[038] EFFECT OF THE BANKART LESION ON ANTERIOR JOINT STABILITY WITH SIMULATED GLENOHUMERAL MUSCLE FORCES
Thay Q Lee, PhD; Patrick J. McMahon, MD
Orthopaedic Biomechanics Laboratory VA Medical Center
Long Beach, CA 90822; email: tqlee@pop.long-beach.va.gov;
pjmcmaho@ccmail.hsis.uci.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A880-RA)
PURPOSE--The objective of this project is to biomechanically assess the contribution of common shoulder injuries to glenohumeral instability, in particular the tear of the origin of the inferior glenohumeral ligament (the Bankart lesion).
METHODOLOGY--To study the effect of the Bankart lesion on glenohumeral joint kinematics and kinetics, a custom shoulder-loading apparatus that utilizes a six-axes load cell, six degrees of freedom (DOF) electromagnetic tracking device, four Differential Variable Reluctance Transducers (DVRT), and a Video Digitizing System (VDS) is required. Using these devices, we can simulate the shoulder muscles and static joint restraints in the joint position of instability to measure: 1) joint compression force, 2) position of the humeral head on the glenoid, and 3) strain in the inferior lenohumeral ligament. Specifically, in fresh cadaveric whole upper extremities, all joints distal to the glenohumeral joint are rigidly fixed with the elbow flexed 90° and the wrist and fingers in extension. The scapula is mounted onto a custom joint-loading frame that enables individual control of simulated muscles as well as the measurement of joint translation and force (resolved into 3 forces along the 3 orthogonal axes with the center of the glenoid as the origin). The joint force is measured using a 6-DOF load cell, and joint translation is measured with an electromagnetic sensor. In the intact joint, the scapula is abducted 30° and sufficient load is then applied to the tendons of the rotator cuff and the deltoid (anterior and posterior portions) to achieve 90° of abduction in the plane of the scapula. The joint is then placed in the apprehension position of full external rotation and horizontal abduction. Joint translation and force are recorded. The glenoid labrum and adjacent IGHL are then incised from the 3 o'clock to the 6 o'clock position on the anterior glenoid bone. After this simulated Bankart lesion, the test is repeated in the same apprehension position. For the simulated Bankart/IHGL stretching, a 5-mm section of the labrum and the adjacent IGHL are resected to additionally simulate IGHL stretching (a permanent increase in IGHL length) and testing is repeated. ANOVA is used to compare the translations and forces of the 3 orthogonal axes.
PROGRESS--The shoulder testing apparatus described in the methodology section has been designed and built. Using this device, the effect of simulated Bankart lesion was determined as well as the strain distribution in the IGHL.
RESULTS--In the intact joint, the magnitude of the force directed perpendicular to the glenoid was 151.39±12.71 N, for simulated Bankart lesion it was 33.27 ± 12.59 N, and for simulated Bankart/IHGL stretching it was 133.37±12.18 N. In the intact joint the magnitude of the force directed anterior to the glenoid was 27.69±12.39 N, for simulated Bankart lesion it was 26.86±8.22 N, and for simulated Bankart/IHGL stretching it was 26.20±7.66 N. In the intact joint the magnitude of the force directed inferior to the glenoid was 25.49±5.39 N, for simulated Bankart lesion it was 26.04±6.27 N, and for simulated Bankart/IHGL stretching, it was 25.92±5.79 N. These differences were not statistically significant (p>0.05). There was also no translation of the humeral head on the glenoid (p>0.05) in comparison of each.
IMPLICATIONS--Although the Bankart lesion is often seen in vivo after an episode of unidirectional anterior glenohumeral instability, this biomechanical study did not demonstrate statistically significant differences in the joint translation or joint forces after simulation of this lesion. Other biomechanical studies have failed to show meaningful change in translation after a simulated Bankart lesion, and an explanation for this finding is that there is an additional stretching (or permanent increase in length) in the anterior band of the IGHL. However in this study, simulation of this condition failed to demonstrate statistically significant differences in not only the joint translation but also the joint forces. This indicates there is additional injury to the glenohumeral joint other than the Bankart lesion and anterior band of the IGHL stretching--possibly including other capsular injury, muscle injury, or bone injury--as components of glenohumeral joint instability.
