New Possibilities for Facial Nerve Repair

The facial nerve is a very useful model for the investigation of nerve repair and regeneration in general, since it contains exclusively (in those parts most frequently involved in surgical procedures) special visceral efferent nerve fibers. It is surprising therefore that so little laboratory research has been directed at this nerve, for motor pathways have been most frequently chosen as the model for assessment of nerve repair in animal experiments and the rat facial nerve does not present a technical problem for the experienced microsurgeon. Repairing the facial nerve is a significant clinical problem,' accounting for a considerable number of cases in the spectrum of clirucal nerve repair. In theory, the ideal means of repairing any nerve is primary end-to-end suture, although the question of whether epineurial or fascicular repair is better remains unresolved.2-5 It should, however, be stressed that such a method of repair is only satisfactory if no tension exists at the suture line. This finding represents the only really significant step forward in research into the mechanisms of peripheral nerve regeneration from the surgeon's point of view in the last 35 years, that is, since the now classic Medical Research Council report of 1954.6 This work, by Terzis et al,7 is, in reality, oversimplified, relying on the erroneous assumption that gap length and tension at the suture line are related in a linear fashion. Nevertheless, ignoring this important principle has perhaps been responsible for more failures of peripheral nerve repair than any other factor within the regard of the

surgeon. One of the great weaknesses in the surgical repair of nerves is that, in addition to a wide heterogeneity in the nature of the injury and associated problems, there exists a comparable heterogeneity in the specialty of the surgeon undertaking the repair. In the United Kingdom, at least, nerve repair exists to a variable degree within the province of orthopaedic, plastic, general, and even occasionally neurosurgeons. The result is inevitably a dilution of expertise and experience. The facial nerve probably fares somewhat better than most, being restricted for the most part to the attentions of otolaryngologists and plastic surgeons. When the problem of suture line tension is recognized, attempts to relieve strain by mobilizing the cut ends of the nerve may result in its further devascularization and produce an equally poor result. Among those involved in large numbers of nerve repairs there has recently emerged a greater willingness to abandon direct suture in favor of grafting. It should be noted that grafts have a set of problems proper to themselves, not least being availability of suitable material and a generally poorer provision of both tropic and trophic influences on the regenerating nerve fibers, but these shortcomings, emphasized by Seddon,3,6pertain to the regenerative properties of the nerve fibers themselves and may, in the final analysis, be less harmful than the excessive connective tissue proliferation caused by tension. The facial nerve beyond the stylomastoid foramen is a medium-sized nerve containing large diameter, fast conducting motor fibers and injuries to it occur

Department of Anatomy, University of Edinburgh Medical School, Edinburgh, and Department of Otolaryngology, City Hospital, Edinburgh, Scotland Reprint requests: Dr. Glasby, Department of Anatomy, University of Edinburgh Medical School, Teviot Place, Edinburgh, EH8 9AG, Scotland Copyright 01992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.

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M.A. Glasby, B.M., B.Ch., M.A., M.Sc., ER.C.S., and LE Sharp, M.B., Ch.B., M.A., ER.C.S.E.

in such a way that grafting is frequently needed. Other factors that must be considered are the presence of bacterial contamination and the mobilization of the nerve stumps. Infection can be avoided by delaying the repair, (secondary suture) and nerve mobilization can be achieved (potentially more readily) after temporal bone excision. However, this is a difficult procedure and may result in additional, more proximal damage to the nerve. In current surgical practice, where a graft is required, a sural nerve autograft is the most frequent choice. For a large nerve, several such strands are laid in parallel to form a cable graft. The harvesting of donor autograft has several disadvantages including discrepancy in size between graft and damaged nerve and thus the need for additional donor nerve to make a cable graft. Cable grafts, not surprisingly, fare less well than single grafts of comparable thickness to the recipient nerve; repairing the facial nerve in most cases represents one of the all too few opportunities to repair an important nerve with a singlestrand graft. For facial nerve repair, a great auricular nerve autograft is also commonly used, partly because the proximity of this nerve to the operation site facilitates skin preparation and access,' and also because the nerve is closer in size to the facial nerve than the sural nerve. One should note, however, that this comparison of sizes relates to the nerve in its entirety and says nothing about the relative sizes of the contained fibers. Either donor nerve, being sensory, is likely to contain smaller nerve fibers, conducting at slower speeds, than the purely motor facial nerve. The removal of a sensory nerve causes an area of anesthesia and the need has long existed for a better graft that should ideally be simple to insert, cheap, and causing minimal morbidity during acquisition. In considering options it is important that it is at least as effective as appropriate methods already available. It is natural to consider prosthetic or bioprosthetic materials for grafts and for many years work involving nerve growth on artificial substrates in vitro has been carried out. However, none of this has shown the slightest potential for in vivo application and remains remote from clinical usage. Weiss and colleagues in the 194UsSl4tried many such artificial substrates in vivo with no success. Experimental work carried out in the laboratory, which ideally should precede clinical trials, has for the most part created nerve lesions simply by crushing the nerve in continuity, and although this situation must be studied as representative of the most simple form of injury, surgical research shows that the clinical problem is more diverse and complex. It is not particularly helpful to make general statements about nerve regeneration from this popular model alone. The established view of peripheral nerve regenera-

