It has been reported in the literature that the sagging of facial fat compartments is not synchronized in the process of aging.1–3 Interestingly, we have observed that there are also great differences in the manifestations of contour deformities that occur during the development of obesity, such as thickened fat pads, cellulite, and drooping rolls in specific regions, which cannot be simply explained by the description of previous studies.4–6
At present, the main approaches for contour deformity are lipectomy and liposuction. Lipectomy is widely used in patients after massive weight loss.7–11 However, the disadvantages are obvious scarring, trauma, and long recovery time. Thus, lipectomy is less advantageous for patients with smaller amounts of excessive skin. Liposuction is a surgical procedure with stealth incisions, quick recovery, and broader indications than lipectomy. However, in back applications, this procedure is less commonly used because of its high suction resistance, bleeding, and association with complications such as hematoma and ecchymosis.12,13
Lockwood5 proposed that the superficial fascial system (SFS) is an important structure affecting subcutaneous fat morphology, and modern imaging techniques have shown the SFS connects all layers as a bridge, allowing the skin/subcutaneous complex (SSC) to present homogeneous mechanical properties when its volume changes.14 The SFS, composed of many elastic and collagen fibers, is the major contributor to SSC biomechanics.15,16 We hypothesized that differences in deformity manifestations may be related to SFS structure and that understanding its anatomical characteristics may provide a better solution to the problems related to liposuction of the back.
The back is a flat and broad area exhibiting different forms of contour deformities. The subcutaneous tissue is less affected by glands, the lymphatic system, and important blood vessels and nerves, which can directly reflect the changes in subcutaneous adipose tissue. Therefore, the back is more suitable as an entry point for studying SSC morphologic change models. The purpose of this study was to understand the SFS structural characteristics of the back and to propose a minimally invasive approach to back liposuction based on the SFS system.
MATERIALS AND METHODS
Twelve full-dorsum female cadaver dissections were performed in the anatomy laboratory. The age range of specimens was 39 to 83 years. Descriptive statistics of demographics are summarized in Table 1. All cadavers were fresh cadavers (with no formaldehyde preservative used) that were less than 24 hours old. Those who had trauma, surgery, or radiation therapy in the back were excluded. This study was conducted according to the guidelines proposed in the Declaration of Helsinki.
Table 1. -
Descriptive Statistics of Demographics
|Mean age ± SD, yr
||52.83 ± 14.33
|Mean weight ± SD, kg
||56 ± 7.59
|Mean height ± SD, m
||1.57 ± 0.06
|Mean BMI ± SD, kg/m2
||22.6 ± 2.59
BMI, body mass index; PMH, previous medical history; HIV human immunodeficiency virus.
Gross dissection was performed in a vertical order from skin to deep fasciae to expose the superficial adipose tissue (SAT), superficial fascia (SF), and deep adipose tissue (DAT) sequentially (Figs. 1 and 2). In the meticulous dissection procedures for the SFS, incisions were directly made from the skin to the deep fascia to form strips of SSC. Four incisions oriented perpendicular to the spine were designed at equal intervals from the cephalic to the caudal end across the dorsum. In the same way, a long incision oriented parallel to the spine is made on the other half of the back at a distance of 6 cm from the spine. To further explore the fine structure and biochemical characteristics, adipose tissue was removed while the fascial tissue was carefully protected.
To verify whether there are regional differences in the biomechanics of the SFS and whether such differences are consistent with the degree of subcutaneous tissue attachment, we proposed the concept of deformation rate to quantify the strength of the SFS and performed the following steps to measure it. Six points are taken at equal intervals on the long incision across the dorsum. A tensile stretch of 5 N was applied to each point through two pulleys fixed above the dissection table. (See Figure, Supplemental Digital Content 1, which shows a schematic demonstrating the measurement approach for determining the deformation rate, https://links.lww.com/PRS/F756.) The deformation distance (L) of the retinaculum cutis was measured and the deformation rate at each point was obtained using the following formula:
Statistical analyses were performed with SPSS version 25 (IBM Corp.). Continuous variables were recorded as means and standard errors. The Shapiro-Wilk test was used to determine whether the data followed a normal distribution. An analysis of variance test was performed to test for differences in deformation rate among the groups. If a statistically significant difference was found with the analysis of variance, the Tamhane test was used as a post hoc multiple comparison test when the variances were not homogeneous. Data were visualized using GraphPad Prism version 8 (GraphPad Software, Inc.).
