Experimental evaluation and finite element analysis of biomechanics at a transfemoral socket interface

Devin, Kirstie Marie, Tang, Jinghua, Moser, David and Jiang, Liudi (2022) Experimental evaluation and finite element analysis of biomechanics at a transfemoral socket interface. BioMedEng22, UCL Institute of Education, 20 Bedford Way, WC1H 0AL, London, United Kingdom. 08 - 09 Sep 2022.

Abstract

Introduction: the lower limb amputee socket interface is subject to prolonged and extensive loading, which may lead to tissue damage and prosthesis rejection. Finite Element Analysis (FEA) has been widely used to evaluate interface biomechanics. However, there is little work combining experimental in-situ measurements (i.e. amputee test) and FEA. This study utilised unique tri-axial pressure and shear (TRIPS) sensors [1] to measure multidirectional loading at the stump/socket interface during ambulation of a transfemoral amputee. A corresponding finite element (FE) model was developed for analysis.

Methods: the participant (weight=81kg, height=178cm, supra-condylar suspension socket) walked along an 8m level walkway. TRIPS sensors were placed at posterior-proximal (PP), anterior-proximal (AP) and anterior-distal (AD) at the stump/liner interface to measure pressure (P), transverse (SC) and longitudinal (SL) shear. A FE model was created (Figure 1a) to mimic the participant’s stump/socket interface. Coefficient of friction of 0.5 was applied to liner/socket interface. Corresponding ground reaction force were applied to distal socket in FEA.

Results & discussion: figure 1b shows experimental P, SC and SL profiles at AD. Pressure exhibited a characteristic “double-hump” profile; peak pressure in early and late stance were similar (29kPa). Notable peak SC (-11kPa) and SL (7kPa) in early stance indicate combined stump lateral rotation and pushing down in the socket. Figure 1c compares peak FEA stress with corresponding sensor outputs at PP, AP and AD. Lower FEA pressure at all sites were observed. We believe this is largely attributable to exclusion of initial interface loading (i.e., baseline) induced by socket design features, such as suspension and load bearing [2]. Addition of sensor baselines to FEA resulted in closer alignment with real amputee data, emphasising the importance of including pre-walking/baseline interface stress in FEA. Detailed results and discussion on experimental amputee data, FEA methodology, and their comparison will be presented.

Conclusion: results show complex interactions at the stump/socket interface, underpinned by pressure and shear measurements in amputee tests and corresponding FEA, whereby inclusion of initial baseline loading is important.

Acknowledgements: this work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) grant EP/S02249X/1 for the Centre for Doctoral Training in Prosthetics and Orthotics.

References:[1] Laszczak P. et al. Med Eng Phys 2016; 38:695-700.[2] Tang J. et al. Med Eng Phys 2017; 49:131-139.

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Contributors

Author: Kirstie Marie Devin

Author: Jinghua Tang

Author: Liudi Jiang

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