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tion is that following transection and reapposition of the nerve the axons and their myelin sheaths degenerate in the distal segment, leaving empty endoneurial tubes that are, in reality, the basement membrane of Schwann cells. Severed axons in the proximal stump undergo sprouting to form small unmyelinated pioneering axons, which enter the endoneurial tubes under the tropic and trophic influences of hypothetical surface and humoral agents variously said to be produced by basement membrane, the Schwann cells themselves, or from end-organs.4-1s Many aspects of this theory derive from in vitro experiments and lack substantiation in vivo and undoubtedly represent an oversimplification. It is clear2J9JJthat endoneurial tubes are not essential for nerve regeneration. They may, however, affect the rate of regeneration early in its history.19-21 Recently, the idea of nerve repair using an autologous bioprosthesis has been reintroduced in the form of the coaxially aligned freeze-thawed skeletal muscle autograft. In its short life history so far, it has enjoyed a modest success, but although early portents are entirely favorable, as yet adequate assessment both in the laboratory and more especially in clinical practice is lacking. In a skeletal muscle where the fibers are longitudinally arranged (such as sartorius), the basement membrane of the myocytes consists of a parallel aligned matrix of tubes with each surrounding a single cell. It is thus similar in its cytoarchitecture and chemical composition to the matrix of Schwann cell basement membrane surrounding the neurons in a nerve. If the muscle cells can be made to degenerate, the result is structurally identical to that of a degenerating nerve except that the tubes are larger in diameter. This is the basis of the concept of the freeze-thawed coaxially aligned skeletal muscle autograft (FTMG), first proposed by Glasby et a1 in 1986.22 These workers showed that coaxially aligned autologous skeletal muscle in which the sarcoplasm had been disrupted by freezing in liquid nitrogen and hypo-osmotic thawing in distilled water provided an orientated matrix of parallel basement membrane tubes that functioned in a manner similar to a nerve graft. These workers subsequently evaluated the physiologic and morphologic properties of nerve fibers and the non-neural components of nerves that had been repaired using freeze-thawed muscle grafts and also the properties of the target organs that they reinnervated. Results have been compared with those of normal nerves and muscles and with nerves repaired using existing techniques.15,16,19-33 This work undertaken initially in rats and confirmed in nonhuman primates became the subject of a formal clinical trial in which FTMGs were used to repair human digital nerves and was reported in 1988.27At present a variety of more extended clinical trials to

