M. E. L. Leow

Assessment of Colour Differences in Silicone Hand and Digit Prostheses: Perceptible and Acceptable Thresholds for Fair and Dark Skin Shades

This study addresses the dilemma of initial clinical and social acceptance of a newly fabricated silicone prosthesis in relation to its colour match to the natural skin. This was achieved by derivation of specific colour difference thresholds defining perceptible and acceptable levels of colour sensitivity. Two separate sets of 10 fair and dark shade digit prosthesis samples were each fabricated with a stepped increase in colour difference (ΔE) against the baseline hand prosthesis. Ninety individuals with normal colour vision scores were selected as colour assessors. The colour difference of each prosthesis in the two series was evaluated visually against the baseline by the assessors, using defined scores. The thresholds for perceptible and acceptable colour difference determined in this study were ΔE = 0.8 and ΔE = 1.8 for the fair series and ΔE = 1.3 and ΔE = 2.6 for the dark series, respectively. The acceptable threshold values differed from the perceptible threshold values by ΔE = 1.0 for the fair-shade samples and ΔE = 1.3 for the dark-shade samples. This study demonstrated that subjective visual assessment is positively correlated with ΔE values computed from colorimetric measurements for both fair and dark-shade silicone samples (p<0.001). This results shows that human subjects with normal colour vision are capable of accurately assessing colour differences. These observations emphasize the importance of subjective feedback on colour by the patient, provided the latter has perfect colour-tested vision. The study also showed that human subjects were less sensitive to perceived colour differences in darker-shade than fairer-shade samples (p<0.001). This finding seems relevant in a clinical setting involving a multi-ethnic patient population.

Metamerism in aesthetic prostheses under three standard illuminants - TL84, D65 and F

This study looks at the effect of metamerism in colour-matching and the assessment of multi-layered silicone rubber finger prostheses. The aim was to identify the choice of illuminants for colour matching the prostheses that would give rise to the least metameric effect between the prostheses and the human skin or the best colour match. The prostheses were prepared and colour matched to a fair-skinned subject under 3 reference illuminants — TL84, D65, F and a combination of illuminants — TL84, D65 and F. The prostheses were then measured for colour using a spectrophotometer based on the CIE indices L∗ a∗, b∗ with each prosthesis assessed separately against the subjects index finger under the reference illuminants-TL84, D65 and F. The prostheses were also assessed by a panel of 50 observers and scored according to colour-match. Colour differences between the skin and prosthesis were measured in the illuminant under which the prostheses were prepared and then under the other reference illuminants. A relationship was obtained between the measured mean colour difference, δE∗, and the mean visual assessment score for each prosthesis. This paper points out the concerns related to the optical phenomenon of metamerism with the colour pigments used. This can affect the colour match of the prosthesis as perceived by the patient. The findings seem to suggest that this metameric colour difference can be minimised if the prosthesis is matched under a combination of lights, which were found to give the best-perceived match.

Fungal colonisation in digital silicone rubber prostheses

The fungal discolouration of silicone rubber prostheses is reported in four cases. In two of the cases, the discolouration was caused by the fungus Candida tropicalis. In the other two cases, two different fungal organisms, namely Trichoderma sp. and Scedosporium prolificans were incriminated. The non-porous silicone rubber layers create an enclosed environment in the suction cup of the prosthesis and preclude ventilation at the prosthesis-stump interface. The moisture as a result of sweat and body warmth in the stump assists fungal growth. Residual salts from the sweat, sebum from sebaceous glands and the residues from petroleum jelly (VaselineTM) applied to facilitate donning, can adhere to the surfaces of the prosthesis and provide the nutrients for fungal growth. Prolonged continuous usages of the prosthesis, the presence of sweaty palms in the users, donning the prosthesis during manual physical activities which induce perspiration, 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 caused a black discolouration and marred the aesthetic quality of the prostheses. As a preventative measure, daily immersion of the prostheses in denture cleaner such as benzalkonium chloride, or water at 60°C for 15 minutes, or decontamination with 70% alcohol is recommended. Prior cleaning to remove organic matter before decontamination is emphasised.

