<p>The problems associated with the prostheses for transtibial amputees are related mainly to the fit and comfort. There has been a steady effort to improve the wearability, stability, and durability of the below-knee prosthesis. The liner in the below-knee prosthesis plays a crucial role in ensuring these quality characteristics. Isotropic liner material that is either highly rigid or highly soft in all directions either act hard and hence result in discomfort or deform too much and eventual loosening of the prosthetic socket. The material hyper-elastic behavior and thickness are both critical in the design of the liner with optimum comfort. Analysis of deformation mechanics of transtibial prosthesis must take into account the interaction of several elements namely, the socket, liner, muscle, tissue, and bones. However, the complicated mechanical behavior of each of these poses severe restrictions on successfully achieving a fully generalized deformation model. In the many experimental and contact stress analysis carried out to optimize the socket fit, numerous hyper-elastic models have been applied to capture the non-linear stress-strain behavior of soft tissues and muscles of the residual limb. Studies on suitability and application of hyper-elastic materials for liner material has not been carried out sufficiently in the literature. Similarly, there are around ten different hyper-elastic models available in the literature but only some of them actually model the physical liner materials available. In this paper, numerical analysis of three different hyper-elastic materials are investigated for their suitability as the liner material bonded to the socket. The suitability for best possible fit has been defined as the ability of the material to allow sufficient elastic deformation in the normal direction for the cushioning effect while undergoing limited shear deformation. The hyper-elastic liner and rigid socket pair have been idealized as adhesively bonded flat layers of suitable thicknesses subjected to various combinations of normal and shear loads. The deformations for a normal load and varied range of shear loads have been compared to conclude on the best-suited material model. The low shear deformation observed for all three liner materials implies that the shear loading will not affect the adhesive bond between the liner and socket and hence will not cause loosening with prolonged usage of the prosthetics. The deformation observed was maximum with Ogden 3-parameter hyper-elastic model, whereas it was least in the case when Mooney Rivlin 3-parameter hyper-elastic model. The results obtained for the Mooney-Rivlin 3-parameter model and Neo-Hookean model are very close to each other.</p>

Analysis of Liner Deformation Behaviour in Transtibial Prosthesis

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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