Collagen and Elastic Fiber Content Correlation Analysis between Horizontal and Vertical Orientations of Skin Samples of Human Body

Background. Unequal distribution of dermal collagen and elastic fibers in different orientations of skin is reported to be one of the multifocal causes of scar related complications. Present study is to understand the correlation pattern between collagen in horizontal (CH) and in vertical (CV) directions as well as that of elastic in horizontal (EH) and vertical (EV) directions. Materials and Method. A total of 320 skin samples were collected in two orientations from suprascapular, anterior chest, lateral chest, anterior abdominal wall, and inguinal regions of 32 human cadavers. Spearman correlation coefficient (r) was calculated between the variables (CH, CV, EH, and EV). Results. Significant positive correlation between CH and CV, and between EH and EV observed in all 5 areas tested. A negative correlation between CV and EV at suprascapular, lateral chest, and inguinal regions and negative correlation between CH and EH at anterior chest and anterior abdominal wall have been identified. Conclusion. Knowledge of asymmetric content of dermal collagen and elastic fibers together with the varied strength and degree of association in the given area provides guidelines to the dermatologists and aesthetic surgeons in placing elective incisions in the direction maximally utilizing the anatomical facts for aesthetically pleasing result.


Introduction
The dermis of the skin has two parts that are accountable for sustaining the epidermis. The papillary part of the dermis is a thin sheet located just below the epidermis. It contains a small number of collagen and elastic fibers. The reticular layer of dermis lies deep into it, which contains larger bundles of collagen and elastic fibers that usually run parallel to surface of the skin.
Skin incisions or injury to the skin is known to produce scar. Hence, appearance of a scar, following wound repair, is a natural process. Intercomplimentary functions of collagen and elastic fibers play a key role in the wound healing and its subsequent consequences resulting in the formation of the scar. Sherratt reported that the types of collagen present in the scar tissue and the normal skin are similar, but with the diverged pattern of arrangement and distribution as compared to normal [1]. Similarly, Rnjak et al. reported the useful role of dermal elastic fibers in the process of wound healing and improvement of scar appearance [2].
Hypertrophic scars more commonly affect young individuals. Females are more prone to hypertrophic scars when compared to males for unknown etiology. The anterior chest, presternal region, shoulders, and deltoid regions are predisposed to hypertrophic scars [3][4][5][6][7]. Anterior chest area is also vulnerable for keloid formation [8]. Nevertheless, scar stretching occurs most frequently in the lower third of the scar overlying the xiphisternum and it may extend onto the abdomen [3]. In this study, we aimed to analyze the possible correlation between collagen and elastic fiber content in dermis of skin samples obtained from horizontal and vertical directions from selected areas of body and its possible effect in scar related complications.

Materials and Method
Three hundred and twenty (320) skin samples (160 each in horizontal and vertical orientations) at 5 different areas of human body were obtained from 32 formalin embalmed adult cadavers of either gender, aged between 50-70 years. Before obtaining the samples, the gross appearance of the skin quality of the cadaver was examined thoroughly to ensure its healthy appearance. The samples were obtained in two different orientations (horizontal and vertical) at randomly selected areas with the following descriptions: (1) Suprascapular area: skin samples were obtained along the superior border of trapezius muscle overlying the scapula. (2) Anterior chest area: skin overlying body of the sternum (at the level of 3rd costal cartilage) along its midline was taken. The vertical section was obtained along the vertical axis of the sternum, while horizontal section was across the former.   (ii) C H and E H (between collagen and elastic fibers in horizontal direction).
(iii) C V and E V (between collagen and elastic fibers in vertical directions).
(iv) E H and E V (elastic fiber content between horizontal and vertical directions).
The results obtained by these calculations were interpreted according to the strength of association (strong, moderate, and low) and degree of correlation (positive or negative) according to reference table (Table 1) after taking into consideration the significant correlation ( < 0.01 or < 0.05).

