CARTILAGE GRAFTING. By LYNDON A. PEER, M.D. Newark, N.J.

Transcription

1 CARTILAGE GRAFTING By LYNDON A. PEER, M.D. Newark, N.J. OF all buried grafts cartilage is probably the most widely used. It is unique in that it adjusts itself to almost any tissue environment, provided it is completely surrounded by nourishing host tissue,and not exposed. Unlike iliac and rib bone grafts, it survives equally well whether in contact with like tissue (cartilage) or some other tissue such as fat, muscle, or fascia. The available clinical and experimental evidence regarding the fate of the various cartilage grafts should enable a surgeon to choose rather definitely between autogenous and homogenous cartilage according to the requirements of any given case. Choice of Cartilage Type.reFresh autogenous cartilage is always the material of choice for transplantation. The cells in autogenous cartilage grafts survive transplantation as living cells i which continue to maintain and service their intercellular matrix. Occasional grafts may be partly absorbed, especially in children or in avascular transplantation sites, but the amount of absorption is less than that which occurs in homogenous grafts for a particular individual. Curiously, one notes that preserved homogenous grafts may be completely absorbed in avascular scarred sites, whereas autogenous grafts tend to remain when transplanted in the same locality at a second operation. Homogenous cartilage, either fresh or preserved, is a valuable second choice when it is not expedient to remove the patient's own cartilage (Peer, 1939, 1941, 1945). Autogenous cartilage is especially indicated in children and young adults, who have a long life expectancy and therefore require longer-lasting grafts than do elderly patients. When large amounts of cartilage are required, as in the reconstruction of both ears in young children, cadaver cartilage may be used together with as much aut0genous cartilage as can be obtained. The cells in fresh homogenous cartilage grafts survive transplantation as living cells, but the matrix is slowly absorbed by host fibroblasts and the exposed chondrocytes disappear. Clinically, preserved homogenous grafts retain their structure about as well as fresh homogenous cartilage grafts, but bank cartilage is preferred because it is more readily available. Absorption and replacement by connective tissue or bone may occur in both autogenous and homogenous cartilage grafts, but the tendency is greater in the foreign graft. Heterogenous cartilage grafts have little if any place in clinical surgery at this time. Ox cartilage preserved in merthiolate solution has been used as grafting material with varying degrees of success (Stout, 1933; Wardill and Swinney, 1947 ; Gillies and Kristensen, 1951 ; Gibson and Davis, 1953). The careful experimental studies regarding the fate of ox cartilage in human tissues by Gibson and Davis indicate that the cartilage acts as an antigen and that the intensity of a Autogenous rib, septal, and ear cartilage grafts buried up to twenty-seven years have been sectioned in the fresh unfixed state and stained with supravital dyes. The chondrocytes in all these grafts were viable cells. 25

2 CARTILAGE GRAFTING 251 the antigen-antibody reaction increases in direct proportion to the duration of the host's exposure to this foreign protein. Preserved cartilage from the giant sting ray (Peer et al.) transplanted in human tissues seems to stimulate a local cellular reaction and a possible antibody reaction in the host tissues which results in destruction of the foreign cartilage graft. In general, all foreign grafts are believed to stimulate an immune response in the host tissues, and this immune response is detrimental to the survival of various homogenous tissue grafts over different periods of time as demonstrated by Medawar (I948). Fresh homogenous grafts of cornea, lens, and cartilage resist absorption, and the cells remain viable 1 because these tissues are avascular and because their gel-like matrix is rich in mucoprotein, which serves to protect the cells from hostile host antibodies (Bacsich and Riddell, I945). Alternatively, in tissues such as homogenous skin grafts, homogenous fat grafts, and homogenous kidney transplants, which are vascular and not sufficiently protected by gel-like mucoprotein, the cells are destroyed in short periods of time presumably by the hostile host antibodies, and the graft matrix disintegrates. The heterograft, being foreign, fares even worse than the homograft (Loeb, x945). Growth of Cartilage Grafts.--Normal growth of all cartilage structures during childhood takes place from the deep layer of connective-tissue cells of the perichondrium. These cells presumably form a matrix substance about themselves, separate from the perichondrium, and become cartilage cells (appositional growth). Growth also occurs by division of cartilage cells followed by the deposition of matrix about each cell separating one from another. After adult life, cartilage ceases to grow, and there is considerable doubt concerning its powers of regeneration following injury--the cartilage wound being filled in by connective tissue associated with little, if any, new cartilage formation. Adult autogenous cartilage grafts retain their cartilaginous structure following transplantation, but usually neither increase nor decrease in size. Dupertuis in I941 demonstrated actual growth of young autogenous and homogenous cartilage grafts in rabbits, and the author (I946) reported evidence of growth in some young human autogenous cartilage grafts. Later, removal of young autogenous rib cartilage grafts buried up to seven and a half years failed to show any increase in size. One is inclined to believe that the growth factor is absent in young human cartilage grafts. At any rate it does not occur consistently and cannot be depended upon from a clinical standpoint. NASAL DEPRESSIONS Rib cartilage grafts were used by von Mangoldt in I899 to support saddle nose, and this method is still employed to-day although some surgeons prefer bone grafts. For the repair of nasal depressions it is wise to introduce the cartilage through a concealed incision made within the nasal cavity, thus avoiding a visible scar. 1 A fresh human homogenous cartilage graft which had been transplanted from an infant to a young child was sectioned in the fresh state and the cells were found to be definitely viable as evidenced by supravital dye stain. In areas where the matrix had been absorbed the cartilage cells were absent, but cells protected only by a thin layer of matrix were living cells. Pre-operative and post-operative measurements demonstrated that the graft was reduced in bulk. The graft was removed four years after transplantation.