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FACIAL NERVE REPAIR-Glasby,

evaluate the technique in large mixed nerves and in other situations that require the use of large grafts (such as in the facial nerve), have been undertaken in parallel with further laboratory work. The freezing in liquid nitrogen and thawing in distilled water kills the muscle cells and causes disruption without structural damage to the basement membrane matrix. This is necessary for the rapid incursion of the pioneering axons, because it has been shown that the use of untreated muscle limits Basement membrane regeneration ~nacceptably.21~22 tubes are not an absolute requirement for regeneration, as was shown21 by orientating the treated muscle block so that its tubes were orthogonal to the nerve axis and unable to be entered by the pioneering axons. Recolonization of the distal stump still took place but with reduced axon numbers over a longer time course and with a less uniform arrangement of the fibers. Even so, each axon ultimately acquired for itself a typical Schwann cell sheath and normal myelination took place thereafter. Davies et all9 used a variety of orientations of the muscle graft to show that the coaxial arrangement, although not an absolute requirement, was associated with the most rapid and most' uniform regeneration and hence provided the most effective pathway to target organs. Thus, it is FTMGs that have been investigated subsequently and used in clinical practice. Advantages of the muscle graft are that it is cheap and simple to harvest and prepare and that it is an autograft. It is inserted using conventional microsurgical methods and it appears to have a uniquely low capacity for infiltration by scar tissue33 when compared with cable grafts. The endoneurial tubes that it provides are large enough to accommodate even the largest nerve fibers, although this might agree with the notion that grafts made from cutaneous nerves contain tubes too small for effective regeneration and maturation of large motor fibers. Whether this is important as a limiting factor in nerve regeneration through grafts is a matter of some contention.2,34,35It is well established,28,36 from experiments using crush axonotmesis in the rabbit and FTMGs in the rat and marmoset, that the largest, fastest conducting fibres never regenerate whatever the injury and it seems unlikely that endoneurial tube size is a determinant of this failure. FTMGs have been widely investigated in the laboratory and also clinically. The models used have been 2 ~ 3marmoset 0~32 the rat sciatic n e r ~ e , ~ 5 ~ ~ 6 ~ 1 9 - 2 3 , 2 5 ~the radial, ulnar, and median nerves,24,26 the sheep femoral nerve,33 the guinea pig sciatic nerve,31 and the human digital nerve.27 The FTMG has been shown to be successful as an interposed graft in each of these situations and there appears to be no indication that the site in any way affects the outcome of grafting. Although work is in progress to evaluate

specifically the facial nerve, adequate data are not yet available. Data obtained from a purely motor branch of the sheep femoral nerve, which has a distribution of fiber sizes and conduction velocities similar to the human facial nerve, however, suggest that application of the technique to the latter should be equally successful. We may make use of earlier experience using other nerve sites to predict the most effective ways in which the facial nerve may be studied. There is no reason to suppose that the techniques of graft harvesting, preparation, and insertion should need to differ. The progression of studies in the rat37 through the nonhuman primate to a carefully controlled clinical trial likewise seems appropriate. In the human, the final assessment of a satisfactory repair is the subjective opinion of the patient of what he can do compared with what he was able to do before injury, but this does not provide any objective criteria for translation elsewhere nor does it answer questions of a mechanistic nature. Laboratory studies, on the other hand, never quite reflect the heterogeneity of either the nerve injury or of the techniques by which it may be repaired, but they do allow very precise controls to be applied and hence yield data that can be interpreted statistically. They are thus invaluable in defining aspects of the technique that should or should not be applied where controlled conditions cannot exist. By far, the greatest problem in using a new surgical technique is knowing how it may be most usefully assessed. Obviously, the starting point must be a simple clinical neurologic examination, but as a quantitative procedure this is unproductive and comparisons can only usefully be made with the opposite side. When motor function is being assessed, compensatory hypertrophy on the opposite side may add to the complexity of the assay. Motor function is harder to assess objectively than sensory function, and this is especially so in the facial nerve. Although a procedure such as the above is useful in assessing the progress of an individual, it can add very little to the assessment of a new technique. In the human, transcutaneous nerve conduction studies and electromyography are applicable to the facial nerve and take evaluation one stage further than clinical examination, but these techniques are notoriously empirical in their interpretation and in the case of the facial nerve, relatively difficult to carry out. Invasive physiologic and morphologic studies provide a firmer quantifiable basis for understanding events in the recovery of nerve function and in animals may be correlated with large volumes of similarly controlled data from other sources. Obviously, they are not possible in humans but the step needed to extrapolate well-controlled, quantitative experimental findings that have been statistically

