Review of Silicone Gel Sheeting and Silicone Gel for the Prevention of Hypertrophic Scars and Keloids

Background. Keloids and hypertrophic scars are fibroproliferative disorders of dermal tissue after skin injury. Many clinical control studies have reported evidence that silicone gel is effective in preventing and alleviating hypertrophic scarring. Whether silicone gel sheeting prevents hypertrophic scars or keloids requires clear evidence of its clinical effectiveness.Objective. This review investigated the effectiveness of silicone gel and silicone gel sheeting for the prevention of hypertrophic or keloid scarring in patients with newly healed wounds. Methods. The authors searched the MEDLINE, EMBASE, CINAHL, and CENTRAL databases (January 1, 1990 to September 24, 2014) for any randomized or quasi-randomized controlled trials or controlled clinical trials comparing silicone gel sheeting or silicone gel with a control group for prevention of hypertrophic scars or keloids. All collected trials were assessed for methodological quality, control group and treatment group, and number of participants developing hypertrophic scars and keloids. The authors calculated risk ratios (RR) from each trial for the development of abnormal scarring and combined these using random-effects model meta-analysis. Between-study heterogeneity was calculated by using the I² statistic. Results. Ten trials in 9 studies were pooled (random effect; I² = 88%). There was a significant difference between the silicone gel sheeting group and the placebo group (RR 0.70; 95% confidence interval, 0.49–0.99; P = .04) in preventing the risk of hypertrophic scars. Conclusion. There was statistical significance in the effectiveness of silicone gel and silicone gel sheeting on the prevention of keloids or hypertrophic scars, especially in skin lesion wounds. However, most of the trials evaluating silicone gel sheeting or silicone gel as a prevention of hypertrophic scars and keloids had poor quality with high or uncertain risk of biases either in study design or in conduct.

Abnormal scarring, including hypertrophic scars and keloids, is common and caused by excessive proliferation of dermal tissue following skin injury. Hypertrophic scars can occur in major skin wounds, including those resulting from surgery, trauma, and burns, while keloids can arise from small injuries or weak inflammation processes, including acne and injections.¹ 

Hypertrophic scars were reported to occur in 39% to 68% of patients postop and in 33% to 91% of patients after burn injury,² whereas an estimated 5% to 15% of patients developed postsurgical keloids.³ High-risk populations include scars in the high-risk anatomical areas (eg, the lower face, presternum, pectoral area, upper back, ears, neck, deltoid region of the upper arms) or patients with a history of forming keloid scars.⁴

Hypertrophic and keloid scarring causes functional and psychological problems for patients. The consensus statement from the International Advisory Panel on Scar Management concluded that silicone-based products are the preferred measurement for preventing hypertrophic or keloid scarring.⁴ A randomized controlled trial (RCT) by Gold et al⁵ showed silicone gel sheeting significantly reduced the incidence of hypertrophic scars or keloids in high-risk individuals with a history of abnormal scarring. Another RCT by Chan et al⁶ also revealed that silicone gels might be able to prevent the development of hypertrophic scars after sternotomy-associated wounding. A meta-analysis by O’Brien and Jones⁷ disclosed that there was only weak evidence of silicone gel sheeting preventing abnormal scarring in high-risk individuals. In summary, clearer evidence about the clinical effectiveness of silicone gel sheeting in preventing hypertrophic scars or keloids is still needed.

Eligibility criteria for selecting studies. The investigators sought data from RCTs, quasi-randomized controlled trials (QRCTs) in which the method for allocating participants to a treatment that was not strictly random (eg, by date of birth, hospital record number, or alternation), or controlled clinical trials (CCTs) where an intervention group was compared to a control group of interventions. Participants had a closed surgical wound on any part of the body. Trials that compared silicone gel sheeting or silicone gel to a placebo or no treatment were included. Studies that were for treatment only were excluded.

Search strategy. The authors searched the MEDLINE, EMBASE, CINAHL, and CENTRAL databases from January 1, 1990, to September 24, 2014, using the strategy described in a systematic review by O’Brien and Pandit.⁷ Abstracts and manuscripts were reviewed independently by 2 reviewers; a third reviewer settled discrepancies. Any RCTs, QRCTs, or CCTs comparing silicone gel sheeting for the prevention of hypertrophic or keloid scars with no treatment or placebo were included. The investigators identified 10 trials from 9 studies (Table) that were analytic studies on the effetiveness of prevention for hypertrophic scars and keloids by silicone gel or silicone gel sheeting compared with placebo. 

Data extraction. Data were extracted by 2 review authors and checked for accuracy by a third review author. Eight characteristics were assessed: study characteristics (design, method of randomization, withdrawals/dropouts, funding source); participants (age, wound location, wound characteristics, scar type); intervention (silicone gel or silicone gel sheeting); control group; outcome measurement; duration of treatment; duration of follow-up; and results.

