Introduction

The preoccupation with physical appearance and the relentless pursuit of body image satisfaction have emerged as significant areas of interest in contemporary society. This is largely due to the beauty standards propagated by the media. However, various skin disorders, including gynoid lipodystrophy, commonly referred to as cellulite, can lead to body dissatisfaction. Cellulite is a perceived change in skin topography, predominantly found in areas abundant in adipose tissue such as the hips, buttocks, thighs, and abdomen [1].

Contrary to popular belief, the etiology and pathophysiology of cellulite remain far from consensus or well-established understanding. Despite the extensive array of scientific articles exploring various treatment types, our knowledge about the actual causes and pathophysiology of cellulite remains limited.

The classification of this condition, which remains widely used today, primarily depends on its mattress phenomenon [2], colloquially referred to as an orange peel [1, 3] or cottage cheese-like appearance [4]. This is characterized by dimples in the skin. In grade 1, there are no signs of the orange peel appearance when the person is either standing or lying down. The orange peel aspect only becomes apparent after a pinch test. In Degree 2, the orange peel aspect spontaneously appears only when the woman is standing, but not when lying down. In Degree 3, the orange peel phenomenon is evident even when the woman is in a resting position [2].

While many authors regard cellulite as merely an aesthetic, gender-related disorder due to the orientation of fibrous septa [2, 5, 6], affecting 80 to 90% of post-pubescent women worldwide [7], we propose a different perspective. Given that the pathophysiology of cellulite is not well-established [8], we posit that it is, in fact, a gender-related inflammatory disease. This view aligns with the findings of other researchers. The classification of cellulite as an inflammatory disease is supported [4, 9,10,11] due to the signs and symptoms it induces, such as edema, pain, fibrosis, and temperature enhancement. These symptoms are particularly pronounced in severe cases of cellulite, as evidenced by infrared thermography [12].

Understanding the pathophysiology of the “orange peel” phenomenon is crucial for advancing scientific knowledge in both invasive and non-invasive treatments for cellulite. These treatments, which are currently being explored, include anti-cellulite cosmetics containing active ingredients that break down fat, surgical procedures, and electrophysical agents [1]. The latter is the primary focus of this study.

Although cellulite is a characteristic found in most women, it can have both physical and emotional effects, particularly on young women, thereby impacting their quality of life [13]. Despite the expansion of the aesthetic industry and concerted efforts to align treatments with scientific advancements, Auh et al. (2018) [14] highlighted a concern in their systematic review. They noted a lack of consistent methodology for quantifying non-invasive fat reduction across all the studies analyzed.

The objective of this systematic review is to evaluate the methodological quality of various types of studies conducted over the past 20 years. These studies have assessed the appearance of cellulite following treatment with one or more electrophysical agents.

Methods

Design

Cellulite is a prevalent topic in the field of aesthetics, primarily because it is viewed as a significant cosmetic concern among women [1]. This perception has led to the use of various electrophysical agents aimed at treating this condition, thereby enhancing beauty and, consequently, boosting self-confidence and self-esteem. Numerous studies have been conducted to evaluate the effects of these electrophysical agents on cellulite treatment. However, the question arises: are the methodologies employed in these studies sufficiently well-designed to provide evidence-based healthcare in routine clinical practice?

To address this query, we conducted a systematic review to evaluate the methodological quality of studies published over a span of 20 years.

Search strategy

Four databases, namely Medline/Pubmed and BVS, Central/Cochrane Library, Lilacs/BVS, and PEDro, were utilized to source studies conducted between 2001 and July 2021. These studies focused on the treatment of cellulite using electrophysical agents.

The PICO process, which stands for population, intervention, control, and outcome, was utilized to formulate the search strategy and establish the inclusion/exclusion criteria [15].

The following keywords and MeSH terms were utilized, combined using Boolean operators as follows: (“cellulite” OR “gynoid lipodystrophy” AND “treatments” AND NOT (“medication” OR “Drugs” OR “pharmaceuticals”) AND NOT “surgery”); (“cellulite” OR “gynoid lipodystrophy” AND “low-level light therapy”); (“cellulite” OR “gynoid lipodystrophy” AND “intense pulsed light therapy”); (“cellulite” OR “gynoid lipodystrophy” AND “phototherapy”); (“cellulite” OR “gynoid lipodystrophy” AND “infrared rays”); (“cellulite” OR “gynoid lipodystrophy” AND “electrical stimulation therapy”); (“cellulite” OR “gynoid lipodystrophy” AND (“ultrasound” OR “ultrasonic waves” OR “low-intensity pulsed ultrasound”)); (“cellulite” OR “gynoid lipodystrophy” AND ( “high-energy shock waves” OR “radio waves”)); (“cellulite” OR “gynoid lipodystrophy” AND “radiofrequency”).

