Abstract
A Finite Element Analysis (FEA) was performed to evaluate the interaction between residual limb and socket when considering the dynamic loads of the gait cycle. Fourteen transfemoral amputees participated in this study, where their residual limbs (i.e., soft tissues and bone), and their sockets were reconstructed. The socket and the femur were defined as elastic materials, while the bulk soft tissues were defined as a hyperelastic material. Each model included the donning, standing, and gait cycle phase, with load and boundary conditions applied accordingly. The influence of adding the dynamic loads related to the gait cycle were compared against the modelling of the static load equivalent to the standing position resulting in changes of 23% ± 19% in the maximum values and in an increase in the size of the regions where they were located. Additionally, the possible correspondence between comfort and the location of peak loadbearing at the residual-limb/socket interface was explored. Consequently, the comfort perceived by the patient could be estimated based on the locations of the maximum stresses (i.e., if they coincide with the pressure tolerant or sensitive regions of the residual limb).
Highlights
IntroductionBoth normal (i.e., perpendicular to the skin) and shear stresses (i.e., tangential to the skin) are applied to the soft tissues of the residual limb, which are not accustomed to bear such elevated loads, inducing the risk of skin problems and chronic pain[1,2,6]
When wearing a prosthesis, both normal and shear stresses are applied to the soft tissues of the residual limb, which are not accustomed to bear such elevated loads, inducing the risk of skin problems and chronic pain[1,2,6]
This study aims to analyse the stress distribution of the residual limb of 14 transfemoral amputees, evaluating which zones are highly exposed to pressure and shear stresses based on FE results
Summary
Both normal (i.e., perpendicular to the skin) and shear stresses (i.e., tangential to the skin) are applied to the soft tissues of the residual limb, which are not accustomed to bear such elevated loads, inducing the risk of skin problems and chronic pain[1,2,6]. The existence of algometers as reliable medical devices for measuring PPT11,12 can lead to easier implementation of new protocols for socket design where pressure tolerant and sensitive regions at the residual limb are defined according to the PPT that patients can endure based on their perception[2,6,13,14] These thresholds are established when critical stresses and strains states exceed tolerable values. FEA on transfemoral amputees have been studied before, there is a need to evaluate the behaviour of the interface under dynamic loads This will allow to analyse higher precision models for residual-limb load and boundary conditions that do not ignore changes in the coupling between the socket and the lower limb due to relative angular movements or axial displacements, or changes of variations in velocity and acceleration[1]. The study compares the perception of comfort and the location of the peak loads (i.e., feeling comfortable when the peak loads are located at pressure tolerant regions or feeling uncomfortable when they are located at pressure-sensitive regions)
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