3 252 BRITISH JOURNAL OF PLASTIC SURGERY If autogenous cartilage, which is the best grafting material, is to be used, the surgeon should bear in mind that any kind of autogenous cartilage may be utilised. When the defect is small, septal cartilage, ear cartilage, and alar cartilage are readily available. Rather deep depressions in the nose can be adequately filled with a composite graft consisting of several segments of septal cartilage capped with a rather broad alar cartilage graft. The alar cartilage bends convexly in conforming to the tension of the nasal skin and thus serves adequately as a smooth covering for the top and sides of the composite graft. Septal bone (Peer, I95I) may be used to supplement the septal cartilage when additional bulk is required, or septal bone capped with alar cartilage can be employed when septal cartilage is absent. ~B FIG. I Saddle depression in lower nose. A, Drawing shows moderate saddle depression of lower nose. B, Two segments of septal cartilage are placed one on top of the other, and this composite graft is shaped to fit the contour of its base. It is often advantageous to cap the outer septal graft with a thin malleable alar cartilage graft. Septal bone may be used in place of septal cartilage when the latter is not available. C, Composite graft in place, restoring dorsal line of nose. Alar cartilage in single or multiple layers may be used to restore the dorsai line of the nose when too much nasal bone or septal cartilage has been removed during a rhinoplasty. Because of its thinness and flexibility Mar cartilage is an excellent grafting material for restoring the contour of the nostril in secondary rhinoplasties to correct the pinched-in depression at the side due to excessive removal of alar cartilage at the time of the original operation. Flattened areas at or above the nasal tip and clefts in the columella may also be repaired with this thin malleable type of cartilage, which always seems to adjust itself to the tension of the nasal skin and to provide an even, soft contour. Occasionally one sees nasal fractures with depressions on one or both sides of the nose just below the bony arch. This is due to separation of the lateral cartilage from its normal attachment to the nasal bone. Such depressions can be nicely filled with an alar cartilage graft. Fortunately it is nearly always possible to remove the posterior three-fourths of an alar cartilage without producing any deformity at the nasal tip. Consequently