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FACIAL PLASTIC SURGERY Volume 8, Number 2 April 1992

evaluated to the human situation may, in fact, be smaller than that necessary when the starting point is the heterogeneous data obtained from clinical studies. To assess a motor nerve for recovery of function, we may look at events in the nerve itself or in the target muscle. Abnormal events in the former may be unimportant if the function of the latter is adequate, but it is more difficult to quantify recovery in the muscle because of the problem of finding adequate controls. The obvious control for function in a nerve is its opposite number, but in the case of a muscle, compensatory hypertrophy during recovery makes such an observation unreliable, although the error acts to underestimate recovery. Equally unreliable are observations on other individuals, however well matched, so that, although the muscle must be assessed for absolute recovery of function, it is better to consider the recovery of the nerve for comparative purposes. Excitability of a nerve is a useful index of its net capacity to conduct impulses and can be standardized to some extent using the strength-duration c~rve.38~39 This can be easily measured in both invasive and transcutaneous studies and a simple plot of stimulus strength against stimulus duration provides a relationship that can be used to compare nerves. The quantity "rheobase" (voltagerequired to

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excite the nerve at an infinitely long duration), as well as being a function of the true threshold of the nerve fiber population, is also a function of the preparation and thus is not suitable for comparative purposes. Standardization of strength-duration curves is therefore necessary using a method such as that derived by Glasby et a1.28 The value of chronaxie, (time to twice rheobase), however, is a unique function of the nerve fiber population and hence a good index of excitability where comparisons need to be made. Figure 1 is an example of how values of chronaxie may be examined at different times after graft insertion to compare the net excitability of nerves repaired with different techniques. It may be seen that in this respect the FTMG compares very favorably with direct tensionless suture, although with all methods excitability never returns to control levels. Chronaxie is a function of the entire nerve fiber population contained in a nerve and does not tell us about the profile of conduction velocities within the population. A purely motor nerve such as the facial would be expected to contain a bimodal distribution of fiber sizes and therefore conduction velocities corresponding to alpha and gamma motoneurons. In assessing the rate of regeneration and more particularly maturation of a repaired nerve, the difference between this profile for the repaired nerve and that of a normal control provides an important and easily

RECOVERY OF CHRONAXIE Determined From Standardised S.D. Curve Nv-Nv

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Figure 1. A comparison of the mean values +- SEM of chronaxies of the standardized strength-duration curves of four populations of ten normal rat sciatic nerves and the nerves of the contralateral legs that had been repaired 300 days previously by direct tensionless suture, equal diameter nerve grafts and freeze-thawed muscle autografts (FTMG). Nv: nerve; GFT: graft; Ctrl: control.

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FACIAL NERVE REPAIR-Glasby,

quantified index of recovery. Moreover, by studying a physiologic variable (conduction velocity) and a related morphologic quantity (fiber diameter), an internal control is generated. Conduction velocity is a function of nerve fiber diameter and of internodal length both of which alter during the process of regenerative growth and maturation. Glasby et a120r28,29have shown that even at 300 days after sciatic nerve repair with an FTMG in the rat a normal profile of conduction velocities has not returned, and Cragg and Thomas36 made similar observations in the rabbit after crush axonotmesis. The results using FTMGs indicate as good a recovery as those obtained by Cragg and Thomas for the less severe injury. It is unclear whether the failure of recovery of the fastest fibers is absolute or that insufficient time had elapsed for complete maturation, although evidence suggesting the latter is sparse and inconclusive and Cragg and Thomas found no significant improvement over the course of a further year. Gattuso et al29.40 have shown that at 300 days after operation in the rat, there is still a leftward shift in the profile of nerve fiber diameters and a reduction in internodal length regardless of the technique of repair. Measurement of internodal length is somewhat tedious, and although the regression relationship of fiber diameter and internodal length used by Gattuso et a129.40 is undoubtedly a better index of morphologic recovery, many workers use the quantity "G-ratio." This is the ratio between axon diameter

