SOME FURTHER OBSERVATIONS ON THE USE OF PRESERVED ANIMAL CARTILAGE

By THOMAS GIBSON, F.R.C.S.(Ed.) Plastic Surgery Unit, Ballochmyle Hospital, Ayrshire

and W. BRIAN DAVIS, B.Sc., M.D., D.P.H. Clinical Laboratories, The Victoria Infirmary, Glasgow

IN a previous paper (Gibson and Davis, 1953) we described the absorption which affects preserved ox cartilage implants and the histological processes involved. The three observations detailed below are to be regarded as an appendix to that paper rather than as a separate contribution.

i. UNUSUALLY LONG SURVIVAL OF CERTAIN BOVINE CARTILAGE IMPLANTS

In our previous communication we commented on the fact that certain block implants of bovine cartilage, as, for example, those used to support the nasal bridge, survived apparently unchanged for a much longer time than we would have expected from histological and experimental observations on the behaviour of this material. Thus Potter (1952) reported a case in which an ox cartilage graft had remained unchanged for six years, while Gillies and Kristenson (1951) illustrated a patient with a similar satisfactory implant after three and a half years. We ourselves have had one in which the patient noticed no change after four years although in the next year absorption became apparent. However, this lengthy survival is by no means a feature of every case and, with the one exception noted, our block implants have all shown signs of absorption after eighteen months.

We suggested as a possible explanation of this occasional anomalous finding the increasing avascularity of the fibrous sheath which replaced the cartilage initially absorbed. But this explanation is not very satisfying, since to be valid it assumes a degree of avascularity which rarely obtains even in old dense fibrous tissue. Recently we have removed from each of two patients a block implant which showed no evidence of surface absorption after twenty and twenty-eight months respectively. Each implant was surrounded by a capsule which was smooth and glistening on the surface adjacent to the cartilage. The histological appearances of these capsules were quite unexpected and shed new light on the problem.

The details of the two patients are as follows : - -

CASE REPORTS

Case i , a male aged 19 years, had a mandibular deformity due to ankylosis of the right temporomandibular joint. The ankylosis had been corrected and the bony asymmetry was suitable for an onlay bone graft, but it was decided to delay this until final ossification of his iliac crests had occurred. The patient was so self-conscious about his deformity, however, that a large block implant of bovine cartilage was inserted as a temporary support. This block was in contact with the outer surface of the mandible

2 A 8 5

86 BRITISH JOURNAL OF PLASTIC SURGERY

and was held in place by the overlying soft tissues. Twenty months later his iliac crests had ossified and he was readmitted to have the definitive bone graft. When the cartilage implant was exposed i t was surrounded by a capsule which was quite tmattached to the cartilage, had a smooth lining, and contained no free fluid.

When most of this had been excised for s tudy (Fig. I) the cartilage was found to be fixed to the mandible from which a bony outgrowth had penetrated deeply into its substance. This is discussed more fully below (Part 3). Apar t from this area of invasion by bone the cartilage seemed unchanged; i n d e e d t h e surface appeared as i f it had been freshly carved for insertion.

Case 2, a male aged 18 years, had bilateral ankylosis of the temporomandibular joint when first seen. The condylar neck on each side was divided and discs of

FIG. i bovine cartilage about 0"5 cm. thick were inserted The excised capsule from Case I. between the cut bone ends. Post-operatively a hmma- The tissue has shrunk and become toma requiring repeated aspiration developed on the folded upon itself during fixation right side ; subsequently the cartilage prolapsed slightly so that the inner surface is now convex. The smooth even nature so that the edge could be felt and seen just underneath

of the lining is evident. × 1'5. the skin. A free range of movement was~ however, maintained. T h e prolapsed piece of cartilage proved

to be an annoyance to the patient when shaving, and it was removed under local

FIG. 2 The lining of the capsule from Case 2 demonstrating the striking resemblance to an epithelial layer. (Masson-

Goldner trichrome.) × I70.

anmsthesia twenty-eight months after its insertion. By then it was considered to have fulfilled its function in promoting the formation of a false joint. At operation it was

SOME FURTHER OBSERVATIONS ON THE USE OF PRESERVED ANIMAL CARTILAGE 87

FiG. 3

A higher magnification of the same section as Fig. 2 to show the irregularity of the nuclei, the absence of basement membrane, and the small masses of

collagen lying between the cells, x 5o0.

FIG. 4

The lining of an infected adventitious bursa. The similarity in appearance to the capsule in Fig. 2 is obvious. (Masson-Goldner trichrome.) x 17o.

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found to be lying completely free in a capsule exactly similar to that described in Case Io The cartilage itself showed no obvious sign of absorption or of surface erosion.

Numerous sections were prepared from different parts of each capsule. Since the histological appearances in each case were precisely similar, the following description applies to both. At first sight the lining membrane appeared to consist of epithelial cells of a columnar or cuboidal type (Fig. 2). Under a higher power (Fig. 3) it can be seen, however, that there is a considerable variation in size, shape, and orientation of the nuclei, that there is no basement membrane, and that small collagenous masses are scattered amongst the cells. In fact this lining membrane appears to be composed of fibroblasts arranged in a pseudo-epithelial layer. The similarity to the " mesenchymal epi the l ium" of a bursa (Fig. 4) is striking.