4 CARTILAGE GRAFTING 253 this area may be regarded as a donor site for alar cartilage, as the ribs provide rib cartilage and the nasal septum septal cartilage. Use of Rib Cartilage Graft.--Deep saddle depression in the nose can be repaired by rib cartilage, which is available in sufficient bulk to fill the cavity adequately. There are several points in the technique of employing rib cartilage grafts for nasal depressions that are sufficiently important to mention. In the first place it is essential to shape the graft so that it conforms evenly with the contour of the tissues on which it rests. A straight piece of rib inserted like a beam of wood is bound to become distorted, due to numerous dead spaces between the surface of the graft and the tissues beneath. Furthermore, this straight beam of cartilage will give a stiff unnatural appearance to the nose and elevate the alar cartilages so that a beak effect is produced at the nasal tip. After the cartilage has been shaped so that it fits snugly, conforming to basal contour lines, the upper portions of the graft resting on the bony bridge should be cross-cut in numerous places to prevent upward or lateral curl of the cartilage post-operatively. If there is a tendency to prominence above the nasal tip, the graft should be shortened or the posterior portions of the alar cartilages should be removed as in rhinoplasty. When a cartilage strut is required in the columella to support the nasal tip it should be inserted through a separate incision in the buccal mucous membrane in such a manner that this columellar graft lies in front of the dorsal beam of rib cartilage. This positioning will nearly always provide a more normal appearing nasal tip than the accepted procedure of inserting the columeuar strut under the dorsal beam of the cartilage. If the columella is retracted the base of the columellar graft can be brought downward and held in place by a catgut suture fixing it to the maxillary bone in front of the nasal spine. If the columella is excessively retracted and bound down by scar tissue the surgeon can obtain relaxation by widely elevating the mucous membrane flaps on each side of the nasal septum so that the graft in the columeua can be brought downward. In severe cases of retracted columella it may be necessary to make relaxing incisions through each elevated mucous membrane flap. The columella must be at a lower level than the free border of each nostril to avoid the appearance of a snub nose, which often occurs after excessive removal of the septal cartilage in rhinoplasty. Incisions in the skin surface of the columella through which a rib graft may be inserted are not advisable because of external scarring. OTHER FACIAL CORRECTIONS Rib cartilage grafts are used also to elevate the depressed nostril floor often seen in wide unilateral harelip, to build out the contour of the jaw bone in atrophy of the face, and to restore the contour of the malar bone, zygoma, and bony brow. One or several segments of rib cartilage can be employed to elevate the eye when it has prolapsed downward due to a depressed fracture of the bony orbital floor. This elevation of the eye will often lessen the distressing double vision with which such patients are afflicted. Further improvement may be obtained by the use of prism lenses. Retruding chin can usually be corrected by inserting cartilage grafts over the bone to increase the prominence of the chin. Small degrees of recession can be

5 254 BRITISH JOURNAL OF PLASTIC SURGERY A B C D E and F FIG. 2 Saddle depression with traction of columella. A, Deep saddle nose deformity with snub tip due to excessive removal of the lower free border of the septal cartilage. B, Front view showing extreme retraction of the columella due to the absence of septal cartilage support. C, An incision,has been made through the buccal mucous membrane and a pocket formed in the columella up to the nasal tip. D, A segment of cartilage from the patient's chest is inserted through the buccal opening into the colttmellar pocket. The base of this cartilage graft may be sutured in front of the nasal spine to bring the cohtmella downward after wide relaxation of the mucous membrane on each side of the septal cartilage. A separate and larger cartilage graft suitably shaped is inserted through an intranasal incision to repair the saddle deformity. This graft should not be in contact with the columellar graft. E, Suture fixing base of columellar graft in front of nasal spine. F, The cartilage strut inserted through a mucous membrane incision may be utilised in young children with double harelip deformity and a short columella. At intervals additional cartilage can be inserted under the base of the strut to influence growth at the columella. The results from this procedure are encouraging and it is preferred to the columella lift which often destroys a good lip repair.

