Mechanobiology and force transduction in scars developed in darker skin types

BACKGROUND: Scarring is a complex process involving many cell types, cytokines and biological pathways including mechanobiology. Some subtle mechanical properties of skin can be assessed by measuring the speed of ultrasound shear wave propagation. The orientation of abnormal skin tension forces can be visualized, particularly in darker skin types, using dermoscopy showing distinct patterns of rete ridges' conformation. AIM: To assess some mechanobiological features of scars in darker skin types. PATIENTS AND METHODS: Large atrophic and hypertrophic surgical scars were examined on the trunk of 35 darker skin subjects. The surrounding skin was used as a comparator. Dermoscopic aspects were recorded. Resonance running time measurements (RRTM) were performed using a shear wave propagation device (Reviscometer). They were performed in four specific directions at given angles with regard to the long axis of the scar. The minimum, maximum and mean RRTM values were recorded at each site. RESULTS: Dermoscopy revealed patterns of melanin deposits in scars distinct from the normal honeycomb network seen in the surrounding skin. Hypertrophic scars showed a patchy pattern of large macular melanoderma dispersed in a lighter background. In these cases, low RRTM values were obtained with little variations according to the orientation of the measurements. By contrast, atrophic scars showed a streaky laddering melanotic pattern under dermoscopy. Higher RRTM values were often obtained, particularly in the transversal direction of the scars. Mechanical anisotropy was greater in the atrophic scars compared with the normal skin. DISCUSSION: Darker skin types represent a model for visualizing the main orientation of the epidermal rete ridges. A correlation was found between the pattern of melanized rete ridges of scars and the main orientation of the intrinsic forces in the skin.