[039] BIOMECHANICS OF THE PATELLOFEMORAL JOINT AND PERIPATELLAR RETINACULUM
Thay Q. Lee, PhD
Orthopaedic Biomechanics Laboratory VA Medical Center
Long Beach, CA 90822; email: tqlee@pop.long-beach.va.gov;
pjmcmaho@ccmail.hsis.uci.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A881-RA)
PURPOSE--The purpose of this study is to quantify the biomechanical properties and in-situ strain and stress in the peripatellar retinaculum. This study is designed to quantitatively assess the functional role of the peripatellar retinaculum in addition to determining the effects of lateral patellar retinaculum release, tibial rotation, and complete transverse patellar fracture (defect).
METHODOLOGY--Fresh frozen human cadaver knees are used with an Instron machine and a custom patellofemoral joint loading jig that permits the measurement of strain in the peripatellar retinaculum while controlling the knee flexion angle, degree of tibial rotation, and tension in the quadriceps muscles (rectus femoris and vastus intermedius as well as vastus medialis and vastus lateralis). The patellofemoral joint contact pressures are measured using Fuji pressure-sensitive film and the mean strain in the peripatellar retinaculum is measured using Differential Variable Reluctance Transducers (DVRT). To determine the in-situ stress and forces in the peripatellar retinaculum, the in-situ strain is first measured in intact knees and the peripatellar retinaculum is then isolated for tensile testing. These results are then correlated to compute in-situ stress and forces in peripatellar retinaculum.
PROGRESS--The patellofemoral joint testing jig has been completed, and the anatomic/physiologic loading conditions for the in-vitro testing of the patellofemoral joint has been determined. The tibial rotation study and the lateral retinaculum release study have been completed, and the patellar fracture study is in progress.
PRELIMINARY RESULTS--Fresh-frozen cadaveric knees were used to determine in-situ strain changes and the patellofemoral contact pressures with respect to tibial rotation and lateral retinacular release. We used anatomic/physiologic loading method developed in our laboratory for in-vitro testing of the patellofemoral joint. Contact area and pressures were measured at 0, 30, 60, and 90° of knee flexion in neutral, and 15° of tibial internal and external rotation using the Fuji film (super-low). The medial retinacular strain was measured using 2 DVRTs placed medially to the patella. All measurements were obtained at 5° increments of tibial internal and external rotation at each of the above-listed knee flexion angles both before and after lateral release. All pre- and postlateral release results were then compared. The total contact area after lateral release did not change at neutral tibial rotation but decreased significantly with internal and external tibial rotation at all knee flexion angles. Lateral release had no effect on the total pressure and the top 10 percent pressure at knee flexion angles of 60 and 90°. At 0 and 30°, however, pressures increased with the tibia at neutral and 15° internal rotation and decreased with 15° external rotation. Lateral release had no effect on medial retinacular strain at 60 and 90° of knee flexion. At 0°, external rotation caused the inferior retinacular strain to increase and the superior strain to remain relatively unchanged. At 30°, similar results were observed with external rotation. With internal rotation, however, superior retinacular strain increased, while inferior retinacular strain became more negative. Our results to date differ from previously reported data that showed release of the lateral retinaculum has no effect on contact pressures of the patellofemoral joint. We believe multiplane loading of the quadriceps mechanism, rather than the previously reported axial loading, contributes to this difference in results. The lack of any detectable change in both retinacular strain and patellofemoral contact pressure at knee flexion angles greater than 30° most likely results from the dominance of bony geometry dictating the kinematics of the patella at these flexion angles, at which the same load was applied to the patellofemoral joint with the patella in a similar position dictated by the femoral trochlear groove and condyles regardless of whether the lateral retinaculum was intact or not.
FUTURE PLANS--We plan to determine the effects of lateral patellar retinaculum release, tibial torsion, and complete transverse patellar fracture (defect).
[040] MECHANICAL REGULATION OF PERI-PROSTHETIC TISSUE REGULATION
Dennis R. Carter, PhD; Gary S. Beaupre, PhD; Stuart B.
Goodman, MD; R. Lane Smith, PhD; Elizabeth Loboa, MS.
