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Biomedical subjects

D S Childress

Publications and source records attributed to D S Childress.

At least 19 recordsLinked to original sources
PubMed1996

Two-dimensional representation of three-dimensional pelvic motion during human walking: an example of how projections can be misleading.

We investigated the movements of skin markers located on the anterior and posterior surfaces of the pelvis during normal walking. Plots of the vertical versus horizontal displacements of the body-surface markers for a single gait cycle yield characteristic horizontal figure-of-eight patterns, often referred to as Lissajous figures. Some literature citations indicate that these figure-of-eight plots represent movement of the body center of mass in the plane perpendicular to the line of progression. We show evidence suggesting that the Lissajous plot for the body center of mass is U-shaped and that the observed figure-of-eight pattern is due to the location of the marker on the body surface coupled with pelvic rotation. A simple rigid-body model is used to demonstrate that pelvic rotation about the vertical axis can appear as horizontal translations in a planar projection. Even small rotations about the vertical axis are observable in the phase relation between horizontal and vertical displacements of surface markers in the projection. As a result, Lissajous plots of vertical versus horizontal displacements, particularly for points on the exterior of a rigid body, may be strongly influenced by rotations. We demonstrate that Lissajous patterns for the model are similar to patterns for the human pelvis during walking and that pelvic rotation has a large influence on Lissajous patterns (vertical movement vs medial-lateral) plotted from pelvic marker data. This demonstration illustrates how two-dimensional representations of three-dimensional movement can lead to incorrect interpretations.

Computer Simulation↗
PubMed1996

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.

Amputation, Surgical↗
PubMed1996

Indentor tests and finite element modeling of bulk muscular tissue in vivo.

The quasi-static response of bulk muscular tissue to indentation was measured on the posterior lower legs of living human subjects. No residual limbs were tested; all subjects had intact lower limbs. For loads up to 7.0 N on an 8.0 mm diameter flat-tipped indentor, the response was repeatable without prior 'preconditioning'. The data at any test location exhibited substantial random scatter, but did not trend up or down with repeated cycles. At these limited loads (< 7.0 N), hysteresis was always evident but was always < or = 10% of the maximum reaction force generated. At these limited loads, stress relaxation, in the time period between 5 and 1200 seconds after indentation, was < 10% (> 90% confidence). At higher load levels (> 12.0 N), greater hysteresis and prolonged stress relaxation were observed, accompanied by minor tissue damage. In order to estimate the composite material stiffness of the tissue, the indentations were modeled using a materially and geometrically nonlinear, large-strain finite element formulation. The resulting composite material stiffness was nonlinear, and could be approximated using the Jamus-Green-Simpson strain energy function; typical values for the coefficients were c10 = 0.0026 MPa, c01 = 0.00064 MPa, and c11 = 0.0057 MPa.

Adult↗
PubMed1996

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.

Amputation, Surgical↗
PubMed1995

The hyper-reinnervation of rat skeletal muscle.

This study examines muscle recovery and related changes in the motor unit population of 'hyper-reinnervated' rat skeletal muscle. Medial gastrocnemius (MG) muscles were hyper-reinnervated by either cutting the MG nerve and implanting it on the MG muscle together with additional hind limb nerves, or by crushing the MG nerve and excising the medial portion (50-70%) of the MG muscle. Our findings were that muscles hyper-reinnervated with multiple nerves recovered muscle mass and strength more fully than did the self-reinnervated muscles, more motor units were formed (up to three times the normal number were found), and the mean motor unit size was significantly smaller. A relatively small percentage of muscle fibers became polyneuronally innervated. In contrast, the number of motor units that were formed in the muscle reduction experiments were not significantly larger than was expected considering the mass of the muscles. We conclude that hyper-reinnervation improves muscle recovery, it may be a useful technique for improving function in denervated muscle, and may serve to provide added sources of EMG control signals in some amputees.

Amputees↗
PubMed1993

Modelling the mechanics of narrowly contained soft tissues: the effects of specification of Poisson's ratio.

Many soft tissues are considered to be virtually incompressible. A number of recent analyses of the mechanics of these tissues have used Poisson's ratios in the range of 0.45 to 0.49 with little or no documentation, the apparent assumption being that a small change in Poisson's ratio will not significantly affect the results. We demonstrate here that the mechanics of a narrowly contained soft tissue are, instead, strongly sensitive to small changes in compressibility about the incompressible limit. Relevant practical examples include analysis of the mechanics of soft tissues within the sockets of artificial legs, pressure sore problems, and the calculation of strains within the soft tissues of a fracture gap.

Artificial Limbs↗
PubMed1992

Automated fabrication of mobility aids (AFMA): below-knee CASD/CAM testing and evaluation program results.

