Newer Techniques in Peripheral Nerve Repair

CHAPTER 32 Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 Newer Techniques in Peripheral Nerve Repair

JAMES W. SMITH, M.D.

Since the 1880's the traditional method of repairing peripheral nerves has been through the use of the epineurial suture (Fig. 32.1) (3, 14, 15, 18-20, 23-26, 31, 32). More recently, there has been an ever increasing volume of evidence to support the belief that fascicular suturing im• proves the results of nerve repair (1, 7, 9-11). One of the reasons why the return of motor and sensory function is less than satisfactory following epineurial repair, seems to be because the fasciculi can easily be de• flected, kinked or misdirected (Fig. 32.2) (6, 17). Ifthis happens many of them can grow blindly into the interfascicular tissue or be deflected away from their corresponding fascicle while the exterior appearance of the nerve is excellent. In contrast, fascicular sutures support the contact between the approximated fascicles, so that regenerating axons have a far better chance to grow across the site of nerve repair and straight down into the corresponding distal fascicles (Fig. 32.3). Millesi and Meissl have reported on the technique of microsurgical interfascicular autografting (16, 17). They felt that these were the tenets of any good nerve repair: 1. A nerve repair should not have any tension across the suture line, not only during the time of the suturing but also after operation. 2. Most, if not all, of the secondary scar tissue originates from the epineurium, and growth of the scar is tremendously accentuated by tension. 3. In cases where interfascicular autografting is to be employed, the epineurium should be removed at the sites of juncture. 4. Thin autografts are best for bridging gaps between nerve ends because their small size and rapid revascularization minimizes the chance of ischemic necrosis. 5. Grafts should be sutured into place using interfascicular and peri• neurial sutures to more exactly reunite fascicles. 6. The operating microscope, bipolar coagulation, and microsurgical instruments are essential to achieving good results with this technique. The primary repair of a divided peripheral nerve begins with identify- 456 NEWER TECHNIQUES IN PERIPHERAL NERVE REPAIR 457 Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021

FIG. 32.1. Epineurial Suture. The epineurial suture is supposed to close all gaps in the epineurium so that no fascicles protrude or escape and form neuromas. ing the cut ends of the nerve and freeing them for 1 to 2 em. in the surrounding tissue by sharp dissection. If the damaged nerve has been severed with a piece of glass or a knife, and suturing is to be done by primary repair, little or no trimming of the nerve ends will be required (12, 21). If the trauma was with a' blunt object or more severe, a secondary nerve repair should be done (8, 13). In these cases the nerve ends need to be trimmed back with a razor blade or a sharp knife in serial slices, one millimeter at a time, until the fasciculi protrude out from the cut surface of the nerve (Fig. 32.4). The cross-section of the nerve at this point should be composed of soft, loose connective tissue rather than scar. This supporting connective tissue, present as epineu• rium, perineurium, and endoneurium makes up from 20 to 80% of the cut surface of a nerve (30). It's important to remember that the fascicular patterns change con• stantly in a way described by Sunderland (30). Surface patterns change over distances of 0.25 to 5 mm., so the longer the nerve segment resected, the more difficult it would be to match up the cut ends of the fascicles.

TECHNIQUE FOR PRIMARY REPAIR OF PERIPHERAL NERVES When a peripheral nerve has been divided, it may be difficult to find the ends in a fresh injury, ifone studies only the cut surface. They tend to retract back from the wound edge because of the elasticity of the mesoneurium and perineurium. Ifthe viability of a part is injeopardy, however, vascular repair takes precedence over any nerve surgery, and the latter should be considered only when it will not decrease the chance for survival of the part or appreciably increase the chance for a complication or infection. When a nerve repair is to be deferred until a later date, it is important to approximate the nerve ends with a single suture to aid in their later identification and to prevent retraction (5). If a small segment of nerve 458 CLINICAL NEUROSURGERY Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021