As a control to Cases I and 2 we were fortunate in having three other patients, all of whom had block implants o f preserved animal cartilage inserted to support the nasal bridge. In each case absorption of the implant was so extensive that it no longer fulfilled its function although some cartilage was still palpable. The main clinical details are given in the accompanying table.

Case. Age.

17

12

19

Source of Block

Implant.

Bovine

Pig

Bovine

Duration.

I5 months

x7months

25mon ths

In all three a second operation was performed in order to insert a more permanent type of implant. The remaining cartilage was found to be firmly fixed to the surrounding tissues, and an attempt was made to remove some of these together with the cartilage. Unfortunately, because of the difficulty of access, this had to be done piecemeal, but sufficient of the " c a p s u l e " was obtained in each case to give a representative picture.

This material was examined by serial section as were also any pieces of cartilage which had soft tissue still adhering to them. No trace of any lining membrane like the pseudo-epithelial layer in Cases I and 2 was seen, but in one piece of cartilage from Case 4 (Fig. 5) there were several areas in which groups of fibroblasts of a similar kind were present but these were arranged in quite haphazard fashion.

As an additional control we have had the opportunity of examining part of the fibrous sheath which developed around an acrylic plate that had been used two years previously to repair a skull defect in a child of 5 years. There was no trace of any lining membrane such as we have described and it would appear, therefore, that such a formation is not due simply to the presence of smooth foreign material.

D i seuss ion . - -We have now examined histologically more than sixty implants of bovine and other animal cartilage of different shapes and sizes after various

sOME FURTHER OBSERVATIONS ON THE USE OF PRESERVED ANIMAL CARTILAGE 8 9

intervals. Cases I and 2 detailed above are the only ones in which we have seen either (a) the cartilage apparently unchanged after a period of twenty months or more, or (b) the type of capsule described. Cases 3, 4, and 5, which were comparable in so far as they were block implants of preserved cartilage and had been in contact with the tissues for a similar length of time, differed in showing marked absorption and no mesenchymal lining of the surrounding tissue. It seems reasonable to suppose, therefore, that these facts are related and that the lack of absorption in Cases I and 2 was due to the formation of this peculiar lining membrane, or more probably that both were the result of some third factor.

FIG. 5 Case 4. An area of fibroblastic rep lacement in the r emnan t s o f a nasal implan t o f preserved pig cartilage, which, because o f absorpt ion, was removed seventeen m o n t h s after insert ion. T h e cells are similar to those of the linin.g i l lustrated in Fig. 3, a l though thei r disposit ion is qui te irregular. ( M a s s o n - G o l d n e r

t r ichrome.) × 400.

This factor, we believe, might be frequent movement in the soft tissues around the implant. In Cases x and 2 such a factor undoubtedly existed, while in Cases 3, 4, and 5 it was probably absent. It is plausible that such tissue movement might prevent the fibroblasts from invading the cartilage, and could also lead to the formation of such a capsule in much the same way as an adventitious bursa is formed; the similarity in structure, shown in Figs. 2, 3, and 4, lends weight to this suggestion. One can readily visualise that if a group of fibroblasts such as those shown in Fig. 5 were detached from the cartilage by movement of the .surrounding soft tissues they might easily come to resemble the lining shown in Figs. 2 and 3. It must be allowed that the cases of long survival of block implants quoted previously were nasal implants in which movement is not an

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obvious feature. It may be that in such instances the patient either has a well- developed nasal musculature or is in the habit of handling the implant.

Whatever the explanation of this phenomenon may be it is obviously of considerable clinical importance. There seems little reason to doubt that a similar kind of capsule could form, for instance, with other varieties of preserved cartilage or even with a living autogenous graft which failed to " take." Capsular formation helps to explain the discrepancies between the undoubted absorption of such implants which is found in histological and experimental studies and its apparent absence in occasional patients. Again, the interesting possibility arises that it might prolong their survival period if patients were advised to " massage" the implant regularly.

2. THE USE OF PRESERVED PIG AND SHEEP CARTILAGE

Our experiments with bovine cartilage implants showed that when successive implants are made the host develops an increasing response to the material. It was believed that this reaction was specific at least for preserved cartilage, and there was also some evidence to suggest a similar specificity for different batches of ox cartilage. It was apparent, therefore, that in a patient in whom such an implant had absorbed, and where it was desirable to carry out a second implant, bovine cartilage should not be used since it would be liable to be absorbed more rapidly than the first. As an alternative to ox cartilage it was thought that material from the pig or sheep might be used in such cases. Armour Laboratories have kindly supplied us with samples of pig and sheep cartilage, preserved and stored in the same way as their bovine material.

