Silicone gel sheeting for treating keloid scars

Fan Tian; Qingling Jiang; Junjie Chen; Zhenmi Liu

doi:10.1002/14651858.CD013878.pub2

. 2023 Jan 3;2023(1):CD013878. doi: 10.1002/14651858.CD013878.pub2

Silicone gel sheeting for treating keloid scars

Fan Tian ¹, Qingling Jiang ¹, Junjie Chen ², Zhenmi Liu ^1,^✉

Editor: Cochrane Wounds Group

PMCID: PMC9808890 PMID: 36594476

Abstract

Background

Keloid scarring is one of the most common types of pathological scarring. Keloid scars that fail to heal can affect a person's physical and psychological function by causing pain, pruritus, contractures, and cosmetic disfigurement. Silicone gel sheeting (SGS) is made from medical‐grade silicone reinforced with a silicone membrane backing and is one of the most commonly used treatments for keloid scars. However, there is no up‐to‐date systematic review assessing the effectiveness of SGS for keloid scars. A clear and rigorous review of current evidence is required to guide clinicians, healthcare managers and people with keloid scarring.

Objectives

To assess the effectiveness of silicone gel sheeting for the treatment of keloid scars compared with standard care or other therapies.

Search methods

We used standard, extensive Cochrane search methods. The latest search date was December 2021.

Selection criteria

We included randomised controlled trials (RCTs) that recruited people with any keloid scars and assessed the effectiveness of SGS.

Data collection and analysis

Two review authors independently performed study selection, risk of bias assessment, data extraction and GRADE assessment of the certainty of evidence. We resolved initial disagreements by discussion, or by consulting a third review author when necessary.

Main results

Two studies met the inclusion criteria. Study sample sizes were 16 and 20 participants. The trials were clinically heterogeneous with differences in causes for scarring (e.g. surgery, infected wounds, and trauma), site (e.g. chest and back), and ages of scars. The duration of follow‐up was three and four and a half months. The included studies reported three comparisons; SGS compared with no treatment, SGS compared with non‐silicone gel sheeting (a dressing similar to SGS but which does not contain silicone), and SGS compared with intralesional injections of triamcinolone acetonide. One trial had a split‐body design and one trial had an unclear design (resulting in a mix of paired and clustered data).

The included studies reported limited outcome data for the primary review outcome of scar severity measured by health professionals and no data were reported for severity of scar measured by patients or adverse events. For secondary outcomes some data on pain were reported, but health‐related quality of life and cost‐effectiveness were not reported. Both trials had suboptimal outcome reporting, thus many domains in the risk of bias were assessed as unclear. All evidence was rated as being very low‐certainty, mainly due to risk of bias, indirectness, and imprecision.

SGS compared with no treatment

Two studies with 33 participants (76 scars) reported the severity of scar assessed by health professionals, and we are uncertain about the effect of SGS on scar severity compared with no treatment (very low‐certainty evidence, downgraded once for risk of bias, once for inconsistency, once for indirectness, and once for imprecision). We are uncertain about the effect of SGS on pain compared with no treatment (21 participants with 40 scars; very low‐certainty evidence, downgraded once for risk of bias, once for inconsistency, once for indirectness, and once for imprecision). No data were reported for other outcomes including scar severity assessed by patients, adverse events, adherence to treatment, health‐related quality of life and cost‐effectiveness.

SGS compared with non‐SGS

One study with 16 participants (25 scars) was included in this comparison. We are uncertain about the effect of SGS on scar severity assessed by health professionals compared with non‐SGS (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). We are also uncertain about the effect of SGS on pain compared with non‐SGS (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). No data were reported for other outcomes including scar severity assessed by patients, adverse events, adherence to treatment, health‐related quality of life and cost‐effectiveness.

SGS compared with intralesional injections of triamcinolone acetonide

One study with 17 participants (51 scars) reported scar severity assessed by health professionals, and we are uncertain about the effect of SGS on scar severity compared with intralesional injections of triamcinolone acetonide (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). This study also reported pain assessed by health professionals among 5 participants (15 scars) and we are uncertain about the effect of SGS on pain compared with intralesional injections of triamcinolone acetonide (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and twice for imprecision). No data were reported for other outcomes including scar severity assessed by patients, adverse events, adherence to treatment, health‐related quality of life and cost‐effectiveness.

Authors' conclusions

There is currently a lack of RCT evidence about the clinical effectiveness of SGS in the treatment of keloid scars. From the two studies identified, there is insufficient evidence to demonstrate whether the use of SGS compared with no treatment, non‐SGS, or intralesional injections of triamcinolone acetonide makes any difference in the treatment of keloid scars. Evidence from the included studies is of very low certainty, mainly driven by the risk of bias, indirectness, and imprecision due to small sample size. Further well‐designed studies that have good reporting methodologies and address important clinical, quality of life and economic outcomes are required to reduce uncertainty around decision‐making in the use of SGS to treat keloid scars.

Plain language summary

What are the benefits and risks of silicone gel sheeting for treating keloid scars?

Key messages

We are uncertain whether silicone gel sheeting improves a scar's appearance more than:

‐ no treatment;

‐ treatment with a dressing similar to silicone gel sheeting that does not contain silicone;

‐ injections of triamcinolone acetonide (a medication) directly into a lesion or below the skin.

We are uncertain about the effect of silicone gel sheeting on pain compared with no treatment.

We do not know if silicone gel sheeting has an effect on pain compared with non‐silicone gel sheeting or intralesional injections of triamcinolone acetonide.

What are keloid scars?

A scar is a mark left on the skin after a wound or injury has healed. Sometimes scars can develop abnormally, forming keloid scars which are raised and unsightly and these can affect people physically and emotionally. Keloid scars often occur after minor injuries and can spread to the skin surrounding the original wound. Keloid scars are difficult to treat and can affect both sexes and occur at any age.

How are keloid scars treated?

Silicone gel sheeting is a soft and flexible wound dressing containing an elastic form of silicone. It has a soft, rubbery texture and can be easily attached to the skin. Silicone gel sheeting is thought to be an optimal option in the treatment of keloid scars. It can be used on healing skin to help soften and flatten a keloid scar.

What did we want to find out?

In this Cochrane Review, we wanted to find out what the benefits and risks of treating keloid scars with silicone gel sheeting are.

What did we do?

We searched for studies that investigated using silicone gel sheeting to treat keloid scars. We searched for randomised controlled trials only, in which the treatment each person receives is chosen at random. These studies give the most reliable evidence about the effects of a treatment.

What did we find?

We found two studies with a total of 36 participants (85 scars) (33 participants (76 scars) completed the study). The participants had keloid scars caused by surgery, infected wounds or trauma. The studies compared the effects of silicone gel sheeting with:

‐ no treatment;

‐ treatment with a dressing similar to silicone gel sheeting that did not contain silicone;

‐ injections of triamcinolone acetonide (a medication) directly into a lesion or below the skin.

One study was conducted in Brazil and another study was conducted in Singapore. They lasted for different lengths of time: three months and four and a half months.

Both studies reported assessments of scars by healthcare professionals but no data were reported in a way that was usable for this review. No studies reported useful results for the person's own assessment of their scar after treatment. Both studies also reported assessments of pain but no data were reported in a way that was usable for this review.

No studies reported useful results for people's well‐being (quality of life); whether people stayed on the treatment (adherence); whether the treatments had any unwanted effects; or whether the treatments were cost‐effective (the benefits of treatment outweighed any extra costs).

Main results

We are uncertain whether silicone gel sheeting improves a scar's appearance more than: no treatment; treatment with non‐silicone gel sheeting; or intralesional injections of triamcinolone acetonide.

We are uncertain about the effect of silicone gel sheeting on pain compared with no treatment. We do not know if silicone gel sheeting has an effect on pain compared with non‐silicone gel sheeting or intralesional injections of triamcinolone acetonide.

Conclusions

We are uncertain whether the use of silicone gel sheeting compared with no treatment, treatment with non‐silicone gel sheeting or intralesional injections of triamcinolone acetonide makes any difference in the treatment of keloid scars.

What are the limitations of the evidence?

We are not confident in the evidence because it comes from very few studies with small numbers of people and poorly reported results, so we are not sure how reliable the results are. Our conclusions would be likely to change if results from further studies become available.

How up‐to‐date is this evidence?

This review includes evidence published up to 15 December 2021.

Summary of findings

Summary of findings 1. Silicone gel sheeting compared with no treatment.

Silicone gel sheeting compared with no treatment
Patient or population: people with keloid scars Setting: hospital and skin centre Intervention: silicone gel sheeting Comparison: no treatment
Outcomes	Silicone gel sheeting compared with no treatment for treating keloid scars	Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Scar severity assessed by health professionals Follow‐up time: medium term (3 months and 4.5 months)	One study reported that scar size, hardness, colour, and intracicatricial pressure were significantly reduced in SGS compared with no treatment. Another study reported a higher proportion of scars with a significant reduction in size (i.e. at least 50% reduction in size) in SGS compared with no treatment, but the difference was not statistically significant.		33 participants with 76 scars (2 studies)	⊕⊝⊝⊝ Very low^a	No study reported evaluable data for this outcome and we summarised the results narratively. The evidence is very uncertain about the effect of SGS on scar severity compared with no treatment.
Scar severity validated by participants	No study reported evaluable data for severity validated by participants.
Adverse events	No study reported evaluable data for adverse events.
Pain Follow‐up time: medium term (3 months and 4.5 months)	The two included studies reported no difference in the number of scars with improvement in pain when comparing SGS with no treatment.		21 participants with 40 scars (2 studies)	⊕⊝⊝⊝ Very low^b	No study reported evaluable data for pain and we summarised the results narratively. We are uncertain about the effect of SGS on pain compared with no treatment.
Adherence to treatment	No study reported evaluable data for adherence to treatment.
Health‐related quality of life	No study reported evaluable data for health‐related quality of life.
CI: confidence interval SGS: silicone gel sheeting
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
^a Downgraded 4 levels: once for risk of bias (two studies were at high risk of bias in the assessment of performance bias); once for inconsistency in terms of scar size between studies; once for indirectness (scar severity in the two studies were not measured by a validated scale as defined in our Methods); once for imprecision with small number of events and limited information to quantify imprecision ^b Downgraded 3 levels: once for risk of bias (two studies were at high risk of bias in the assessment of performance bias); once for indirectness (pain in the two studies were not measured by a validated scale as defined in our Methods); once for imprecision with a small sample size and limited information to quantify imprecision

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Summary of findings 2. Silicone gel sheeting compared with non‐silicone gel sheeting treatment.

Silicone gel sheeting compared with non‐silicone gel sheeting treatment
Patient or population: people with keloid scars Setting: hospital Intervention: silicone gel sheeting Comparison: non‐silicone gel sheeting
Outcomes	Silicone gel sheeting compared with non‐silicone gel sheeting for treating keloid scars	Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Scar severity assessed by health professionals Follow‐up time: 4.5 months	The included study reported no difference between SGS and non‐SGS group in the scar size, hardness, colour, and intracicatricial pressure.		16 participants with 25 scars (1 study)	⊕⊝⊝⊝ Very low^a	No evaluable data were available for this outcome and we summarised the results narratively. We are uncertain about the effect of SGS on scar severity compared with non‐SGS.
Scar severity validated by participants	No study reported evaluable data for severity validated by participants.
Adverse events	No study reported evaluable data for adverse events.
Pain Follow‐up time: 4.5 months	The included study reported no significant difference in the symptomatic relief of pain between SGS and non‐SGS group.		16 participants with 25 scars (1 study)	⊕⊝⊝⊝ Very low^b	No evaluable data were available for this outcome and we summarised the results narratively. We are uncertain about the effect of SGS on pain compared with non‐SGS.
Adherence to treatment	No study reported evaluable data for adherence to treatment.
Health‐related quality of life	No study reported evaluable data for health‐related quality of life.
CI: confidence interval SGS: silicone gel sheeting
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
^a Downgraded 3 levels: once for risk of bias (high risk of bias in the assessment of performance bias); once for indirectness (scar severity was not measured by a validated scale as defined in our Methods); once for imprecision with a small sample size and limited information to quantify imprecision ^b Downgraded 3 levels: once for risk of bias (high risk of bias in the assessment of performance bias); once for indirectness (pain was not measured by a validated scale as defined in our Methods); once for imprecision with a small sample size and limited information to quantify imprecision

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Summary of findings 3. Silicone gel sheeting compared with intralesional injections of triamcinolone acetonide.