In order to maintain systematic integrity and guide the selection of studies, we adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines [16].

Selection criteria

Inclusion criteria

This systematic review included all types of peer-reviewed studies, specifically white literature, that presented results of cellulite treatment:

  • in women aged between 15 and 59 years,

  • with any electrophysical agent such as, laser, LED, ultrasound, radiofrequency, Infrared light and pulsed magnetic field device and mechanical tissue manipulation device, and.

  • articles written in English, Portuguese, Spanish, or French.

Exclusion criteria

This review excluded articles:

  • involving animals experimentation,

  • involving men,

  • involving treatments with medications, cosmetics, or other active principles,

  • involving elderly women, i.e., ≥ 60 years,

  • studies written in different languages from the ones mentioned above,

  • studies before 2001, and

  • secondary studies, comments, and grey literature.

Study identification

The articles were independently screened by two investigators (CL and CC) based on their titles, abstracts, and full texts. The inclusion of a study was determined through consensus between the two investigators. The final selection was subsequently reviewed by a third, experienced researcher.

Data extraction, primary and secondary outcomes

The data was extracted in the following manner: author(s), year of publication, study period, study design, sample size, inclusion and exclusion criteria, electrophysical agents used in cellulite treatment, description of the intervention, and primary and secondary outcomes.

Methodological quality appraisal

In order to evaluate the methodological quality across a wide array of study designs, we employed the QualSyst tool [17]. This tool was chosen due to its provision of scoring systems for both quantitative and qualitative studies. Two investigators independently assessed and categorized the studies. Studies were deemed to be of strong quality if the QualSyst score exceeded 80%, of good quality if the score ranged from 70 to 80%, of adequate quality if the score fell between 50 and 69%, and of limited methodological quality if the score was below 50% [18].

The methodological quality of the studies was appraised by two researchers (CL and CC). Any conflicts that arose during the evaluation were then reviewed and mediated by a third researcher until a consensus was reached.

Results

Search output and flow

Initially, a total of 556 articles were identified: 379 from Medline, 159 from Central, and 18 from Lilacs. However, after applying the inclusion criteria, only 32 articles remained, as depicted in Fig. 1 below.

Fig. 1
figure 1

Overview of screening and selection process for the systematic review according to PRISMA

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Of the 556 studies initially identified, duplicate articles were excluded, and the remaining titles and abstracts were analyzed. This process resulted in 74 studies being deemed eligible for comprehensive assessment. However, only 54 of these articles were available in their entirety for review.

Upon thorough analysis of the complete texts, six were excluded due to the inclusion of male participants in their samples. Four studies were disregarded as they incorporated women aged 60 or older. One article focused on lipedema, while another was centered around animal experimentation. Five studies were omitted as they utilized an active principle in conjunction with an electrophysical therapy or pertained to a non-electrophysical therapy. One text was a letter to the editor, and another was a non-experimental study. Two studies were excluded due to the inclusion of a surgical procedure. Lastly, one duplicate article was discovered that had initially slipped through our preliminary analyses.

Main characteristics of the included studies

A total of 726 women underwent cellulite evaluations, primarily utilizing grade rating scales. These scales were often used in conjunction with one or more additional cellulite measurement tools, including photography, ultrasonography, thermography, biopsies, and magnetic resonance imaging (MRI; refer to Table 1).

Table 1 Numbers of participants, methods of cellulite evaluation, and theories of cellulite pathophysiology mentioned in each study included in this systematic review
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The most commonly used tool to evaluate the severity of cellulite, among all the studies included in this review, was Nürnberger and Müller, compounding to 34.4%. However, many studies (37.5%) did not use any grade rating scales to evaluate cellulite. They relied only on photographs and/or other resources. Other cellulite grade rating scales, such as the Cellulite Severity Scale (CSS; 12.5%), Ulrich classification (6.2%), Curri's classification (6.2%), and Comprehensive cellulite grading scale (3.1%) were used in some of the studies as well (Table 1).

