External and Internal Neurolysis

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Chapter 21 External and Internal Neurolysis

The Peripheral Nerve Operation

The general principles that underlie any surgical procedure apply to peripheral nerve operations. There are, however, some specific points that should be emphasized for patients undergoing peripheral exploration and repair.

The Day Before

The surgeon should review all pertinent information and, particularly, the duration of time between the time of nerve injury and surgery. The first appropriate target muscle should be memorized (e.g., the brachioradialis in the case of a midhumeral radial nerve injury). If a previous operation has been performed, the operative note should be reviewed. This record should be read with a very critical eye. Inappropriate nomenclature could alert the surgeon to the fact that the previous surgeon may not have had mastery of the field. (e.g., a reference to the cords of the brachial plexus when the surgery was in the supraclavicular space, or a reference to operating on nerve fibers, which are invisible to the human eye). Disproportionally long descriptions of how a nerve was particularly guarded and protected suggest that the operative note may have been revised once that an injury to that nervel was proclaimed clinically in the postoperative period. The surgeon should have a clear idea as to the probable site of pathology (e.g., is this likely to be a C5 and C6 spinal nerve injury or is it more likely to be musculocutaneous nerve pathology?).

Presurgical Pause

A brief, formal meeting of the surgeon, anesthetist, and operating room nurse should be held before the start of every case. Confirmation is sought as to the patient’s identity and the side and site of the proposed surgery. The probable duration of operation is reported and whether blood is likely to be required. The anesthetist should understand that no tourniquets will be used and that after exposure, the surgeon will want to stimulate the nerve or nerves and look for an appropriate muscular response. In appropriate cases, nerve action potentials (NAPs) will be recorded. All hospital protocols (e.g., preoperative antibiotic infusion) are checked for completeness. The informed consent document is reviewed so that everyone is reminded of what the patient has (and has not) consented to.

Operating Room Set-Up

The positioning of the patient, instrument table, back tables, the surgeon and assistant, and, possibly, the operating microscope should be explicitly rehearsed. On occasion, procedures are prolonged, and—particularly if microsurgery is contemplated—the positions of both surgeon and assistant should be reasonably relaxed and comfortable. The operating nurse should be quite clear as to whether sural nerve grafts may be harvested or whether a limb will be moved significantly during surgery. If this foresight is not a rule, surgeons may find that they are operating in peculiar, crouched positions for several hours or that aseptic technique is broken by unexpected movement of limbs during surgery.

Instrumentation

The operating room nurse should be confident that all instruments have been appropriately handled prior to their sterilization before the operation. Delicate microsurgical instruments require very careful handling and expensive endoscopic tools may have specific and special sterilization requirements.

A general set of instruments for routine nerve exposures should contain as few instruments as possible, as long as the inventory is appropriate for the intended procedure. A wide variety of self-retaining retractors is required. Plastic loops of various caliber and color are a significant aid to nerve dissection.

A set of microsurgical instruments should be prepared separately, because these are not required in every case. Once again, there should be standardization of the instrument pack, although it is not unreasonable to allow the microsurgeon a favorite needle holder or specific forceps design.

All significant peripheral nerve operations require appropriate instrumentation to manage vascular damage. In the main set, instruments should be present for this purpose. A more sophisticated vascular pack should be available to the operating room should serious difficulties be encountered.

Changing Gears

All should understand that the operation will not proceed at a uniform pace. Routine exposures should be completed with dispatch. Outstanding surgeons appear to operate slowly but complete procedures without delay. The secret is that there are no wasted movements. The surgeon is an absolute master of the anatomy. Operations are conducted through fascial planes whose anatomy is clearly comprehended. Muscle is rarely cut. Much is achieved by sharp dissection with a knife, using confident and safe technique; thus the field is relatively bloodless. Trainees should acquire all skills in an appropriate skills laboratory, not the operating room. A trainee who operates in a cell-by-cell manner with excruciating slowness shows clear evidence of a lack of anatomical mastery, and the supervising surgeon should remove such an operator immediately. A trainee who fumbles with the knot of an 8-0 suture under the microscope demonstrates too short a time devoted to skill acquisition in the laboratory

Normal nerve should be exposed on either side of the pathology whenever possible. The surgeon then “changes gears.” Operating loupes are worn where appropriate to ensure that planes are utilized accurately. At the completion of this phase, normal proximal and distal nerve and the lesion itself are dissected out. The response to direct stimulation of the nerve proximal to the lesion is carefully noted, because this is an accurate indicator of the degree of severity of the nerve injury, provided an appropriate time has elapsed since the insult. Where appropriate, NAP recordings are made.

