheral nerve injury that initiate hours or days after the trauma; however, they may be observed occasionally in clinical practice, for example, in injection injuries). Some of the patients will improve, and the prognosis of such lesions is good for the great majority of them. Other patients will not improve, and eventually they will need a surgical intervention in order to obtain a better recovery. However, some deficits may become worse in time—what may indicate a continued or progressive increasing pressure onto the involved nerve (e.g., the development of a pseudoaneurysm in a nearby artery; or the presence of a clot on a tunnel nerve area) and may demand an urgent surgery for decompression. 4
10.4 Causes of Traumatic Peripheral Nerve Injury
As described earlier, traumatic peripheral nerve injuries are basically classified as closed or open, and operative timing is mainly dictated by type of the lesion. However, there are a number of different possible causes that has the potential to damage the peripheral nervous system, named as follows:
Stab wounds are characteristically open lesions that result from clean and sharp lacerations. They are more often provoked by objects with a cutting edge in one or both of its borders, such as a knife or a glass. Neurological deficits associated with such type of injury are always associated with nerve transection (partial or total) or neurotmesis (Sunderland Grade V injury). Little trauma to the nerve stumps and minimal local tissue trauma is the rule in most of these cases.
Open injuries secondary to lacerations may also be caused by blunt trauma. In these cases, the nerve is divided by jagged metal or saws, especially chain saws, where a ragged, torn skin wound is usually observed. Local damage is often more extensive in such type of injury, and associated vascular or bone trauma may also be present. It is not infrequent that the wound may show gross contamination. The extension of the nerve injury is usually longer than those associated with stab wounds, and it is usually difficult to evaluate it in the first days that follow the trauma. Moreover, these injuries are associated with a large amount of scar tissue formation following the healing process, and this fibrosis may prevent appropriate nerve regeneration if an early nerve suture is attempted. 5
Gunshot wounds are open injuries with little or no tissue exposure, with some unique features that require different approach from the other wounds provoked by penetrating mechanism. Such lesions have a variable degree of intraneural derangement. Most of the missile trajectories are associated with neural injury that do not directly strike the nerve, but instead provide a near miss. The projectile may provoke contusive forces that result in dual stretching to the neural tissue: as the missile approaches the nerve, the nerve explodes away from the missile’s trajectory and then implodes back when the missile passes by. Such damage extends over a length of the nerve, and produces a swollen and hemorrhagic neural segment. These forces may produce a combination of conduction block, axonotmesis, or neurotmesis, and a neuroma-in-continuity is often observed. The proportion of axonotmetic and neurotmetic changes will determine the potential for useful regeneration. These injuries may also result in vascular and bone trauma, and the formation of acute hematoma, traumatic pseudoaneurysm, or arteriovenous fistula has the potential to determine nerve compression. 6
Bone fractures may also be implicated as a cause of injury to adjacent nerves. The dislocation of a bony fragment may result in lesion by mechanism of stretching, direct compression, or ischemia. In all of these situations, the injury is considered and managed as closed. Good examples are the classical pattern of radial nerve palsy that follows a fracture of the middle third of the humerus, or an injury of the suprascapular nerve associated with fractures of the scapula.
There are cases in which the lesion is promoted by a mechanism of ischemia of the nerve. It is a mechanism of injury that is frequently linked to deformations associated with nerve compressions. In these cases, a quick nerve recovery should be expected. The most common example is the so-called Saturday night palsy, associated with a radial nerve compression. However, more serious injuries may be associated with the mechanism of ischemia: Volkmann’s contracture that follows vascular injuries may result in disastrous lesions in even more than one nerve at once, which are often associated with poor recovery.
The most common cause for closed injuries is traction or stretching
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
