SURFACE OPTIMIZATION OF A SOCKET FOR A TRANSFEMORAL AMPUTEE THAT REDUCES THE STRESSES VARYING THE FRICTION COEFFICIENT

The shear stresses and pressures in the socket-stump interface were calculated for
four transfemoral amputees, using the finite element method. A dynamic explicit model was
developed for the simulation of the fitting procedure of the socket and the applying of the
loads corresponding to the support phase during the gait, and a constitutive multilayer hyperelastic model was employed for the soft tissues (skin, fat and muscle) because of their large
strains and displacements, and lineal isotropic models for the bone and socket.
In order to determine the influence of the friction coefficient on the socket-skin interface, its
value was varied from a minimum value of 0.5 to a maximum of 1.0. Then, the zones where
the greatest pressures and stresses occurred were identified, where the use of a horizontal
strip was proposed with a variation of the friction coefficient from 0.2 to 0.6, in order to observe its effect on the obtained stresses. The strip has a width of 10 cm and is located approximately 2.0 cm below the ischial support of all the individuals. It was observed that the pressure does not change significantly when varying the friction coefficient. However, the average
shear stress tends to rise when increasing the friction coefficient, and after applying the strip
the average shear stress reduced up to 25%, while the pressure variation was not significant.
Finally, the experimental validation of the behavior of the friction coefficient between the
polypropylene and the skin was performed with a sclerometer. This experiment considered
factors such as the patient’s sweat, the amount of hair and the surface texture of the polypropylene coating, and it proved that the surface texture of the coating must be accounted for
when measuring the friction coefficient.