Subgroup analysis. Three subgroup analyses were conducted by risk, wound type, and management. First, studies were divided into 3 subgroups by risk of developing abnormal scarring. Individuals with no previous history of hypertrophic scar or keloid formation after injury or surgical procedures were classified into the “low risk” group; the “high risk” group consisted of individuals with a positive history of hypertrophic scar or keloid formation after previous surgery or trauma. A third group, classified as “risk not mentioned,” included trials without mentioning risk of abnormal scarring. Second, trials were divided by wound type (procedural or anatomical site): sternotomy wounds, breast reduction, skin lesion, and wound not mentioned (where the trial did not note the site of the wound and the surgical procedure). Third, the trials were classified into 3 subgroups based on treatment modality: the silicone gel group, the silicone gel sheeting group, and the unclassified group (where the trial did not mention the type of intervention, silicone gel, or silicone gel sheeting).

Assessment of bias risk in the included studies. The methodological quality of the included studies was assessed by using the Cochrane Collaboration tool for assessing risk of bias.⁸ The risk of bias tool addresses 7 study characteristics: random sequence generation, allocation concealment, blinding of participants, blinding of personnel, blinding of outcome assessment, incomplete outcome data, and selective reporting. Each characteristic was classified into 1 of 3 groups by the reviewer’s judgment: high, low, or unclear risk. In the risk of bias summary, a yellow icon meant unclear risk, green meant low risk, and red meant high risk.

Outcome measurement. The outcome measurement was the number of patients who developed keloid or hypertrophic scarring as determined by blood flow, hyperpigmentation, erythema, scar thickness, and regularity of scar in each study.

Statistical analysis. The investigators calculated the risk ratio (RR) with 95% confidence intervals (CI) of each trial for development of abnormal scarring and combined these using random effects model meta-analysis. Between-study heterogeneity was calculated by using the I² statistic. Publication bias was inspected by means of funnel plots for each comparison. If there is no publication bias in funnel plots, all studies should have symmetric distribution along the axis. Analyses were conducted by RevMan 5.3 (Version 5.3.5; Cochrane Collaboration, London, UK).

A flow diagram of the database search and review is illustrated in eFigure 1. There were 10 trials in 9 studies that compared silicone gel sheeting with no treatment or placebo for prevention of hypertrophic scars and keloids (Table). Nine studies (Ahn et al,⁹ Gold,¹⁰ Cruz-Korchin,¹¹ Niessen et al,¹² Gold et al,⁵ Chan et al,⁶ Signorini and Clementoni,¹³ de Giorgi et al,¹⁴ and Chittoria and Padi¹⁵) included patients with healed surgical wounds, and 1 (Gold¹⁰) included patients who had keloid scars removed by carbon dioxide laser. Two of the trials described patients according to their risk of developing abnormal scarring; Gold¹⁰ recruited high-risk patients, while Gold et al⁵ recruited low-risk and high-risk patients and presented the results of these 2 groups separately, where the high-risk group included patients with a history of abnormal scarring but the low-risk group did not.⁵  

In the low-risk group,⁵ there was no statistical difference between routine postoperative care and topical silicone gel sheeting. In the high-risk group, 2 trials^5,10 individually reported no significant difference if topical silicone gel sheeting was used postoperatively. However, when both low-risk and high-risk patients were pooled (using a random effects model, 856 total scars in 10 trials), the silicone gel sheeting had a significant effect on preventing abnormal scarring (RR 0.7; 95% CI, 0.49–0.99).⁵ Cruz-Korchin¹¹ found that silicone sheeting was effective in preventing the formation of hypertrophic scars (20 subjects; RR 0.45; 95% CI, 0.19–1.07). Niessen et al¹² reported a significant difference favoring the control group (119 subjects; RR 2.71; 95% CI, 1.19–6.22). Signorini et al¹³ reported a significant difference between the silicone gel group and control group (72 scars; RR 0.25; 95% CI, 0.10–0.63); de Giorgi et al¹⁴ showed silicone gel had a significant effect on the prevention of abnormal scarring (110 patients; RR 0.50; 95% CI, 0.31-0.80). In Chan et al’s study⁶ and Chittoria and Padi’s study,¹⁵ there were no effects on the prevention of hypertrophic scar development, but both studies showed smaller scar formation in the silicone gel group compared with the control group through the Vancouver scar scale. When all 10 trials were pooled (random effect; I² = 88%), there was no significant difference in the treatment group compared with the control group (RR 0.70; 95% CI, 0.49–0.99; P = .04). The results are illustrated in eFigure 2, and the funnel plot is shown in eFigure 3.