In addition to cellulite grade rating scales, photography emerged as a prevalent tool, utilized in 87.5% of the studies. Ultrasonography, which provides visualization of the epidermis and dermal thickness, was employed in 34.4% of the studies reviewed. Thermography, a method that measures skin temperature to grade cellulite severity, was used in 12.5% of the studies. Biopsies, conducted to investigate potential histological changes, were featured in 12.5% of the studies. MRI, a tool used to visualize skin architecture, was only present in one study, accounting for 3.1% of all the studies included in this review (Table 1).

Table 1 illustrates the disparity in theories regarding cellulite etiology among the studies included in this review. In 18.7% of the studies, cellulite was characterized as an inflammatory condition, while 12.5% described it as non-inflammatory. Notably, the remaining 68.7% of the studies did not express any particular stance on the pathophysiology of cellulite.

The methods of cellulite evaluation, as well as the electrophysical agents used for cellulite treatment, varied significantly across the studies. As depicted in Fig. 2, 35% of the studies employed a combined therapy approach to treat cellulite. This approach is defined as the application of two or more different technologies within the same therapy session. Radiofrequency was used as a treatment method in 28% of the studies, while 16% utilized shock wave therapy for cellulite treatment. In 9% of the studies, the outcomes of two different electrophysical agents were compared within the same study. Laser treatment was used in another 9% of the studies, and a mere 3% employed electrolipolysis as a treatment method for cellulite.

Fig. 2
figure 2

The graph shows the percentage of electrophysical agents used to treat cellulite in studies between 2011 and 2021

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Overall, electrophysical agents, despite their varying mechanisms of action, have demonstrated an improvement in the appearance of cellulite and have proven to be safe for treating this condition (Table 2).

Table 2 This table provides a summary of all 32 studies included in this systematic review. It details the technologies used to treat cellulite in each study, outlines the study designs, and presents a consensus of QualSyst scores along with methodological quality outcomes
Full size table

Methodological appraisal by QualSyst

Table 2 illustrates that out of the 32 studies included in this review, only two (6.2%) were evaluated as having strong and good methodology through the QualSyst tool. These were the study by Maia et al. (2020) [50], which utilized shock wave therapy for cellulite treatment, and the study by Jackson; Roche; Shanks (2013) [41], which employed photobiomodulation (laser) as a cellulite treatment method. It is noteworthy that both studies were randomized controlled trials, wherein participants were randomly assigned to either the treatment or control groups.

Of the ten studies evaluated (31.2%), each demonstrated adequate methodology. Four of these studies [27, 28, 33, 44] were identified as randomized controlled trials. However, the randomization in these studies was limited to the lower limbs, typically using the contralateral side as a control due to its non-treated status. Only in the study by Machado and colleagues (2011) [33] was the contralateral side used to test a different cellulite treatment technology. Furthermore, the majority of these studies did not specify their randomization method. Two additional studies [34, 42] were also randomized controlled trials. These studies randomly assigned participants to either treatment or control groups, utilizing laser and shock wave technologies, respectively, for cellulite treatment. Another study was a pilot study [30], employing radiofrequency technology for cellulite treatment. A further study was a non-randomized controlled trial [39], which also used radiofrequency for cellulite treatment. Lastly, two studies [29, 43] did not specify their study design, but both employed radiofrequency technology for cellulite treatment (Table 2).

The remaining 20 studies, constituting 62.5% of the total, were evaluated using limited methodologies. Of these, seven studies claimed to be randomized controlled trials, but the randomization was conducted between the lower limbs, as previously mentioned. Furthermore, the method of randomization was not specified in the majority of these studies. Among these seven studies, three [19, 24, 31] utilized combined therapy, one [21] compared the outcomes of two different electrophysical agents, one [45] employed shock wave therapy, one [25] used radiofrequency, and one [37] treated cellulite with photobiomodulation. The remaining studies, classified as having limited methodology, included three pilot studies that used radiofrequency [46] and combined therapy [22, 32] for cellulite treatment; two case studies that employed electrolipolysis [38] and shock wave [26] as cellulite treatments; two non-randomized controlled trials, one of which [35] compared two different technologies for cellulite treatment, and the other one [49] used shock wave therapy for cellulite treatment; two cohort prospective studies [36, 40], that both used combined therapies for cellulite treatment; and four studies that did not specify the study design. Of them three [20, 47, 48] also treated cellulite with combined technologies, and one [23] treated cellulite with radiofrequency (Table 2).

