The Journal of Laryngology and Otology November 1979. Vol. 93. pp. 1087-1089

Sterilization of homograft ossicles by gamma radiation By M. HOROWITZ

IN recent years considerable interest has been aroused in the sterilization of homograft material for tympanoplasty, and a variety of methods have been employed to this end. The use of any preservative material should satisfy the following criteria:— (1) It should render the tissue sterile. (2) It should preserve the morphological structure of the tissue. (3) There should preferably be no antigenicity remaining in the tissue. (4) It should maintain adaptability for clinical use. (5) It should produce no ototoxicity or inflammatory reaction in the middle ear when the graft is used. Most of the modalities in use have employed storage by liquids, though one method of freeze drying at 80°C, after sterilization with 2 per cent ethylene oxide, has been tried. This maintained a shelf-life of bone homografts, stored in vacuo, of several years (Wright, 1972). Three moist storage methods have been mainly used, namely: 70 per cent ethyl alcohol; 4 per cent formaldehyde at ph. 5-6; and Cialit, a mercurial compound, at 1:5,000 strength. Marquet (1971), for instance, prefers Cialit after fixing the material first in formaldehyde, whilst various other authors recommend 70 per cent alcohol or formaldehyde alone. The fate of the homograft in vivo, following preservation, has been widely studied. In particular antigenic property, change in molecular structure and, in the case of ossicles, any evidence of regeneration of bone in the graft. Van der Broek and Kuijpers (1974, 1976) gave a full review of the fate of tympano-ossicular homografts in rats, using the three moist storage methods already mentioned. They stated that all three solutions killed micro-organisms and rendered autolytic enzymes inactive. However, alcohol and formaldehyde affected the molecular structure of proteins, whilst Cialit destroyed nuclear structures as well as causing some disintegration of fibrous tissue. If formaldehyde was used, a lymphocytic response occurred around the graft, suggesting an immunological response. In addition, the antigenic property of the material was preserved with this compound. 1087

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M. HOROWITZ

FIG. 1 Homograft ossicle stored in plastic capsule.

The possibility of osteogenesis in ossicular homografts has also been investigated, using the property of fluorescence of new bone in ultraviolet light, after parenteral injection of tetracycline. Van der Broek and Kuijpers (1974, 1976) also add that Cialit, alcohol and freeze-drying preserve the osteogenic properties of the bone homograft. The results elsewhere have been somewhat equivocal, although Kerr and Smyth (1971) and Marquet (1971) did find evidence of osteogenesis and, according to Marquet, only in bone which had been in close contact with living periosteum. Thus, all these methods of preservation adhere to the essential criteria of sterilization of homograft ossicular material. However, they suffer from one disadvantage, in that ossicular homografts need washing in saline to remove the preservative, often up to two hours before use. The author, therefore, has used a dry method of sterilization, using gamma radiation, which would allow the ossicular homograft to be available at a moment's notice.

STERILIZATION OF HOMOGRAFT OSSICLES BY GAMMA RADIATION

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Method of sterilization

The homograft ossicles (incus and malleus) were obtained from autopsy cases, avoiding cases of known syphilis, hepatitis or malignancy. The ossicle was placed in a plastic capsule, and sealed separately in a plastic envelope. The package was then subjected to 2 million rads of Cobalt 60 gamma radiation at the Regional Medical Physics Unit at Newcastle-upon-Tyne. It was then stored ready for instant use. The initial batch was subjected to safety checks. There was no residual radiation from the ossicular material and the batch was sterile. Routine checks for sterility have subsequently been made from stored material and have been found to be satisfactory. This method has been in use by me in this department for over eight years, to my satisfaction. The ossicles were only slightly softer, were easily shaped and drilled, with little increase in brittleness. No complications have resulted in any of the patients where the material was used, in particular no infection or rejection of the graft has occurred. The amount of absorption of the bone graft has not been studied, nor has regeneration of bone. The advantages of sterilization by gamma radiation are therefore:— (1) The material remains sterile right up to the time it is needed, thus avoiding any need for pre-cleansing from the preservative. (2) No trace of gamma radiation is left in the homograft material, thus avoiding possible ototoxicity or tissue reaction. (3) The morphological structure of the bone and its facility for shaping to the requirements of the operation are maintained, as with other methods. Summary and conclusion

A dry method of sterilization is presented which, in the author's hands, over the last eight years, has proved a satisfactory, useful and reliable alternative mode of preservation of homograft ossicles. Acknowledgement

I wish to thank Dr. M. J. Day, Principal Physicist, Regional Medical Physics Unit, Newcastle-upon-Tyne, for his co-operation and help in the sterilization of the ossicular homograft material. REFERENCES KERR, A. G.( and SMYTH, G. D. L. (1911) Journal ofLaryngology and Otology, 85, 337. MARQUET, J. (1971) Journal of'Laryngology and Otology, 85,523. VAN DER BROEK, P., and KUOTERS, W. (1974) Acta Otolaryngologica (Stockholm), 77,335. VAN DER BROEK, P., and KUIJPERS, W. (1976) Journal ofLaryngology and Otology, 90,907. WRIGHT, J. L. (1972) Journal of Laryngology and Otology, 86,1. Address for reprints: M. Horowitz, Consultant E.N.T. Surgeon, North Riding Infirmary, Middlesbrough, Cleveland, England.

Sterilization of homograft ossicles by gamma radiation.

The Journal of Laryngology and Otology November 1979. Vol. 93. pp. 1087-1089 Sterilization of homograft ossicles by gamma radiation By M. HOROWITZ I...
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