Rehabilitation Research and Development Center (153), VA
Palo Alto Health Care System, 3801 Miranda Avenue, Palo
Alto, CA 94304; Department of Functional Restoration,
Division of Orthopaedic Surgery, and the Division of
Biomechanical Engineering, Stanford University, Stanford, CA
94305; email: beaupre@bones.stanford.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A501-4RA)
PURPOSE--Mechanobiology is the study of how mechanical or physical stimuli regulate biological processes, clearly a study that can play a critical role in the fixation of joint replacements, both cemented and cementless. The purpose of this study is to examine the role of shear/tensile strains in the differentiation of pluripotential tissue and the role of hydrostatic pressure in the differentiation of pluripotential tissue.
METHODOLOGY--This study uses theoretical, experimental, and computational models to investigate the role of mechanical stimuli in the differentiation of pluripotential tissues. Our theoretical model is based on the assumption that compressive hydrostatic pressure will direct pluripotential cells down a chondrogenic pathway, significant shear or tensile strain will lead to fibrogenesis, and minimal levels of pressure and shear/tensile strain will result in osteogenesis in the presence of an adequate vascular bed. Our experimental studies are based upon an established animal model in which a commercially pure titanium chamber designed to create a state of pure shear strain is implanted unilaterally in the proximal tibial metaphysis in rabbits. Finally, analytical and computational models are used to quantify the state of stress and strain within the implanted chamber.
PROGRESS--Shear chambers have been implanted in six animals.
RESULTS--During an initial 8-wk period, the outer chamber becomes fully osseointegrated with the metaphyseal cortex. The second phase of experiment is to determine the time course of osteogenesis within the chamber in the absence of applied motion. The third phase is to determine how an imposed shear strain modulates the osteogenesis process. Analytical and computational models will be used to quantify the state or stress and strain within the shear chamber and within a novel compression chamber developed by Tagil and Aspenberg.
[041] MECHANICAL LOADING EFFECTS ON CARTILAGE REPAIR AND REGENERATION
Robert Lane Smith, PhD; Dennis R. Carter, PhD; Andrew
Hoffman, MD; David J. Schurman, MD
Rehabilitation R&D Center, VA Palo Alto Health Care
System, Palo Alto, CA 94304; Dept of Functional Restoration,
Stanford University School of Medicine, Stanford, CA 94305;
email: smith@roses.stanford.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A857-RA)
PURPOSE--This study addresses mechanisms by which mechanical loads influence rehabilitation of joint function through cartilage repair and regeneration. The goal is to develop information applicable to interventional techniques for restoration of joint function in arthritis. The experimental aims test the effects of varying levels and frequencies of hydrostatic pressure on articular chondrocyte matrix synthesis, proteoglycan gene expression, and cartilage type-specific collagen synthesis. The hypothesis addressed in this study is that cartilage repair and regeneration requires proper mechanical and biological stimulation.
METHODOLOGY--The experiments involve the isolation and culture of articular chondrocytes for exposure to intermittent hydrostatic pressure at levels of 1, 5, and 10 MPa at frequencies of 0.1, 1, and 10 Hz. Mechanical loading is carried out by placing culture dishes containing the cells in high-density monolayers into medium-filled bags contained in a high-pressure vessel. After loading, the cell culture medium is collected for analysis of protein, proteoglycans, and glycosaminoglycan content. The cell monolayer is then extracted using a modification of the guanidinium isothiocyanate methodology for recovery of total cellular nucleic acid. Semi-quantitative RT-PCR methodology using cDNA and primer pairs designed for amplification of cartilage-specific markers has been applied for analysis of mRNA signal levels. Replicate samples are tested for statistically significant differences using analysis of variance with multiple comparison testing by the general linear method applying Tukey's correction.
PROGRESS--The experimental protocols have continued to explore effects of intermittent hydrostatic loading on cartilage type-specific collagen mRNA levels. The primary question was to determine whether intermittent hydrostatic pressure would down regulate expression of type I collagen while stabilizing or increasing type II collagen. Progress has involved optimization of the PCR conditions for analysis of type II and type I collagen mRNA levels relative to a reference signal for beta-actin. Multiple sets of chondrocyte cultures have been exposed to intermittent hydrostatic pressure at 10 MPa with a frequency of 1Hz for time periods of 2, 4, 8, 12, and 24 hrs and have yielded a profile for collagen mRNA expression. Analysis of the chondrocyte response to intermittent hydrostatic pressure was extended to include cells in suspension cultures in addition to cells maintained in high-density monolayers. Total medium proteins were analyzed using SDS-PAGE and silver staining. Quantification of the protein profiles was carried out using optical scanning and data analysis with NIH Image.