Silicone gel sheeting compared with intralesional injections of triamcinolone acetonide
Patient or population: people with keloid scars Setting: skin centre Intervention: silicone gel sheeting Comparison: intralesional injections of triamcinolone acetonide
Outcomes	Silicone gel sheeting compared with intralesional injections of triamcinolone acetonide for treating keloid scars	Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Scar severity assessed by health professionals Follow‐up time: 3 months	The included study reported that SGS was less effective than intralesional injections of triamcinolone acetonide in success rates (without any definition).		17 participants with 51 scars (1 study)	⊕⊝⊝⊝ Very low^a	No evaluable data were available for this outcome and we summarised the results narratively. The evidence is very uncertain about the effect of SGS on scar severity compared with intralesional injections of triamcinolone acetonide.
Scar severity validated by participants	No study reported evaluable data for severity validated by participants.
Adverse events	No study reported evaluable data for adverse events.
Pain assessed using a 5‐point scale defined by study authors (0 = none, 4 = severe) Follow‐up time: 3 months	The included study reported a fewer number of scars with an improvement in pain in SGS compared with intralesional injections of triamcinolone acetonide.		5 participants with 15 scars (1 study)	⊕⊝⊝⊝ Very low^b	No evaluable data were available for this outcome and we summarised the results narratively. The evidence is very uncertain about the effect of SGS on pain compared with intralesional injections of triamcinolone acetonide.
Adherence to treatment	No study reported evaluable data for adherence to treatment.
Health‐related quality of life	No study reported evaluable data for health‐related quality of life.
CI: confidence interval SGS: silicone gel sheeting
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
^a Downgraded 3 levels: once for risk of bias (high risk of bias in the assessment of performance bias); once for indirectness (scar severity was not measured by a validated scale as defined in our Methods); once for imprecision with small number of events and limited information to quantify imprecision ^b Downgraded 4 levels: once for risk of bias (high risk of bias in the assessment of performance bias); once for indirectness (pain was not measured by a validated scale as defined in our Methods); twice for serious imprecision with a small sample size, small number of events, and limited information to quantify imprecision

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Background

Description of the condition

Pathological scarring in the skin, occurring as a result of surgery, trauma, burn, vaccination or various skin diseases, has been a major medical problem of increasing prevalence (Nagaraja 2017). Each year, in high‐income countries alone, approximately 100 million people develop scars as a result of 55 million elective operations and 25 million operations following trauma (Sund 2000). Physiologically, scarring is part of the natural dynamic process of wound healing to re‐establish baseline skin integrity, function and aesthetics. However, for many wounds, a deviation in any phase of wound healing (e.g. disruptions in cellular and molecular signalling) can result in aberrant and sometimes excessive scar formation (Betarbet 2020). Excessive scarring can significantly affect a person's physical and psychological function by causing pain, pruritus (itching), and cosmetic disfigurement.

Keloid scars are one well‐known type of excessive pathological scarring (Huang 2013). They are visible and elevated scars that typically project beyond the boundaries of the original wound and rarely regress spontaneously (Gauglitz 2011; Hu 2018). Keloid scars are benign, hyper‐proliferative (abnormally high rate of proliferation of cells) growths of dermal fibroblasts, with excessive deposition of extracellular matrix (ECM) components, especially collagen, fibronectin, elastin, proteoglycans and growth factors (Kelly 2004). Keloid formation results from an imbalance of increased synthesis of ECM components and decreased degradation of these products.

Keloid scars can affect both sexes equally and occur at any age, especially between the ages of 10 and 30 years (Halim 2012). The reported incidence of keloid scars varies widely depending on the studied population. According to a review published in 1956, the incidence of keloids in the general population ranged from a high of 16% among adults in the Democratic Republic of the Congo (known at the time of the review as the Belgian Congo, and subsequently as Zaire) to a low of 0.09% in England (Bloom 1956). There is a lack of updated data on the incidence of keloid scars in the general population in the literature on this subject. It is widely accepted that darker‐skinned populations have a higher incidence of keloid formation than lighter‐skinned populations, ranging from 4.5% to 16%, with higher incidences during puberty and pregnancy (Viera 2011).

Differences between keloid scars and hypertrophic scars

Keloid and hypertrophic scars are both caused by abnormal wound healing and are characterised by pathologically excessive fibrosis in the skin (Arno 2014). It is sometimes difficult to distinguish between these two types of pathological scars, which may pose a major challenge to further scar therapy (Arno 2014).

Keloid scars often appear as pink to purple, shiny, round, plump and highly erythematous (superficial reddening of the skin) protuberances. Keloids can develop after minor injuries and may even spontaneously form on the sternal region without obvious injury. These scars can project beyond the original wound borders and do not regress spontaneously (Gauglitz 2011; Slemp 2006). They usually affect the sternal skin, shoulder, upper arms and earlobe, but rarely the palms of the hands or soles of the feet (Seifert 2009), and do not cause contracture. They are commonly seen in darker‐skinned populations, and have never been reported in albino populations (Halim 2012).

Hypertrophic scars are red, raised and mostly linear scars occurring in any region of the body, and they can cause contracture when joint regions are affected (Rabello 2014). Hypertrophic scars do not extend beyond the boundary of the original injury and tend to regress spontaneously within one year (Seifert 2009).

Description of the intervention

The potential usefulness of silicone in gel form for treating burn scars and contractures was first observed in the early 1980s (Perkins 1983). Within the next few years, several uncontrolled or controlled studies documented the successful use of silicone gel in the treatment of hypertrophic scars and keloids (Ahn 1989; Lee 1996; Mercer 1989). Silicone‐based products have been manufactured in various forms over the past three decades, including: silicone cream compounds (Sawada 1992); silicone oil or gel with additives such as vitamin E (Palmieri 1995); in combination with other dressings (Davey 1991); and as custom‐made silicone applications. This particular review focuses only on commercially produced adhesive silicone gel sheeting (SGS).

SGS is a soft and flexible sheet with a good adhesiveness that allows the sheet to be easily attached to the skin. It is semi‐occlusive and allows moisture and oxygen to pass through. SGS is composed of medical grade silicone (cross‐linked polydimethylsiloxane polymer) combined with a silicone membrane backing (Katz 1992), which is considered to give it increased durability and ease of handling (Mustoe 2008).

To achieve optimum results from SGS therapy, people with keloid scars are required to wear the SGS over the scar for at least 12 hours each day for a period of three to six months (Jeschke 2012). The sheets can be reused until they lose integrity but should be washed daily with mild soap and water to prevent rashes and infections (Meaume 2014). SGS can be applied to the scar as soon as re‐epithelialisation of the wound has completed. SGS may not be suitable for use on large areas of skin, mobile body parts, or on exposed areas such as the face and hands (Monstrey 2014). Compliance with this treatment is another frequent concern (McCarty 2010).

How the intervention might work

The potential mechanism of action of silicone therapy has not been completely determined, but is thought to involve occlusion (blockage or closing of blood vessels) and hydration of the outer layer of the epidermis (Mustoe 2008; Westra 2016). It has been shown that scar tissue is more prone to transepidermal water loss, possibly reflecting the decreased water barrier function of this outer layer (Mustoe 2011). A high level of water loss from the epidermis may result in dehydration of the epidermis, which may subsequently activate dermal fibroblasts which increase collagen production and eventually lead to excessive scarring (Mustoe 2008). Studies have demonstrated that SGS can create a moisture‐retaining environment that prevents dehydration of the outer layer of skin, which in turn limits the activation of fibroblasts and subsequent collagen production (Gilman 2003; Tandara 2008). The hydration effect of SGS could also increase the diffusion of soluble factors, such as cytokines, which also induce a decrease in collagen synthesis by fibroblasts (Hoeksema 2013). These mechanisms of hydration may play a key role in inhibiting the formation of keloid scarring and reducing scar elevation, volume and thickness. In addition, a significant increase in skin surface temperature under SGS may accelerate collagen breakdown, thus decreasing the excessive collagen deposition and improving the appearance of keloid scars (Musgrave 2002).

Why it is important to do this review

Keloid scarring is one of the most common types of pathological scarring (Huang 2013). Keloid scarring that fails to heal may cause cosmetic disfigurement, functional debilitation and physical impairment, which could ultimately lead to considerable psychological stress to people suffering from them and decrease their health‐related quality of life (Van den Broek 2014). The management of keloids to reduce the disease burden is therefore important. However, a complex aetiology, various therapies with unclear mechanisms, and a general lack of evidence for proven safe and effective treatments have resulted in no universally recognised regimens for keloid scarring (Gold 2014; Van den Broek 2014). SGS is currently recommended as an optimal option of non‐invasive measures in the treatment of keloid scars (Monstrey 2014), but there is no up‐to‐date systematic review assessing its effectiveness for this type of scar. An extensive Cochrane Review evaluated the effectiveness of SGS for the prevention and treatment of hypertrophic or keloid scarring, and concluded that overall research quality was low, and any effects of SGS were obscured by the poor quality of the research (O'Brien 2013). This review grouped together hypertrophic and keloid scars, making no distinction between them when conducting the comparisons, and assessed SGS combined with other therapies. One review published in 2016 assessed the effectiveness of topical silicone (gel or gel sheeting) for keloid scars and reported an insignificant reduction in scar size compared with non‐treatment (Wang 2016). Another investigated the effectiveness of silicone gel and SGS for the prevention of hypertrophic or keloid scarring and reported that most included trials were of poor quality (Hsu 2017), and that there were clinical heterogeneities (e.g. interventions, the nature of the products) which impacted on interpretation. Another more recent review grouped SGS with other therapies and failed to differentiate the treatment effects of SGS for keloid and hypertrophic scarring (Bao 2020). Considering the fact that there are many differences in the epidemiological, clinical and histological aspects of hypertrophic scars and keloids, a separate evaluation of the efficacy of SGS for keloids is desirable to summarise current evidence. A rigorous systematic review that evaluates the effectiveness of SGS for keloids and takes the most recent data into account is required to guide clinicians, healthcare managers and people suffering from keloid scarring.

This review is the second in a suite of new reviews formed by splitting the existing review, Silicone gel sheeting for preventing and treating hypertrophic and keloid scars (O'Brien 2013), into individual reviews looking separately at treatment and prevention of hypertrophic or keloid scars, respectively.

Objectives

To assess the effectiveness of silicone gel sheeting for the treatment of keloid scars compared with standard care or other therapies.

Methods

Criteria for considering studies for this review

Types of studies

We included any published or unpublished randomised controlled trials (RCTs) that evaluated the effects of SGS in the treatment of keloid scars, irrespective of publication status or language. We also included cluster‐randomised trials. We excluded quasi‐randomised trials i.e. trials where the method for allocating participants to different treatments is not strictly random, e.g. by date of birth, day of the week, month of the year, medical record number, or the order in which participants were included in the study (alternation). We also included studies with a split‐body design where people with two similar scars are enrolled and each scar is randomised to one of the interventions, or a split‐wound design where one half of a scar is randomised to one treatment and the other half to a different treatment. These approaches are similar to the 'split‐mouth' approach (Lesaffre 2009).

