Socket interface pressure and amputee reported outcomes for comfortable and uncomfortable conditions of patellar tendon bearing socket: a pilot study

The objectives of the current study were to compare intra-socket pressure differences between comfortable and uncomfortable socket conditions, and the usefulness of subject perception of satisfaction, activity limitations, and socket comfort in distinguishing between these two socket conditions. Five unilateral trans-tibial amputees took part in the study. They answered the Socket Comfort Score (SCS) and Trinity Amputation and Prosthetic Experience Scale (TAPES) questionnaires before the interface pressure (in standing and walking) was measured for the uncomfortable socket condition at five regions of the residual limb. Participants were then provided with a comfortable socket and wore it for two weeks. Participants who were satisfied with the socket fit after two weeks repeated the SCS and TAPES questionnaires and interface pressure measurements. The differences between the test results of the two conditions were not statistically significant, except for the interface pressure at the popliteal region during the early stance phase, TAPES socket fit subscale, and the SCS. Due to large variability of the data and the lack of statistical significance, no firm conclusion can be made on the possible relationship between the interface pressure values and the patient-reported outcomes of the two socket conditions. A larger sample size and longer acclimation period are required to locate significant differences.N/

Effect of curvature on lower extremity residual limb models

Indentor tests are one of the most common ways for in vivo estimation of human residual limb soft tissue bulk elastic and viscoelastic material properties. Due to large strains and displacements encountered during indentation, elementary strength of materials approaches yield crude approximations of the material properties. A common procedure, therefore, is to construct a finite element model of the tissue in the vicinity of the test site. The material properties of soft tissue are identified by matching the force-displacement characteristics of the finite element model to that of indentor experiments. The effect of residual limb surface curvature on force-displacement characteristics of finite element models are investigated. Results indicate that limb surface curvature effects are negligible compared to other modeling assumptions

Device for viscoelastic assessment of the residual limb bulk soft tissue response to load

An extant tissue tester designed for rate-controlled indentation of the bulk soft tissues of lower extremity residual limbs was modified to include force feedback (proportional control) and enable creep testing. This device employs a digital linear actuator and a load cell that measures the reaction force resulting from tissue indentation. The current force value, f, is compared to the target force (ft) prescribed by the user. If the force falls outside of the region: 0.99 ftft) proportionally, based on the relative difference between f and ft

Nonlinear viscoelastic material property estimation for lower extremity residual limbs

Human soft tissue is known to exhibit a nonlinear stress-strain relationship, as well as time dependent behavior such as creep and relaxation. The ability of computer models to simulate the response of lower extremity soft tissue loading is dependent on how well the tissue material properties approximate actual tissue behavior. Axisymmetric finite element models of residual limb soft tissue in the vicinity of an indentor test site were constructed to estimate parameters of a viscoelastic material formulation. A two-term Prony series viscoelastic material model approximates the relaxation and creep behavior of the lower extremity residual soft tissue in compression fairly well

In vivo indentation of lower extremity limb soft tissues

In vivo rate-controlled indentation tests, force relaxation trials, and creep studies were conducted on the soft tissues of the residual limbs of individuals with trans-tibial amputation. The cyclic indentation tests indicated that the bulk soft tissue response to compressive load is nonlinear and rate-dependent. The force relaxation studies indicated that substantial relaxation (35-80%) may occur, with equilibration typically occurring in less than 60 seconds. Most of this relaxation (20-70%) occurred within 5 seconds after loading. Tissue creep was also marked, ranging from 20 to 110% over two minute