6 CARTILAGE GRAFTING 255 improved by the insertion of septal cartilage supplemented by septal bone. One should carefully evaluate the occlusion in severe cases of receding chin and have a consultation with an orthodontist to determine the advisability of setting the jaw forward rather than merely adding to the prominence of the chin. After the lower jaw has been set forward as far as possible to obtain better occlusion, the remaining degree of receding chin can be corrected by inserting cartilage to give additional prominence. In ankylosis of the jaw the ascending ramus is often rather short, and removal of a segment of bone to provide a false joint produces further shortening. A segment of cartilage about the size of the removed bone may be inserted between the detached upper and lower bony segments to prevent shortening of the ramus. If the cartilage graft is sufficiently large the length of the ramus may be actually increased, as suggested by Dufourmentel and Darcissac (I935). Braithwaite and Hopper (I952) have used preserved ox cartilage for this purpose. In general, one feels that cartilage as an onlay graft tends to retain its bulk and contour better than rib and iliac bone. Bone grafts inserted between severed bony segments to restore continuity and function, especially where there is movement as in the jaw, or movement and weight-bearing as in the tibia, appear to retain their structure quite well. When rib and iliac bone grafts are applied as simple onlay grafts in contact with the jaw to restore contour and in the brow or skull to build out depressions, the grafts often are gradually reduced in size. Contrariwise, for saddle depressions in the nose, bone grafts from the rib and ilium appear to retain their general bulk effectively according to the surgeons who have used them for this purpose (Carter, 1932 ; Mowlem, I94I), even though the grafts are not in actual contact with the nasal bones. Rib and iliac bone grafts not in contact with bone elsewhere in the body are absorbed and replaced by fibrous tissue. Thus it appears that the nasal tissues constitute a specially favourable transplantation site. DICED CARTILAGE GRAFTS Diced cartilage grafts (Peer, I943), as the name suggests, consist of numerous small segments of cartilage which can be packed or moulded into any desired contour like wet grains of sand. The term _" diced" is descriptive because in early cases the grafts were obtained by pinning a rib cartilage segment to a wooden block, making linear cuts in the cartilage, and then cross-cutting the rib, much as a cook dices carrots in preparing a salad. In practice, however, the small segments were used in the form of flat shavings rather than cubes, because the thin shavings pack together without presenting sharp comers, which may produce a prominence beneath the overlying skin. Use in SkuU.--Diced cartilage grafts were first used by the author in skull depressions, the multiple segments being introduced in the cavity and gently patted in a rounded contour. The scalp skin was then sutured over the rounded surface of the cartilage mass. This method provides a smooth, even contour and is so simple in execution that in the hands of a good operating team, with good operative assistance, a large depression in the frontal region can be repaired in an hour (Fig. 3).

7 256 BRITISH JOURNAL OF PLASTIC SURGERY Microscopic examination of the diced cartilage grafts following transplantation at various intervals up to four years has been made. The sections demonstrated that the spaces between the small cartilage segments were occupied first by blood and later by ingrowing connective tissue accompanied by numerous small blood-vessels. Each small cartilage graft rested against adjoining cartilage at some A ~ B C I3 E 0~,~.~ FIG. 3 Skull depression. A, Drawing represents patient with deep depression in frontal area, the skin and scar lying directly over the dura. B, Scalp skin elevated exposing defect in bone. The brain pulsates beneath the covering of dura and scar tissue. C, Pieces of rib cartilage removed from right side of patient's chest are diced into many fine segments. D, The diced cartilage grafts are introduced over the exposed dura with a spoon. E~ The mass of diced cartilage grafts is patted into a smooth, even contour like wet grains of sand. F, The inverted T-incision is sutured over the rounded mass of diced cartilage grafts. G, Cross-sectional view of defect. H~ Cross-sectional view of defect with diced cartilage grafts in place.

8 CARTILAGE GRAFTING 257 points (with a thin layer of connective tissue between), thus preventing contracture of the cartilage mass. The bulk of the diced cartilage grafts collectively was increased by the addition of the numerous small spaces between the cartilage, and for this reason the diced cartilage grafts actually filled a larger space than the solid rib cartilage from which they were cut. Autogenous diced cartilage grafts had living chondrocytes, normal-appearing matrix with occasional bone formation in or outside the grafts, and a general absence of invasion and absorption. Preserved diced cartilage grafts showed definite invasion and absorption in some grafts, whereas in others the matrix, with dead ceils, appeared to resist invasion quite well. The tendency to bone formation was more pronounced in the preserved cartilage than in the autogenous cartilage. Diced cartilage grafts, in the author's opinion, have a field of usefulness in repairing depressions in the frontal region of the skull which is equal to any other method in use at the present time. From a theoretical standpoint the effectiveness of bone grafts should be greater than that of cartilage, since in using bone the surgeon is replacing an absent tissue with a similar one. Late examination of skull depressions repaired with iliac bone demonstrates considerable absorption in some cases, but the reduced bone grafts appear to have bony contact with margins of the skull bone and thus provide protection for the brain. Some neurosurgeons hold that autogenous grafts of skull bone do not make bony contact with the adjacent skull bone of the host when used as free grafts. Gilbert Horrax of the Lahey Clinic believes that only a fibrous union occurs in such cases. Tantalum plates and other foreign bodies have a field of usefulness in elderly patients with skull defects and in cancerous patients with doubtful prognosis. Diced preserved cadaver cartilage grafts rather than autogenous cartilage may be employed as a substitute for metallic foreign-body implants when the prognosis is doubtful. Other Uses in Facial Region.--Diced cartilage grafts have also been used to repair mastoid fistula, to build out the prominence of the malar bone to correct receding chin, and, indeed, to restore contour in any bony deficiency of the face as a substitute for bone grafts. Grafts of this type packed in a perforated vitallium mould will conform to the shape of the mould like wet sand in a sand mould (Peer, 1943, 1944, 1948). When a perforated ear mould is filled with cartilage segments and buried beneath the patient's abdominal skin, connective tissue and blood-vessels grow through the openings in the mould. In situ they nourish the cartilage and fasten the separate segments together in a solid plaque. If the mould remains in place for about five months the plaque will be bound together by mature connective tissue with tough collagenous fibres, so that the cartilage can be removed from the mould as a solid ear structure. This cartilage framework may be inserted beneath the skin in the region of an absent ear to form the structural support for a new auricle (Fig. 4). It is interesting to note that the cartilage plaque is entirely autogenous, being composed of the patient's own cartilage, which is bound together by autogenous connective tissue and supplied by autogenous blood-vessels. The cells and matrix of the cartilage, the connective tissue, and many of the blood-vessels survive this free transplantation, and a new blood-vessel supply arises mainly through end-to-end anastomosis between severed blood-vessels in the host bed and those 3 8