RESULTS--Multivariate analysis of articular chondrocyte mRNA levels in high-density monolayer cultures following loading with intermittent hydrostatic pressure at 10 MPa at 1 Hz confirmed the expression of type II collagen mRNA signal. Type II collagen mRNA signal was increased at early periods of loading (4 and 8 hrs) and then decreased at later periods. Type I collagen mRNA expression remained at just detectable levels. Signal levels for beta-actin mRNA did not vary with exposure to intermittent hydrostatic pressure. Analysis of protein profiles showed that variations in the proteins present in the chondrocyte culture medium depended on the time of applied load. For a given experiment, protein profiles were identical for triplicate loaded and unloaded samples. Protein levels varied across the time periods tested with certain species exhibiting changes within the first 4 to 8 hrs and other forms exhibiting changes at the later time periods (12 and 24 hrs).
FUTURE PLANS--The experimental protocols will continue by examining effects of different levels of intermittent hydrostatic pressure on cells in suspension and in monolayer culture. In addition, the protein analysis will be extended to two-dimensional gel electrophoresis so that the molecular identity of the proteins can be determined by microsequencing. Quantification of the chondrocyte response is currently focused on the analysis of aggrecan core protein mRNA signal. Proposed work will also include analysis of matrix metalloproteinase expression in the chondrocyte culture medium.
[042] ANATOMICAL BASIS OF OSSEOPERCEPTION
Robert R. Myers, PhD; Rickard Branemark, MD, PhD; Magnus
Ysander, MD; Kjell Olmarker, MD, PhD; Bjorn Rydevik, MD,
PhD; P-I Branemark, MD, PhD
Department of Anesthesiology (9151), VA Medical Center,
San Diego, CA 92161; Department of Orthopaedics, Gothenburg
University, Gothenburg, Sweden; The Institute of Applied
Biotechnology, Gothenburg, Sweden; email:
rmyers@ucsd.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2198-RA)
PURPOSE--Bone is innervated by unmyelinated fibers immunoreactive to calcitonin gene-related peptide (CGRP) and other primary afferent neuropeptides, but the function of these nerves is not completely understood. Approximately 30 percent of nerve fibers in bone originate from the sympathetic ganglia, and thus may have a primary role in efferent control of vascular caliber rather than in sensory transmission. Unmyelinated nerve fibers are also associated with nociception, and it is possible that a large percentage of these fibers subserve polymodal nociception or other sensory functions such as proprioception that are traditionally thought to be mediated via myelinated afferents.
The concept of sensory function in bone is relatively new and its exploration has been stimulated by the finding that the anchoring of prostheses to titanium implants in bone produces a sensory perception not seen with traditional prostheses. The phenomenon is termed osseoperception and is of great importance because of its ultimate clinical benefit. Patients have improved feedback control of their prosthesis and gain better psychological acceptance of the limb substitute. As its clinical value is already being demonstrated, we need to focus on the basic science aspects of this phenomenon to further develop its utility.
The purpose of this new research program is to test the hypothesis that osseointegrated titanium fixtures anchoring prosthetic devices are associated with increased sensory nerve fiber density in remodeled bone and structural/functional changes in sensory and sympathetic neurons that underly the improved prosthetic perception reported by humans.
METHODOLOGY--The methodological procedures are oriented around the following specific aims: 1) Quantify changes in nerve fiber density in remodeled bone; 2) Determine immunohistochemical characteristics of nerve fibers in bone; 3) Determine location and function of neuronal cell bodies innervating bone; and 4) Quantify changes in sensory and sympathetic neurons innervating bone after titanium implant osseointegration. To accomplish these goals, we will study the changes in sensory innervation of rat femur bone implanted with titanium fixtures to establish an anatomical basis for the improved sensory perception noted by humans whose prostheses are similarly anchored to bone. This will be a temporal study to fully characterize the sensory neuropathologic events associated with bone injury and repair, and the unique ability of titanium to become osseointegrated both structurally and functionally. We will use retrograde labeling techniques and immunohistochemistry to identify nerve terminals in femur and their corresponding cell bodies in dorsal root and sympathetic ganglia.
