Preservation methods of allografts and their (lack of) influence on clinical results in partial thickness burns
Introduction
Allografts, also called homografts, are tissues or organs transplanted from a donor of the same species but of a different genetic constitution. In wound care in general, and burn care in particular, the primary types of allografts used are amnion membrane and cadaver skin.
With initial routine use dating as far back as the 1950s [1], [2], [3], [4], [5] the use of allografts is still a mainstay in the treatment of burns [6], [7].
The main indication for allografts is partial thickness burns [8], [9] where they are known to promote reepithelialisation [10], [11] and pain relief [12], [13], [14], [15]. Human allografts are also widely used for wound bed preparation [16], [17] after excision of deep dermal or full thickness burns and as an overlay over autografts in the sandwich or intermingled techniques [18], [19]. Although less commonly used than in burn care, allografts are also part of the armamentarium utilized in non-thermal trauma [20] and skin ulcer care [5], [21].
To assure reliable availability allografts are often stored in tissue banks [22]. Most commonly, glycerol and cryopreservation are used as storage and preservation methods. Both techniques have their own advantages and disadvantages but an essential difference between cryopreservation and 85% glycerol preservation is the level of viability of the preserved tissues [23], [24], [25]: glycerol preservation preserves the morphology of the cells but they are non-viable, whereas cryopreservation allows for a certain level of viability after the tissues are thawed.
Secondary analysis of the results of two surveys, conducted with 9 years separating them, on the type of allografts used in burn care indicates that cryopreservation techniques are primarily used in the United States, while most Western European burn centres prefer glycerol preservation [8], [9]. In many discussions with clinicians we largely have observed the same dichotomy. The “rest of the world” does not seem to have such a clear preference.
Those who prefer viable cells often state that the growth factors and other compounds delivered from these cells into the wound lead to superior clinical performance. Using the hypothesis that increased viability is reflected in better clinical performance, we have undertaken a review of the literature to analyse if any evidence exists that this hypothesis is, indeed, valid. We also looked at other aspects of preservation methods, such as antimicrobial and inflammatory properties that have the potential to contribute positively or negatively to healing results.
Section snippets
Methods
An extensive literature search was initiated, primarily on whether different preservation techniques used for amnion and cadaver skin lead to different clinical outcomes, with reepithelialisation speed, percentage of healing and long term results as the primary criteria.
We also searched for data on secondary aspects of preservation techniques which may have an influence on the primary outcomes, such as viability and immunogenicity of the tissues, antimicrobial properties and the potential of
Discussion and limitations
In total, 17 studies were found on partial thickness burns, treated with different types of allograft, with a total of 696 burns (Table 1).
Given that many consider allograft treatment the “golden standard [10], [11], [21], [71],” the number of published clinical trials is small. Moreover, the methodology of most of the trials was poor and outcomes studied diverse and ranging from days of hospitalization, reepithelialisation percentage and time, percentage of patients that had to undergo
Conclusion
The literature on allografts and clinical outcomes is of poor quality. The data collected in the studies are too diverse to allow for a true scientific comparison or statistical analysis. This is particularly surprising because of the existing convictions about superiority of one preservation technique over another. It is also because of these strong convictions that we felt publishing this overview was worthwhile, although we realize that the analysis of the literature itself does not follow
Conflict of interest
None declared.
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