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o FIG. 32.2. The findings of Edshage are demonstrated (6). A good epineurial closure does not mean that all of the internal architecture of the nerve has been restored. So, even though the epineurium appears well approximated, the fascicles within may actually be (A) properly aligned; (B) misdirected; (C) if a dead space exists, this may result in excessive scar and poor axonal growth across the juncture could result; or (D) there may be kinking. is missing so that the ends cannot be approximated, the ends should be tacked to the bed, or some other fixed structure, to keep them from retracting. This procedure will minimize one of the great problems that repeatedly makes secondary nerve repair more difficult- the gap be• tween the two ends. In a fresh nerve injury, even though there has been no loss of nerve substance, this gap is present because the nerve ends retract on account of the elasticity in the mesoneurium. In order to NEWER TECHNIQUES IN PERIPHERAL NERVE REPAIR 459 restore continuity, it is often necessary initially to place gentle traction on both ends of the nerve to get them together. Ifprimary nerve repair is to be undertaken, the next step is to prepare the cut ends. Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 Funiculi can be seen protruding slightly from the ends of the nerve• like wires extending from a section of cable; the epineurium slips back and forth over the bundles. Seddon and Medewar call this the "prepuce test" (20). Each individual fasciculus also has an independence of move• ment from its surrounding perineurium. This independent mobility of each fasciculus and each surrounding connective tissue layer, one from another, is a prominent feature of normal nerve tissue. It is markedly diminished or almost totally absent in nerve being prepared for a secondary repair because of the increased amount of fibrosis present. This difference makes the primary repair of a peripheral nerve an entirely different problem, from a technical point of view, from that of a secondary repair. In a primary repair, the mobility of each fasciculus has to be con• trolled to keep it from retracting, protruding too far, kinking or being displaced in one direction or another. So, "skewer sutures" or "guide sutures" need to be inserted to bolster the internal architecture and to help make an orderly preparation for the biological repair. As the suturing is begun, it is important to try to re-establish the original relationship of the nerve ends. There are at least four ways in which proper alignment can be restored and rotational error minimized. One way is to study the epineurial blood vessels on either side of the division and line them up. Another is to match up the mirror-like images of the nerve bundles in the cut ends. Sometimes there is a small groove or idiosyncrasy in the contour on either side which will help. Finally, the mesoneurium normally extends down from the underside of a nerve to its underlying bed (28). Even ifthe mesoneurium is not intact

FIG. 32.3. Corresponding fascicles are approximated by a perineurial suture in order to bring the nerve ends into proper alignment. No more than one or two sutures are required for each fasciculus or groups of fasciculi. 460 CLINICAL NEUROSURGERY