To test the specificity of this reaction, the first experimental implants were made on a patient who had previously shown a very intense reaction to bovine cartilage (Case I : Gibson and Davis, 1953). He had a series of four very massive clinical implants of diced bovine cartilage in I949-5o, and an experimental implant made at the end of that time showed microscopically the most intense reaction that we have seen. In a further implant made one year later the activity of the reaction was practically unchanged. In 1953, two and a half years later, a series of experimental implants were made subcutaneously at the costal margin. These included one of pig and one of sheep and two controls of bovine cartilage ; of the latter, one was material supplied by Armour Laboratories, the other was prepared by ourselves.

When the implants were excised two and a half months later it was found that the microscopical appearances of all were similar ; the degree of reaction was that which we associate with a " first implant." The controls of bovine cartilage showed none of the intense reaction which had been apparent two or three years before: either the host's response had subsided or it was not active against the two batches used. This experiment was repeated, using two different batches of bovine cartilage, but since the reaction in the various samples was again of the same order no comment as to specificity can be made. A problem of this sort is more readily resolved if animals are used and our colleague Dr J. H. Cooper is proceeding with this work.

We have, however, made a total of three experimental implants of pig cartilage and four of sheep in the human subject to determine whether the microscopical appearances differ significantly from those of bovine cartilage; typical examples

soME FURTHER OBSERVATIONS ON THE USE OF PRESERVED ANIMAL CARTILAGE 9I

are shown in Figs. 6 and 7. The presence of peripheral absorption of the cartilage and of fibrosis, the infiltration by round cells, and the presence of occasional giant cells are all precisely as one would expect with similar bovine cartilage implants.

FIG. 6 FIG. 7 Fig. 6.--An experimental implant of diced preserved pig cartilage removed after two and a half months. The typical surface erosion, absorption, and fibrous replacement are seen. (Masson-

Goldner trichrome.) × 22. Fig. 7.--An experimental implant of diced preserved sheep cartilage removed after two months. The appearances in this and in the preceding figure are similar to those observed with preserved

ox cartilage. (Masson-Goldner trichrome.) × 67.

3. DIRECT REPLACEMENT OF A BOVINE CARTILAGE IMPLANT WITH CANCELLOUS BONE

In Case I referred to above it was mentioned that the cartilage implant was found to be fixed to the outer surface of the mandible by a bony outgrowth which had penetrated deeply into the block. At the initial operation the periosteum had been stripped from the mandible in the usual way and the block laid against the bare bone. T h e cartilage had now to be forcibly detached from the mandible and it was then seen that the bony outgrowth was a dome-shaped mass, apparently of cancellous bone, about I cm. in diameter and up to o. 5 cm. thick ; this was removed from the mandible by means of a chisel. Fig. 8 is a photograph of the detached fragment and of the cavity it occupied.

When the sections were examined (Fig. 9) the fragment was seen to consist of bovine cartilage which had been infiltrated and partly replaced by cancellous bone. In some areas there was an at tempt at marrow formation. While there were occasional centres of fibroblastic activity, there was nothing to suggest that there had been initial fibrous replacement of the cartilage followed by ossification. The picture was one of direct replacement of the cartilage by bone. In retrospect it is unfortunate that the block of cartilage and the bony spur had been forcibly separated: more information might have been obtained i f the growing edge of the bone had been examined in situ.

While the explanation of this phenomenon forms an interesting topic for speculation we do not feel justified in propounding any hypothesis on the basis of this single instance and merely record its occurrence. I t is a matter, however,

9 2 BRITISH JOURNAL OF PLASTIC SURGER.

of some importance, since if it could be expected to occur with regularity preserve~ cartilage implants might prove of more permanent value.

FIG. 9 Case I. A section of the bony outgrowth shows recognisable areas of bovine cartilage in the cancellous

bone. (Masson-Goldner trichrome.) × 5 6.

FIG. 8

Fig. 8.--Case I. The cavity in the cartilage implant (above) was filled by a bony outgrowth from the mandible (below). Only a portion of the whole implant is shown. × I '5.

SUMMARY

Three further observations on the behaviour of preserved animal cartilage are recorded.

I. In each of two patients a preserved ox cartilage implant was found apparently unchanged after twenty and twenty-eight months respectively. In both cases a capsule with a smooth lining had formed around the implant. The histology of this lining is described and compared with that of an adventitious bursa.

It is suggested that the capsular formation might be the result of frequent movement in the tissues around the implant. This was a feature of these cases and was absent in a control series of three similar implants which, after a corresponding period, showed marked absorption and no trace of a capsule.

2. Experimental implants of pig and sheep cartilage have shown evidence of absorption similar to that of bovine cartilage.

3. The occurrence of direct replacement of bovine cartilage by cancellous bone is reported.

We are grateful to Mr J. Scott Tough for his permission to record the cases under his care, to Mr A. Archibald for his technical assistance, and to Mr 1t. Gray for the photographs.

REFERENCES

GIBSON, T., and DAVIS, VJ. B. (I953). Brit. J. plast. Surg., 6, 4. GILLIES, H., and KRISTENSON, H. K. (I95I). Brit. J. plast. Surg., 4, 63. POTTER, J. (I952). Personal communication.