Types of participants

We included people with keloid scars. We accepted study authors' definitions of what they classed as 'keloid scars', if it was clear that only keloid scars were the focus of the study. We placed no restrictions on the age, sex, race or ethnicity of participants. Trials recruiting people with scars located on any part of the body, caused by any form of skin injury or treated with any previous therapeutic intervention, e.g. surgical excision, were all eligible for inclusion.

We included studies that recruited participants with keloid scars alongside people with other types of scars (hypertrophic scars) if the proportion of participants with keloid scars was at least 75%. If this proportion was unclear, we excluded the study. We also included studies with mixed scars if randomisation was stratified by scar type, and data for the keloid scars were presented separately. We excluded all other mixed scar trials.

We included RCTs that evaluated treatment of scarring alongside prevention of scarring only when randomisation was stratified for this factor and results for prevention and treatment were reported separately.

Types of interventions

We included studies where the type or schedule of SGS was the only systematic difference between study intervention regimens. This review therefore aimed to include comparisons of SGS with each other and/or placebo and/or usual treatment or no intervention. We anticipated that we could include studies evaluating one or more types of comparisons as follows:

SGS compared with no intervention, placebo or other scar treatments;
different types of SGS compared with each other;
different schedules, timings or doses of SGS compared with the same SGS used in an alternative schedule, timing or dose.

All of these types of comparisons could potentially include SGS used as part of a bundle of interventions in the treatment of keloid scars as well as a single intervention. We expected co‐interventions designed to reduce keloid scars; for example, pressure therapy or corticosteroid injections. However, these co‐interventions had to be delivered similarly to all comparison groups, as this review aimed to determine the effect of SGS specifically.

Types of outcome measures

Primary and secondary outcomes are listed below. If a study was otherwise eligible (i.e. correct study design, population and intervention or comparator) but did not report a listed outcome, then we contacted the study authors, where possible, to confirm whether an outcome of interest to us was measured but not reported. If it was still unclear whether an outcome was measured or not, we included the study and recorded these details. We reported outcome measures at the latest time point available (assumed to be length of follow‐up if not specified) and the time point specified in the methods as being of primary interest (if this was different from the latest time point available). For all outcomes, we classed assessment of outcome measures from:

less than eight weeks as short‐term;
eight weeks to one year as medium‐term;
more than one year as long‐term.

Primary outcomes

Severity of keloid scars, assessed by health professionals or other staff, measured using a validated scale. These included the Vancouver Scar Scale (VSS), the Manchester Scar Scale or the Patient and Observer Scar Assessment Scale (POSAS) (Draaijers 2004; Idriss 2009). Two versions of the VSS have been widely adopted for the assessment of scars: original VSS and modified VSS (Fearmonti 2010). The latter incorporated subjective parameters including pain (evaluated by Visual Analog Scale (VAS)) and pruritus into the original VSS.
Severity of keloid scars, assessed by participant using a validated scale; for example, POSAS (Draaijers 2004; Idriss 2009).
Adverse events (measured using a survey, questionnaire or data capture process), where a clear methodology for the collection of adverse event data was provided. This included making it clear whether (i) events were reported at the participant level or if multiple events per person were reported; and (ii) that an appropriate adjustment was made for data clustering. Where available, we extracted data on all serious and all non‐serious adverse events. We did not extract individual types of adverse events, such as pain or infection, which require specific assessment under this outcome; rather, we used the assessment of any event classed as adverse by the participant or health professional, or both, during the trial.

Secondary outcomes

Pain (including pain at dressing change). We included pain only where mean scores with a standard deviation were reported using a specific scale validated for the assessment of pain levels, such as a VAS. If any studies assessed the scars using a modified VSS, we extracted and reported the score for pain (evaluated by VAS) in the scale.
Adherence to treatment, measured by physician or patient report, or both. If any studies compared SGS with no intervention, adherence to treatment in the no intervention group could not be measured. We did not include this comparison in the meta‐analysis and only reported this outcome narratively where possible.
Participant health‐related quality of life or health status, measured using a standardised generic questionnaire (e.g. EuroQol five dimensions questionnaire (EQ‐5D), Short Form 36‐item (SF‐36), Short Form 12‐item (SF‐12) or Short Form 6‐item (SF‐6)), or wound‐specific questionnaires such as the Cardiff Wound Impact Schedule at noted time points. We did not include ad hoc measures of quality of life that were not likely to be validated and would not be common to multiple trials.
Within‐trial cost‐effectiveness analysis comparing mean differences in effects with mean cost differences between the two arms: data extracted were incremental mean cost per incremental gain in benefit (incremental cost‐effectiveness ratio (ICER)). We also considered other measures of relative cost‐effectiveness (e.g. net monetary benefit, net health benefit).

Search methods for identification of studies

Electronic searches

We searched the following electronic databases to identify reports of relevant clinical trials:

Cochrane Wounds Specialised Register (searched 15 December 2021);
Cochrane Central Register of Controlled Trials (CENTRAL; 2021, Issue 11) in the Cochrane Library (searched 15 December 2021);
MEDLINE Ovid including In‐Process & Other Non‐Indexed Citations (1946 to 15 December 2021);
Embase Ovid (1974 to 15 December 2021);
CINAHL Plus EBSCO (Cumulative Index to Nursing and Allied Health Literature; 1937 to 15 December 2021).

The search strategies for the Cochrane Wounds Specialised Register, CENTRAL, MEDLINE Ovid, Embase Ovid and CINAHL Plus EBSCO can be found in Appendix 1. In MEDLINE Ovid we combined the subject‐specific strategy with the sensitivity‐ and precision‐maximising version of the Cochrane Highly Sensitive Search Strategy for identifying randomised trials (2008 revision) (Lefebvre 2021). We combined the Embase Ovid search with the Embase Ovid filter developed by Cochrane UK (Lefebvre 2021). We combined the CINAHL Plus EBSCO search with the trial filter developed by Glanville 2019. There were no restrictions with respect to language, date of publication, or study setting.

We also searched the following clinical trials registries for ongoing studies:

US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (www.clinicaltrials.gov; searched 15 December 2021);
World Health Organization International Clinical Trials Registry Platform (www.who.int/clinical-trials-registry-platform; searched 15 December 2021).

Searching other resources

Searching reference lists of included trials and relevant reviews

We identified other potentially eligible trials or ancillary publications by searching the reference lists of retrieved included trials, as well as relevant systematic reviews, meta‐analyses and health technology assessment reports.

Searching by contacting individuals or organisations

When necessary, we contacted authors of key papers and abstracts to request further information about their trials. We also examined the content of the European Wound Management Association conference proceedings (2012 to 2020) and systematic reviews in the field that might have referred to data we had not found, and contacted key manufacturers (e.g. Mölnlycke Health Care and Smith & Nephew) to ask about unpublished and ongoing work.

Adverse effects

We did not perform a separate search for adverse effects of interventions used. We only considered adverse effects described in the included studies.

Data collection and analysis

We carried out data collection and analysis according to the methods stated in the published protocol (Tian 2021), which were based on the Cochrane Handbook for Systematic Reviews of Interventions (Li 2022).

Selection of studies

Two review authors (FT and QJ) independently screened titles and abstracts of all the potential studies we identified as a result of the search for inclusion and coded them as 'retrieve' (eligible or potentially eligible or unclear) or 'do not retrieve'. After this initial assessment, we obtained full‐text copies of all studies that appeared potentially eligible. Two review authors (FT and QJ) independently checked the full papers for eligibility. We resolved disagreements through discussion, or by consultation with a third review author (ZL) if required.

Where required and possible, we contacted study authors where the eligibility of a study was unclear. We recorded all reasons for exclusion of studies for which we had obtained full copies. We completed a PRISMA flowchart to summarise this process (Liberati 2009). Where studies were reported in multiple publications and reports, we obtained all publications. Data extraction was performed at the level of the study rather than the report.

Data extraction and management

We extracted and summarised details of the eligible studies using a data extraction form. For eligible studies, two review authors (FT and QJ) extracted data independently and resolved disagreements by discussion, drawing on a third review author (ZL), where required. Where data were missing or unclear from reports, we attempted to contact the authors of the original reports to request further details. Where a study with more than two intervention arms was included, we only extracted data from intervention and control groups that met the eligibility criteria.

We extracted the following data, where possible.

Country of origin
Type of wound preceding scar (e.g. surgical, burn, trauma)
Unit of randomisation (e.g. participant or wound)
Unit of analysis (e.g. participant or wound)
Trial design (e.g. parallel, cluster)
Number of participants randomised to each trial arm
Eligibility criteria and exclusion criteria
Details of treatment regimen received by each intervention group
Duration of treatment
Details of any co‐interventions
Primary and secondary outcome(s) (with definitions and time points)
Outcome data for primary and secondary outcomes (by intervention groups)
Duration of follow‐up
Number of withdrawals (by intervention groups)
Publication status of study
Source of funding for trial

Given that the primary outcomes (e.g. severity) were related to continuous and ordinal outcome data, we had planned to transform the reported data format (e.g. median and range) to the data format required by meta‐analysis, where available (e.g. mean and SD), but this was not necessary.

Assessment of risk of bias in included studies

Two review authors (FT and QJ) independently assessed each included study using the Cochrane approach for assessing risk of bias as detailed in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We resolved discrepancies through discussion or by consulting a third review author (ZL). The Cochrane tool for assessing risk of bias addresses specific domains: sequence generation; allocation concealment; blinding of participants and personnel; blinding of outcome assessors; incomplete data; selective outcome reporting; and other issues. In this review, we recorded issues with unit of analysis; for example, where a paired or cluster trial had been undertaken but analysed at the individual level in the study report (Appendix 2). We assessed blinding of participants and personnel, blinding of outcome assessment, and incomplete outcome data for each of the review outcomes separately. We noted that blinding of participants and personnel to treatment would be difficult considering the nature of SGS and, therefore, the risk of bias judgement in this domain would be high risk. However, if any studies had aimed to minimise performance bias by design and through measures such as documenting protocol deviations and active minimising of differential care or co‐interventions, they would not have been considered at high risk of bias. We presented our assessment of risk of bias using two risk of bias summary figures: one that was a summary of bias for each domain across all studies, and a second that showed a cross‐tabulation of each trial by all of the risk of bias domains.

For trials using cluster‐randomisation, we would have considered the risk of bias arising from: recruitment bias; baseline imbalance; loss of clusters; incorrect analysis; and comparability with individually‐randomised trials (Higgins 2022; Appendix 3).

Measures of treatment effect

For dichotomous outcomes such as amputations and adverse events, we calculated the risk ratio (RR) with 95% confidence intervals (CIs). For continuous outcomes, we presented the mean difference (MD) with 95% CIs, if all trials used the same or a similar assessment scale. If trials used different assessment scales, we used the standardised mean difference (SMD) with 95% CIs.

Unit of analysis issues

In this review, we recorded issues with unit of analysis. Examples of unit of analysis issues can occur where a paired or cluster trial has been undertaken but has been analysed at the individual level in the study report. Where studies randomised at the participant level and measured outcomes at the scar level (e.g. scar improvement), we planned to consider the participant as the unit of analysis when the number of scars assessed appeared to be equal to the number of participants (e.g. one scar per person). One potential issue for the unit of analysis which we anticipated was that randomisation may have been conducted at the participant level, with the allocated treatment used on multiple wounds per participant (or a proportion of included participants), but with data presented and analysed per wound (clustered data). We did not identify any trials which had such cluster designs, however.

