Evaluating socket interface pressure and shear for a trans-femoral amputee with synchronised gait event detection

Abstract

Introduction interface loading characteristics between the lower limb residuum and prosthetic socket is critical for tissue health, walking stability and overall rehabilitation outcomes. Dynamic interface pressure and shear have been reported to show complex biomechanical coupling [1]. Load characteristics at different residuum locations are expected to vary during gait. However, so far, there are few reports on synchronised measurement between gait events and interface loading to help understand load transfer mechanisms. A wearable stress sensing system and inertial measurement unit (IMU) were used capture interface loading profiles and synchronised gait events, respectively, on a trans-femoral (TF) amputee.

Methods: a left-sided TF amputee participated (weight 56 kg, ischial containment socket). An IMU was mounted distal to the prosthetic knee pivot (Fig 1a) and tri-axial pressure and shear sensors [2] were placed on the inner socket at known load-bearing regions (Fig 1b), i.e., posterior-distal (PD), posterior-proximal (PP) and anterior-proximal (AP) to measure pressure (P), circumferential (SC) and longitudinal shear (SL). The participant walked at self-selected speed along a level-surfaced corridor. IMU and sensor data outputs were synchronised.

Results and Discussion: Fig 2. shows typical angular velocity (AV) and P measured at PD. AV was used to identify timing of key gait events [3] including initial contact (IC), mid-stance (MST), toe-off (TO) and mid-swing (MSW) based on which interface P, SC and SL were obtained at different sites (Fig 3a-d). At IC (Fig 3a), P at PP (18±2kPa) was higher than that at AP (6±2kPa) as the residuum pushes against the PP location of the socket wall [1]. In MST and TO, P were relatively well-distributed (P of 27-34kPa and 20-25kPa, respectively). In MSW, significant reduction of P was obtained at AP (3±1kPa) accompanied by higher SL (8±1kPa) compared to other sites, indicating the residuum moving up in the socket.

Conclusion: this is a first-of-its-kind results linking gait events with interface pressure and shear data for lower limb amputees, which enables the study of load transfer mechanism. Detailed studies will be presented to analyse real-world kinetic and kinematic analysis while conducting activities of daily living.

Acknowledgments
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] J. Tang et al., Med Eng Phys, 2017; 49:131-139.
[2] P. Laszczak et al., Med Eng Phys, 2016; 38(7):695-700.
[3] Z. Aftab & R. Shad, PLOS ONE, 2022; 17(5): e0266726

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Identifiers

ORCID for Kirstie Devin: orcid.org/0000-0001-6794-2375

ORCID for Jinghua Tang: orcid.org/0000-0003-3359-5891

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

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