correlated significantly with an increase in superficial fatty layer thickness (rp = 0.925, P<0.001) whereas increasing age correlated significantly with a decrease in its thickness (rp = -0.172, P=0.003). Multifactorial linear regression revealed the following formula to compute the thickness of the superficial fatty layer based on information of age and BMI:
Male: Thickness of superficial fatty layer in mmn: -7.026+(0.610*BMI)-(0.039*Age)
Female: Thickness of superficial fatty layer in mm: -9.750+(0.712*BMI)-(0.035*Age)
DISCUSSION
superficial fatty layer in various regions of the body: face, neck, arms, abdomen, buttock, and thighs. The results reveal that the thickness varies based on location, with smallest mean values for the lateral neck of 3.71mm ± 0.55 [range, 2.00–5.00mm] and greatest values for the gluteal region of 20.52mm ± 10.07 [range, 6.10–38.40mm]. Based on the results obtained we were able to compute a formula whereby the thickness of the superficial fatty layer could be estimated if information on gender, age, and the BMI of the patient is available. The results reveal that the formula computed is different for each body region which accounts for the variation in superficial fatty layer thickness.
The strengths of the study are the large sample size (n=150) with equal distribution of males and females (each n=75) and a balanced distribution of age (n=30 per decade: 20–29 years, 30– 39 years, 40–49 years, 50–59 years, and 60–69 years) and BMI (n=50 per group: BMI ≤24.9 kg/m2, BMI between 25.0 and 29.9kg/ m2 BMI ≥30kg/m2). This unique cohort allows analysis of the thickness of the superficial fatty layer per each anatomic region of clinical interest in individuals 50 years apart, and capability to draw conclusions about the influence of age on the variation in thickness relevant for biostimulator injections. Using three different BMI groups facilitates investigation of the influence of body habitus on superficial fatty layer thickness within and across the different age groups and genders. Another strength of the study is the non-invasive nature of the ultrasound imaging. Real time measurements were obtained without skin contact and applied pressure, ie sound waves were transmitted via the visualization gel, preserving the original tissue thickness.
Limitations of the study are that the ultrasound-based measurements were performed with subjects standing in an upright position. This might potentially limit the applicability of the measurements as some biostimulator injections are performed with the patient in the supine or prone position which can cause a shift in soft tissue proportions and thus a change in the reported thicknesses. Futures studies, however, will need to provide evidence for this potential postural change. Another limitation is that this study investigated Fitzpatrick types I–III patients. It is unclear whether the results are generalizable to darker skinned patients.
The results of the present study confirm clinical observations where different magnitudes of superficial fatty layer thickness are observed. In the lateral neck, superficial fatty layer thickness is 3.71mm ± 0.55 [range, 2.00–5.00 mm] whereas in the gluteal region the thickness is 20.52mm ± 10.07 [range, 6.10–38.40 mm]. This difference in thickness influences treatment strategies especially when injecting biostimulators. The superficial fatty layer is not a homogenous mass of fat composed of adipocytes exclusively but is rather a highly organized compound structure with honeycomb-like architecture.23,25 This architecture is formed by adipocytes arranged in fat lobules which are surrounded by walls composed of fibrous connective tissue.25 These fibrous connective tissue walls together form a 3D fibrous connective tissue framework which encloses the fat lobules. Together, these fibrous connections form septae which attach to the underside of the dermis25 and expand into deeper layers. The deep attachment of these septal connections is the superficial fascia.16,18 Together, the skin, the superficial fatty layer, the connective tissue fibers that connect the skin to the superficial fascia and the superficial fascia itself are considered to be a functional biomechanical unit which has been previously termed the superficial fascial system.17,19-24 The thickness of the superficial fatty layer which increases in thickness with increasing BMI values15,16,18 influences the status of the superficial fascial system.