In a deliberate fashion, the gears are once again changed. Suction pressure is significantly reduced so as not to accidently aspirate nerve graft. Assistants are banned from blotting the wound with surgical sponges, to prevent them from carrying off delicate grafts in the process. A decision is made as to whether grafts will be required; if so, those grafts should be dissected out without any injury to the axons they contain.

A further gear change is signaled by the conclusion of the nerve surgery. It must be emphasized that fatigue should not encourage shoddy work or substandard shortcuts at this stage. The steps that conclude the operation should be taken with as much care and skill as the opening stages.

Particular attention should be paid to keeping the patient immobile until the surgeon signals the anesthetist that it is safe for movement to occur. The transfer of the patient from table to gurney and from gurney to bed must be supervised and conducted by experienced personnel who retain their concentration despite many hours of taxing and tiring surgery. (Nothing quite spoils the surgeon’s day after a difficult and taxing high sciatic nerve repair than to have the patient’s leg dropped during transfer to the gurney.)

The Operative Note

The operative note should be dictated immediately following surgery. A common error is to find endless paragraphs describing routine approaches and then cursory or minimal description of the nature, dimensions, and other characteristics of the nerve pathology and the exact record of what was done. The record is a record of fact and no embellishments should be offered (e.g., “a black silk suture was found tied tightly around the musculocutaneous nerve,” or “a wire suture was found around the proximal sciatic nerve tightly constricting the nerve at the level of the hip joint”). No comment should be added concerning the previous operator’s skill. If the pathology is found to be relevant to a potential medical-legal discussion (e.g., a radial nerve transfixed by a screw into the humerus), it is a good idea to have a senior colleague come into the operating room to witness and record the occurrence. In this circumstance, it is particularly important that the senior surgeon (not the junior assistant) dictate the operative note so that the facts are clearly described, and so it is noted that the matter was witnessed by a colleague. These maneuvers prevent endless subsequent discussions in legal arenas. In every operation, the surgeon is a witness of fact, and the facts should be described with accuracy, in the interests of the patient and the previous operator. On no account whatsoever should operating notes ever be altered, substituted, or “lost.”

Anatomy

The amount of anatomy learned in medical training is adequate for that purpose and totally inadequate for surgical training. The importance of “the surgeon’s view” (i.e., the anatomy seen at operation), is appropriately stressed, but it must be emphasized that that limited knowledge is also totally inadequate for the performance of safe and expeditious surgery.

The major component of the preoperative diagnosis, and hence the surgeon’s vision of what will be found at surgery, is derived from careful clinical appraisal. In turn, the physical examination is based on an understanding of anatomy, not on the rote learning of various tests.

There is no substitute for diligent training under a specialist anatomist. “Surgical anatomy” emphasizes the particular points that are of importance to the surgeon, and we attempt in this book to pass on those points we learned from master surgical anatomists, bolstered by our own experience in thousands of cases. Space does not permit a full discussion of anatomy in this volume. We believe the “keys” are important, but the reader must engage in appropriate dissections, study anatomy specimens, read atlases, both diagrammatic and, more importantly, realistic, learn the osteology and consult the spectacular anatomy Web sites, until familiarity leads to mastery. Learn the patterns first, then the osteology, then add the soft parts. Eventually you will have the joy of greeting your “friends” (key landmarks) every day in the operating room. The patient has put trust in you. Be certain that your preparation makes you worthy of that trust.

External Neurolysis

• External neurolysis is the initial step in most peripheral nerve dissections. It consists of freeing the nerve and injury sites from surrounding connective tissues or scar in a 360-degree fashion. It can be done with a scalpel or surgical scissors, without magnification.

• Normal nerve is attached to adjacent longitudinal structures such as the tendons, vessels, fascial planes, and periosteum by a fine, filmy extension of the epineurium called the mesoneurium.

• When healthy, it is fine enough to be transparent. The mesoneurium carries the collateral, more transverse (or sometimes oblique) arteries and veins that relate to the extensive longitudinal vascular system of the nerve. This layer is usually diminished at, as well as above and below, any lesion site.

