Objective To build three-dimensional (3-D) finite element models for local advancement skin flap, by which the post-operative local strain and local stress of skin were figured out to assist in the design of skin flap in clinic. Methods The biomechanical parameters of human forehead skin were obtained in vitro from biomechanical experiments. The 3-D finite element model of local advancement skin flap was set up by MSC Marc/Mentat 2005 (3-D finite element software). Six models were built with the same flap but different skin defects, to simulate post-operative local strain of skin and local stress of skin in different models. Results Post-operative local stress of skin increased with the skin flaps stretching, but the relationship between increase and stretching did not meet the linear rule. Skin flap was able to stretch to 40 % of its initial length in theory if we did not consider blood supply of it. When the skin flap stretched over 40 % of its initial length, the maximal stress could exceed the yield limit. Conclusion It is an effective and workable way to simulate local advancement skin flap using 3-Dfinite element model and biomechanical parameters of human skin. The stretch ratio of local advancement skin flap should be not over 40% for safety.

Objective To observe responses of brain evoked by somatic stimuli in healthy subjects with blood oxygenation level-dependent functional magnetic resonance imaging.Methods There were 30 healthy subjects in the study. Block design was used infunctional MR imaging. In experimental tasks somatic stimuli was executed to the hands of every subject at duration 1000 ms,interstimulus intervals 1000 ms.The professional software-SPM99 was performed to process the images.Results For healthy subjects to somatic stimuli, significant activation was observed in bilateral primary and secondary somatic cortex of precentral gyri and postcentral gyri, and temporallobes. Scattered activations could be seen in frontal lobes, supramarginal gyri and hemisphere of cerebella. There was more intensiveactivation in right hemisphere than that in left. There was no significant difference between the activation evoked by somatic stimuli of leftand right extremities. Conclusion somatic stimuli can evoke significant activations in bilateral primary and secondary somatic cortex.Temporal lobes and other brain areas join in the process of somatic stimuli.