In cellulite, an aesthetic condition which predominantly affects post-pubertal females, increasing BMI is a risk factor for its development and its severity.14 It was recently demonstrated that the fibrous connections between the skin and the superficial fascia contribute to the stability of the superficial fascial system and that this stability is primarily influenced by gender with females having less stable subdermal fibrous connective tissue architecture.14 In the same cadaveric investigation, males were shown to have a higher number of fibrous connective tissue septae per area spanning the distance between the dermis and the superficial fascia. This resulted in significantly increased tensile strength values versus females when tested in an experimental load-until-failure study design.14
The results of those previous investigations demonstrate that the subdermal fatty layer, containing the fibrous connective tissue septae, is of crucial importance for maintaining skin tension and position. Alterations to this delicate arrangement influences skin surface appearance of which the most frequent are skin laxity and surface irregularities frequently observed in cellulite and aging. These aesthetic conditions can be explained by alterations in the superficial fascial system: reduced tension of the superficial fascial system can result in skin laxity whereas increased tension of the superficial fascial system and its components (like the superficial fatty layer due to increased
The strengths of the study are the large sample size (n=150) with equal distribution of males and females (each n=75) and a balanced distribution of age (n=30 per decade: 20–29 years, 30– 39 years, 40–49 years, 50–59 years, and 60–69 years) and BMI (n=50 per group: BMI ≤24.9 kg/m2, BMI between 25.0 and 29.9kg/ m2 BMI ≥30kg/m2). This unique cohort allows analysis of the thickness of the superficial fatty layer per each anatomic region of clinical interest in individuals 50 years apart, and capability to draw conclusions about the influence of age on the variation in thickness relevant for biostimulator injections. Using three different BMI groups facilitates investigation of the influence of body habitus on superficial fatty layer thickness within and across the different age groups and genders. Another strength of the study is the non-invasive nature of the ultrasound imaging. Real time measurements were obtained without skin contact and applied pressure, ie sound waves were transmitted via the visualization gel, preserving the original tissue thickness.
Limitations of the study are that the ultrasound-based measurements were performed with subjects standing in an upright position. This might potentially limit the applicability of the measurements as some biostimulator injections are performed with the patient in the supine or prone position which can cause a shift in soft tissue proportions and thus a change in the reported thicknesses. Futures studies, however, will need to provide evidence for this potential postural change. Another limitation is that this study investigated Fitzpatrick types I–III patients. It is unclear whether the results are generalizable to darker skinned patients.
The results of the present study confirm clinical observations where different magnitudes of superficial fatty layer thickness are observed. In the lateral neck, superficial fatty layer thickness is 3.71mm ± 0.55 [range, 2.00–5.00 mm] whereas in the gluteal region the thickness is 20.52mm ± 10.07 [range, 6.10–38.40 mm]. This difference in thickness influences treatment strategies especially when injecting biostimulators. The superficial fatty layer is not a homogenous mass of fat composed of adipocytes exclusively but is rather a highly organized compound structure with honeycomb-like architecture.23,25 This architecture is formed by adipocytes arranged in fat lobules which are surrounded by walls composed of fibrous connective tissue.25 These fibrous connective tissue walls together form a 3D fibrous connective tissue framework which encloses the fat lobules. Together, these fibrous connections form septae which attach to the underside of the dermis25 and expand into deeper layers. The deep attachment of these septal connections is the superficial fascia.16,18 Together, the skin, the superficial fatty layer, the connective tissue fibers that connect the skin to the superficial fascia and the superficial fascia itself are considered to be a functional biomechanical unit which has been previously termed the superficial fascial system.17,19-24 The thickness of the superficial fatty layer which increases in thickness with increasing BMI values15,16,18 influences the status of the superficial fascial system.
In cellulite, an aesthetic condition which predominantly affects post-pubertal females, increasing BMI is a risk factor for its development and its severity.14 It was recently demonstrated that the fibrous connections between the skin and the superficial fascia contribute to the stability of the superficial fascial system and that this stability is primarily influenced by gender with females having less stable subdermal fibrous connective tissue architecture.14 In the same cadaveric investigation, males were shown to have a higher number of fibrous connective tissue septae per area spanning the distance between the dermis and the superficial fascia. This resulted in significantly increased tensile strength values versus females when tested in an experimental load-until-failure study design.14
The results of those previous investigations demonstrate that the subdermal fatty layer, containing the fibrous connective tissue septae, is of crucial importance for maintaining skin tension and position. Alterations to this delicate arrangement influences skin surface appearance of which the most frequent are skin laxity and surface irregularities frequently observed in cellulite and aging. These aesthetic conditions can be explained by alterations in the superficial fascial system: reduced tension of the superficial fascial system can result in skin laxity whereas increased tension of the superficial fascial system and its components (like the superficial fatty layer due to increased