9 258 BRITISH JOURNAL OF PLASTIC SURGERY in the graft. Some new penetrating capillary growth occurs from the host vessels into the substance of the graft connective tissue. Probably this new penetrating capillary growth later connects with the surviving vascular system of the graft. A B C Fro. # Removal of diced cartilage ear from mould and transplantation in ear region. A, Diced cartilage grafts have been placed in a perforated vitallium ear mould, and the mould with its content of cartilage buried beneath a patient's abdominal skin. When the mould is removed five months later and the two halves of the mould separated, the cartilage will be removed in the form of a firm ear structure. Be The diced cartilage ear framework is inserted in a previously delayed pocket beneath the skin in the ear region. The framework is about I in. higher than the normal ear to allow for subsequent sagging. C, The wound edges are sutured and a firm dressing is applied to press the skin against the cartilage framework. A drain may be inserted in the lower angle of the wound. The drain is removed after forty-eight hours without disturbing the firm dressing holding the skin against the cartilage.

10 CARTILAGE GRAFTING 259 Diced Cartilage Grafts in Other Surgical Fields.--The extreme malleability of diced cartilage grafts and the conformity of the small segments to a perforated mould of any desired shape led the author to suggest their use to a number of surgical colleagues at St Barnabas Hospital. Dr John Flanagan of Newark became interested in the idea and designed perforated vitallium mould in the shape of a thin concave-convex disc which might be employed on the ear-mould principle to form a new articular surface of cartilage. If inserted over the head of the femur the cartilage disc might permit FIG. 5 Ankylosis of hip joint. A, Following the ear-mould principle shown in Fig. 4, diced cartilage has been placed in a perforated vitallium mould designed to form a concave-convex disc and the mould buried beneath the abdominal skin. When the mould is removed five months later the diced cartilage segments are formed in the shape of a cartilage cap. B and C, Different views showing configuration of cartilage cap. D, Cartilage cap sutured over exposed head of femur to form a smooth articulating surface. E, Head of femur covered with cartilage cap is placed in contact with socket. movement in ankylosis of the hip joint. The vitallium mould i was filled with diced segments of a patient's rib cartilage and buried beneath the abdominal skin, When the mould was removed after a period of four months, the cartilage segments were firmly bound together in the form of a thin cartilage cap. With the cap inserted as a cover for the head of the femur, the patient at the present time---twenty months after the operation--is walking and weight-bearing about as well as if a vitallium cap had been used (Fig. 5). Dr George Simms of Rutherford, New Jersey, has successfully used diced cartilage to reinforce the fascia in recurrent ventral and inguinal hernia. One of his patients with a large ventral herniation had a recurrence of the hernia following operative repair with a dermagraft. At a second operation diced cadaver cartilage grafts from the cartilage bank were introduced over the surface of the thin muscle fascia and in some areas directly over the peritoneum. The subcutaneous tissue i Made by the Austenal Company of New York City.