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FIG. 32.4. Preparing nerve ends for repair. A thin, narrow strip of plastic (such as polyethylene or "Vi-drape") can be placed around the nerve end and is then tightened like a noose with a right-angled clamp and put under slight tension. A razor blade or a dermatone blade is used to cut it in 1 mm. sections. These sections can be studied to be certain any severely damaged areas are removed prior to suturing. An excellent inter• face is also established for the suturing. at the site of nerve injury, remnants of it can be identified and used as a guide in correcting rotational error. The dissecting microscope allows the surgeon to study the fasciculi to see if all damaged and devitalized tissue has been removed prior to the repair. If the pneumatic tourniquet is being used and there is no color contrast, the extent of damage is often difficult to evaluate. Many surgeons find it advantageous to use a somewhat diluted mixture of methylene blue (1%) in order to improve this contrast along the cut margin. Very little is needed, and it can be applied to the cut nerve end with a sterile toothpick. This helps to outline the epineurium and the nerve bundles more clearly (29). Magnification is advantageous in the repair of both large and small nerves (28). In the larger mixed nerve, it helps to prevent rotational errors and to secure the proper alignment of motor and sensory funiculi. In the smaller nerves, it aids in a more accurate closing of the epineu• rium. Apparently, if the epineurium of a digital nerve is closed accu• rately so that there is no gap through which a funiculus can protrude, NEWER TECHNIQUES IN PERIPHERAL NERVE REPAIR 461 the chance of a painful neuroma at the site of nerve repair is markedly reduced. This is an especially important consideration in the fingers, where the amount of subcutaneous tissue is limited and it is less than Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 adequate for padding if the nerve is not properly repaired. In the past most authors have suggested placing "guide sutures" through the epineurium for help in aligning it properly. We insert several perineurial guide sutures of 7-0 nylon as the initial step before approximating nerve ends (Fig. 32.5). These are placed through the epineurium about 1 cm. back from the cut end and run horizontally down the nerve along the perineurial surface of a fascicle and out to the cut surface of the nerve end. A corresponding site is selected on the other cut end of the nerve and the guide suture is passed down along the perineurium and out through the epineurium injust the reverse order in which it was inserted. If two to four sutures of this type (7-0 nylon) are accurately inserted, they can be used in the realignment and also will serve well as traction or "stay sutures" to pull the ends together for the repair. Epineurial sutures are placed accurately, one on each side of the nerve, but slightly more on its anterior surface, about 120degrees apart. Several 7-0 nylon sutures might be needed to overcome the tendency for the ends to retract away from one another. Attention should be directed to lining up the "mirror-like patterns" of the funiculi so that any discrepancy in rotation is corrected as these sutures are placed into the epineurial sheath. The anterior repair should be performed first with a 7-0 or 8-0 microsurgical suture, and then the posterior repair performed. At the completion of the suturing, it is important to inspect the line of juncture to be sure that there are no defects in the epineurium through which funiculi can protrude. If the suture line is rolled between the fingers as one rolls a cigarette, the lining up of the funiculi will be further facilitated. The funicular guide sutures on each side of the repair can be threaded onto a large cutting needle and passed out through the skin. They can be tied to one another after the wound is closed. These funicular guide sutures are removed at 7 days by cutting one side of the loop and pulling on the other when the edema and early stages of healing have fixed the funiculi to one another at the site of nerve juncture. Splinting of the extremity should hold it in, such a position that there will be no tension on the nerve ends during the 3 to 6 weeks of healing.

SECONDARY NERVE REPAIR When a secondary repair is to be performed the proximal and distal stumps should be explored away from the area of scar, where the more normal nerve tissue is located. The nerve stumps will be adherent within the area of the scar. Nerve dissection is started in normal tissue 462 CLINICAL NEUROSURGERY Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021

FIG. 32.5. Combined fascicular-epineurial repair. (A) Several small "skewer" sutures are placed adjacent to and parallel with the course of more major fasciculi. These perineurial fascicular sutures help to align the internal fasciculi. (B) Epineurial approx• imation is achieved with a few epineurial sutures. (C) The "skewer" sutures can be brought through the skin and fixed to it with adhesive tape. A week or so later one end of the "skewer" sutures can be released from the skin. Tension on the other end pulls them out to minimize the number of foreign bodies at the site of the nerve juncture. The remaining epineurial sutures maintain the integrity of the repair. proximal and distal to the nerve defect where the epineurium can be identified and incised longitudinally and the major fascicles and groups of fascicles isolated. The dissecting microscope aids in this procedure and decreases the chances of damaging nerve tissue. The fascicles are readily identified and can be freed from one another in the normal tissue, and the dissection is directed from this point toward the end of each nerve stump. Longitudinal vessels can be ligated and coagulated with the bipolar coagulator. NEWER TECHNIQUES IN PERIPHERAL NERVE REPAIR 463 As the area of injury is approached, the fascicles and the connective tissue between them become more and more fibrotic and difficult to dissect (2). Eventually the fascicles become components of the scar Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 tissue at the level of the transection and lose their individual identity. So, at this level, fascicles are transected individually or as groups, with a sharp razor blade or with fine sharp scissors. Because the scarring varies from one area of the nerve to another, transection of the fascicles can be done at different levels so that major fascicles and minor groups offasciculi can be separated according to the extent of their involvement in the scar tissue and neuroma. Once the separation has been com• pleted, each nerve end should be composed of from four to six fascicles, or groups of fasciculi of different lengths (16). No attempt should be made to free all of the fascicles, or all of the minor fascicles from one another, because this makes the repair an impracticality. When there is little or no nerve gap, interfascicular suturing can be carried out. When there is a sufficiently large gap so that tension will be present across the nerve juncture, fascicular grafting will be necessary (Fig. 32.6). If a sketch is made of the two stumps after the dissection is completed, the fascicular patterns of the stumps can be compared to aid in defining and identifying the corresponding groups of fascicles in each stump. At the wrist level or even in the forearm, this is usually quite easy. The longer the nerve segment is sacrificed or damaged, the more proximal the level of the injury, and the more difficult it may be to identify which fascicles correspond with one another.