• Once the nerve is cleared of tissue in a 360-degree fashion proximal and distal to the lesion, one can encircle the nerve with a Penrose drain or, in the case of small nerves, a plastic loop.

• Then, by gentle retraction, the borders of the nerve lesion, including that on the backside of the surgical field, can be exposed. Gentle traction on adjacent soft tissues with a moist sponge or fine-toothed forceps helps the surgeon dissect a scar away at the injury or lesion site (Figures 21-1 and 21-2).

• It is usually best to establish healthy planes in the nerve both proximal and distal to the lesion. Working from a proximal site to a distal site for this portion of the dissection is most likely to spare branches. For a lesion in continuity, the surgeon becomes a sculptor attempting to restore some form and outline to the overall shape of the nerve.

• Scar is gradually removed by a No. 15 scalpel or fine scissors until some of the nerve itself is displayed (see Figures 21-1 and 21-2). Of course, with badly thickened or neuromatous nerves, this is not possible. Further dissection awaits the outcome of stimulation and recording studies.

• More thorough removal of a scar at an epineurial level may be indicated for a lesion that transmits a NAP and is associated with neuritic pain.

• If the injured nerve is left with only an external neurolysis, it is because it has been determined that repair is either not necessary (because of transmission of NAPs), or not feasible.

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Figure 21-1 External neurolysis. The scar surrounding the injury site is dissected away.

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Figure 21-2 Sciatic external neurolysis through the injury site reveals that both components are in continuity. A, Skin incision. B, Sciatic nerve seen. C, Both tibial and peroneal components can be seen.

Internal Neurolysis

Definition

• Internal neurolysis involves an internal dissection of the nerve, splitting it into at least its larger fascicles or sometimes groups of smaller fascicles but maintaining their integrity. Magnification of some sort aids accuracy (Figures 21-3 and 21-4).

• When an injury or a lesion in continuity is present that conducts a NAP and the patient has severe pain, a careful internal neurolysis may be of benefit. There is the risk, however, that such manipulation may further reduce function.

• Another indication for internal neurolysis is a partial nerve lesion, with or without regeneration, as shown by preoperative and intraoperative electrical studies. Under these circumstances, a portion of the cross-section of the nerve may be more involved by injury and a secondary scar than the rest of the nerve.

• The fascicles of the relatively good portion can be split away from the bad portion by a careful internal neurolysis, and both can be evaluated by stimulation and recording studies. The nontransmitting portion can then be resected and repaired, usually by grafts, while the better portion undergoes only a neurolysis. This is a split or partial repair. Such findings and the requisite partial repair suggest a relatively favorable functional outcome for the patient.

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Figure 21-3 Internal neurolysis. The perineurium surrounding fascicles is respected. A, After resection of some of the epineurium, an interfascicular dissection or internal neorolysis can be performed. Munyon tips are placed beneath one fascicle in this drawing. B, The No. 15 scalpel blade is used to dissect between the fascicles or groups of fasciclesm, as others that have already been dissected are displayed by small plastic loops. C, In this case a fascicular lesion is found. D, A scar and neuroma are dissected away from a fascicle.

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Figure 21-4 Internal neurolysis reveals discontinuity of some fascicles.

Controversies Surrounding Neurolysis

• The value of internal neurolysis when there is no element of neurapraxia and no conduction through a lesion in continuity that is several months old is doubtful.

• Those who believe in the efficacy of such a procedure feel that release of individual fascicles from surrounding scar may reverse a localized conduction block. This may be so in a lesion shown to be neurapraxic by intraoperative recording of NAPs above and below a lesion in continuity but with no conduction across the lesion.

• Another opinion is that internal neurolysis of the complete lesion aids the axonotmetically injured fascicles in regenerating more readily or more completely.

• In our view, if there is no conduction through such fascicles or the whole nerve, and sufficient time has elapsed for recovery, “freeing” or dissecting by internal neurolysis does not provide a very useful function. Under such circumstances, resection and repair may be the better course.

• If a NAP is recorded, yet a portion of the nerve looks badly injured, it is usually better to split the badly injured fascicles away from the more functional ones and to repair them. At the same time, those fascicles that are conducting should be spared resection.

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