A technique of acrylic nail fixation in multilayered silicone finger prostheses

A technique for the secure fixation of acrylic nails in multilayered silicone finger prostheses is described. The secure fixation of the nail to the prosthesis is achieved by a method of “sandwiching” portions of the nail between the silicone layers of the prosthesis akin to the overlapping of the nail by the anatomical nail fold and nail wall. In addition the use of a cynoacrylate adhesive ensures strong surface to surface bonding.

RTV silicone elastomers in hand prosthetics: properties, applications and techniques

In this technical note, an overview of RTV (room-temperature-vulcanising) silicone elastomers is provided. The properties and applications of 3 different types of RTV silicones in producing prostheses for the hand are discussed. Vinyl polysiloxanes are excellent silicone impression materials that offer the advantages of a rapid cure, near exact duplication of fine details and ease of removal of the cured impression without permanent deformation. RTV-2 dimethyl polysiloxanes are ideal for mould-making and fabricating prostheses given their favourable qualities that range from ease of pigmentation, adjustable consistency, manageable curing rate and accuracy in recording fine details in the liquid state to excellent stain-resistance, elasticity and biodurability in the vulcanised state. RTV-1 dimethyl polysiloxanes are self-curing, readyfor-use silicones that adhere adequately well to most substrates and are useful for extrinsic hue modifications and waterproofing of the prosthesis. The basic techniques for each of these applications are also discussed. The cure-inhibition of addition-curing RTV silicones by sulphur-, tin- and nitrogen-containing contaminants and its damaging consequence is highlighted. A compilation of known contaminating agents is provided so that prior contact with these objects can be avoided when working with addition-curing silicones. The precautionary measures to prevent the problem are also outlined.

Creating a model for fabricating a partial hand glove prosthesis using the realigned casts of the contralateral digits

A method for creating a model for fabricating a partial hand glove prosthesis is described. The realigned casts of the corresponding digits of the contralateral uninjured hand were used to substitute for the lost digits on a cast of the stump. The technique allows an exact reproduction of the anatomical and fine surface details of the digits. It has the advantage of customisation, allowing a close match in the size, shape and surface characteristics of the prosthesis to that of the remaining digits of the hand.

Techniques in hand and digit prostheses.

A comprehensive range of treatments and modalities are available for the patient with an amputated digit or hand. Most centers are capable of replanting the amputated parts or of surgical reconstruction of the missing defects. If the digit is not salvageable, more demanding techniques for surgical reconstruction have been well described. Some of these include pollicization, digital transfer, pulp or other tissue transfer, tissue lengthening, joint transfers, and toe transfers. Fitting an aesthetic prosthesis is an added modality that could augment these surgical techniques or become an option, if all else fails. The indications for fitting a cosmetic prosthesis depend on how the prosthesis is perceived in terms of hand function. We have observed that fitting prostheses restores body image, which, in turn, facilitates the total rehabilitation of the patient after mutilating injuries to the hand. This article describes the techniques of making hand and digit prostheses that have been developed at our department since 1987.

Fitting very short finger stumps with silicone prosthesis: A nonsurgical method.

Background and Aim: The fitting of short finger stumps with silicone prosthesis is a challenge because of the suboptimal finger–prosthesis contact due to length and distal tapering of digital stumps. The purpose of this report was to describe and evaluate the Micropore™–polyvinyl chloride tube technique for fitting short finger stumps. Technique: For a total of 10 patients, short finger stumps were fitted using the technique. A short length of polyvinyl chloride tube, trimmed and contoured to fit, was secured on the distal stump tip with Micropore tape. The prosthesis was worn over the polyvinyl chloride tube extension. Three different fitting methods were evaluated: fitting with and without the Micropore–polyvinyl chloride tube technique, and with the use of skin adhesive on the stump. Discussion: All patients achieved a very secure prosthetic fit with the Micropore–polyvinyl chloride tube technique. No incidences of prosthesis slippage were reported at the longest follow-up of 30 months. The Micropore–polyvinyl chloride tube technique is an effective method for fitting short finger stumps. Clinical relevance The Micropore–polyvinyl chloride tube technique presents a nonsurgical method for fitting short finger stumps. It can help avert late outcomes whereby patients, after having undergone surgery to enable fitting, found they no longer need prosthesis.