Dorsal Anatomical Layers and Fat Distribution
The SAT in the back was thick and evenly distributed, with few regional changes (Fig. 1). Further comparison of superficial fat thickness on the back and buttocks also showed no regional changes (Fig. 2). Vertically oriented retinacula cutis superficialis (RCS) were discovered between the skin and the superficial fascia (SF). The RCS are dense and concentrated in the back, dividing the SAT into cube-shaped units.
The SAT and DAT are separated by the SF. The SF between the thoracic vertebrae and the scapula, the dorsal thoracic fascia, is dense and possesses abundant vascularity. The SF and deep fascia are connected at the spinous processes and form zones of adherence, thus separating the SSC on both sides of the back, which allows the SSC on each side to function independently. The same connection of SF and deep fascia is observed at the medial border of the scapula and along the iliac crest.
DAT is distributed unevenly. In the upper back, it is thickened laterally in the scapular region close to the posterior axillary line (Fig. 1). In the lumbar triangle region, the thickness varies significantly (Fig. 2, above). The thickest area, located lateral to the erector spinae and superficial to the gluteus medius, is known as the iliac crest deposit, where the DAT is considerably thickened compared with the SAT. A perforator vessel running through the deep fat was observed at the junction of the lumbar triangle region and buttock (Fig. 2, above). In the upper back, the retinaculum cutis profundus (RCP) was closely connected with the supraspinatus ligament and formed a fibrous septum directed obliquely upward to the cranial side. In the lumbar triangle region, the RCP has a horizontal oblique laminar structure and is tightly bound to the thoracolumbar fascia. After removal of all subcutaneous tissue, the point of maximum indentation17 can be seen at the junction of the anterior edge of latissimus dorsi and the lateral edge of musculus obliquus externus abdominis along the inferior edge of the twelfth rib (Fig. 3). The vectorial cross-sections suggested that fat deformity in the suprascapular region, the buffalo hump, results from the thickening of the DAT (Fig. 4).
Regional Variations and Fine Structure of the SFS
In the transverse incisions in each region, the SSC in the scapular and subscapular regions was lifted to expose the deep fascia (Fig. 5). Microscopically, the retinaculum cutis consists of loose interlobular fascia and stiff functional fascia. Macroscopically, the RCP of the scapular region gradually lengthens from medial to lateral, and its combination with the deep fascia gradually changes from compact to lax. In the infrascapular region, the RCP binds more loosely to the deep fascia than in the scapular region. Differences were quantified along the craniocaudal incision excepting the suprascapular region, where the SSC was too compact to be lifted to a processable level and therefore was excluded from the analysis (Fig. 6). The SFS in the infrascapular region was loose with a transparent appearance, and the SFS in the scapular and lumbar triangle regions was denser with an opaque or white appearance. Under a tensile force of 5 N, the deformation rates of the RCS and RCP in the above regions were measured (Table 1). The deformation rate of the RCS (Fig. 7) was 5.31 ± 0.43 mm/N in the scapular region, 5.75 ± 0.70 mm/N in the infrascapular region, and 5.38 ± 0.96 mm/N in the lumbar triangle, with no significant difference (P = 0.308). The deformation rate of the RCP (Fig. 8) in the infrascapular region (19.33 ± 4.40 mm/N) was significantly higher than that in the scapular region (7.49 ± 2.76 mm/N) and lumbar triangle (9.33 ± 5.38 mm/N), and there was no significant difference in the deformation rate between the scapular region and lumbar triangle (Table 2).
Table 2. -
||RCS Deformation Rate
||RCP Deformation Ratea
P = 0.308
P < 0.001
RCS, retinaculum cutis superficialis; ANOVA, analysis of variance.
aTamhane for RCP.
bS (scapula) versus I (infrascapula) < 0.001; S versus lumbar triangle (L) = 0.669; I versus L < 0.001.