There were instances of clustered data ‐ that is, where a proportion of individually‐randomised trial participants had outcome data collected and reported on multiple scars. We did not treat this as a cluster trial since not all participants had multiple scars. Instead, they were considered trials that incorrectly included a mixture of individual and clustered data. We noted these trials and recorded the issue in the risk of bias assessment. We extracted and presented data but they were not used for any further analyses.

We planned to incorporate clearly‐conducted, fully‐clustered trials into meta‐analyses if the trial was analysed correctly. If a cluster trial had been conducted but incorrectly analysed, we would have recorded this as part of the risk of bias assessment. When possible, we planned to approximate the correct analyses based on the guidance in the Cochrane Handbook (Higgins 2022), using information on:

the number of clusters (or groups) randomised to each intervention group; or the average (mean) size of each cluster;
the outcome data ignoring the cluster design for the total number of participants (e.g. number or proportion of participants with events, or means and standard deviations (SD)); and
an estimate of the intracluster (or intraclass) correlation coefficient (ICC).

We included only the relevant arms where multiple trial arms were reported in a single trial. If two or more intervention regimens were compared with the control and were eligible for the same meta‐analysis, we planned to pool the intervention arms and compare them with the control. If the study data could not be analysed correctly, we extracted outcome data and presented them without further analyses.

We also included studies with split‐body design, where either people with two eligible scars were enrolled and each scar was randomised to one of the interventions, or where one half of a scar was randomised to one treatment and the other half to a different treatment. These studies should be analysed using paired statistical methods which reflect the reduced variation in evaluating different treatments on the same person. Although trial authors may have analysed paired data, it was impossible for review authors to extract paired data due to the poor presentation for results.

We adopted a pragmatic but conservative approach to analyses including clustered and paired data in an included study. We planned to include such studies in meta‐analyses where possible (where unadjusted clustered data would produce overly narrow CIs and unadjusted paired data overly wide CIs) and would have undertaken sensitivity analyses to explore the impact of including data that had been inappropriately unadjusted. Where the sensitivity analysis produced a materially different result to the primary analysis, we prespecified that we would have used these analyses as the basis for the GRADE assessment and the summary of findings tables.

Dealing with missing data

Excluding participants post‐randomisation from the analysis, or ignoring those participants who are lost to follow‐up, or both, compromises the randomisation, and potentially introduces bias into a trial. If there was a possibility that study authors could provide some missing data, we attempted to contact them. When a trial did not specify participant group numbers before dropout, we presented only complete case data.

For continuous variables, we reported all analyses as complete case analyses and did not conduct any data imputations. We assessed the amount of attrition and the potential for introduction of bias and reported on this as part of the risk of bias assessment. Where there were missing data, such as standard deviations, we planned to calculate these estimates using all available data, wherever possible (Higgins 2011). If calculation was not possible, we contacted the study authors for further details. Where these measures of variation remained unavailable and we were unable to calculate them, we excluded the study from any relevant meta‐analyses.

Assessment of heterogeneity

To assess heterogeneity, we firstly considered clinical and methodological heterogeneity, i.e. the degree to which the included studies varied in terms of participant, intervention, outcome, and characteristics such as duration of follow‐up. We planned to supplement this assessment of clinical and methodological heterogeneity with information regarding statistical heterogeneity, assessed using the Chi² test (taking a P value of less than 0.10 to indicate statistically significant heterogeneity), and quantified heterogeneity with the I² measure (Higgins 2003). I² examines the percentage of total variation across RCTs that is due to heterogeneity rather than chance (Higgins 2003). In general, I² values of 30% or more may represent moderate heterogeneity (Higgins 2003), and values of 75% or more indicate considerable heterogeneity (Deeks 2022). However, these figures are only a guide, and it has been recognised that statistical tests and metrics may miss important heterogeneity. Thus, our overall assessment of heterogeneity would have rated the Chi² test and I² measure in combination with the methodological and clinical assessment of heterogeneity. See Data synthesis for further information about how we dealt with potential heterogeneity in the data analyses.

Assessment of reporting biases

Reporting biases often arise when the dissemination of research findings is influenced by the nature and direction of results. Publication bias is one of a number of possible causes of 'small study effects'; that is, a tendency for estimates of the intervention effect to be larger in smaller RCTs. Funnel plots are commonly used to examine whether small study effects would be present in a meta‐analysis. A funnel plot is a simple scatter plot of the intervention effect estimates from individual RCTs against some measure of each trial's size or precision (Page 2022). We planned to present funnel plots for meta‐analyses comprising 10 RCTs or more using Review Manager 5.4 (Review Manager 2020).

Data synthesis

We combined details of included studies in a narrative review according to type of comparator, type of surgical wound, and then by outcomes and time period. We would have undertaken pooling when there were sufficient studies that were appropriately similar in terms of wound type, intervention type, duration of follow‐up, and outcome type. For the outcome of pain, we would have pooled the extracted pain scores with other specific assessments of pain using VAS if possible. As it was not appropriate or feasible to undertake meta‐analysis, we considered synthesis of relevant data following the 'Synthesis Without Meta‐Analysis (SWiM) in Systematic Reviews: Reporting Guideline' (Campbell 2020; McKenzie 2022). Following this guidance, we considered carefully how narrative syntheses were presented to maximise relevance and ease of interpretation.

In terms of meta‐analytical approach, we were unable to pre specify the amount of clinical, methodological and statistical heterogeneity in the included studies. Thus, we planned to use a random‐effects approach for meta‐analysis. We would only have used a fixed‐effect approach when clinical heterogeneity was thought to be minimal, and statistical heterogeneity was not statistically significant for the Chi² value and 0% for the I² assessment (Kontopantelis 2013). We would have adopted this approach as it was recognised that statistical assessments could miss potentially important between‐study heterogeneity in small samples, hence the preference for the more conservative random‐effects model (Kontopantelis 2012). Where clinical heterogeneity was thought to be acceptable or of interest, we would have conducted meta‐analysis even when statistical heterogeneity was high, but we would have attempted to interpret the causes behind this heterogeneity, and considered using meta‐regression for that purpose, if possible (Thompson 1999).

Where possible, we planned to present our data using forest plots. For dichotomous outcomes, we planned to report the summary estimate as an RR with 95% CI. Where continuous outcomes were measured in the same way across studies, we planned to present a pooled MD with 95% CI. We also planned to pool SMD estimates where studies measured the same outcome, but used different scales.

We would have obtained pooled estimates of treatment effect using Review Manager 5.4 software (Review Manager 2020).

Subgroup analysis and investigation of heterogeneity

Studies about the mechanism of scar development have reported that scar formation is affected by wound healing (Yordanov 2014). Where feasible, we planned to consider prespecified scar aetiologies, i.e. burn, surgery, trauma etc. to investigate whether there was potential heterogeneity in the treatment outcomes.

Sensitivity analysis

We planned to assess the impact on results of removing from meta‐analyses studies classed as having a high risk of bias for any domain. We also planned to assess the impact of including studies with incorrectly‐analysed paired or clustered data in meta‐analyses.

Summary of findings and assessment of the certainty of the evidence

We present the main results of the review in summary of findings tables. We assessed the certainty of the body of evidence associated with specific outcomes according to the principles of the GRADE system (Guyatt 2008), and constructed summary of findings tables using GRADEpro GDT software (GRADEpro GDT).

These tables present main results concerning the certainty of the evidence, the magnitude of the effects of the interventions examined and the sum of available data for the main outcomes (Schünemann 2022a). The summary of findings tables also include an overall grading of the evidence associated with each of the main outcomes using the GRADE approach, which defined the certainty of a body of evidence as the extent to which one can be confident that an estimate of effect or association was close to the true quantity of specific interest. The certainty of a body of evidence involves consideration of within‐trial risk of bias (methodological quality), directness of evidence, heterogeneity, precision of effect estimates and risk of publication bias (Schünemann 2022b). We included the following main outcomes in the summary of findings tables.

Severity of keloid scars reported by health professionals
Severity of keloid scars reported by participant(s)
Adverse events
Pain
Adherence to treatment
Health‐related quality of life

For relevant outcomes reported for comparisons not included in the summary of findings tables, we presented a GRADE assessment narratively.

When evaluating the within‐trial risk of bias, we downgraded the GRADE assessment only when we classified a study as being at high risk of bias for one or more domains. We did not downgrade for unclear risk of bias assessment unless an outcome finding had unclear risk of bias in all domains, where we considered it as being at high overall risk of bias.

Following GRADE guidance (GRADE 2013), in assessing the precision of effect estimates, we assessed the size of CIs, downgrading twice for imprecision when there were very few events and CIs around effects included both appreciable benefit and appreciable harm. We considered the CI to be especially fragile where there were fewer than 50 participants. We also considered event rates in determining fragility.

Results

Description of studies

See Characteristics of included studies; Characteristics of excluded studies; and Characteristics of studies awaiting classification.

Results of the search

The search identified 484 records after duplicates were removed which were screened for eligibility. Of these, 14 studies were obtained as full texts for further assessment. We included only two of these studies in this review and excluded the remaining 12 studies (Figure 1). There were no ongoing studies. We identified three studies that are awaiting classification. See Characteristics of included studies; Characteristics of excluded studies; Characteristics of studies awaiting classification tables for full details of the studies identified. We contacted study authors for additional information and missing data, and have noted any responses in relevant tables.

Included studies

Types of studies

Of the two included studies (both RCTs), one had an unclear design (general parallel design in which some but not all participants had multiple scars evaluated) (De Oliveira 2001), and one had a split‐body design (three scars of similar size in each individual were selected) (Tan 1999).

Both studies used scars as the unit of randomisation and analysis (De Oliveira 2001; Tan 1999).

Both studies had three arms (De Oliveira 2001; Tan 1999).

The included studies were conducted in Brazil (De Oliveira 2001) and Singapore (Tan 1999).

The time of follow‐up in the included studies was three months (Tan 1999) and four and a half months (De Oliveira 2001).

Types of participants

Age and sex at baseline

The two studies randomised 36 participants with 85 keloid scars (33 participants (76 scars) completed the study; sample size: 16 participants (25 scars) and 20 participants (60 scars)) (De Oliveira 2001; Tan 1999). Both studies reported participant sex; 21 participants were male and 15 participants were female. De Oliveira 2001 included participants aged between 15 and 53 years; Tan 1999 reported the age of included participants ranged between 19 and 40 years.

The aetiology of keloid scars

De Oliveira 2001 enrolled participants with keloid scars which resulted from acne, surgery, earrings, infected wound, herpes and trauma. The wound type of another included study was unclear (Tan 1999).

Duration of keloid scars

De Oliveira 2001 and Tan 1999 reported the duration of keloid scars were more than three months and more than two years, respectively.

Care settings

One study recruited participants from hospitals (De Oliveira 2001) and one study enrolled participants from a skin centre (Tan 1999).

Types of interventions

De Oliveira 2001 assessed the effectiveness of SGS in the treatment of keloid scars compared with two control groups: non‐SGS and no treatment. Tan 1999 evaluated the effectiveness of SGS on keloid scars, compared with intralesional injections of triamcinolone acetonide or no treatment.

Source of funding

The source of funding in the included studies was unclear (De Oliveira 2001; Tan 1999).

Excluded studies

We excluded 12 studies after investigation of the full texts. Six studies were not considered to be RCTs; four studies included participants with multiple scar types and the proportion of participants with keloids was less than 75% or unknown; and two studies evaluated other interventions rather than SGS. See Characteristics of excluded studies for further details.

Ongoing studies

We did not identify any ongoing studies.

