Investigation of Lower-limb Tissue Perfusion during Loading

An extant tissue indentor used for amputee residual limb tissue indentation studies was modified to include laser Doppler flowmetry (LDF) to enable measurement of tissue perfusion during indentation. This device allows quantitative assessment of the mechanical and physiological response of soft tissues to load, as demonstrated by indentation studies of the lower-limb tissues of young healthy subjects. Potential measures of interest include the relative change in tissue perfusion with load and the time delays associated with the perfusion response during tissue loading and unloading. Such measures may prove useful in future studies of residual limb tissues, improving our understanding of tissue viability risk factors for individuals with lower-limb amputation

Effect of Tilt Sensor versus Heel Loading on Neuroprosthesis Stimulation Reliability and Timing for Individuals Post-Stroke during Level and Non- Level Treadmill Walking

Study background: Non-level walking may adversely affect stimulation of neuroprostheses as initial programming is performed during level walking. The objectives of this study were to assess stimulation reliability of tilt and heel sensor-based neuroprosthesis stimulation during level and non-level walking, examine stimulation initiation and termination timing during level and non-level walking, and determine whether heel or tilt sensor-based stimulation control is more robust for non-level ambulation. Methods: Eight post-stroke individuals with drop foot who were able to actively ambulate within the community were selected for participation. Each subject acclimated to the neuroprosthesis and walked on a treadmill randomly positioned in inclined, level and declined orientations. The primary measures of interest were stimulation reliability and timing. Results: Statistically significant differences in tilt, but not heel, sensor-based stimulation reliability were observed between level and non-level walking trials. Tilt sensor-based stimulation initiation occurred significantly closer to swing as the treadmill processed from declined to inclined orientations. No statistically significant differences in stimulation reliability or timing were observed between theoretical heel versus clinical tilt sensor-based stimulation control. Discussion and conclusions: Tilt sensor-based stimulation reliability may be adversely affected by non-level walking. Differences in stimulation initiation timing with tilt sensor-based control during non-level walking may be advantageous as stimulation initiation closer to swing during inclined ambulation may allow for greater ankle plantar flexion to assist with forward progression. Despite a lack of significant differences in stimulation reliability or timing between sensors, theoretical heel sensor-based stimulation control exhibited more consistent stimulation timing with less variability than for tilt sensor-based stimulation during non-level ambulation

A Rehabilitation Engineering Course for Biomedical Engineers

This paper describes an upper division elective course in rehabilitation engineering that addresses prosthetics and orthotics, wheelchair design, seating and positioning, and automobile modifications for individuals with disabilities. Faculty lectures are enhanced by guest lectures and class field trips. Guest lecturers include a prosthetist and a lower extremity amputee client, an engineer/prosthetist specializing in the upper extremity, and a rehabilitation engineer. The lower extremity prosthetist and his client present a case study for prosthetic prescription, fabrication, fitting, alignment, and evaluation. The engineer/prosthetist contrasts body-powered versus externally powered upper extremity prostheses and associated design, fitting, and functional considerations; he also discusses myoelectric signal conditioning, signal processing, and associated control strategies for upper extremity prosthetic control. Finally, the rehabilitation engineer presents case studies related to assessment and prescription of mobility aids, environmental control systems, and children\u27s toys. The course also includes visits to a local prosthetic and orthotic facility to observe typical fabrication, fitting, and alignment procedures and a driver rehabilitation program for exposure to driver assessment, training, and common vehicle modifications. These applications of biomedical engineering to persons with disabilities have been well received by the students and have furthered interdisciplinary design and research projects

Parametric Analysis Using the Finite Element Method to Investigate Prosthetic Interface Stresses for Persons with Trans-tibial Amputation

A finite element (FE) model of the below-knee residual limb and prosthetic socket was created to investigate the effects of parameter variations on the interface stress distribution during static stance. This model was based upon geometric approximations of anthropometric residual limb geometry. The model was not specific to an individual with amputation, but could be scaled to approximate the limb of a particular subject. Parametric analyses were conducted to investigate the effects of prosthetic socket design and residual limb geometry on the residual limb/prosthetic socket interface stresses. Behavioral trends were illustrated via sensitivity analysis. The results of the parametric analyses indicate that the residual limb/prosthetic socket interface stresses are affected by variations in both prosthetic design and residual limb geometry. Specifically, the analyses indicate : 1) the residual limb/prosthetic liner interface pressures are relatively insensitive to the socket stiffness ; 2) the stiffness of the prosthetic liner influences the interface stress distribution for both the unrectified and patellar-tendon-bearing (PTB) rectified models-- the external load state appears to influence the interface pressure distribution, while the prosthetic socket rectification appears to influence the interface shear stress distribution ; 3) the interface pressures are - very sensitive to the prosthetic rectification ; 4) the shape and relative bulk of soft tissue may significantly influence the interface pressure distribution ; 5) the interface pressure distribution is also influenced by the residual limb length; and 6) the stiffness/compliance of the residual limb soft tissues may significantly alter the interface pressure distribution

Generic, Geometric Finite Element Analysis of the Transtibial Residual Limb and Prosthetic Socket