Illouz6 observed and described the existence of some “fixed points” on the human body. Lockwood5 defined these points as “zones of adhesion” and states adhesion is greatest in creases and folds and less so over bulges of deep fat deposits. However, Taylor18 reported that the zones of adhesion above the iliac crest are independent of the overlying deep fat collections and mapped the strength of the adhesion by observing the cadaver muscle fascia. In this study, we further investigated the anatomical explanation of the adhesion strength and quantified this property. Specifically, the subcutaneous laxity/density/adhesion strength is a macroscopic representation of the denseness of the distribution of functional fascia. In our meticulous dissection, we observed regional differences in this density, which is consistent with previous reports of microscopic observations.14,15,19 However, because the fascia is three-dimensional and cannot be accurately described by density in any single vectorial direction, we defined deformation rates to facilitate further comparison. Differences in deformation rates across the dorsal SFS were verified by statistical methods, and this topography of differences did not coincide with maps of fat thickness variation, which contributed to the diversity of dorsal contour deformities. That is, the appearance of the SSC is determined by the combination of variable fat thickness and different SFS deformation rates. If fat accumulation is combined with low-deformation-rate SFS, the SSC is less likely to be lax, forming a fat pad–like deformity. If the fat thickening is at a site with high deformation rate, it potentially produces expansion, excursions, and sagging. The results of this study revealed macroscopic patterns and microscopic structures of dorsal SFS, which explain the diversity of dorsal contour deformities and why dorsal liposuction is considered laborious.
Macroscopic Patterns of SFS Variation Align with Clinical Observations
The SFS was dense and had a low deformation rate in the scapular and lumbar triangle regions, whereas the subscapular region was relatively loose and had a high deformation rate, which matched the regional differences observed in back contour deformity (Fig. 9). An increase in fat volume results in distinctive regional outcomes. The suprascapular region and lumbar triangle region expand in thickness to form a fat pad. The lateral scapular region and infrascapular region expand both vertically and horizontally, and the direction of fat roll deformity depends on the positional relationship between the zones of adherence and the vector of gravitational effect. Furthermore, the deformation rate algorithm is also applicable to the zones of adherence/adhesion, which can be considered as densification/condensation of the retinacula cutis2,14 and therefore features the minimum deformation rate. As observed clinically, the zones of adherence along the spinous process and the medial scapula do not expand (Table 2).
Clinical Implications from the Microstructure of the SFS
The anatomical results demonstrate the close interaction between dorsal SFS and adipose lobules. To facilitate the understanding of the dynamic anatomy of the SSC at different deformation rates and the interaction of the components, a simplified illustration is shown in Figure 10. Obesity and contour deformity may be considered a disease state and are more than just hypertrophy of adipose. Correcting the “sick” SSC involves two aspects: first, removal of the expanding fat; and second, retraction of the cutaneous envelope after removal of that which expanded it. The elastic SFS network provides a dynamic anchor, permitting an adaptation to stress in all directions that enable tissues to spring back to their original state when the tensile force disappears.
The importance of protecting the SFS during liposuction has been widely recognized, and surgical complications (eg, irregularities, hematoma, and pain) are considered to be related to SFS injury.4,20,21 With the further findings of the SFS substructures in this study, it is necessary to discuss which substructure needs preservation precisely, as this has potential significance for surgical design and may be generalizable to other regions.
On the basis of the results of this article and review of the literature including immunofluorescence studies,16 histologic studies,15 in vivo computed tomographic images, and 3T magnetic resonance imaging scanning,14 we believe that functional fascia is the key to SSC retraction after liposuction and preventing vascular and nerve damage, and this is why we have named it functional fascia.
The richness and organization of the elastic component of the functional fascia suggests that it plays a major role in the mechanical behavior.15
It is reported that the subcutaneous vascular and nervous elements are surrounded and protected by the functional fascia.14 In the back, fat lobules are separated by more densely distributed functional fascia, and the liposuction cannula that can move easily in other areas (eg, abdomen) is blocked by functional fascia with smaller gaps. The surgeon has to apply stronger force to move the cannula, which possibly causes avulsion injuries to the functional fascia. How to target nonfunctional fat removal and preserve functional fascia in this special area deserves further discussion. Rohrich et al.4 proposed that the zones of adherence should be avoided in liposuction to prevent complications, and only small cannulas (<3.0 mm) could be used in case of necessity. From a microstructural point of view, the zones of adherence feature the lowest deformation rate and the densest functional fascia. Choosing a thinner cannula to match the narrower gap may also work in preventing functional fascia and its accompanying vascular nerve avulsions in the low-deformation-rate dorsal region. We hypothesize that thinner cannulas and reduced forces provide the opportunity for the cannula tip to slide over the elastic net and complete breakthrough in the relatively weak interlobular septa. However, a thin cannula increased the possibility of deflection against fibrotic tissue in back areas, leading to difficulty in tracking the cannula tip with palpation. We use a conical tip to avoid resistance that impedes the path of a cannula and alters its direction, keeping the tip in a controllable trajectory. The cannula should be positioned tangential to the back to minimize the risk of pneumothorax.
