The Tensile Reduction Effects of Silicone Gel Sheeting

Sir: Despite the widespread use of the silicone gel sheet for the treatment of hypertrophic scars and keloids, its mechanism of action remains undetermined. In addition, there is no single hypothesis that can explain why it does not have a positive effect on all scars. In this article, we focus on the tensile reduction effects of silicone gel sheet on scars by performing visual analysis in a finite element study. The geometry of keloids, normal skin, fat, and silicone gel sheet structures were reproduced using DISCUS software (DISCUS Software Co., Columbus, Ohio). The contours were transferred to ADINA analytical software (ADINA R & D, Inc., Watertown, Mass.) to rebuild the volumes and mesh them. Moreover, we tested the various properties of gel sheets such as hardness and thickness to determine which were the most appropriate for reducing the tension around scars. Silicone gel sheet was effective in reducing the tension at the border between the scar and normal skin, although additional tension was produced on the normal skin under the lateral edge of the silicone gel sheet (Fig. 1). The silicone gel sheet transferred the tension from the border of scars to the lateral edge of the silicone gel sheet. Moreover, silicone gel sheet with the hardness of normal skin (normal skin hardness, 1) or more was the most effective. However, silicone gel sheet with hardness greater than normal skin produced more side effects, such as dermatitis, desquamation, itching, and erythema. Furthermore, silicone gel sheet with the thickness between normal skin and half of that was the most effective when side effects were considered (Fig. 2).Fig. 1.: The standard scar model and the silicone gel sheet applied model. The normal model (above) indicates high stretching tension, as indicated by the red and yellow coloring, around the border between the scar and normal skin (keloid stress). However, in the silicone gel sheet model (below), there are no red or yellow triangular elements around the border. In addition, stress changes in the triangular element of normal skin under the edge of the silicone gel sheet were observed (skin stress). This may be one of the causes of contact dermatitis or desquamation of normal skin observed after long silicone gel sheet use.Fig. 2.: Graph showing the stress change around the border between the scar and normal skin and around the border between the silicone gel sheet (SGS) and normal skin as a function of sheet hardness and thickness. The maximum stress around the border between the scar and normal skin remained nearly unchanged with hardness between 1 and 2 (normal skin hardness, 1). This indicates that silicone gel sheet hardness of normal skin would be sufficient to diminish the stress change at the border. Softer silicone gel sheet was weaker in diminishing the stress (bold blue line). The stress change in the triangular element at the edge of the scar and normal skin is inversely proportional to sheet thickness (bold red line). It was notable that very thin dressing, such as a polyurethane film, did not produce a dynamic effect, and harder and thicker silicone gel sheet produced more stress in normal skin.Clinically, we use silicone gel sheet that is slightly wider than the scar area. It is known that a silicone gel sheet shorter than the scar area is not effective. This use may agree with our results in the aspect of tensile reduction. Furthermore, Quinn1 reported that covering the wound with a silicone gel on a polyurethane film (0.06 mm thick) was not effective, although hydration of the polyurethane film covering the silicone gel sheet was almost as effective as the silicone gel sheet. We hold that a silicone gel sheet with a polyurethane film would not reduce tension because its surface is too smooth. If the effect of gel sheeting is indeed tensile reduction, our data suggest that the effect would not be restricted to sheets composed of silicone alone but would also work with sheets composed of other materials. In support of this hypothesis, many investigators have already tested nonsilicone gels,2 hydrogels,3 and polyethylene gels4 in clinical settings. In these studies, they confirmed that there was little or no difference between silicone gel sheets and other types of gel sheet. Despite the proven efficacy of well-characterized nonsilicone gels in a prospective controlled trial, Ricketts et al. stated that there is still no satisfactory explanation for the action of silicone gel sheet. We suggest that tensile reduction could be a valid explanation. This is the first report investigating the tensile reduction effect of silicone gel sheet. A silicone gel sheet with the hardness of normal skin was the most effective, and the most efficient thickness of the silicone gel sheet was between 0.5- and 1.0-fold that of normal skin. Satoshi Akaishi, M.D., Ph.D. Department of Plastic, Reconstructive, and Aesthetic Surgery Nippon Medical School Hospital Tokyo, Japan Masataka Akimoto, M.D., Ph.D. Department of Plastic and Reconstructive Surgery Nippon Medical School Chiba Hokuso Hospital Chiba, Japan Hiko Hyakusoku, M.D., Ph.D. Rei Ogawa, M.D., Ph.D.