Finite element analysis was used to investigate the stress distribution between the residual limb and prosthetic socket of persons with transtibial amputation (TTA). The purpose of this study was to develop a tool to provide a quantitative estimate of prosthetic interface pressures to improve our understanding of residual limb/prosthetic socket biomechanics and prosthetic fit. FE models of the residual limb and prosthetic socket were created. In contrast to previous FE models of the prosthetic socket/residual limb system, these models were not based on the geometry of a particular individual, but instead were based on a generic, geometric approximation of the residual limb. These models could then be scaled for the limbs of specific individuals. The material properties of the bulk soft tissues of the residual limb were based upon local in vivo indentor studies. Significant effort was devoted toward the validation of these generic, geometric FE models; prosthetic interface pressures estimated via the FE model were compared to experimentally determined interface pressures for several persons with TTA in a variety of socket designs and static load/alignment states. The FE normal stresses were of the same order of magnitude as the measured stresses (0-200 kPa); however, significant differences in the stress distribution were observed. Although the generic, geometric FE models do not appear to accurately predict the stress distribution for specific subjects, the models have practical applications in comparative stress distribution studies

Nonlinear Elastic Material Property Estimation of Lower Extremity Residual Limb Tissues

The interface stresses between the residual limb and prosthetic socket have been studied to investigate prosthetic fit. Finite-element models of the residual limb-prosthetic socket interface facilitate investigation of the mechanical interface and may serve as a potential tool for future prosthetic socket design. However, the success of such residual limb models to date has been limited, in large part due to inadequate material formulations used to approximate the mechanical behavior of residual limb soft tissues. Nonlinear finite-element analysis was used to simulate force-displacement data obtained during in vivo rate-controlled (1, 5, and 10 mm/s) cyclic indentation of the residual limb soft tissues of seven individuals with transtibial amputation. The finite-element models facilitated determination of an appropriate set of nonlinear elastic material coefficients for bulk soft tissue at discrete clinically relevant test locations. Axisymmetric finite-element models of the residual limb bulk soft tissue in the vicinity of the test location, the socket wall and the indentor tip were developed incorporating contact analysis, large displacement, and large strain, and the James-Green-Simpson nonlinear elastic material formulation. Model dimensions were based on medical imaging studies of the residual limbs. The material coefficients were selected such that the normalized sum of square error (NSSE) between the experimental and finite-element model indentor tip reaction force was minimized. A total of 95% of the experimental data were simulated using the James-Green-Simpson material formulation with an NSSE less than 5%. The respective James-Green-Simpson material coefficients varied with subject, test location, and indentation rate. Therefore, these coefficients cannot be readily extrapolated to other sites or individuals, or to the same site and individual some time after testing

Sensory Changes in Adults with Unilateral Transtibial Amputation

The purpose of this study was to describe the sensory changes in adults with unilateral transtibial amputation (TTA), as any loss of sensation may have significant impact on the successful use of a prosthesis. Sensory modalities of light touch, deep pressure, vibration, and superficial pain (pinprick) were examined on the residual and contralateral limbs of 16 veterans with TTA. Six subjects demonstrated normal sensation on the contralateral limb and impaired sensation of superficial pain, vibration, and/or light touch on the residual limb. Superficial pain was the most frequently impaired sensation, and vibration and superficial pain sensation appeared to be age-dependent, with increased impairment observed in the elderly. Deep pressure sensation was intact in all subjects. These preliminary data suggest that although neither the amputation nor the prosthetic rehabilitation resulted in impaired deep pressure sensation, these two factors contributed to minimal impairment of light touch and vibration, and significant impairment of the superficial pain sensation

A Review of Prosthetic Interface Stress Investigations

Over the last decade, numerous experimental and numerical analyses have been conducted to investigate the stress distribution between the residual limb and prosthetic socket of persons with lower limb amputation. The objectives of these analyses have been to improve our understanding of the residual limb/prosthetic socket system, to evaluate the influence of prosthetic design parameters and alignment variations on the interface stress distribution, and to evaluate prosthetic fit. The purpose of this paper is to summarize these experimental investigations and identify associated limitations. In addition, this paper presents an overview of various computer models used to investigate the residual limb interface, and discusses the differences and potential ramifications of the various modeling formulations. Finally, the potential and future applications of these experimental and numerical analyses in prosthetic design are presented

Effect of Ankle Orientation on Heel Loading and Knee Stability for Post-stroke Individuals Wearing Ankle-foot Orthoses

Background: Those who experience lower extremity weakness or paralysis following a stroke often exhibit gait deviations caused by the inability to completely lift their foot during swing. An ankle-foot orthosis (AFO) is commonly prescribed for individuals post stroke with this mobility impairment. Study design: Randomized controlled trial. Objectives: To determine whether significant differences could be observed in post-stroke individuals ambulating with an experimental AFO set at three different ankle orientations. Methods: Gait analysis was conducted for eight post-stroke individuals ambulating with an experimental AFO set in three different randomly selected ankle orientations: 5° dorsiflexion, 5° plantarflexion, and neutral alignment. Temporospatial (velocity, cadence, stride length and step length), kinematic (knee angle), kinetic (external knee moment), and plantar force (heel) data were assessed. Within-subject statistical analysis was conducted using the repeated measures ANOVA to determine whether observed differences between the three orientations were significant. Results: Post-stroke individuals generally exhibited less knee flexion during loading response when their AFO was aligned at 5° plantarflexion. Six of the eight subjects demonstrated increased knee flexion moment during loading response with the plantarflexed versus dorsiflexed alignment. The plantarflexed ankle orientation also resulted in greater peak heel contact force during loading response. Conclusions: Post stroke individuals may demonstrate less knee flexion during loading response and increased knee flexion moment (with respect to a dorsiflexed orientation) when their AFO is aligned in 5° plantarflexion. The fixed plantarflexed ankle orientation consistently resulted in greater peak heel contact force during loading response. Clinical relevance Plantarflexed AFOs are contraindicated for individuals with prior history of pressure sores on their heels. Post stroke individuals placed in 5° dorsiflexion may demonstrate increased knee flexion, enhanced shock absorption, decreased knee flexion moment, and decreased heel pressure (with respect to a plantarflexed orientation) during loading response