and fiber diameter for myelinated nerves, which is normally distributed within a population. As long as the population size is large, (more than 400 axons), a mean value for this quantity can be statistically compared with similarly obtained values using Student's t test. Figure 2 shows how values for G-ratio compare at different times after grafting for normal nerves and those repaired by three different techniques. Myelinated fiber numbers by 300 days have always equaled and sometimes exceeded values in control nerves (Fig. 3). This finding must be interpreted with care; counting nerve fibers has been attractive to many workers wishing to assess recovery, but methods of estimating fiber numbers other than absolute counting are notoriously inaccurate and sprouting at the proximal stump is a prodigious attempt to maximize regenerative capacity41Only a proportion of such fibers will make end-organ contact and only those that do will mature and conduct impulses. Fiber counting estimates regenerative capacity but not regenerative achievement. It would only be reliable at the endpoint of the regenerative process, and we cannot know when this might be. The morphologic appearances of nerves repaired with muscle grafts are shown in Figures 4 through 6. These are all resin-embedded transverse sections of a purely motor branch of the sheep femoral nerve repaired with a 5 cm FTMG. This situation is analogous to that of the facial nerve. All photographs were taken using an electron microscope and are at a final

RECOVERY OF DISTAL G-RATIO G-Ratio = (Axon Diameter/Fibre Diameter) Nv-Nv Nv-GFT F.TMG - CTRL N=10

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TIME AFTER GRAFTING (days) Figure 2. A comparison of the values of G-ratio in the same populations of animals considered in Figure 1. See Figure 1 for abbreviations.

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FACIAL PLASTIC SURGERY Volume 8, Number 2 April 1992

FACIAL NERVE REPAIR-Glasby,

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T l M E AFTER GRAFTING (days) Figure 3. A comparison of the mean values 5 SEM of total myelinated fiber numbers in the same populations of rats considered in the Figures 1 and 2. See Figure 1 for abbreviations.

Figure 4. An electron micrograph of a transverse section of a normal purely motor branch of the sheep femoral nerve (branch to vastus lateralis). This should be compared with Figures 5 and 6. ( x 3000.)

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Figure5. An electron micrograph of a transverse section through a freeze-thawed skeletal muscle autograft used to repair the sheep femoral nerve trunk 10 months previously. Note the similar axon diameter but poorer myelination when compared with normal nerve and the encirclement of groups of fibers by laminae of perineurium to form minifascicles. ( x 3000.)

magnification of 3000 times. This technique gives much superior pictures to light microscopic techniques and the use of paraffin sections for studying details of nerve morphology is now considered obsolete. For morphometric studies, we use resin embedded osmium-stained preparations that are cut at 1 Fm, counterstained with toluidine blue and viewed using an oil-immersion lens. When it is necessary to consider detailed morphology electron micrographs are rnandatory.20,21,25,29,3Or32,33 Figure 4 is a transverse section of normal nerve. It should be compared to Figures 5 and 6, both at the same magnification showing, respectively sections through the muscle graft and through the repaired nerve distal to the graft. Grafting had taken place 10months previously. The relative immaturity of the neural components and the different distribution of connective tissue is clearly seen. However, the appearances of the latter two figures as regenerated nerves are entirely acceptable and indeed very encouraging. Return of physiologic function at this time would be as complete as might be expected.28.36 The application of both physiologic and morpho-

metric techniques to the experimental model of the rat sciatic nerve repaired with the FTMG has yielded a large body of specifically controlled and quantified information about the technique. This has provided a means of usefully predicting from invasive studies which methods of assessment available to human patients may be most illuminating. Between the rat and human clinical use, those indices of recovery providing the most quantitative information were tested in the nonhuman primate,24.26 and this strategy provided a firm basis on which to approach Ethical Committees for the acceptance of the technique for clinical trials. A similar strategy would be appropriate in considering the facial nerve. In addition in our laboratory experiments we are able to perform more sophisticated assessments in this situation, since the facial nucleus can be entered stereotaxically and used for physiologic stimulation and recording. Additionally it is possible, using retrograde neuronal tracers, to quantify the extent of the new connections made after facial nerve repair and to assess whether there has been any alteration in the size and distribution of the facial nerve motoneuron

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FACIAL PLASTIC SURGERY Volume 8, Number 2 April 1992

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Figure6. An electron micrograph of a transverse section through the motor branch to vastus lateralis of the repaired nerve trunk distal to the graft in Figure 5. The characteristics of the neural elements are similar but the compartmentation by perineurium is absent. ( x 3000.)

pool. These experiments are in progress and will be reported later. In the periphery, experience with the sciatic nerve suggests that attention would be most profitably centered on the chronaxie of the strengthduration curve and the G-ratio for immediately useful results. At present, we may conclude from studies of the type reviewed here that there is little difference in the rate and extent of recovery of function between nerves repaired using FTMGs and those repaired by the best of other means. This is especially true in the laboratory and early clinical results suggest the same. What must be borne in mind are the relatively ideal conditions of the laboratory study compared with the heterogeneity of clinical cases, but controlled conditions have provided results that can be interpreted statistically and thus can be used in the prediction of future applications.