In 1988 the Department of Veterans Affairs Rehabilitation Research and Development Service, under the directorship of Margaret J. Giannini, M.D., began a nationally directed computer-aided design and computer-aided manufacturing (CAD/CAM) research program for the Automated Fabrication of Mobility Aids (AFMA). Under this program CAD/CAM research and development centers were established at the Prosthetics Research Study in Seattle, WA; at Northwestern University and the VA Lakeside Medical Center in Chicago, IL; and at the VA Medical Center and New York University Medical Center in New York, NY. These three centers conducted a collaborative program: (a) to introduce CAD/CAM technologies to prosthetists, physicians, therapists, and rehabilitation health care professionals in the United States; (b) to evaluate the feasibility of using CAD/CAM systems in clinical prosthetics settings; (c) to test and evaluate the University College London-Bioengineering Center's and the University of British Columbia-Medical Engineering Resource Unit's respective systems for the computer-aided design and computer-aided manufacture of prosthetic sockets (CASD/CAM) for below-knee amputees; and, (d) to obtain quantitative data for refinement of the CASD/CAM systems tested, and for the development of new, enhanced, more efficacious, and expedient systems.

Adult↗
PubMed1988

Pendular model of paraplegic swing-through crutch ambulation.

Kinematics of swing-through crutch ambulation for an individual with complete T11-T12 spinal cord injury was examined and quantitative aspects of the body-swing phase used to formulate and evaluate a 3-link pendular model. Model simulation parallels measured kinematics when shoulder motion is forced to follow the measured motion while hips and crutch tips are free pivots. Shoulder control contributes to increased ground clearance, influences timing and stride length, and gives flowing gait. Results indicate that mechanical work requirements during the body-swing phase are low. Metabolic energy demands exceed mechanical work requirements, due particularly to support of the body by the arms and shoulders. Exploiting low mechanical work requirements of the body-swing phase might be achieved through alternative mechanisms to assist ground clearance and to stabilize the wrists, arms, and shoulders while weight bearing.

Adult↗
PubMed1984

Design and evaluation of a prosthesis control system based on the concept of extended physiological proprioception.

This paper describes the design and evaluation of an experimental prosthesis-control system based on the concept of extended physiological proprioception (EPP). It was originally hypothesized that EPP control effected by residual shoulder motion could be effectively applied in multifunctional prostheses for shoulder disarticulation amputees. The experimental system developed for this study utilized a force-driven control scheme and a shoulder motion transduction system in which direct cable linkages to the prosthesis components were used to implement EPP position-servo relationships between shoulder elevation-depression and prosthesis elbow flexion, and between shoulder protraction-retraction and prosthesis wrist rotation. The results of experiments performed with this prosthesis (and with an experimental velocity-controlled prosthesis implemented for comparison purposes) clearly demonstrated the superior performance provided by EPP control of prosthesis function.

Arm↗
PubMed1984

An analysis of extended physiological proprioception as a prosthesis-control technique.

This research was devoted to an investigation of the practicality and potential effectiveness of applying the concept of extended physiological proprioception (EPP) to the control of upper-limb prostheses. The purpose of this study was to verify that EPP control, implemented by coupling prosthesis function to residual shoulder motion in a position-servo relationship, could be effectively applied in multifunctional prostheses for shoulder disarticulation amputees. Although Simpson has shown that the principle works, the authors wanted to quantify its effectiveness and analyze its limitations. Studies were performed analyzing the feasibility of using shoulder elevation-depression and protraction-retraction as prosthesis control inputs. The results of this study showed that a prosthesis mechanism with nonlimiting dynamic response characteristics and shoulder-activated EPP control of wrist rotation and elbow flexion/extension, exhibited functional characteristics comparable to those of the physiological elbow and wrist as defined by tracking capabilities. The results of this investigation also showed that shoulder-effected position control of prosthesis function has considerably more potential for providing effective control than similarly effected velocity control.

Arm↗
PubMed1981

Digital approaches to myoelectric state control of prostheses.

The design of a new three-state myoelectric control system is presented. This controller determines its operating state from the initial rate of increase of the myoelectric signal, and the concept is realized in great measure through digital logic techniques. Proportional control of both active states (same dynamic range) is a unique feature of the controller. A microcomputer was interfaced in a simple way with myoelectric potentials to simulate the three-state controller described and to simulate various other state-determined control methods (some multifunctional). This was found to be a valuable method of evaluating control schemes without building the actual devices.

Adult↗
PubMed1981

Relationships of the surface electromyogram to the force, length, velocity, and contraction rate of the cineplastic human biceps.

A series of experiments was performed to measure the relationships between the integrated surface EMG and the mechanical state of the cineplastic biceps muscle of one subject. The muscle was studied during static and dynamic isometric contractions at different muscle lengths and during constant velocity isotonic contractions at different loads. The cineplastic biceps results are compared with results obtained from the intact biceps.

Arm↗