RF- radiofrequency; IR—infrared light; VAC—mechanical suction-based massage device; US – ultrasound; LED – light-emitting diode; PMF – pulsed magnetic fields.

Discussion

A detailed search was conducted in the primary health science databases over a period of 20 years, focusing on cellulite treatment with electrophysical agents. Out of the 556 articles collected, only 32 met our inclusion criteria.

Overall, the outcomes of cellulite treatments were highly promising, despite the vast array of electrophysical agents used and their varying mechanisms of action.

However, were these studies robust enough to guide clinical routines based on evidence? In other words, can we rely on the quality of these studies to incorporate these various electrophysical agents into the daily treatment of cellulite in aesthetic clinics? The scientific evidence, in addition to the methodological quality of the clinical trials, was deemed insufficient.

The results of most studies, accounting for 62.5%, were evaluated as limited (with a score below 50%) using the QualSyst tool. In contrast, only 6.2% were assessed as strong or good (with a score above 80% and ranging from 70 to 80%, respectively). This suggests a dearth of high-quality studies in the literature to guide aesthetic clinicians in their routine treatment of cellulite with electrophysical agents. There could be several reasons for this outcome. Firstly, despite the extensive search conducted, it was challenging to find a clear definition of cellulite pathophysiology. This difficulty extended to finding an accurate method to evaluate this dysfunction. Consequently, without an ideal method to measure the study’s target, it becomes problematic to assess subsequent results with products that affect this target.

Luebberding, Krueger, and Sadick (2015) [1] argue that the current methods for measuring cellulite grades lack sufficient reproducibility and precision. Consequently, this makes the evaluation of anti-cellulite products and procedures challenging.

A recent review [51] has concluded that the scales currently in use possess limitations due to their qualitative assessment of cellulite or their inability to capture clinically relevant features of cellulite. However, the review recommends the combined application of the Clinician Reported Photonumeric Cellulite Severity Scale (CR-PCSS) and the Patient Reported Photonumeric Cellulite Severity Scale (PR-PCSS). These are validated tools that offer both clinician and patient perspectives on cellulite. It is crucial to note that none of the studies examined in this review utilized either of these tools.

Additionally, they advocated for the use of reliable imaging techniques to characterize cellulite and assess treatment efficacy51 more effectively. It was only recently that we demonstrated the potential of infrared thermography as a valuable tool for the diagnosis and evaluation of cellulite treatments [52].

The second reason for the poor methodological quality appraisal pertains to the inadequate randomization methods employed in most studies included in this review. Despite claiming to be randomized controlled trials, many studies either failed to use a robust method of randomization, neglected to mention the randomization method used, or improperly randomized the lower limbs of volunteers, using the contralateral side as a control. This is in contrast to the proper procedure of random distribution and, crucially, concealed allocation of volunteers into treatment and control groups, as advocated by a “true” randomized controlled trial [53]. Furthermore, the other types of studies included in this review were generally poorly designed, thereby limiting the accuracy of their conclusions.

The methodology and subsequent results could be influenced by the randomization of lower limbs and the use of the contralateral side, which is the non-treated side, as a control. This is due to the potential systemic effects that electrophysical agents can produce. This phenomenon was observed by Adatto et al. (2010) [54] and Russe-Wilflingseder; Russe (2010) [55], who noted that the control side was impacted by the acoustic wave treatment administered to the treated side.

The ideal study design for interventional studies, i.e., studies that analyze the effects of a treatment in humans, is a randomized controlled trial. This design is considered the gold standard in evidence-based research due to its high quality of evidence, as explained by Hariton and Locascio (2018) [53]. However, the development of such studies often encounter challenges such as ethical considerations, practicality, sample size, and cost. In light of these drawbacks, well-developed observational studies can provide valuable insights, even in the absence of randomization, by effectively limiting bias and confounding factors [56]. Nevertheless, randomization remains a crucial tool for reducing bias and examining the relationship between an intervention and its outcomes [53].