REFERENCES 1. May M (ed): The Facial Nerve. New York, Thieme-Stratton, 1986

Sunderland S: Nerves and Nerve Injuries, 2nd ed. Edinburgh: Churchill Livingstone, 1978 Seddon HJ (ed): Surgical Disorders of Peripheral Nerves, 2nd ed. Edinburgh: Churchill Livingstone, 1975 Mackinnon SE, Dellon AL: Surgery of the Peripheral Nerve. New York: Thieme, 1988 Lundborg G: Nerve Injury and Repair. Edinburgh: Churchill Livingstone, 1988 Seddon HJ (ed.): Peripheral Nerve Injuries. Medical research Council Special Report Series No282. London: H.M.S.O. 1954 Terzis J, Faibisoff 8, Williams HB: The nerve gap; suture under tension verses graft. Plast Reconstr Surg 56:166-170, 1975 Weiss P: Nerve reunion with sleeves of frozen-dried artery in rabbits, cats and monkeys. Proc Soc Exp Biol54:274-277, 1943 Weiss P: In vitro transformation of spindle cells of nerve origin into macrophages. Anat Rec 88:205-221, 1944 Weiss P: The technology of nerve regeneration; a review. Sutureless tubulation and related methods of nerve repair. J Neurosurg 1:400-500, 1944 Weiss P, Campbell CJ: Nerve fibre counts and muscle tension after nerve regeneration in the rat. An J Physiol140:616-626, 1944 Weiss P, Edds MV: Spontaneous recovery of muscle following partial denervation. Am J Physiol 145:587-607, 1945 Weiss P, Edds MV, Cavanaugh M: The effect of terminal connexions on the calibre of nerve fibres. Anat Rec 92:215233, 1945 Weiss P, Taylor AC: Further evidence against "neurotropisrn" in nerve regeneration. J Exp Zoo1 95:233-257, 1944

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Glasby MA, Davies AH, Gattuso JM, Huang CL-H, Wyatt JP: The effect of distal influences on rat peripheral nerve regeneration through muscle grafts. Neuro-Orthopedics 6: 61-66, 1988 Huang CL-H, Gattuso JM, Glasby MA, Gschmeissner SE: Regeneration of myelinated nerve fibres into branches of the sciatic nerve repaired with treated muscle grafts. Clin Anat 3:121-132, 1990 Politis MJ: Specificity in mammalian peripheral nerve regeneration at the level of the nerve trunk. Brain Res 328:271-276, 1985 Politis MJ, Ederle K, Spencer PS: Tropism in nerve regeneration in vivo. Attraction of regenerating axons by diffusible factors derived from cells in distal nerve stumps of transected peripheral nerves. Brain Res 253:l-12, 1982 Davies AH, De Souza BA, Gattuso JM, Glasby MA, Gschmeissner SE, Huang CL-H: Peripheral nerve growth through differently orientated muscle matrices. NeuroOrthopedics 4:62-73, 1987 Glasby MA: Nerve growth in matrices of orientated muscle basement membrane: Developing a new method of nerve repair. A review. Clin Anat (in press) Glasby MA, Gschmeissner SE, Hitchcock RJI, Huang CL-H: Dependence of nerve regeneration through muscle grafts on the availability and orientation of basement membrane in rats. J Neurocytol 15:497-510, 1986 Glasby MA, Hitchcock RJI, Huang CL-H: Effect of muscle basement membrane on regeneration of rat sciatic nerve. J Bone Joint Surg 68:829-833, 1986 Glasby MA, Gschmeissner SE, Hitchcock RJI, Huang CL-H, de Souza BA: Comparison of nerve regeneration through nerve and muscle grafts in rat sciatic nerve. Neuro-Orthopaedics 2:21-28, 1986 Glasby MA, Gschmeissner SE, Huang CL-H, d e Souza BA: Degenerated muscle grafts used for peripheral nerve repair in primates. J Hand Surg 11:347-351, 1986 Gschmeissner SE, Gattuso JM, Glasby MA, Huang CL-H: Functional reinnervation of muscles after nerve repair with muscle grafts. Demonstration using a new combined stain. Neuro-Orthopedics 5:l-9, 1988 Gattuso JM, Davies AH, Glasby MA, Gschmeissner SE, Huang CL-H: Recovery of neuromuscular transmission after peripheral nerve repair with muscle autografts in the nonhuman primate. J Bone Joint Surg 70:524-529, 1988 Norris RW, Glasby MA, Gattuso JM, Bowden REM: Peripheral nerve repair, a new technique using muscle autografts. J Bone Joint Surg 70:530-533, 1988 Glasby MA, Gattuso JM, Huang CL-H: Recovery of peripheral nerves after surgical repair with treated muscle grafts. (1) Physiological assessment. Neuro-Orthopedics 5:59-66, 1988 Gattuso JM, Glasby MA, Gschmeissner SE: Recovery of peripheral nerves after surgical repair with treated muscle

