Biomechanical analysis of the lower limb amputee socket interface

Abstract

The lower limb prosthetic socket provides a critical interface, which transfers loads between the ground and the residuum. Many amputees report issues related to residuum pain primarily induced by poor socket fit, leading to unsatisfactory rehabilitation outcomes. From a scientific perspective, residuum and socket have been treated as a rigid body. Effective methods, which could provide quantitative measurements of multi-directional loads (i.e. the kinetics) and relative motion (i.e. kinematics) at the residuum/socket interface, are not currently available. The in-situ measurement of kinematic and kinetic parameters and indeed their correlations during amputee walking would help to obtain a comprehensive understanding of the biomechanics at the critical residuum/socket interface.
In this thesis, means of assessing residuum/socket interface mechanics has been developed, incorporating the kinematics and kinetics, to comprehend the interface biomechanics. A novel kinematic model was developed to evaluate the interface kinematics based on a 3D motion capture system. The model was applied on both knee disarticulation and trans-tibial participants. Repeatable interface kinematic waveforms (coefficient of multiple correlation of up to 0.988) were obtained on level walking studies over a 2-year period. The model is highly sensitive to walking speed, terrain and prosthetic components. For example, a 21% of increase in walking speed led to an increase in angular and axial displacements of approximately 23% and 6%, respectively. In addition, a novel tri-axial pressure and shear (TRIPS) sensor system, capable of measuring both dynamic pressure and shear stresses, was used to evaluate the interface kinetics as a function of gait cycle (GC). The multi-directional stresses obtained from key loading bearing locations of the residuum suggested that the interface loading is dependent on walking speed, terrain, prosthetic components and socket suspension system. For example, changes to the latter by the removal of one sock resulted in a reduction of the stresses at the proximal location of approximately 30% and an increase of stresses at the distal location of the residuum of up to 28%. Subsequently, the combination of the novel kinematic model and the body interface sensor system was applied to study their correlation, providing a first-of-its-kind approach which shed light on the in-situ interface biomechanics. The method for assessing socket interface mechanics established here therefore provides a stepping stone to quantitatively assist in the socket fitting process and the monitoring of residuum tissue health.

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ORCID for Liudi Jiang: orcid.org/0000-0002-3400-825X

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