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Fungal colonisation in digital silicone rubber prostheses M. E. L. LEOW*, A. K. KOUR*'****, T. J. J. INGLIS**'***, G. KUMARASINGHE*** and R. W. H. PHO*'**** *Department of Orthopaedic Surgery, The National University of Singapore, Singapore **Department of Microbiology, The National University of Singapore, Singapore ***Department of Laboratory Medicine, National University Hospital, Singapore ****Department of Hand and Reconstructive Microsurgery, National University Hospital, Singapore Abstract
is recommended. Prior cleaning to remove The fungal discolouration of silicone rubber organic matter before decontamination is prostheses is reported in four cases. In two of the cases, the discolouration was caused by the fungus Candida tropicalis. In the other two Introduction
cases, two different fungal organisms, namely Silicone elastomers are widely used in the Trichoderma sp. and Scedosporium prolificans were incriminated. The non-porous silicone prostheses. One of the problems identified with rubber layers create an enclosed environment in the use of this material is a black discolouration the suction cup of the prosthesis and preclude caused by fungal growth (Masella et al., 1975; ventilation at the prosthesis-stump interface. Makila and Hopsu-Havu, 1976; Pigno et ah, The moisture as a result of sweat and body 1994). In nasal prostheses, this has been warmth in the stump assists fungal growth. attributed to the continual exposure to moist air Residual salts from the sweat, sebum from and secretions that constantly pass through the nasal aperture. Although silicone digital petroleum jelly (Vaseline™) applied to prostheses have been prescribed to patients for facilitate donning, can adhere to the surfaces of over a decade (Pillet, 1983; Beasley, 1987; the prosthesis and provide the nutrients for Alison and McKinnon, 1992; Campbell et al., fungal growth. Prolonged continuous usages of 1992; Leow et al., 1996; Pereira et al, 1996; the prosthesis, the presence of sweaty palms in O'Farrell et al., 1996) there have been no the users, donning me prosthesis during manual reported incidences of fungal colonisation. physical activities which induce perspiration, However, the conditions associated with the use washing of hands with the prosthesis on and warm humid climatic conditions have been identified as factors predisposing the prosthesis to fungal colonisation. The fungal growth discolouration in finger prostheses for which a caused a black discolouration and marred the aesthetic quality of the prostheses. As a preventative measure, daily immersion of the Materials and methods
The authors have developed a custom-made benzalkonium chloride, or water at 60°C for 15 digital prosthesis using a silicone elastomer minutes, or decontamination with 70% alcohol (Leow et al., 1996; Pereira et al., 1996). The prostheses are made from a medical grade of silicone elastomer (Cosmedica Ltd, Newport, UK). Colour pigments (Cosmedica Ltd,
Professor Robert W. H. Pho, Department of Newport, UK) are intrinsically mixed with the Orthopaedic Surgery, The National University of silicone to match the basic colour of the Singapore, 10 Kent Ridge Crescent, Singapore 119260. Tel: (+65)7724340; Fax: (+65)7732558 patient's skin. No anti-fungal agents are incorporated. The prostheses are moulded with layers of the silicone rubber tinted to differing shades of colour, the outer layers of the prostheses which correspond with the epidermis and superficial dermis are rendered translucent while the inner layers which correspond to the inner dermis and subcutaneous tissues are rendered opaque. This is to mimic the stratified anatomy of the skin and achieve a life-like Fig 2. Another prosthesis in which the black appearance. A layer of touch-up colouration is discolouration had invaded the translucent outer layers, "sandwiched" between the layers of silicone rubber at the finger joints and nail to enhance the details and colouration at these areas. The with the black discolouration for examination hollow part of the prosthesis which corresponds under the light microscope using the xlO and with the deficit in the segment is packed with a filler material comprising a mixture of silicone examined from end to end, with particular elastomer and polystyrene beads. The contact attention to the distribution of the black surface of the silicone polystyrene core which sits snugly on the distal stump is sealed with a layer of silicone rubber to prevent moisture Laboratory investigations revealed fungal In a follow-up review of 34 cases fitted with the prostheses for over two years or more, four discolouration. Brightfield microscopy showed cases of black discolouration in the prostheses a distinct layer of mycelial growth in the caused by fungal growth were encountered sections taken through the areas affected with (Figs. 1 and 2). The discolouration was rough in texture (Fig. 1) and found to be extremely Laboratory investigations and microscopy: resistant to cleaning with 70% alcohol. Besides Various strains of bacteria were identified in the the black discolouration, the problems of wear scrapings from the affected areas of the and tear and a yellowing discolouration caused prostheses. These included Straphylococcus, Micrococcus, Corynebacterium spp., and Laboratory investigations and microscopy: Flavobacterium meningosepticum. Three fungal Scrapings were taken from the areas affected by species were isolated from all the affected the black discolouration for bacteriological and prostheses, namely Candida tropicalis, from myocological investigations. Transverse two of the cases, and Trichoderma sp. and sections were made through the areas affected Scedosporium prolificans each from the other two cases. Investigations also reveal an invasion of the inner layers of the prostheses by fungal growth. Fungal hyphae were seen forming a distinct layer in the silicone material (Fig. 3). The fungal discolouration was seen as black spots and patches on the inner surfaces of the prosthesis in contact with the stump, including the sealed surfaces of the silicone-polystyrene core. In all four cases, the patients reported it to have occurred between 10-18 months post-fitting. This progressed