PROGRESS--The experimental program has just begun. Data collected to date have been from human patients implanted with titanium fixtures for lower limb, upper limb, and thumb prostheses. The first were implanted in 1990 and have been followed continuously since then. Recently, 20 with osseointegrated femur prostheses were evaluated. The results show an overall satisfaction of nearly 90 percent with the procedure. The great majority of the patients reported an improved sensory perception ability in the prosthetic limb.
FUTURE PLANS--Both the clinical program and experimental program are continuing in parallel. All newly recruited subjects treated with osseointegrated prostheses in the lower limb will be vibrametically tested, comparing sensory function pre- and postoperatively. The experimental program will continue with an animal series using a titanium implant model of enhanced osseointegration. In this phase, the work will concentrate on quantifying changes in nerve fiber density and determining immunohistochemical characteristics of nerve fibers in remodeled bone.
[043] THE EFFECT OF HYDROSTATIC PRESSURE ON INTERVERTEBRAL DISC METABOLISM
Scott D. Boden, MD; William Hutton, DSc; William A.
Elmer, PhD
VA Medical Center, Decatur, Georgia 30333
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A834-3RA)
PURPOSE--We are testing the hypothesis that hydrostatic pressure directly affects the synthesis of collagen and aggrecan by the intervertebral disc cells. We are doing this by using pressure vessels to apply hydrostatic pressure to disc cells cultured in alginate.
METHODOLOGY--Fresh cells were harvested from the lumbar intervertebral discs of dogs. The cells were cultured until they reached confluency. Then, using the alginate gel system, the cells were exposed (for up to 9 days) to specific values of hydrostatic pressure inside two stainless steel pressure vessels. One vessel was kept at 1 MPa and the other at atmospheric pressure. We compared the effects of 1 MPa against atmospheric pressure by measuring the incorporation of [3H]-proline and [35S]-sulfate into collagen and proteoglycans for the anulus cells and for the nucleus cells separately, and determining whether this was reflected by changes in the levels of mRNA for aggrecan and types I and II collagen.
PROGRESS--Several important results emerged. As compared to atmospheric pressure: 1) in the incorporation studies, the nucleus and anulus cells exhibited a differential response to a hydrostatic pressure of 1 MPa. Collagen and aggrecan synthesis were stimulated in the nucleus cells and inhibited in the anulus cells. 2) There was no significant increase in cell proliferation, as measured by DNA content, at 1 MPa for both the anulus and nucleus cells. 3) The mRNA levels of collagen (col1A1 and col2A1) and aggrecan increased at 1 MPa in both the nucleus cells and anulus cells.
This experiment shows that hydrostatic pressure affects the synthesis of collagen and aggrecan by the intervertebral disc cells. Our higher pressure value (1 MPa) roughly corresponds to the intradiscal pressure that would occur during a forward bend of about 15 to 20° while holding a 10-kg mass in each hand. The lower pressure value (atmospheric pressure) corresponds to the intradiscal pressure that would occur while lying supine with 500 N of traction. Thus, our lower pressure is below the range of any activity. It would seem that our upper pressure (1 MPa) is a more normal pressure for the disc and our lower pressure (atmospheric) a nonphysiological, experimental pressure. In other words, does our experiment compare the effect of a normal hydrostatic pressure on the disc cells with the effect of very low hydrostatic pressure?
FUTURE PLANS--The next stage of the project involves using cyclic pressure. The apparatus has been built and we are at present collecting data.
[044] THE BIOMECHANICS OF FOOT DEFORMITIES AND ALTERNATIVES FOR SURGICAL CORRECTION
Bruce Sangeorzan, MD; Allan Tencer, PhD; Richard
Harrington, MS; Randall Ching, PhD; Chimba Mkandawire,
BS
VA Puget Sound Health Care System, 1660 S. Columbian
Way, Box 358280, MS151, Seattle, WA 98108; Department of
Orthopaedics, Biomechanics Lab, University of Washington,
Seattle, WA 98195
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2034-RA)
PURPOSE--Acquired flatfoot deformity is a significant problem that leads to pain and affects other joints of the lower limb. Our primary goal is to understand the biomechanical mechanism of this deformity, specifically, which ligaments are most likely to be involved based on the loads they carry and their anatomic locations. The secondary goal is to understand which surgical corrections (tendon transfers, fusions, calcaneal lengthening) provide the optimal biomechanical restoration of the flatfoot to the normal foot.