Studies awaiting classification

We identified three studies that are awaiting classification, as we were unable to obtain the full‐text versions (Boutli‐Kasapidou 2005; Muti 1994; Quddus‐ur‐Rehman 2012).

Risk of bias in included studies

See Figure 2; Figure 3 Risk of bias assessment of included studies. Overall, both studies had a high risk of bias in the domain of performance bias (De Oliveira 2001; Tan 1999).

Review authors' judgements about each risk of bias item presented as percentages across all included studies.

Review authors' judgements about each risk of bias item for each included study

Allocation

Adequacy of randomisation process

The included studies were both assessed as having unclear risk of bias as they reported no information about the methods used to generate the randomisation sequence.

Allocation concealment

Neither of the included studies provided enough details for us to make a judgement for this domain, and so both were rated as having unclear risk of bias.

Participants and personnel

The blinding of participants and personnel was not possible due to the distinct differences between interventions. We judged such blinding not to have been done in the included studies, and rated this domain as having high risk of bias.

Outcome assessment

The blinding of outcome assessment is especially important in wound‐care studies for outcomes that have a subjective element to their assessment, such as severity of scarring. Although Tan 1999 stated that "Intracicatricial pressure was measured blindly by two researchers on day 135", it was unclear for other outcome assessments. The other included study provided no information for us to make a judgement (De Oliveira 2001). Thus, both studies were rated as having unclear risk of bias.

Incomplete outcome data

All included studies were rated as having low risk of attrition bias, as the analysis accounted for all participants (De Oliveira 2001), or the trial reported the reason for exclusion and missing data was balanced in numbers across intervention and control groups (Tan 1999).

Selective reporting

We judged all included studies to be at low risk of bias for the domain of selective reporting, as the trial reports suggested that all prespecified outcomes were reported.

Other potential sources of bias

Due to insufficient information in the studies, we judged De Oliveira 2001 and Tan 1999 to be at unclear risk of bias.

Effects of interventions

See: Table 1; Table 2; Table 3

See Table 1; Table 2; Table 3. Outcome data are summarised in Table 4.

1. Study Characteristics.

Study	Scar characteristics	Comparison/length of follow‐up	Scar severity assessed by health professionals or other staff	Scar severity validated by participant	Adverse events	Pain	Adherence to treatment	Health‐related quality of life	Cost‐effectiveness
Tan 1999	Not reported	Group A (n = 20): silicone gel sheet (Cica‐Care^TM) used for 12 h daily. Group B (n = 20): intralesional injections of triamcinolone acetonide (40 mg/mL) conducted once every 4 weeks. Group C (n = 20): no treatment. Treatment time: group A, group B, group C – 12 weeks	Reduction in size (i.e. at least 50% reduction in size): group A: 2/17 (12%); group B: 16/17 (94%); group C: 0/17 (0%). Improvement in erythema: group A: 1/17 (6%); group B: 10/17 (59%); group C: 0/17 (0%).	Not reported	No adverse events were recorded with either treatment.	Improvement in pain was assessed on a 5‐point scale defined by study authors (0 = none, 4 = severe), and it only reported the number of scars that had an improvement in pain: group A: 0/5; group B: 3/5; group C: 0/5.	Not reported	Not reported	Not reported
De Oliveira 2001	Various types of scars (including acne, surgery, spontaneous, earring, infected wound, herpes, and trauma) on shoulder, abdomen, dorsum, ear, face, trunk, upper limb, breast	Group A (n = 8): silicone gel sheeting used for 24 h daily Group B (n = 7): non‐silicone gel sheeting used for 24 h daily Group C (n = 10): no treatment Treatment time: group A, group B, group C – 4.5 months	Length and width were measured with a flexible transparent metric ruler: length index: group A: 0.11; group B: 0.08; group C: 0, width index: group A: 0.12; group B: 0.14; group C: 0. Colour was measured by comparison of colour sheet: detailed data were not reported but it reported a statistically significant difference between group A and group C (P = 0.001). Intracicatricial pressure: group A: 1.41; group B: 1.50; group C: 2.69. Hardness: detailed data were not reported but it reported a statistically significant difference between group A and group C (P < 0.001).	Not reported	Not reported	Detailed data were not reported. Although it reported a reduced pain in group A and group B, there was no significant difference between 3 groups (P = 0.653).	Not reported	Not reported	Not reported

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Comparison 1: SGS compared with no treatment (two studies, 36 participants (85 scars) ‐ 33 participants (76 scars) completed the study)

Two studies were included in this comparison (De Oliveira 2001; Tan 1999).

Primary outcome: scar severity assessed by health professionals

De Oliveira 2001 included 16 participants with a total of 25 scars and randomised scars to three arms (SGS; no treatment; and non‐SGS ‐ this latter treatment is considered in comparison 2). The follow‐up time was four and a half months (medium‐term follow‐up). The scar severity was assessed by scar size, hardness (measured on a five‐point scale (1 = mild hardness, 4 = severe hardness)), colour, and intracicatricial pressure (defined as the pressure necessary to inject a 0.5 mL of triamcinolone solution into the scar tissue); all of the measured parameters were significantly reduced in the SGS group compared with no treatment. Tan 1999 included 20 participants with a total of 60 scars (three scars of similar size in each participant were selected). Only 17 participants with 51 scars completed all assessments (three participants dropped out of the trial). Each scar was randomly assigned to one of the three arms (SGS; no treatment; and intralesional injections of triamcinolone acetonide ‐ this latter treatment is considered in comparison 3) and followed up for 12 weeks (medium‐term follow‐up). The reduction in scar size and improvement in erythema were measured by physicians and study authors reported a higher proportion of scars with a significant reduction in size (i.e. at least 50% reduction in size) in the SGS group (2 scars, 12%) compared with no treatment group (0 scars), but the difference in proportion was not statistically significant (P > 0.05). No useful data were available for meta‐analysis. We reported these data in Table 4 but did not analyse them further. We are uncertain about the effect of SGS on scar severity compared with no treatment (very low‐certainty evidence, downgraded once for risk of bias, once for inconsistency, once for indirectness, and once for imprecision). No sensitivity analysis or subgroup analysis was performed due to the small number of included studies.

Secondary outcomes: pain

De Oliveira 2001 compared the symptomatic relief of pain between SGS and no treatment, and reported no significant difference. Tan 1999 assessed pain perceived by the participants using a five‐point scale (0 = none, 4 = severe) after 12 weeks of follow‐up, and reported no difference in the number of scars that had an improvement in pain between SGS and no treatment group. No useful data were available for meta‐analysis, and we reported these data in Table 4 but did not analyse them further. We are uncertain about the effect of SGS on pain compared with no treatment (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). No sensitivity analysis or subgroup analysis was performed due to the small number of included studies.

No data on other review outcomes including scar severity assessed by patients, adverse events, adherence to treatment, health‐related quality of life and cost‐effectiveness were available.

Comparison 2: SGS compared with non‐SGS (one study, 16 participants (25 scars) ‐ 16 participants (25 scars) completed the study)

One study was included in this comparison (De Oliveira 2001).

Primary outcome: scar severity assessed by health professionals

De Oliveira 2001 compared the SGS with non‐SGS in terms of scar size, hardness, colour, and intracicatricial pressure, and found no significant difference between these two groups. No useful data were available for meta‐analysis. We reported these data in Table 4 but did not analyse them further. We are uncertain about the effect of SGS on scar severity assessed by health professionals compared with non‐SGS (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). No sensitivity analysis or subgroup analysis was performed due to the small number of included studies.

Secondary outcomes: pain

De Oliveira 2001 compared the symptomatic relief of pain between the SGS and non‐SGS group, and reported no significant difference. No useful data were available for meta‐analysis. We are uncertain about the effect of SGS on pain compared with non‐SGS (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). No sensitivity analysis or subgroup analysis was performed due to the small number of included studies.

No data on other review outcomes including scar severity assessed by patients, adverse events, adherence to treatment, health‐related quality of life and cost‐effectiveness were available.

Comparison 3: SGS compared with intralesional injections of triamcinolone acetonide (one study, 20 participants (60 scars)‐ 17 participants (51 scars) completed the study)

One study was included in this comparison (Tan 1999).

Primary outcome: scar severity assessed by health professionals

Tan 1999 randomly allocated keloid scars to treatment with SGS or intralesional injections of triamcinolone acetonide (40 mg/mL), and reported that the SGS was less effective than intralesional injections of triamcinolone acetonide in success rates (without any definition). No useful data were available for meta‐analysis. We reported these data in Table 4 but did not analyse them further. We are uncertain about the effect of SGS on scar severity compared with intralesional injections of triamcinolone acetonide (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and once for imprecision). No sensitivity analysis or subgroup analysis was performed due to the small number of included studies.

Secondary outcomes: pain

Tan 1999 compared the pain perceived by participants using a five‐point scale (0 = none, 4 = severe) between SGS and intralesional injections of triamcinolone acetonide, and presented a fewer number of scars with an improvement in pain in the SGS group. No useful data were available for meta‐analysis. We reported these numbers in Table 4 but did not analyse them further. We are uncertain about the effect of SGS on pain compared with intralesional injections of triamcinolone acetonide (very low‐certainty evidence, downgraded once for risk of bias, once for indirectness, and twice for imprecision). No sensitivity analysis or subgroup analysis was performed due to the small number of included studies.

No data on other review outcomes including scar severity assessed by patients, adverse events, adherence to treatment, health‐related quality of life and cost‐effectiveness were available.

Discussion

See Table 1; Table 2; Table 3.

Summary of main results

We included two studies with a total of 36 participants (85 scars) (33 participants (76 scars) completed the study) comparing SGS with no treatment, non‐SGS, or intralesional injections of triamcinolone acetonide in three comparisons for keloid scars.

Primary outcome: scar severity assessed by health professionals

Assessment of the scar severity based on a validated scale is essential for evaluating the effectiveness of the interventions. However, neither of the included studies used a validated scale to measure this key outcome. Thus, no further analyses were conducted and we reported the results narratively. We are uncertain about the effect of SGS on scar severity compared with no treatment, non‐SGS, and intralesional injections of triamcinolone acetonide (very low‐certainty evidence).

Secondary outcome: pain

Pain is a major concern to people with burns and to medical personnel, but the included studies reported no evaluable data for us to conduct further analyses. We are uncertain about the effect of SGS on pain compared with no treatment, non‐SGS, and intralesional injections of triamcinolone acetonide (very low‐certainty evidence).

Overall completeness and applicability of evidence

As a result of the extensive literature searches, we consider that this review covers all potential RCT evidence on SGS for treating keloid scars, compared with no treatment, placebo or other scar treatments. However, there are limitations in the completeness and applicability of the evidence identified.

We only included two studies with a total of 36 participants (85 scars) after a detailed assessment for eligibility. The age of the included participants ranged from 15 to 53 years. Both studies included participants with keloid scars, but only one study (16 participants with 25 scars) reported the aetiology of scars (e.g. surgery, infected wounds, and trauma). The duration of keloid scars among study participants was more than three months and two years. Participants were recruited in hospital settings from high‐income and middle‐income countries. Due to the different causes and ages of the scars, any findings from this review might be solely applicable to the participants with similar keloid scars. Moreover, the included studies have a relatively small sample size, which may raise a concern of insufficient power.

Both studies provided limited data on the primary outcomes of scar severity assessed by health professionals and no data were reported for severity assessed by patients and adverse events. Although the included studies measured different characteristics of scars (e.g. size and colour) after treatment, no validated scale was adopted to assess the scar severity. The suboptimal outcome reporting means it was not feasible or appropriate to undertake meta‐analysis, and the possibility of comparing the results with other reviews is limited. For the secondary outcomes, one study assessed the pain perceived by participants using a five‐point scale, but reported limited data to enable us to calculate the most appropriate measures of mean difference (MD) and standard deviation (SD) (Tan 1999). Another study measured the changes in symptomatic relief of pain but no useful data were reported (De Oliveira 2001). Other secondary outcomes (e.g. participant health‐related quality of life and cost‐effectiveness) were not reported in either study. The follow‐up time was relatively short, with a follow‐up duration of three months and four and a half months.