to cover a wider area and penetrated deeper into the material over a 3-4 week period with continued use (between 8-10 hours per day). As the outer layers of the prosthesis are translucent, the black Fig 1. An affected prosthesis showing a black discolouration became visible when the fungus discolouration caused by fungal growth on the internal penetrated through the opaque inner layers and the silicone rubber prostheses affected with a similar discolouration. The non-porous property of silicone rubber added to the conditions associated with the use of the prostheses provided the conditions of moisture, warmth and nutritional support for fungal growth. Entrapped perspiration in the suction cup prosthesis: A secure prosthetic fit created an airtight seal between the non-porous prosthesis and the stump. Doffing of the prosthesis is achieved by creating an inlet for the entry of air to diffuse the vacuum effect. This same Fig 3. A transverse section through the affected areas of requirement for a suction cup prosthetic fit has the prosthesis (shown in Fig. 2) as seen under Brightfield the disadvantage of precluding cutaneous ventilation. It not only precipitates perspiration but traps the sweat on the stump when the invaded the outer-inner layer interface. In one prosthesis is donned for extended hours. The case, the black discolouration had spread to the problem can be compounded by a humid tropical outer layers of the prosthesis causing an climate. The moisture from perspiration and body warmth of the stump provide an ideal microscopic observation revealed turfs of fungal hyphae (mycelia) invading the outer layers of observation noted in these cases was the presence the prosthesis (Fig. 3). The discolouration of a sweaty palm. This is a contributing factor in marred the aesthetic quality of the prosthesis. promoting the conditions for fungal growth. moist upon removal of the prosthesis. All nutritional support is needed to sustain fungal patients indicated perspiration in their stump as growth. These nutrients can possibly come both one of the problems they encountered with the extrinsically and intrinsically from the inside daily use of their prosthesis. No physical signs surface of the prosthesis. The authors have of fungal growth were observed on the stump in noted in this study that patches of residues any of the affected cases. There were no allergic reactions in the stump in any of the four cases. (Vaseline™) applied to facilitate donning, However, two patients experienced discomfort residual salts from sweat and sebum from the due to the surface roughness (Fig. 1) created by sebaceous secretions adhered to the inside the fungal colonisation within the suction cup. surface of the prosthesis. This provided the initial extrinsic nutritional requirements for Discussion
fungal growth to start with. It is also possible Various commensals are present in the skin. that the vaseline and sebaceous secretion are absorbed into the silicone material. This may distribution are transient and vary from time to provide the intrinsic source of nutrients which time. Their multiplication is contained under encouraged the fungus to penetrate into the normal use of the hand. However, if there is an increase in the level of moisture and warmth Of relevance was the patients' care of the with availability of nutritional support, some prostheses. Instructions on the care of the fungal species may thrive. In the silicone soft prosthesis as advised to the patients included lining (Silastic 390) of dentures, two fungus cleaning the inner surfaces of the prosthesis strains, Candida albicans and Candida daily using a cotton-bud soaked with a mild tropicalis were reported to be responsible for the black discolouration often encountered with bacterial and fungal growth, the importance of their use (Masella et ai, 1975). In this study, keeping the surfaces of the prosthesis dry was Candida tropicalis and two other fungal species, namely, Trichoderma sp. and Scedosporium prolificans were incriminated in prescribing a silicone rubber prosthesis to prevent fungal growth. Masella and coworkers (1975) showed that daily immersion of the ALISON A, MACKINNON SE (1992). Evaluation of digital dental prostheses in benzalkonium chloride prostheses. J Hand Surg 17A, 923-926.
(Zephiran, Winthrop Laboratories, New York), BEASLEY RW (1987). Hand and finger prostheses. or water at 60°C for 15 minutes was found to be JHandSurg 12A, 144-147.
an effective measure to prevent the growth of CAMPBELL GS, GOW D, HOOPER G (1992). Low cost the Candida albicans and Candida tropicalis in cosmetic hand prostheses. J Hand Surg 17B, 201-203.
silicone lining on dentures. Since the black discolouration in the finger prostheses of the LEOW EL, KOUR AK, PEREIRA BP, PHO RWH (1996). Colour-matching in hand and finger prostheses: the above patients was caused by fungal invasion, a Asian perspective. Hand Surg (Asia Pacific) 1, 37-43. similar preventive measure could be adopted. Cleaning the inner surfaces of the prosthesis is MAKILA E, HOPSU-HAVU VK (1976). Mycotic growth and soft denture lining materials. Acta Odont Scand important to remove dirt and grease before immersing in a disinfectant, or before applying 70% alcohol for decontamination. Pigno et ah, MASELLA RP, DOLAN CT, LANEY WR (1975). The prevention of the growth of Candida on silastic 390 (1994) also found that using an antifungal agent soft liner for dentures. J Prosthet Dent 33, 250-257. (Clotrimazole) incorporated into the silicone O'FARRELL DA, MONTELLA BJ, BAHOR JL, LEVIN LS rubber elastomer was effective in inhibiting the (1996). Long-term follow-up of 50 Duke silicone growth of fungus in vitro. However, the clinical prosthetic fingers. J Hand Surg 21B, 696-700.
application and long term results were not PEREIRA BP, KOUR AK, LEOW EL, PHO RWH (1996). Benefits and use of a digital prostheses. J Hand Surg
21A, 222-228.
Acknowledgements
PIGNO MA, GOLDSCHMIDT MC, LEMON JC (1994). The efficacy of antifungal agents incorporated into a facial prosthetic silicone elastomer. J Prosthet Dent 71, 295
financial support provided by the National Science and Technology Board through two PILLET J (1983). Esthetic hand prostheses. J Hand Surg

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