METHODOLOGY--A unique tension transducer has been developed in our laboratory that estimates ligament tension using cable theory. Under that theory, the application of known force at a right angle to a tendon of known length produces deflection, and the amount of deflection pependicular to the axis of the tendon then allows extrapolation of its tension.
This transducer is used to measure tension in the following ligaments in the examination of the mechanics of cadaveric feet: anterior deltoid (AD), talonavicular (TN), superomedial calcaneonavicular (SMCN), cervical and lateral calcaneonavicular (LCN). These ligaments are likely the most compromised structures in an acquired flatfoot deformity. Ligament tensions are measured with the foot in a specialized foot-loading apparatus that enables quasi-static loading of the foot in the heel-rise, mid-stance, and heel-strike phases of gait. The foot will be loaded up to one body weight of compression on the tibia-fibula complex and with the appropriate tendon tensions on the following tendons: peroneus longus, tibialis anterior, tibialis posterior, extensor digitorum longus, extensor hallucis longus, flexor digitorum longus, flexor hallucis longus, and the Achilles tendon.
Each foot is measured three times. The first measurements are taken after initial dissection; the second, after flatfoot deformity created; and the third, after reconstruction. Subjecting the foot to cyclic compressive loading creates flatfoot deformities. Feet will be randomly distributed into groups of five to compare the three reconstructive techniques.
PROGRESS--The ligament tension transducer has been calibrated with a nylon cable to verify the cable-theory equations. Repetitive studies have been performed to assess reproducibility of the tension transducer on ligaments of the foot loaded in heel-strike, mid-stance, and heel-rise. A new flatfoot model is being investigated that does not involve cyclic loading of the foot, but induces creep in the ligaments under a constant compressive load.
RESULTS--The ligament tension transducer uses ligament excursion for the input variable and the pulling force of the ligament as the output. We found that the greater the excursion of the transducer, the more accurate of an estimation in ligament force: 1-mm excursions consistently yielded at least 95 percent accuracy when estimating forces up to 150 N, whereas 0.2-mm excursions yielded 75 percent accuracy. We performed repeatability studies at one-third body weight, with the normal foot in heel-strike, mid-stance, and heel-rise. We measured tension in the AD, LCN, SMCN, and cervical ligaments. The average standard deviation was about 10 percent of the mean. General trends from our repeatability studies show that the SMCN is the most taut ligament in heel-strike and mid-stance, whereas the cervical ligament is the most taut ligament in heel rise. The LCN shows greatest contribution in heel strike with very little contribution in the other stances. The AD contributes little in mid-stance, but significant contributions in heel-strike and heel-rise. The SMCN contribution is greater than the sum of the other ligaments in the heel-strike and mid-stance gait phases.
[045] ANKLE RANGE OF MOTION AS A DETERMINANT OF PLANTAR PRESSURE DISTRIBUTION IN AMBULATORY DIABETICS
Joseph Czerniecki, MD; Bruce Sangeorzan, MD; Kelly
Weaver, MD
VA Puget sound Health Care Systems, VA Rehab Research &
Development Center, 1660 S. Columbian Way (151), Seattle, WA
98108; Departments of Orthopedics and Rehabilitation
Medicine University of Washington, Seattle, WA 98185;
email: czerniecki.joseph_m@seattle.va.gov
Sponsor: VA Rehab R&D Center for Excellence in Amputation, Prosthetics, Limb Loss Prevention Grant #A0806-C
PURPOSE--Foot ulceration in the diabetic is one of the most significant factors contributing to the risk of amputation. Although many variables are involved in the development of foot ulceration, alterations in foot mechanics may be a significant contributor. Diabetes is associated with changes in the mechanical characteristics of the soft tissues, including those of tendon and joint capsule. There is an increase in tissue stiffness and a loss of joint range of motion in diabetics. The purpose of this study is to establish whether a reduction in ankle dorsiflexion is associated with increases in the peak plantar pressures under the metatarsal heads of ambulatory diabetics. Additionally we hope to characterize the relative contribution of tightness of the Gastrocnemius and Soleus muscles to the dorsiflexion endpoint.