OVERCOMING NERVE GAPS The definition of what constitutes a nerve gap is still a controversial matter. A nerve gap exists from the very moment a nerve is cut because the cut ends always spring apart. However, with a freshly cut nerve, so long as there has been no loss of substance, continuity can be re-

FIG. 32.6. The component parts of each fascicle will change, even over short dis• tances. The fascicle may also change its location within the substance of the nerve. With the loss of substance, in this case, the proximal fascicular group that corresponds to one distally was found at a point 45 degrees rotated away from it. When a nerve graft is to be inserted, this should always be taken into account so that in so far as possible, corre• sponding fascicles are approximated. 464 CLINICAL NEUROSURGERY established with minimal tension across junctures after the ends have been stretched out. However, with secondary repairs, approximation of nerve ends may be quite a different matter. Whether or not the nerve Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 gap can be overcome by mobilizing nerve ends, stretching the nerve, flexing a limb, or rerouting the nerve depends upon the size and location of the nerve gap (14). Seddon concluded that the largest gap he could close by this technique and still preserve good function was a maximum of 5 to 7 em. (27). Sunderland contends that in some instances up to 12 em. gaps can be overcome by mobilization, stretching, and rerouting when it's absolutely necessary (30). On the other hand, Millesi feels that when the nerve ends are 2 em. apart or more, even with the joints of the extremity in full extension, the gap should be overcome by the use of an autograft in every case (16). An exception is when lesions of the ulnar nerve are located at the elbow; ifa 4 em. gap is found, he transposes the nerve and performs a direct suture. In all other cases he prefers to repair the nerves by grafting because this provides him the possibility of immobilizing the limb for only 10 days time before beginning active exercise and electrical therapy. When a nerve graft is needed, the sural nerve is usually selected for its length, minimal loss of function, and ease of removal. The length of the graft and the number of nerve segments required is determined by the nerve injured and the donor nerve selected. When the donor is to be the sural nerve, the nerve is exposed through a small vertical incision behind the lateral malleolus. The incision should be made just anterior to the lateral border of the Achilles tendon. It's best to use a pneumatic tourniquet. Here, in the subcutaneous tissue, the sural nerve can be found just behind and adjacent to the lesser saphenous vein. By separat• ing it from the vein and pulling gently on it, the course of the nerve can be identified along the calf. It courses proximally between the two heads of the gastrocnemius, and sometimes it can be identified by palpating the muscular groove through which it passes beneath the skin and by gently pulling the nerve to identify its more proximal course. Four or five transverse incisions are used for removing the nerve. When it's removed a nerve segment measuring between 20 and 35 em. can be expected, and this is usually sufficient for nerve grafting. The nerve graft can be divided into segments slightly longer than the defect existing between the two prepared nerve fascicles (Fig. 32.6). For the ulnar nerve, usually four segments of graft are needed, for the median nerve five or six. Any remaining fat and connective tissue should be removed from the ends of the grafts at the sites they are to be sutured to the nerve. Thus, grafts of appropriate length are inserted between the ends of the corresponding fascicles or groups of fascicles (Fig. 32.7). The dissecting microscope is a great aid in carefully and NEWER TECHNIQUES IN PERIPHERAL NERVE REPAIR 465

Nerve Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021

FIG. 32.7. Nerves the size of the median or the ulnar nerve will often require three or four sural nerve graft segments in order to provide the best possible bridge for axons crossing from the proximal stump to the distal end of the nerve. In this example, the nerve in C is dissected apart just enough so that it separates into four component parts. Each one should be about the same diameter as the sural nerve segment as used in D. Then, four segments of sural nerve can be used to bridge the gap. In this case, nerve graft a' is matched to a, b' to b. In Figure H we see how only one or two sutures of 10-0 nylon are used for each juncture. exactingly approximating corresponding ends of the grafted fascicles or groups of fasciculi. A single suture of 10-0nylon is used to maintain the exact juncture between the ends of the graft and nerve fasciculus. This suture is passed through the perineural tissues of a fasciculus and the graft, and then tied very loosely. Keeping tension at a minimum at the 466 CLINICAL NEUROSURGERY suture site minimizes the tendency to produce a connective tissue reac• tion, and only a very minimum of buried suture material is left behind.