grafts. (2) Morphometric assessment. Neuro-Orthopedics, 6:l-6, 1988 Gattuso JM, Glasby MA, Gschmeissner SE, Norris RW: A comparison of immediate and delayed repair of peripheral nerves using freeze-thawed autologous skeletal muscle grafts in the rat. Br J Plast Surg 42:306-313, 1989 Glasby MA, Evans S, Huang CL-H: Nerve regeneration through treated muscle grafts during experimental treatment with antileprotic drugs. Neuro-Orthopedics 8:l-7, 1989 Gschmeissner SE, Gattuso JM, Glasby MA: The morphology of nerve fibres regenerating through freeze-thawed autologous skeletal muscle grafts in rats. Clin Anat 3:107-119, 1990 Glasby MA, Gilmour JA, Gschmeissner SE, Hems TEJ, Myles LM: The repair of large peripheral nerves using skeletal muscle autografts. A comparison with cable grafts in the sheep femoral nerve. Br J Plast Surg 43:169-178, 1990 Simpson SA, Young JZ: Regeneration of fibre diameter after cross-union of visceral and somatic nerves. J Anat 79:48-65, 1945 Berry C, Hinsey JC: The recovery of diameter and impulse conduction in regenerating nerve fibres. Ann NY Acad Sci 47:559-577, 1946 Cragg BG, Thomas PK: The conduction velocity of regenerated peripheral nerve fibres. J Physiol (Lond) 171:164-175, 1964 Mackinnon SE, Hudson AR, Hunter DA, Trued S: Nerve regeneration in the rat model. Peripheral Nerve Repair Regeneration 1:41-48, 1986 Aminoff MF: Electromyo~raphyin Clinical Practice, 2nd ed. Edinburgh: Churchill Livingstone, 1987 Lenman JAR, Ritchie AE: Clinical Electron~yography,4th ed. Edinburgh: Churchill Livingstone, 1987 Gattuso JM: Some studies on peripheral nerve regeneration through freeze-thawed muscle grafts. Master of Philosophy thesis, University of London, London, 1988 Morris JH, Hudson AR, Weddell G: A study of degeneration and regeneration in the divided rat sciatic nerve based on electron microscopy Zellforsch 124:165-203, 1972

Throughout the entire period of development of the muscle grafting technique and its evaluation, the work has been most generously supported by the Sir Jules Thorn Charitable Trust. Work in progress on the facial nerve is supported by The Cunninhgham Trust, The Mason Medical Foundation, and The Royal College of Surgeons of Edinburgh. The authors would also like to thank, Dr. J.M. Gattuso, S.E. Gschmeissner, Dr. C.L-H. Huang, and Professor Lynn Myles for their continuing help and encouragement.

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FACIAL PLASTIC SURGERY Volume 8, Number 2 April 1992

New possibilities for facial nerve repair.

New Possibilities for Facial Nerve Repair The facial nerve is a very useful model for the investigation of nerve repair and regeneration in general,...
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