METHODOLOGY--We shall enroll 60 ambulatory diabetic subjects and 30 controls. Each subject will have his/her dorsiflexion endpoint measured with knee extended and with the knee flexed to 90°, using a custom measuring device. This instrument instantaneously measures and displays the imposed torque about the ankle, the position of the hindfoot in the coronal plane, the EMG activity in the anterior and posterior compartments of the leg, and the position of the foot in the sagital plane. With this instrument, dosiflexion endpoint of each subject will be measured in subtalar neutral position, with no muscular influence and with an experimental torque that will be consistent between all subjects studied. After this, the plantar pressure under the feet will be measured with a commercially available package for collecting dynamic pressure distribution data during ambulation. With this data collection system, we will evaluate whether reduced ankle dorsiflexion is correlated with increases in peak plantar pressure during ambulation.
PROGRESS--The instrumentation package is in the final stage of construction. Preliminary data have been collected. The test re-test reliability of these data are better than published reliability data on clinical goniometric assessments.
FUTURE PLANS--Our intent is to evaluate a group of diabetic and normal subjects, as described above, to determine if equinus contracture at the ankle is associated with increased metatarsal head plantar pressures.
[046] THE EFFECT OF PERIOSTEUM ON THE IMPACT RESISTANCE OF BONES
Katsuhika Kitaoka, MD, PhD; Subrata Saha, PhD
Robert W. Christensen Biomechanics Laboratory,
Bioengineering Alliance of South Carolina, Department of
Bioengineering, Clemson University,
Clemson, SC 29634-0905; email: ssaha@clemson.edu
Sponsor: Clemson University, Clemson, SC 29634-0905
PURPOSE--The periosteum is a layer of dense fibrous connective tissue which surrounds the external surface of most bones. It is highly adherent to the epiphyseal region and somewhat less adherent in the diaphyseal region. The role of periosteum in the blood supply of bones has been investigated by several investigators; its osteogenic potential, particularly its important role in fracture repair, is also well recognized. However, the role of periosteum in the biomechanics of bone fracture has not been studied in detail. In this study we investigated whether the presence of periosteum contributes to increased resistance to bone fracture, when subjected to impact loading.
METHODOLOGY--Seven pairs of adult goat ribs were tested. The periosteum was maintained intact in one bone of each pair, while in the other it was stripped off. Two parts, the diaphysis and the metaphysis, were cut from each rib. Each specimen was 32 mm long. A drop weight testing machine (Dynatop model 830-I) was used to load the bones under impact conditions. Impact loading to failure was obtained by dropping a 4.26 kg mass from a height of 22.5 cm. Values for the maximum load and the total energy absorbed were derived from the load deformation curve recorded automatically for each specimen.
RESULTS--For the diaphyseal bone samples, the maximum load for the normal ribs with the periosteum was almost the same as that for those without; however, the total energy absorbed for the normal bones with periosteum was 42 percent greater. This difference was statistically significant (p<0.005). These results indicate that the increased energy absorption capacity of the periosteum-covered bones was due to increased maximum deformation of these specimens as there was no increased load.
In the metaphyseal part, the maximum impact load for the periosteum-covered bones was 47 percent greater (p<0.02). Furthermore, the total energy absorbed for the normal ribs was 4.4 times higher compared to the ribs without the periosteum (p=0.0153).
IMPLICATIONS--In an earlier study, Huller and Nathan tested adult dog ribs and rabbit long bones in bending, but found no significant differences in the load-carrying and energy-absorption capacities for the bones with and without the periosteum. Thus, for the diaphyseal region, our result of the same maximum load values for both groups of bone agrees with theirs. Our significant differences in the energy-absorption values are perhaps because we tested the bone specimens at a much higher loading rate. Furthermore, for the metaphyseal region, we found significant differences in the load-carrying and the energy-absorption capacities, perhaps because the periosteum in the metaphyseal region was almost twice as thick as that in the diaphyseal region, as documented by our histological analysis. Our study indicates that the periosteum may play an important role in resisting bone fracture under impact loading conditions.
FUTURE PLANS--To further verify our results, we plan to test the bond strength of the periosteum to the bone for the diaphyseal and metaphyseal regions.
[047] MICROCRACK LABELLING AND FATIGUE STRENGTH OF COMPACT BONE
T. Clive Lee, MD, PhD, FRCSI; Fergal J. O'Brien, BA,
BAI; David A. Hardiman BA, BAI; Colm Ryan, BA, BAI; Adriele
Prina Mello; David Taylor, PhD
Department of Anatomy, Royal College of Surgeons in
Ireland, Dublin 2; Politecnico di Torino, Turin, Italy and
Mechanical Engineering Department, Trinity College, Dublin
2, Ireland; email: tclee@rcsi.ie.
