Biomechanical Characterization of Soft and Hard Tissues for Finite Element Modeling of Hands
Eduardo M. Sosa, PhD, Benjamin Giertych, MD, Joshua Parenti, MS, Samuel Llavina, BS, Alan Mizener, BS, Austin Roberts, MPH and Shafic Sraj, MD, West Virginia University, Morgantown, WV
Finite element modeling (FEM) has been focused on the wrist, extensor tendons, carpal tunnel, and individual fingers but not the hand. FEM of the whole hand has a significant potential for simulating and assessing surgical intervention, thus reducing the need for cadaver studies. FEM requires the definition of material characteristics of the different tissues (Figure 1). The purpose of this study is to determine the biomechanical properties of the major structures of the hand, including bones, tendons, muscles, and skin.
We investigated the biomechanical behavior of dorsal and palmar skin, metacarpal and phalangeal bones, flexor and extensor tendons, and thenar and hypothenar muscles. We used uniaxial, planar, and biaxial tensile loading, confined compression, and three-point bending where appropriate (Figure 2). All specimens were mounted to an electromechanical test frame and loaded to failure at a rate of 25mm/min.
Four matched pairs of fresh-frozen human hands were used for this study. The average age was 64 (SD 8.9). Specimens were dissected and extracted for testing. For the skin, we found an average maximum uniaxial load of 27.4 N (SD 21.0) and 27.1 N (SD 11.4); average maximum planar tensile force of 681 N (SD 459) and 574 N (SD 172), and average maximum biaxial tensile force of 565 N (SD 401) and 520 N (SD 188) for dorsal and palmar sides, respectively. Thenar and hypothenar muscle specimens under confined compression showed a volume change ratio of 0.95 at a force of 1000 N. Three-point bending tests showed an average maximum load of 1005 N (SD 276) and 871 N (SD 502) for metacarpal and proximal bones, respectively. Tensile testing of tendons showed an average breaking force of 523 N (SD 113), 692 N (SD 154), and 636 N (SD 176) for EDC, FDP, and FDS tendons, respectively.
Biomechanical evaluation of soft and hard tissues specific to the hand provides valuable strength and deformation information needed for a reliable finite element model of the hand that can be used for multiple applications.
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