Results
Descriptive statistics of Spearman's rho correlation coefficient ( ) and the level of significance ( ) as computed from the selected areas of body are presented in Table 2 and corresponding scatter plots of significant (two-tailed) correlations are depicted in Figures 1-5. Comprehensive data with statistically significant ( < 0.01 or < 0.05) correlation coefficient with the pattern of strength of association in each area are given in Table 3. Spearman's correlation revealed a statistically significant positive correlation between C H and C V in all areas: suprascapular area ( = 0.75, < 0.01), anterior chest area ( = 0.56, < 0.01), lateral chest area ( = 0.55, < 0.01), anterior abdominal wall ( = 0.57, < 0.01), and inguinal region ( = 0.77, < 0.01).
Significant negative correlations between C H and E H were seen only at anterior chest area ( = −0.55, < 0.01) and in anterior abdominal wall ( = −0.57, < 0.01).
Statistically significant negative correlation between C V and E V was also seen at suprascapular ( = −0.37, < 0.05),

Discussion
The management of scar in the clinical setup is one of the most challenging tasks for aesthetic surgeons. This has not been resolved even after the incisions had been made on the skin in accordance with the standard lines of choice. The varied quantity and asymmetric content of dermal collagen and elastic fibers in different orientations of skin plane affecting the formation of scar remain a possibility [12]. Asymmetric distribution of dermal collagen and elastic fibers in different regions of human body is said to have    regional discrepancies. It may be depending on the texture of the skin, as in head and neck region [13], anatomic, functional, or physical cause of skin tension as applicable in trunk region [10], and may be due to effect of various forces like burst force and stretch force exerted at joints [14]. These factors are found to be applicable in the management of wound healing consequences and scar management. Selective incision on the skin was preferred to be line of Langer's. However, in some topographic sites of human body these lines are obscure and poorly differentiated. Conversely, role of an unequal distribution of dermal collagen and elastic fibers, as observable in two different orientations of the skin, is worth noticeable. Understanding the possible correlation between the collagen and elastic fibers between two different skin planes serves a valuable basis in the management of aesthetic procedures.
The correlation pattern analysis revealed that skin over the suprascapular area had strong positive correlation between C H and C V and between E H and E V . Lateral chest showed moderate positive correlation between C H and C V and low positive correlation between E H and E V . Inguinal region also showed strong positive correlation between C H and C V and moderate positive correlation between E H and E V contents. But all three areas exhibited low negative correlation between C V and E V .
This indicates that the content of collagen and elastic fibers in these areas changes in accordance with their positive manner of correlation across two directions (horizontal and vertical), while, in the vertical direction, the content change between collagen and elastic fibers would be in reversed manner due to negative correlation between them.
In the remaining two areas, that is, anterior chest area and anterior abdominal wall, moderate positive correlation was observed between C H and C V , and between E H and E V . And in both areas, moderate negative correlation between C H and E H was observed. Therefore, in these areas, both  the collagen and elastic fibers content between horizontal and vertical directions change in positive manner, but along the horizontal direction when collagen is increased corresponding elastic fiber content will be decreased and vice versa occurring consequently due to negative correlation effect. Previous research study analyzing the unequal distribution of dermal collagen and elastic fibers across two directions in these areas reported that the abdomen area with higher content of both collagen and elastic fibers in horizontal direction accomplishes the functional cause factor together with Langer's line concept. Whereas the suprascapular, presternal, and lateral chest areas fulfill the dominance of functional cause factor over anatomical cause. Thus, in these areas, the collagen content in horizontal direction is significantly higher than vertical direction without any similar changes in their elastic fiber content between two directions. The groin area, on the other hand, witnesses the nullified effect of elastic fibers that necessitates its increased content in vertical direction without the changes of collagen content [10].
To summarize, significant positive correlation between C H and C V and between E H and E V as observed in all areas tested is dependent on the functional reason due to local stretch force effect rather than the anatomical cause factor as reported earlier [10]. This correlation pattern in these areas is in accordance with the collagen content pattern in two different directions as the collagen content is more in horizontal direction than in their vertical direction (C H > C V ).
On the other hand, negative correlation between C H and E H at anterior chest and anterior abdominal wall and negative correlation between C V and E V at suprascapular, lateral chest, and inguinal regions have been observed. This may be due to the fact that, in certain areas, constant active or passive stretch force works for the movements and gravity (as weight of upper limb which constantly produces rotation force on scapula/pulls the shoulder downward direction). The effect of these forces may be more in one or more directions which necessitates the requirement of increased elastic fiber content  in that specific direction. Accordingly, the higher allotment of elastic fibers in horizontal direction than in the vertical direction (E H > E V ) was attributed to the areas where the negative correlation between C H and E H was noted, while reversal of this was seen in the remaining areas where the negative correlation between C V and E V exists.

Conclusion
Understanding the pattern of asymmetric content of dermal collagen and elastic fibers in a given area together with the stress on proposed incision in that area and degree of association between them in two different planes provides a valuable guideline to the dermatologists and surgeons in elective incisions that necessitates providing aesthetically pleasing results and in the management of scar related complications.