Biomechanical interaction at a transtibial residuum/socket interface during ambulation

Abstract

1. Introduction
The socket interface for lower limb amputees is critical for comfort, safety and overall rehabilitation outcomes. There are limited studies focused on dynamic socket interface biomechanical interactions during ambulation, especially for transtibial (TT) amputees [1]. Combined measurement of pressure and shear at load bearing regions of the interface is important to provide biomechanical understanding of the complex loading profile during ambulation. Thin flexible tri-axial pressure and shear (TRIPS) sensors [2] capable of measuring these multidirectional forces were reported for transfemoral amputees [3,4] though TT residuum/socket interface study has not been reported.

2. Research question
We aim to study the TT residuum/socket interface biomechanical interaction as a function of gait cycle and terrain.

3. Methods
Three TRIPS sensors were placed at kick-point (KP), patella-tendon (PT), and superior popliteal fossa (SPF) of inner socket wall (Fig. 1a) of a male TT participant (body mass 81kg, height 183cm, total surface bearing socket). The participant walked at a self-selected pace over a level surface, then up and down an 8◦ ramp.

4. Results
Fig. 1b-d showed mean±1SD of pressure (P), circumferential shear (SC) and longitudinal shear (SL) as a function of gait cycles. For level walking, pressures at weight acceptance (WA) are 335±9kPa (KP), 76 ±2kPa (PT) and 94±2kPa (SPF). Fig. 1 b-dii shows SC at KP reaches -137±4kPa in WA while negligible at PT and SPF. Fig. 1biii and diii show SL at KP (124±5kPa) and SPF (19±2kPa) act in proximal direction in WA, whereas SL in Fig. 1ciii acts distally at PT (-6±0.5kPa).

5. Discussion
P, SC and SL dominate at KP compared with those from PT and SPF. At KP, pressure in WA (335±9kPa) is higher than that in terminal stance (TS) (201±8kPa). In contrast, pressure at PT in WA (76±2kPa) is lower than that for TS (103±3kPa). This indicates higher PT pressure is required during TS to propel limb forward. High peak values of SC at KP (bii) of -137±4kPa (WA) and -91±4kPa (TS) suggests significant transverse rotation while SL at KP (124±5kPa) (biii) also suggests
simultaneous pistoning effect during WA.

When walking down a ramp, enhanced pistoning resulted in increased S L at KP and SPF compared with level walking (biii and diii). Also, greater braking force caused slightly higher SC at KP and SPF, indicating increased effort to maintain balance. When walking up a ramp, P, SC and SL increased at PT compared with level walking as the knee propels forward onto higher ground.

References
[1] G. H. Pirouzi, N. A. Abu Osman, A. Eshraghi, S. Ali, H. Gholizadeh, and W. A. B. Wan Abas, "Review of the socket design and interface pressure measurement for transtibial prosthesis," (in eng), ScientificWorldJournal, vol. 2014, p. 9, 2014, doi: 10.1155/2014/849073.
[2] P. Laszczak, "Development of tri-axial pressure and shear (TRIPS) sensors for lower limb prosthetics," in The Institution of Engineering and Technology (IET), ed. The Healthcare Technologies Student and Early Career Awards 2015: IET, 2015, p. 20 minutes 36 seconds.
[3] J. Tang et al., "A combined kinematic and kinetic analysis at the residuum/socket interface of a knee-disarticulation amputee," Med Eng Phys, vol. 49, pp. 131-139, Nov 2017, doi: 10.1016/j.medengphy.2017.08.014.
[4] P. Laszczak et al., "A pressure and shear sensor system for stress measurement at lower limb residuum/socket interface," Med Eng Phys, vol. 38, no. 7, pp. 695-700, Jul 2016, doi: 10.1016/j.medengphy.2016.04.007.

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Identifiers

ORCID for Kirstie Marie 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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