Based on the SFS topography, the functional protection concept, and the characteristics of Asian women, we summarized the following simplified zones for the back region (Fig. 11). First, the suprascapular zone belongs to the low-deformation-rate model. It was considered to be composed of fat tissue that is too hard for liposuction, and excisional lipectomy has been the traditional approach for this zone.12 Anatomical results demonstrated that the reason lies in its dense and developed SFS, and the authors have offered less invasive recommendations for this situation (Table 3). For patients with a dorsocervical fat pad, adequate liposuction of the DAT is very important. In addition, areas with a well-developed SFS have better retraction abilities, contributing to good postoperative outcomes. Second, the scapular zone is characterized by a gradual increase in the deformation rate from the midline to the axillary region. The fat in the axillary region is often ignored in liposuction. The anatomical results demonstrated that the region around the axilla features loose RCP with thick DAT, making the SSC more mobile during surgery. It is reported that liposuction of the axillary region increased the incidence of pneumothorax; thus, extra care should be taken in this area.22 In the authors’ clinical practice, a 3-mm cannula is used for tumescent infiltration and liposuction in the DAT layer, and a 2.5-mm cannula is used in the SAT with incision at the intersection of the posterior axillary line and the axillary fold.17 Pinch the SSC up off the chest wall and maintain constant awareness of the cannula tip to minimize the risk of chest penetration. Ideal aesthetic outcome includes defining the contour of the scapula, smoothing the lateral dorsal line, and extending the distance from the acromion to the posterior border of the axillary fold crease. Third, the subscapular zone belongs to the high-deformation-rate model and requires adequate release of the fat lobule to obtain the maximum retraction. Criss-crossing technique is important to make an obvious contraction effect. For patients bothered by back roll deformity without extreme skin redundancy, liposuction can make good correction with a minimal stealth scar (Fig. 12). Fourth, the lumbar triangle zone belongs to the low-deformation-rate model. Anatomical results demonstrate the considerable DAT accumulation in this zone. Adequate assessment of the fat thickness in this area helps the surgeon to have a clearer prognosis of the endpoint of the procedure, avoiding a conservative level and volume of liposuction that may result in more fat residue and failure to achieve optimal contouring results. Preoperative localization of the penetrating vessels (eg, using ultrasound) and placing the marked area at the very end of the operation helps to avoid the vessel traumatized early in the operation that then remains bleeding throughout the operation.
Table 3. -
|Retinacula cutis density
|Cannula diameter, mm
||Axillary fold (plus bra-strap line)
Some shortcomings of this study should be noted. First, this study included only women, mandating further research in men. Second, only Asian specimens are included in present dissections, as cadaver freshness is important and long-term transport can affect the accuracy of the results. Several studies have indicated racial differences in skeletal framework and fat topography,23–26 and whether the anatomical pattern of the dorsal SSC differs between races remains to be further investigated. Third, emerging technologies such as ultrasound-assisted liposuction, laser-assisted liposuction, and radiofrequency-assisted liposuction are not covered. Further research is needed to explore the underlying SFS responses to different energy settings (eg, pulsed or continuous delivery mode). Furthermore, our data collection may be biased by several factors, including relative freshness, preservation mode of cadavers, and environment temperature. The degree of bias and the direction in which this biases the results is unknown. This article could be regarded as a preliminary work for later research on soft-tissue modeling.
Regional changes in the SFS of the back explain the observed contour deformities in Asian women. An understanding of the SSC provides the basis for zoning and improves surgical precision of liposuction. A less invasive treatment plan with broader indications can be achieved with removal of the expanding fat and protection of SFS functionality. The mechanical behavior of the SSC can be better understood and predicted by mastering the characteristics of the SFS.
The authors have no financial interest or conflict of interest to declare in relation to the content of this article.
This work was supported by National Natural Science Foundation of China grant 81801926.
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