Overall, the suboptimal outcome reporting, the variations in scar characteristics and the small number of included studies indicate that the current evidence is incomplete and of limited value to decision makers.

Quality of the evidence

For the comparisons assessed in this review, we judged the evidence relating to key outcomes to be of very low certainty. This is attributable to the risk of bias, inconsistency due to different study characteristics, indirectness, serious imprecision due to small sample size and small number of events, as well as limited information to quantify imprecision. We downgraded the certainty of evidence due to the high risk of bias for the blinded participants and personnel domain. Although blinding of participants and personnel may be very difficult from a practical perspective, it is possible to minimise performance bias by design and through measures such as documenting protocol deviations. However, neither study in this review did this and both had other methodological limitations as well as an unclear risk of bias for at least three domains.

For studies with a split‐body or split‐wound design, paired statistical methods are required to account for the reduced variation between different treatments. One included study with such a design did not use a paired statistical method (Tan 1999). Another study (De Oliveira 2001) had an unclear design, i.e. a generally parallel‐group design where some, but not all, participants had multiple scars evaluated, which indicates poor design and study execution.

The evidence presented in the included studies (De Oliveira 2001; Tan 1999) is relatively old and a list of potentially important outcomes (e.g. scar severity assessed by participants and adverse events) were not reported. Although these studies measured varying scar characteristics, it was unclear whether the professionals were adequately trained in the assessments. Also, details of the study setting and study personnel were often poorly reported.

Potential biases in the review process

We followed prespecified methods to review evidence so as to prevent potential bias in the review process. This included a comprehensive electronic search, with transparent and reproducible methods. Moreover, in order to avoid errors in the review process, strict collection and evaluation of data was performed by the review authors. But it is possible that we may have missed some published studies that were outside our search strategy. In addition, the full texts of three potentially eligible studies were not available. We attempted to contact study authors by email but received no responses. As the included studies measured outcomes differently or reported outcome data in ways that could not be meta‐analysed, we did not perform any meta‐analysis in summarising the findings. Moreover, due to the limited number of studies, we did not implement prespecified subgroup analyses or sensitivity analyses in this review. Another concern might be the bias introduced by commercial funding. Since the funding sources were not reported in the included studies (De Oliveira 2001; Tan 1999), it was difficult to determine an impact of funding sources on our results.

Agreements and disagreements with other studies or reviews

We found two systematic reviews that assessed the effectiveness of several interventions in treating keloid scars (Bao 2020; Wang 2016). Wang 2016 focused on a range of external topical medications including SGS, onion extract gel, hydrocolloid dressing, hydrocortisone, silicone, and vitamin E lotion. It included six studies that focused on SGS, but we excluded three of these studies (Berman 1999; Chernoff 2007; Gold 1994) (see Table 2). There was one other study that we did not include in this review: Palmieri 1995 aimed to compare vitamin E added to SGS with SGS for treatment of hypertrophic and keloid scars (SGS was not the systematic difference between these two arms). Both Wang 2016 and our review included De Oliveira 2001 and Tan 1999. It should be noted that our review excluded those studies with an unclear proportion of keloid scars, while Wang 2016 included them as part of the results. Also, Wang 2016 conducted a combined analysis from two studies (Gold 1994; Tan 1999) but one of the studies had an ambiguous description of the outcomes for keloid scars (Gold 1994). Thus, the findings in Wang 2016 require a more cautious interpretation and we cannot directly compare those results with our review. Furthermore, Wang 2016 did not conduct a GRADE assessment, while we used GRADE and highlighted the very uncertain evidence for many findings, mainly due to risk of bias and serious imprecision.

Another more recent review published by researchers in China included 22 studies with 17 therapies for keloid and hypertrophic scars (Bao 2020), only one of which focused solely on SGS for treating keloids (Tan 1999) (also included in our review). Other included studies often grouped SGS with other therapies and failed to disentangle the treatment effects of SGS for keloid and hypertrophic scars (Bao 2020). Also, GRADE assessment was not performed in this recent review.

Authors' conclusions

Implications for practice.

This review draws together all relevant studies that evaluated SGS for the treatment of keloid scars. The robust review process considered only RCTs, excluding studies that indicated that participants had been allocated using alternation.

From the two studies identified, there is insufficient evidence to demonstrate whether the use of SGS compared with no treatment, non‐SGS, or intralesional injections of triamcinolone acetonide makes any difference in the treatment of keloid scars. Evidence from the included studies is of very low certainty, mainly driven by the risk of bias, indirectness, and imprecision due to small sample size. SGS is believed to be a favourable non‐invasive measure in the treatment of keloid scars (Monstrey 2014); however, there is a lack of evidence regarding the effect of SGS on keloid scars compared with common alternative treatments to guide current practice. Given the absence of evidence, clinical practitioners' choice of treatment for keloid scarring should be informed by current high‐quality national guidelines, costs and potential side effects when choosing between alternatives.

Implications for research.

SGS has been recommended in the treatment of keloid scars, whereas the current evidence regarding the value of SGS on keloid scarring is limited and of very low quality. Given the importance of scar healing for patients, future research including large robust RCTs in this area is required. Meanwhile, future studies should, alongside the standard elements of good practice, consider the following points:

have a clearly defined and well implemented design, such as parallel, cluster, split‐body or split‐site design, with appropriate analyses and interpretations of the collected data;
have sufficient sample size to allow clinically important differences to be detected;
provide details of randomisation, allocation concealment, and blinding of outcome assessment;
ensure protocols are designed to minimise the potential for performance bias;
have a standardised objective and validated scar assessment tool to assess scar severity both for health professionals and for patients;
collect and report detailed adverse event data, health‐related quality of life data using validated measures, and cost‐effectiveness data.

History

Protocol first published: Issue 2, 2021

Acknowledgements

The authors are grateful to the following peer reviewers who provided feedback (including consumer peer review comments) on the protocol and the review: Chunhu Shi, Beryl De Souza and Karin Dearness. Thanks are also due to Faith Armitage for copy editing the protocol and Anne Lethaby for copy editing the review.

Elements of the Methods section are based on the standard Cochrane Wounds protocol template.

Appendices

Appendix 1. Search strategies

Cochrane Wounds Specialised Register

1 MESH DESCRIPTOR Cicatrix EXPLODE ALL AND INREGISTER

2 MESH DESCRIPTOR Keloid EXPLODE ALL AND INREGISTER

3 keloid* OR cicatrix OR scar OR scars OR scarring OR scarred AND INREGISTER

4 #1 OR #2 OR #3 AND INREGISTER

5 MESH DESCRIPTOR Silicones EXPLODE ALL AND INREGISTER

6 MESH DESCRIPTOR Silicone Elastomers EXPLODE ALL AND INREGISTER

7 silicone* AND INREGISTER

8 (cica‐care or silastic or (advasil NEXT conform) or bapscarcare or ciltech or dermatix or mepiform or (scar NEXT FX) or silgel) AND INREGISTER

9 #5 OR #6 OR #7 OR #8 AND INREGISTER

10 #4 AND #9 AND INREGISTER

The Cochrane Central Register of Controlled Clinical Trials (CENTRAL)

#1 MeSH descriptor: [Cicatrix] explode all trees

#2 MeSH descriptor: [Keloid] explode all trees

#3 keloid* OR cicatrix OR scar OR scars OR scarred OR scarring:ti,ab,kw

#4 #1 OR #2 OR #3

#5 MeSH descriptor: [Silicones] explode all trees

#6 MeSH descriptor: [Silicone Elastomers] explode all trees

#7 silicone*:ti,ab,kw

#8 (cica‐care or silastic or (advasil NEXT conform) or bapscarcare or ciltech or dermatix or mepiform or (scar NEXT FX) or silgel):ti,ab,kw

#9 #5 OR #6 OR #7 OR #8

#10 #4 AND #9 in Trials

The Cochrane Central Register of Controlled Clinical Trials (CENTRAL) via Cochrane Register of Studies

1 MESH DESCRIPTOR Cicatrix EXPLODE ALL AND CENTRAL:TARGET

2 MESH DESCRIPTOR Keloid EXPLODE ALL AND CENTRAL:TARGET

3 keloid* OR cicatrix OR scar OR scars OR scarring OR scarred AND CENTRAL:TARGET

4 #1 OR #2 OR #3 AND CENTRAL:TARGET

5 MESH DESCRIPTOR Silicones EXPLODE ALL AND CENTRAL:TARGET

6 MESH DESCRIPTOR Silicone Elastomers EXPLODE ALL AND CENTRAL:TARGET

7 silicone* AND CENTRAL:TARGET

8 (cica‐care or silastic or (advasil NEXT conform) or bapscarcare or ciltech or dermatix or mepiform or (scar NEXT FX) or silgel) AND CENTRAL:TARGET

9 #5 OR #6 OR #7 OR #8 AND CENTRAL:TARGET

10 #4 AND #9 AND CENTRAL:TARGET

11 (NCT0* or ACTRN* or ChiCTR* or DRKS* or EUCTR* or eudract* or IRCT* or ISRCTN* or JapicCTI* or JPRN* or NTR0* or NTR1* or NTR2* or NTR3* or NTR4* or NTR5* or NTR6* or NTR7* or NTR8* or NTR9* or SRCTN* or UMIN0*):AU AND CENTRAL:TARGET

12 http*:SO AND CENTRAL:TARGET

13 #11 OR #12

14 #10 AND #13

Ovid MEDLINE

1 exp Cicatrix/

2 exp Keloid/

3 (keloid* or cicatrix or scar or scars or scarring or scarred).ab,ti.

4 1 or 2 or 3

5 exp Silicones/

6 exp Silicone Elastomers/

7 silicone*.ti,ab.

8 (cica‐care or silastic or (advasil adj conform) or bapscarcare or ciltech or dermatix or mepiform or (scar adj FX) or silgel).ti,ab.

9 5 or 6 or 7 or 8

10 4 and 9

11 randomized controlled trial.pt.

12 controlled clinical trial.pt.

13 randomi?ed.ab.

14 placebo.ab.

15 clinical trials as topic.sh.

16 randomly.ab.

17 trial.ti.

18 or/11‐17

19 exp animals/ not humans.sh.

20 18 not 19

21 10 and 20

Ovid Embase

1 exp scar/

2 exp keloid/

3 (keloid* or cicatrix or scar or scars or scarred or scarring).ab,ti.

4 1 or 2 or 3

5 exp silicone derivative/

6 exp silicone/

7 exp silicone gel/

8 exp silicone dressing/

9 silicone*.ab,ti.

10 (cica‐care or silastic or (advasil adj conform) or bapscarcare or ciltech or dermatix or mepiform or (scar adj FX) or silgel).ti,ab.

11 5 or 6 or 7 or 8 or 9 or 10

12 4 and 11

13 Randomized controlled trial/

14 Controlled clinical study/

15 Random$.ti,ab.

16 randomization/

17 intermethod comparison/

18 placebo.ti,ab.

19 (compare or compared or comparison).ti.

20 ((evaluated or evaluate or evaluating or assessed or assess) and (compare or compared or comparing or comparison)).ab.

21 (open adj label).ti,ab.

22 ((double or single or doubly or singly) adj (blind or blinded or blindly)).ti,ab.

23 double blind procedure/

24 parallel group$1.ti,ab.

25 (crossover or cross over).ti,ab.