Clark et al. (2013) [57] highlighted the issue of inadequate reporting in trials, attributing this to a lack of training in trial methodology. They recommended several measures to address this problem. Firstly, authors should adhere to the Consolidated Standards of Reporting Trials (CONSORT). Secondly, randomized controlled trials should be reviewed by a trained methodologist. Lastly, they emphasized the importance of allocation concealment post-randomization, suggesting that this should be a mandatory requirement when registering a trial on the International Clinical Trial Registry.

Regrettably, our findings continue to align with the conclusions drawn by Clark et al. (2013) [57]. Of the four studies that were classified as “true” randomized controlled trials, only one [50] was evaluated using a robust methodology. Another study [41] was assessed using a sound methodology, while the remaining two studies [34, 42] were evaluated using an adequate methodology, as determined by the QualSyst tool.

It is worth noting that adequate methodology is defined as studies that fall within a quality assessment score range of 50–70% (or 0.50 to 0.70). In our interpretation, studies with methodological scores of 0.55 and 0.6, such as the two methodologically adequate randomized controlled trials previously mentioned, possess significantly lower methodological quality compared to a study scored at 0.7.

In discussing randomized controlled trials, it is crucial to note that despite Jackson, Roche, and Shanks (2013) [41] declaring no conflicts of interest, Steven Shanks is the owner of Erchonia Corporation. This company manufactures the low-level laser device utilized in this study. Consequently, this connection could have unintentionally influenced the final outcomes.

The third factor contributing to the classification of studies with limited methodological quality was the focus on combined therapies. These therapies, which comprised 35% of the studies included in this review, involve the use of two or more different electrophysical agents to treat cellulite in a single session. Of these studies on combined therapies, only one [27] were classified as having adequate methodology. However, they scored low at 0.50, while the remaining studies were all classified as having limited methodological quality.

Each electrophysical agent operates via a distinct mechanism of action. Therefore, how can we confidently attribute the results to the combined effect of all these resources? How can we ascertain whether one resource is not counteracting the effect of another, thereby allowing the third one to treat cellulite independently? It is noteworthy that nearly all studies involving combined therapies were assessed with limited methodological quality, which was not a mere coincidence.

The validity of these inquiries is further compromised when we examine studies that compare two different technologies or two combined therapies applied to each lower limb. The majority of these studies were evaluated with limited methodological quality. For instance, the study by Machado et al. (2011) [33] was assessed with adequate methodology, but still received a low score (0.55). As previously mentioned, we are already aware that some electrophysical agents can produce a systemic effect. However, how can we accurately compare two different technologies with distinct mechanisms of action? Undoubtedly, the conclusion drawn from such a comparison will not be precise enough to guide clinicians in selecting the most effective technology for treating cellulite.

The studies, as organized in ascending order of publication year in Table 2, suggest a shift in scientific focus over time. It appears that the questions raised may have influenced the direction of research, as there has been a noticeable decrease in the number of studies on combined therapies and comparison technologies in recent years compared to earlier periods.

A limitation of this review lies in the difficulty of categorizing the studies as either qualitative or quantitative in order to adhere to the QualSyst checklist. Kemt, Lee, and Cook (2004) [17] posited that the QualSyst tool may not accurately assess the methodological quality of the studies due to the subjectivity inherent in the questions on both the quantitative and qualitative studies’ checklists. This issue is further compounded by the lack of standard operational definitions of internal validity in the literature, as well as the absence of a universally accepted “gold standard” against which to compare their tool.

A further limitation of this review is the diversity of study designs analyzed. Although the QualSyst tool may not provide precise measurements of the methodological quality of these studies, it enables researchers to seek answers that may not be obtainable solely through randomized controlled trials. This tool facilitates a comprehensive search across a wide range of documents, from peer-reviewed articles to gray literature [17].

Conversely, a significant strength of this study lies in its comprehensive examination of the methodological quality of research conducted over the past two decades. This research has tested electrophysical agents for cellulite treatment and can guide clinicians in the aesthetic field in their daily practices. Furthermore, this systematic review serves as a gateway for scientists interested in conducting research in this area, which is currently lacking in studies with a high quality of evidence.

Conclusion

In summary, our findings indicate that the methodological quality derived from clinical studies concerning the use of electrophysical agents for treatment remains subpar.

Further research, utilizing robust experimental designs and more precise assessment techniques, is required to ascertain the most effective treatment strategies.

While this study does not dispute the efficacy of current cellulite treatment techniques, it underscores the necessity for further research of superior methodological quality.