Grafts should be used as individual bridges between component parts, Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 inserted so that they make good contact between the cut surfaces of the nerve ends. This increases their chance of survival and yet lessens the chance that part of the graft does not take. In any case where an end-to-end suture can be carried out, it is important to match up the corresponding fascicles by noting their size and relative position in the nerve. It is sometimes possible to determine the original anatomical relationship between the two ends of the nerve by matching up corresponding blood vessels on the epineurial surface or by noting the comparative configurations of the fascicles in the two ends of the nerve. Matching up mirror images allows a better identification of component parts. Once matching is complete and the largest fascicle is identified, it can be sutured to the corresponding one on the opposite side of the nerve. Care should be taken to avoid more than a minimal dissection of the fascicles in such a case, because too much dissection may leave a gap between fascicles. After all single fascicles and groups of fascicles have been sutured together, a few remaining sutures can be placed in the epineurium in order to complete the closure. Immobilization should be done in a way that tension is taken off the site of nerve repair. A plaster splint or cast may be necessary in order to accomplish this. The site of repair is immobilized for 3 weeks. During the 4th week the patient wears the splint but takes it off three times a day to get the joints loosened up and to work on establishing a good range of motion. We now feel interfascicular nerve grafting should always be used when there has been an extensive loss of nerve substance or "a marked retraction of the nerve ends so that even extensive freeing will not allow approximation without tension. As a matter of fact, autografts of nerve should be considered any time there will be significant tension at the site of a repair. The studies of Seddon and others suggest that the length of a nerve graft has nothing, or at most very little, to do with its chance of success (27). Nerve grafts are revascularized along their entire length in a segmental fashion rather than by a vascular ingrowth from the ends. Therefore, the length of the graft should not have a significant bearing on the eventual outcome. The diameter of the graft, however, does appear to be important, for all grafts rely upon an ingrowth of the vessels for survival; if the diameter of a graft is so large that its revascularization cannot be accomplished within an unknown but criti• cal period of time, necrosis and degeneration will result. Nerves of the caliber of the median and ulnar nerves are probably revascularized promptly when used as free grafts, and their size does not directly affect NEWER TECHNIQUES IN PERIPHERAL NERVE REPAIR 467" the chances of success; however, the ultimate function of larger nerves, such as the sciatic, is certainly altered by their diameter.

The antigenicity of a graft is a major factor in its ultimate survival Downloaded from https://academic.oup.com/neurosurgery/article/24/CN_suppl_1/456/4100525 by guest on 05 October 2021 and function (13). Autogenous grafts will not be antigenic. We have preferred to use them, favoring the autograft over freeze-dried, irradi• ated nerve allografts. The latter appear to have the potential for restor• ing only about 1/10 the function of an autograft (22). Allografts of the freeze-dried, irradiated type seem more likely to be the next most potentially successful substitute for the autograft because their degree of antigenicity is reduced to a minimum by this process. They should be serving primarily as an architectural conduit for transporting regener• ating axons across the gap between the two nerve ends. It seems, at least theoretically, that if a nerve segment corresponding to the one needed for replacement were taken from a cadaver the chances of anatomical and architectural similarity would be increased in favor of a more proper restoration of function. Cable grafts ignore completely the proximal and distal patterns within the ends of a nerve. Two additional factors in favor of autogenous fascicular grafts, of course, are that they are autogenous and that revascularization can be accomplished more readily. For a number of years many surgeons used Silastic cuffs around the sites of nerve anastomosis to prevent or minimize external scar forma• tion and to favor structural support of the nerve repair (4). There is considerable doubt whether Silastic cuffs are effective, and they may in fact add to intraneural scarring.

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