26 ((assign$ or match or matched or allocation) adj5 (alternate or group$1 orintervention$1 or patient$1 or subject$1 or participant$1)).ti,ab.

27 (assigned or allocated).ti,ab.

28 (controlled adj7 (study or design or trial)).ti,ab.

29 (volunteer or volunteers).ti,ab.

30 trial.ti.

31 or/13‐30

32 (exp animal/ or animal.hw. or nonhuman/) not (exp human/ or human cell/ or (human or humans).ti.)

33 31 not 32

34 12 and 33

EBSCO CINAHL Plus

S33 S9 AND S32

S32 S31 NOT S30

S31 S10 OR S11 OR S12 OR S13 OR S14 OR S15 OR S16 OR S17 OR S18 OR S19 OR S20 OR S21 OR S22 OR S23 OR S24

S30 S28 NOT S29

S29 MH (human)

S28 S25 OR S26 OR S27

S27 TI (animal model*)

S26 MH (animal studies)

S25 MH animals+

S24 AB (CLUSTER W3 RCT)

S23 MH (crossover design) OR MH (comparative studies)

S22 AB (control W5 group)

S21 PT (randomized controlled trial)

S20 MH (placebos)

S19 MH (sample size) AND AB (assigned OR allocated OR control)

S18 TI (trial)

S17 AB (random*)

S16 TI (randomised OR randomized)

S15 MH cluster sample

S14 MH pretest‐posttest design

S13 MH random assignment

S12 MH single‐blind studies

S11 MH double‐blind studies

S10 MH randomized controlled trials

S9 S4 AND S8

S8 S5 OR S6 OR S7

S7 TI ( (cica‐care or silastic or (advasil N1 conform) or bapscarcare or ciltech or dermatix or mepiform or (scar N1 FX) or silgel) ) OR AB ( (cica‐care or silastic or (advasil N1 conform) or bapscarcare or ciltech or dermatix or mepiform or (scar N1 FX) or silgel) )

S6 TI silicone* OR AB silicone*

S5 (MH "Silicones+")

S4 S1 OR S2 OR S3

S3 TI ( (keloid* or cicatrix or scar or scars or scarring or scarred) ) OR AB ( (keloid* or cicatrix or scar or scars or scarring or scarred) )

S2 (MH "Keloid")

S1 (MH "Cicatrix+")

US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov)

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | Scar Keloid

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | Keloid

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | Keloid Scar Following Surgery

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | cicatrix, keloid

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | Cicatrix

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | scar

silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel | Scarring

World Health Organization International Clinical Trials Registry Platform

keloid OR cicatrix OR scar OR scars OR scarred OR scarring [Title] AND silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel

keloid OR cicatrix OR scar OR scars OR scarred OR scarring [condition] AND silicone OR silicones OR cica‐care OR silastic OR advasil conform OR bapscarcare OR ciltech OR dermatix OR mepiform OR scar FX OR silgel

Appendix 2. Risk of bias assessment (individually‐randomised controlled trials)

1. Was the allocation sequence randomly generated?

Low risk of bias

The investigators describe a random component in the sequence generation process such as: referring to a random number table; using a computer random number generator; coin tossing; shuffling cards or envelopes; throwing dice; drawing of lots.

High risk of bias

The investigators describe a non‐random component in the sequence generation process. Usually, the description would involve some systematic, non‐random approach, for example: sequence generated by odd or even date of birth; sequence generated by some rule based on date (or day) of admission; sequence generated by some rule based on hospital or clinic record number.

Unclear

Insufficient information about the sequence generation process to permit judgement of low or high risk of bias.

2. Was the treatment allocation adequately concealed?

Low risk of bias

Participants and investigators enrolling participants could not foresee assignment because one of the following, or an equivalent method, was used to conceal allocation: central allocation (including telephone, web‐based and pharmacy‐controlled randomisation); sequentially numbered drug containers of identical appearance; sequentially numbered, opaque, sealed envelopes.

High risk of bias

Participants or investigators enrolling participants could possibly foresee assignments and thus introduce selection bias, such as allocation based on: use of an open random allocation schedule (e.g. a list of random numbers); assignment envelopes without appropriate safeguards (e.g. envelopes were unsealed, non‐opaque, or not sequentially numbered); alternation or rotation; date of birth; case record number; any other explicitly unconcealed procedure.

Unclear

Insufficient information to permit judgement of low or high risk of bias. This is usually the case if the method of concealment is not described or not described in sufficient detail to allow a definite judgement; for example, if the use of assignment envelopes is described, but it remains unclear whether envelopes were sequentially numbered, opaque and sealed.

3. Blinding ‐ was knowledge of the allocated interventions adequately prevented during the study?

Low risk of bias

Any one of the following.

No blinding, but the review authors judge that the outcome and the outcome measurement are not likely to be influenced by lack of blinding.
Blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken.
Either participants or some key study personnel were not blinded, but outcome assessment was blinded and the non‐blinding of others unlikely to introduce bias.

High risk of bias

Any one of the following.

No blinding or incomplete blinding, and the outcome or outcome measurement is likely to be influenced by lack of blinding.
Blinding of key study participants and personnel attempted, but likely that the blinding could have been broken.
Either participants or some key study personnel were not blinded, and the non‐blinding of others likely to introduce bias.

Unclear

Either of the following.

Insufficient information to permit judgement of low or high risk of bias.
The study did not address this outcome.

4. Were incomplete outcome data adequately addressed?

Low risk of bias

Any one of the following.

No missing outcome data.
Reasons for missing outcome data unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias).
Missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups.
For dichotomous outcome data, the proportion of missing outcomes compared with observed event risk not enough to have a clinically relevant impact on the intervention effect estimate.
For continuous outcome data, plausible effect size (difference in means or standardised difference in means) among missing outcomes not enough to have a clinically relevant impact on observed effect size.
Missing data have been imputed using appropriate methods.

High risk of bias

Any one of the following.

Reason for missing outcome data likely to be related to true outcome, with either imbalance in numbers or reasons for missing data across intervention groups.
For dichotomous outcome data, the proportion of missing outcomes compared with observed event risk enough to induce clinically relevant bias in intervention effect estimate.
For continuous outcome data, plausible effect size (difference in means or standardised difference in means) among missing outcomes enough to induce clinically relevant bias in observed effect size.
'As‐treated' analysis done with substantial departure of the intervention received from that assigned at randomisation.
Potentially inappropriate application of simple imputation.

Unclear

Either of the following.

Insufficient reporting of attrition or exclusions to permit judgement of low or high risk of bias (e.g. number randomised not stated, no reasons for missing data provided).
The study did not address this outcome.

5. Are reports of the study free of suggestion of selective outcome reporting?

Low risk of bias

Either of the following.

The study protocol is available and all of the study’s prespecified (primary and secondary) outcomes that are of interest in the review have been reported in the prespecified way.
The study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified (convincing text of this nature may be uncommon).

High risk of bias

Any one of the following.

Not all of the study's prespecified primary outcomes have been reported.
One or more primary outcomes are reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not prespecified.
One or more reported primary outcomes were not prespecified (unless clear justification for their reporting is provided, such as an unexpected adverse effect).
One or more outcomes of interest in the review are reported incompletely so that they cannot be entered in a meta‐analysis.
The study report fails to include results for a key outcome that would be expected to have been reported for such a study.

Unclear Insufficient information to permit judgement of low or high risk of bias. It is likely that the majority of studies will fall into this category.

6. Other sources of potential bias. Low risk of bias The study appears to be free of other sources of bias. High risk of bias There is at least one important risk of bias. For example, the study:

had a potential source of bias related to the specific study design used; or
has been claimed to have been fraudulent; or
had some other problem.

Unclear

There may be a risk of bias, but there is either:

insufficient information to assess whether an important risk of bias exists; or
insufficient rationale or evidence that an identified problem will introduce bias.

Appendix 3. Risk of bias assessment (cluster‐randomised controlled trials)

In cluster‐randomised trials, particular biases to consider include:

recruitment bias;
baseline imbalance;
loss of clusters;
incorrect analysis; and
comparability with individually‐randomised trials.

Recruitment bias can occur when individuals are recruited to the trial after the clusters have been randomised, as the knowledge of whether each cluster is an 'intervention' or 'control' cluster could affect the types of participants recruited.

Cluster‐randomised trials often randomise all clusters at once, so lack of concealment of an allocation sequence should not usually be an issue. However, because small numbers of clusters are randomised, there is a possibility of chance baseline imbalance between the randomised groups, in terms of either the clusters or the individuals. Although not a form of bias as such, the risk of baseline differences can be reduced by using stratified or pair‐matched randomisation of clusters. Reporting of the baseline comparability of clusters, or statistical adjustment for baseline characteristics, can help reduce concern about the effects of baseline imbalance.

Occasionally, complete clusters are lost from a trial, and have to be omitted from the analysis. Just as for missing outcome data in individually‐randomised trials, this may lead to bias. In addition, missing outcomes for individuals within clusters may also lead to a risk of bias in cluster‐randomised trials.

Many cluster‐randomised trials are analysed by incorrect statistical methods, not taking the clustering into account. Such analyses create a 'unit of analysis error' and produce over‐precise results (the standard error of the estimated intervention effect is too small) and P values that are too small. They do not lead to biased estimates of effect. However, if they remain uncorrected, they will receive too much weight in a meta‐analysis.

In a meta‐analysis including both cluster‐ and individually‐randomised trials, or including cluster‐randomised trials with different types of clusters, possible differences between the intervention effects being estimated need to be considered. For example, in a vaccine trial of infectious diseases, a vaccine applied to all individuals in a community would be expected to be more effective than if the vaccine was applied to only half of the people. Another example is provided by a Cochrane Review of hip protectors. The cluster trials showed a large positive effect, whereas individually‐randomised trials did not show any clear benefit. One possibility is that there was a 'herd effect' in the cluster‐randomised trials (which were often performed in nursing homes, where compliance with using the protectors may have been enhanced). In general, such 'contamination' would lead to underestimates of effect. Thus, if an intervention effect is still demonstrated despite contamination in those trials that were not cluster‐randomised, a confident conclusion about the presence of an effect can be drawn. However, the size of the effect is likely to be underestimated. Contamination and 'herd effects' may be different for different types of cluster.

Characteristics of studies

Characteristics of included studies [ordered by study ID]

De Oliveira 2001.

*Study characteristics*
Methods	Unclear design (general parallel‐group design in which some but not all participants had multiple scars evaluated). Setting: hospital Country: Brazil Date study conducted: not stated Follow‐up period of 135 days. Assessment time points were at the beginning (day 0), 30, 60, 90, 120, 135 Unit of randomisation: scar Unit of analysis: scar Study personnel: unknown
Participants	26 participants with a total of 41 scars (only 16 participants with a total of 25 scars were keloid scars) Sex: of 16 participants with keloid scars, 3 were male and 13 were female. Wounds type: acne, surgery, earrings, infected wound, herpes, trauma Location: presternal, shoulder, abdomen, dorsum, ear, face, trunk, upper limb, breast Inclusion criteria: participants between the ages of 15 and 53 years, and participants who had not received radiation or corticosteroids in the last 12 months and whose lesions were older than 3 months Exclusion criteria: not reported Key baselines covariates: not reported
Interventions	Group A (n = 8): silicone gel sheeting used for 24 h daily Group B (n = 7): non‐silicone gel sheeting used for 24 h daily Group C (n = 10): no treatment Treatment time: group A, group B, group C – 4.5 months
Outcomes	Primary review outcomes: • Severity assessed by health professionals at 135 days: not reported The study authors reported the hardness, length, width, colour and intracicatricial pressure of the scars using different measurements and tools. Secondary review outcomes: • Pain: not reported
Notes	Some, but not all, participants had multiple scars evaluated, indicating that the study had a poor design and execution. Funding: not reported
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “Patients were randomly chosen to receive silicone or non‐silicone gel dressings in a 4.5‐month controlled prospective study.” Comment: not reported how sequence for randomisation was generated
Allocation concealment (selection bias)	Unclear risk	Unclear how allocation concealment was conducted
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: not possible to blind participants and personnel
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: “Intracicatricial pressure was measured blindly by two researchers on day 135.” Comment: only the pressure was assessed blindly and it was unclear about other outcomes.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: no evidence of incomplete outcome data
Selective reporting (reporting bias)	Low risk	Quote: “The following parameters were evaluated: symptomatic relief of pain and itching, induration (hardness), linear measurements (length and width), colour, intracicatricial pressure.” Comment: outcomes were properly specified in the Methods section, and all the prespecified clinical outcomes were presented in Table 2‐5. A published protocol was not available.
Other bias	Unclear risk	Not reported

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Tan 1999.