11 260 BRITISH JOURNAL OF PLASTIC SURGERY and abdominal skin were then sutured over the diced cartilage grafts and a firm pressure dressing applied. The diced cartilage grafts became bound together by connective tissue in the form of a large pancake-like plaque, which served as an internal or buried truss. The patient had no recurrence of this large ventral hernia two years after operation. With.the assistance of the author, Dr Henry Brodkin of Newark built up several new ribs to protect the heart in patients who had had extensive removal FIG. 6 Defect in chest cage. A, Defect in left side of chest cage exposing the heart, which pulsates visibly beneath the skin and scar covering. B, A cylinder of tantalum or stainless-steel wire mesh is filled with diced cadaver cartilage grafts. It is wise to make additional large openings in the mesh to permit the free entrance of host connective tissue and blood-vessels. C, Three wire meshes filled with diced cartilage grafts are fastened to intact rib cartilages in a vertical direction to bridge the defect. The skin incision is sutured and a firm pressure dressing applied. of the cartilage. This was accomplished by introducing diced cadaver cartilage grafts in tantalum mesh and fastening the open ends of the mesh with a pursestring wire suture to retain the mass of cartilage segments within the mesh. The tantalum mesh with its content of cartilage was sutured to the sternum at one end and to the posterior rib segments horizontally at the other end, or, in some instances, in a vertical direction so as to bridge the defect in the chest cage. Connective tissue grew through the openings in the mesh and bound the cartilage segments together in the form of a solid rib structure, which served to give support for the soft tissues of the chest and to provide protection for the heart (Fig. 6). In collaboration with Dr Robert Green of South Orange, New Jersey, diced cartilage has been used for filling large bony defects in infants with spina bifida.

12 CARTILAGE GRAFTING 261 The method is indicated particularly in patients with a large cord herniation, associated with an extensive bony defect and insufficient fascia, muscle, and skin for adequate closure and coverage. Double pedicle skin flaps are elevated at the sides and resutured in place to allow adequate blood supply to develop in the flaps. Two weeks later the thin skin covering the herniation is removed, the cord elements are reduced, and the best possible closure is obtained by suturing fascia and muscle over the bony defect. Diced cadaver cartilage grafts are then introduced over the fascia and muscle and sometimes directly over the cord content. A sheet of tantalum or stainless steel screen may be sutured over the defect to keep the diced cartilage grafts out of the spinal cord opening when fascia and muscle closure is inadequate. The lateral skin flaps are then elevated and sutured to cover the plaque of the grafts. If the child does not die from hydrocephalus or meningitis, the diced cartilage grafts will become bound together by fibrous tissue and the solid plaque will prevent a herniation of nerve elements from the spinal cord. SUMMARY I. Autogenous cartilage is always the tissue of choice for grafting purposes. Preserved or fresh homogenous cartilage grafts are a valuable second choice; and heterogenous cartilage from the 0x, sting ray, or shark should be considered only when homogenous cartilage is not available--if it should be considered at all. 2. The reason for the long survival time of the cells in fresh homogenous cartilage grafts is quite possibly the protective nature of the gel-like matrix, which prevents the entry of host antibodies. A similar mucoprotein is present in cornea and lens (Bacsich and Riddell, 1945) and in the capsules of pneumococci (Wyburn, 1949). 3. In humans there is good evidence that young cartilage grafts do not grow or increase in size after transplantation regardless of the presence or absence of perichondrium. 4. Attention is called to the advantages of introducing a cartilage strut through an incision in the buccal mucous membrane for support of the nasal tip in saddle nose deformity. This strut, which can also be used to correct retraction of the columella, should be located in front of the beam of cartilage supporting the dorsal line of the nose. 5. Diced cartilage grafts have a wide clinical field of application. Their successful use is dependent on a simple physiological theory or law : connectivetissue cells abhor unlined and. artificial dead spaces in the body as nature abhors a vacuum. The numerous dead spaces between the diced cartilage segments are occupied by fibroblasts, and these fibroblasts elaborate collagenous fibres and cement substance which serve to bind the cartilage grafts together in the form of a solid plaque. 6. The clinical use of ox cartilage by Gillies and others is not criticised in this paper ; Gillies, who may be aptly called the father of modern plastic surgery, has forced plastic surgeons to consider the merits of the cartilage heterograft and to produce evidence against its use. One should not ignore the possibility that future discoveries may reveal some way to render the cartilage heterograft more acceptable to human tissues.

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