A proposal for the pre‐evaluation protocol of below‐knee socket design - integration pain tolerance with finite element analysis

Abstract

The design of a fitted socket is a fundamental critical issue in ameliorating the disability of an amputee. In this study, an evaluation protocol integrated finite element analysis with the pain-pressure-tolerance (PPT) of soft-tissue, is proposed to provide a quantitative socket design guideline prior to the socket being fabricated. A subject using a Kondylen-Bettung-Münster socket was selected in this study. Two FE models (the original Kondylen-Bettung-Münster and a newly designed total-surface bearing socket) were established based on computer tomography images. The surface-to-surface contact elements were employed to simulate the contact and sliding behaviors at the stump-socket interface. The PPT of the soft-tissue was measured by a hand-held indentor system. Comparing the simulated peak interface pressure with the PPT, both sockets demonstrated a safe margin (PPT / peak interface pressure) greater than two. These large safe margin values were consistent with the subjective assessment, as acceptable, of the amputee on both sockets. To conclude, using a nonlinear contact finite element simulation integrated with the PPT of each individual, it is possible to evaluate the socket fitness prior to the fabrication of the socket. Based on the results, for a fitted socket design the peak interface pressure under single leg standing should be much less than the PPT value. The acceptable range of safe margin value for a fitted socket should further be justified by more subjects.

Physically Based Modelling and Simulation to Innovate Socket Design

“…Lee and Zhang [16], Sanders and Daly [17], Silver-Thorn and Childerss [18] considered bony structure as rigid or fixed; while Goh et al [6], Jia et al [19][20], Lee et al [21], Wu et al [22] assumed a fixed socket. For the bone structure common values of Young's modulus E are 10000 or 15000 MPa with a Poisson's ratio ν equal to 0.3; for the socket, E is usually considered equal to 15000 MPa and ν from 0.3 to 0.39.…”

“…Lee et al [21], using the same computational model, considered the prosthetic socket and residual limb as two deformable bodies in contact with different shapes and implemented the simulation of the pre-stresses produced by donning the stump into the socket. Wu et al [22] adopted the surface-to-surface contact element since it is better than the traditional point-to point contact pairs. Colombo et al [7] adopted an explicit FE code (LS-DYNA rev.…”

“…Young's modulus for soft tissue is around 0.2 MPa, while Poisson's ratio is 0.45 or 0.49 [6,7,[17][18][19][20][21][22]; only Zachariah and Sanders [23] assumed E equal to 0.965 MPa. Lin et al [24] and Zhang and Roberts [25] considered a more refined model for soft tissues subdividing them into specific regions, such as patellar tendon and popliteal depression; while Faustini et al [26] increased to 25% soft tissues Young's modulus where the pre-stresses were the highest.…”

A digital patient for computer-aided prosthesis design

“…Figure 7. TT critical areas and related pain thresholds and tolerances [17,18]. (Online version in colour.)…”

“…We derived the pain threshold (the minimum pressure that induces pain) and the pain tolerance (the maximum tolerable pressure) for most significant zones from Lee et al [17] and Wu et al [18].…”