*Study characteristics*
Methods	3‐arm RCT, paired study (split‐body design: 3 scars of similar size in each individual were selected). Setting: skin centre Country: Singapore Date study conducted: not stated Follow‐up period of 12 weeks. Assessment time points were at the beginning (week 0), 4, 8, and 12 weeks. Unit of randomisation: scar Unit of analysis: scar Study personnel: physician
Participants	20 participants with a total of 60 scars (17 participants with 51 scars completed the study). Sex: of 20 participants 18 were male and 2 were female. Wound type: not reported Location: chest and back Inclusion criteria: with multiple (at least 3) keloids Exclusion criteria: not reported Key baselines covariates: not reported
Interventions	Group A (n = 20): silicone gel sheet (Cica‐Care^TM) used for 12 h daily Group B (n = 20): intralesional injections of triamcinolone acetonide (40 mg/mL) conducted once every 4 weeks Group C (n = 20): no treatment Treatment time: Group A, Group B, Group C – 12 weeks
Outcomes	Primary review outcomes: • Severity assessed by health professionals at 12 weeks: not reported The study authors reported the number of scars with reduction in size (i.e. at least 50% reduction in size) and improvement in erythema. Secondary review outcomes: • Pain assessed by a 5‐point scale defined by study authors (0 = none, 4 = severe); mean scores with standard deviation of pain were not reported.
Notes	Three participants were dropped from the trial (1 defaulted from follow‐up and 2 defaulted from the treatment plan). Paired statistical method was not used in the analysis. Funding: not reported
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “The keloids were located on the same anatomic site in each patient, i.e. the chest or back. The first acted as control and was not given any treatment, the second was treated with occlusive silicone gel sheet and the third was treated with intralesional injections of triamcinolone acetonide (40 mg/mL)”. Comment: not reported how sequence for randomisation was generated
Allocation concealment (selection bias)	Unclear risk	Unclear how allocation concealment was conducted
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: not possible to blind participants and personnel
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: “Three patients were dropped from the trial (one defaulted from follow‐up and two defaulted from the treatment plan)”. Comment: the reason for exclusion was given and missing data balanced in numbers across intervention and control groups.
Selective reporting (reporting bias)	Low risk	Quote: “The following parameters were recorded by two physicians at each visit: (1) dimensions of the keloid (length, width and height), (2) change in colour and texture, and (3) improvement in the symptoms of pain and/or pruritus using a five‐point scale (0 = none, 4 = severe)”. Comment: outcomes were properly specified in the Methods section, and all the prespecified clinical outcomes were presented in Table 1. A published protocol was not available.
Other bias	Unclear risk	Not reported

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RCT: randomised controlled trial

Characteristics of excluded studies [ordered by study ID]

Study	Reason for exclusion
Aköz 2002	Ineligible study design ‐ not an RCT
Berman 1999	Included multiple scar types. The proportion of participants with keloid scars was less than 75%. Unable to obtain keloid scar data separately
Chernoff 2007	Included multiple scar types. The proportion of participants with keloid scars was unknown. Unable to obtain keloid scar data separately
Gold 1994	Included multiple scar types. The proportion of participants with keloid scars was unknown. Unable to obtain keloid scar data separately
Grella 2015	Ineligible study design ‐ not an RCT
Hirshowitz 1993	Ineligible study design ‐ not an RCT
Hosnuter 2007	Included multiple scar types. The proportion of participants with keloid scars was less than 75%. Unable to obtain keloid scar data separately
Paquet 2001	Ineligible study design ‐ not an RCT
Stromps 2014	Ineligible study design ‐ not an RCT
Wat 2013	Ineligible intervention ‐ not SGS
Westra 2016	Ineligible study design ‐ not an RCT
Wong 1996	Ineligible intervention ‐ not SGS

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RCT: randomised controlled trial SGS: silicone gel sheeting

Characteristics of studies awaiting classification [ordered by study ID]

Boutli‐Kasapidou 2005.

Methods	Not available
Participants	Not available
Interventions	Not available
Outcomes	Not available
Notes	Unable to obtain full text

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Muti 1994.

Methods	Not available
Participants	Not available
Interventions	Not available
Outcomes	Not available
Notes	Unable to obtain full text

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Quddus‐ur‐Rehman 2012.

Methods	Not available
Participants	Not available
Interventions	Not available
Outcomes	Not available
Notes	Unable to obtain full text

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Differences between protocol and review

For studies that reported no evaluable data, we conducted a GRADE assessment and presented these assessments in a narrative format in summary of findings tables. This was not pre‐planned. For studies that reported an unclear risk of bias in the assessment of selection bias or blinding, we did not downgrade the GRADE assessment as we had pre‐planned. We downgraded the GRADE assessment only if an outcome finding had unclear risk of bias in all domains, where we considered it as being at high overall risk of bias.

For some outcomes, data that we planned to extract were not reported in the studies we included. We were unable to assess the following outcomes as the included studies did not measure them: scar severity validated by participants, adverse events, adherence to treatment, health‐related quality of life, and cost‐effectiveness.

Contributions of authors

Fan Tian: conceived the review; designed the review; co‐ordinated the review; extracted data; checked quality of data extraction; analysed or interpreted data; undertook quality assessment; checked quality assessment; performed statistical analysis; checked quality of statistical analysis; produced the first draft of the review; contributed to writing or editing the review; advised on the review; performed previous work that was the foundation of the current review; wrote to study authors/experts/companies; provided data; performed economic analysis; performed translations; approved final review prior to submission.

Qingling Jiang: designed the review; co‐ordinated the review; extracted data; checked quality of data extraction; analysed or interpreted data; undertook quality assessment; checked quality assessment; performed statistical analysis; checked quality of statistical analysis; produced the first draft of the review; contributed to writing or editing the review; advised on the review; performed previous work that was the foundation of the current review; provided data; performed economic analysis; performed translations; approved final review prior to submission.

Junjie Chen: designed the review; co‐ordinated the review; contributed to writing or editing the review; advised on the review; performed translations; approved final review prior to submission.

Zhenmi Liu: conceived the review; designed the review; co‐ordinated the review; extracted data; checked quality of data extraction; analysed or interpreted data; undertook quality assessment; checked quality assessment; performed statistical analysis; checked quality of statistical analysis; produced the first draft of the review; contributed to writing or editing the review; advised on the review; secured funding; performed previous work that was the foundation of the current review; wrote to study authors/experts/companies; provided data; performed economic analysis; performed translations; approved final review prior to submission; is guarantor of the review.

Contributions of the editorial base

Gill Norman (Editor): edited the protocol and the review; advised on methodology, interpretation and content; approved the final protocol and review prior to publication.

Gill Rizzello (Managing Editor): co‐ordinated the editorial process; advised on content; edited the protocol and the review.

Sophie Bishop (Information Specialist): designed the search strategy, ran the searches and edited the methods section.

Tom Patterson (Editorial Assistant): checked the references and edited the Plain Language Summary.

Sources of support

Internal sources

West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, China

Internal sources

External sources

National Institute for Health Research, UK

This project was supported by the National Institute for Health Research, via Cochrane Infrastructure funding to Cochrane Wounds. The views expressed are those of the authors and not necessarily those of the NIHR, NHS or the Department of Health and Social Care.
Sichuan Science and Technology Program, Sichuan, China

This project was supported by Sichuan Science and Technology Program: 2019JDJQ0028. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the Sichuan Science and Technology Program.

Declarations of interest

Fan Tian: none known

Qingling Jiang: none known

Junjie Chen: none known

Zhenmi Liu: I am an Editor with Cochrane Wounds and was not involved in the editorial process for this review.

Chunhu Shi (peer reviewer): noted that he and the contact author were colleagues in the same department at the University of Manchester

New

References

References to studies included in this review

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[CD013878-bib-0008] Hirshowitz B, Ullmann Y, Har-Shai Y, Vilenski A, Peled IL. Silicone Occlusive Sheeting (SOS) in the management of hypertrophic and keloid scarring, including the possible mode of action of silicone, by static electricity. European Journal of Plastic Surgery 1993;16(1):5-9. [Google Scholar]

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[CD013878-bib-0011] Stromps JP, Dunda S, Eppstein RJ, Babic D, Har-Shai Y, Pallua N. Intralesional cryosurgery combined with topical silicone gel sheeting for the treatment of refractory keloids. Dermatologic Surgery 2014;40(9):996-1003. [DOI] [PubMed] [Google Scholar]

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[CD013878-bib-0013] Westra I, Pham H, Niessen FB. Topical silicone sheet application in the treatment of hypertrophic scars and keloids. Journal of Clinical and Aesthetic Dermatology 2016;9(10):28. [PMC free article] [PubMed] [Google Scholar]

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PERMALINK

Silicone gel sheeting for treating keloid scars

Fan Tian

Qingling Jiang

Junjie Chen

Zhenmi Liu

Abstract

Background

Objectives

Search methods

Selection criteria

Data collection and analysis

Main results

Authors' conclusions

Plain language summary

Summary of findings

Summary of findings 1. Silicone gel sheeting compared with no treatment.

Summary of findings 2. Silicone gel sheeting compared with non‐silicone gel sheeting treatment.

Summary of findings 3. Silicone gel sheeting compared with intralesional injections of triamcinolone acetonide.

Background

Description of the condition

Differences between keloid scars and hypertrophic scars

Description of the intervention

How the intervention might work

Why it is important to do this review

Objectives

Methods

Criteria for considering studies for this review

Types of studies

Types of participants

Types of interventions

Types of outcome measures

Primary outcomes

Secondary outcomes

Search methods for identification of studies

Electronic searches

Searching other resources

Data collection and analysis

Selection of studies

Data extraction and management

Assessment of risk of bias in included studies

Measures of treatment effect

Unit of analysis issues

Dealing with missing data

Assessment of heterogeneity

Assessment of reporting biases

Data synthesis

Subgroup analysis and investigation of heterogeneity

Sensitivity analysis

Summary of findings and assessment of the certainty of the evidence

Results

Description of studies

Results of the search

1.

Included studies

Types of studies

Types of participants

Age and sex at baseline

The aetiology of keloid scars

Duration of keloid scars

Care settings

Types of interventions

Source of funding

Excluded studies

Ongoing studies

Studies awaiting classification

Risk of bias in included studies

2.

3.

Allocation

Adequacy of randomisation process

Allocation concealment

Participants and personnel

Outcome assessment

Incomplete outcome data

Selective reporting

Other potential sources of bias

Effects of interventions

1. Study Characteristics.

Comparison 1: SGS compared with no treatment (two studies, 36 participants (85 scars) ‐ 33 participants (76 scars) completed the study)