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Analysis of Liner Deformation Behaviour in Transtibial Prosthesis


 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 either acts hard and hence result in discomfort or deforms too much and results in 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. A generalized deformation model taking into account the interaction of the socket, liner, muscle, and tissue becomes cumbersome. In the literature, numerous hyper-elastic models have been applied. Studies on suitability and application of hyper-elastic materials for liner material has not been sufficiently carried out. In this paper, the suitability of liner materials in terms of their ability to allow sufficient elastic deformation in the normal direction for the cushioning effect while undergoing limited shear deformation has been investigated. 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.