Subgroup analysis of different wound types found a statistically significant effectiveness of prevention by silicone gel material in the skin lesion wound group (I² = 0%; RR 0.44; 95% CI, 0.30–0.64; P < .0001), but an insignificant effectiveness in the breast reduction, skin graft donor site, and sternotomy groups as illustrated in eFigures 4 and 5.

The effectiveness of silicone gel and silicone gel sheeting in trials was presented in total and in subgroups. There was statistical significance in the effectiveness of silicone gel sheeting in the prevention of hypertrophic scars and keloids (I² = 0%; RR 0.41; 95% CI, 0.24–0.72; P = .002), but statistical insignificance in the effectiveness of the silicone gel as illustrated in eFigures 6 and 7.

Each risk of bias item for the 9 studies was classified into 3 group: unclear risk (yellow), low risk (green), and high risk (red); the results are shown in eFigure 8. 

In theory, topical silicone gel sheeting might prevent abnormal scarring by limiting skin stretching during wound healing,¹ though there is weak evidence that silicone gel sheeting can prevent abnormal scarring.⁴ Atkinson et al¹⁶ supported the effect of tape fixation on the prevention of hypertrophic scars after a caesarean section in 70 women. Berman et al¹⁷ listed the possible mechanisms of silicone elastomer sheeting in scar treatment, including increased temperature, increased hydration and oxygen tension, direct action of the silicone oil, polarized electric charge leading to scar shrinkage, and immunologic effects modulating the fibrogenic cytokine. Reish and Eriksson’s study¹⁸ suggests that occlusion and hydration are likely the mechanisms of the therapeutic action of silicone gel sheeting rather than an inherent anti-scarring property of silicone.However, no distinct mechanism has been defined; thus, limiting skin stretching, occlusion, and hydration may explain the prophylaxis effect of silicone gel sheeting in abnormal scarring. 

A meta-analysis by O’Brien and Jones⁷ reported weak evidence of the benefits of silicone gel sheeting for the prevention for abnormal scarring in high-risk people, but the poor quality of included trials means a great deal of uncertainty remains. 

To help tackle this uncertainty, the investigators searched databases and included studies that had tested silicone gel and silicone gel sheeting as prevention management. The authors pooled the results from studies on silicone gel sheeting and silicone gel based on their similar effectiveness reported in the study by Kim et al.¹⁹ However, subgroup analyses were also conducted to investigate possible differences in the effectiveness of silicone gel and silicone gel sheeting for the prevention of hypertrophic scars in different risk groups and wound types. 

Across all of the studies included in this review, there are clinical heterogeneities that should raise some awareness when interpreting results. Patient populations in the studies were of different ethnicities. The interventions were with silicone sheets or gels; there should be some differences in the nature of the products, though both are made from silicone, and their uses in method and time were not the same throughout the studies. The control regiments of the control groups were different as well; some used surgical tape as a control while some adopted no treatment for their control (Table). Additionally, all studies were measured in different times with different standards.

Despite the clinical heterogeneities mentioned above, there were no major limitations that made a meta-analysis unfeasible. The clinical heterogeneities across all studies mentioned herein are acceptable and their kinds are common in all other meta-analyses.

There were methodological problems with adequately reporting study randomization protocols or allocation concealment or a failure to undertake an intention-to-treat analysis in several trials. eFigure 8 shows the different risk of bias in each included trial. Blinding of outcome assessors was poorly reported. Most studies were of a poor quality; this results in weak evidence of the benefits of silicone gel sheeting as a prevention method for abnormal scarring. Therefore, the authors suggest more studies testing the effectiveness of silicone gel material with adequate randomization, and objective outcome measurements should be done. 

There was statistical significance in the effectiveness of silicone gel and silicone gel sheeting on the prevention of keloids or hypertrophic scars, especially in skin lesion wounds. However, most of the trials evaluating silicone gel sheeting or silicone gel as a prevention of hypertrophic scars and keloids had poor quality either in study design or in conduct, and thus were with high or uncertain risk of biases. Further studies using silicone gel material for specific wound sites with better study design are suggested. 

From the Department of Surgery, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan; and Department of Otolaryngology – Head and Neck Surgery, Keelung Chang Gung Memorial Hospital, Keelung, New Taipei, Taiwan; and Department of Surgery, Kaohsiung, Chang Gung Memorial Hospital, Kaohsiung, Taiwan

Address correspondence to:
Yi-Wen Tsai, MD
Department of Surgery
Kaohsiung, Chang Gung Memorial Hospital
No.123, Dapi Road
Niaosong District 
Kaohsiung City 833 
Taiwan (R.O.C.)
yi-wen_tsai@hotmail.com

Disclosure: The authors disclose no financial or other conflicts of interest.