Biomechanical properties of scalp flaps and their correlations to reconstructive and aesthetic surgery procedures

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Abstract
In formulating an accurate pre-operative plan when performing plastic surgery, the biomechanical properties of the soft-tissues involved should always be taken into account. No study has yet been carried out regarding the tensiometric peculiarities of the human scalp. The aim of the present study was to measure the load-elongation properties of the human scalp, in an attempt to characterize it through the constants of a stress-strain theory. This would provide plastic surgeons with information needed to test the soundness of the various surgical techniques currently adopted, as well as a way to better plan a reconstructive or aesthetic procedure on the scalp. Data were collected by stepwise loading 20 scalp flaps, obtained by a reversed-Y scalp incision down to and through the galea aponeurotica, together with 1 -cm undermining, on the subgaleal layer, along both sides of the sagittal scalp incision. The tissue's stress response to displacement was visualized as a three-phase characteristic. Initially linear (load range: 0 to 500 g), the scalp's compliance gradually reduced (load range: 500 to 1500 g) and eventually demonstrated an exponential stress-strain characteristic of rapidly increasing stiffness (load range: 1500 to 5000 g). Young's modulus E was derived from the mean-values curve, and was found to be equal to 117.1 g/ mm. These data have practical implication for studying the effects of complex surgical closures on the one-dimensional stress distribution of the scalp, while allowing the use of analytical methods to predict the consequences of closure design in various plastic surgery procedures on the scalp.