Sponsor: Health Research Board of Ireland, 73 Lower Baggot Street, Dublin 2, Ireland; Royal College of Surgeons in Ireland, St Stephen's Green, Dublin 2, Ireland
PURPOSE--In vivo, bones suffer from fatigue failures (stress fractures) and fatigue cracking has been implicated in the control of remodelling and adaptation. Our aim has been to understand the basic mechanisms of fatigue failure in bone and try to link the process of fatigue damage with that of repair in vivo. We have identified a series of fluorescent stains that are site-specific as they chelate Ca2+ ions lining the crack walls and have shown that these chelating agents can be used sequentially. However, substitution of one agent for another was observed, and the purpose of this study was to establish the relative binding affinity of each agent for Ca2+ ions. A second aim was to compare theoretical and experimental data on the fatigue properties of compact bone.
METHODOLOGY--Ion chromatography was carried out in order to determine the affinity of each of the agents. This technique is based on a separation process whereby the amount of calcium present in a solution of each agent and calcium chloride is measured. This gives an indication of the quantity of calcium ions that have failed to be chemically bound to each of the chelating agents. Compact bone specimens from bovine tibiae were tested in cyclic compression at a stress range of 100 MPa, measuring the number of cycles to failure and the reduction of stiffness during the test.
PROGRESS--The optimal dye sequence was established using ion chromatography. Confirmatory tests were carried out on bone samples where substitution of dyes was minimal. Using this sequence, it was found that by applying the agents at different intervals during a fatigue test, it was possible to monitor microcrack growth during the course of a compressive fatigue test. Twenty specimens were fatigue tested in compression, and their stiffness and residual strength were measured.
PRELIMINARY RESULTS--Alizarin was found to have an average calcium peak height of 14.59. This indicated that it had the greatest affinity for calcium ions, whereas xylenol orange, the next strongest agent, had an average peak height of 28.56. Calcein blue had a value of 29.73 and calcein 30.67. Oxytetracycline was the weakest agent and had an average height of 31.76. Failure occurred at an average of 35,000 cycles and showed a degree of scatter similar to that observed by other workers. This corresponds to a strength at 100,000 of 91.6 MPa, which compares well to the theoretical prediction of 92.3 MPa.
FUTURE PLANS--Microcrack number and growth in length will be related to loss of bone stiffness and strength. Microcrack morphology in serial sections will be recorded and, via a new computer package, a 3-D reconstruction made. The theoretical model of bone fatigue will be further developed and expanded to include the repair process. It is hoped that this will provide some insights into the conditions necessary for adaptation processes such as deposition and that it will prove useful in fracture prediction and prosthesis design.
[048] MECHANICS OF BACKWARD FALLS AS A RISK FACTOR TO COLLES' FRACTURES: FEASIBILITY STUDY
Kyu-Jung Kim, PhD; William Cooney, III, MD; Stephan
Irby, MS; Ronald Linscheid, MD; Kai-Nan An, PhD; Kenton R.
Kaufman, PhD
Mayo Clinic/ Mayo Foundation, Rochester, MN 55905;
email: kimk2@mayo.edu
Sponsor: Mayo Foundation, Rochester, MN 55905; National Institutes of Health, Bethesda, MD 20832
PURPOSE--Backward falls are one of the major risk factors for wrist fractures, especially among older women. Despite a few conflicting theories on pathomechanisms of distal radial fractures, there is a reasonable agreement that external impact force plays a key role in developing fractures. Due to the vectorial nature of impact force, however, the magnitude, direction, applied location, and rate of loading need to be taken into account to understand its role. This is best determined from the body kinematics and dynamics during the fall arrests. This feasibility study addresses the basic understanding of the fall arrest biomechanics among healthy controls in landing on a hand during the simulated cable-released backward falls, and examines the role of the upper limbs in absorbing or transferring the body momentum to themselves or other body parts. A testing platform was built for the study to measure the kinetics of backward falls.
METHODOLOGY--A force measurement system was custom-built using a six-component load cell. A LabView data acquisition program was developed and validated to record hand impact forces. A testing platform was built with a custom cable-release mechanism to simulate forward and backward falls. Protective equipment (knee and elbow pads, hockey helmet, and safety harness) were procured.
PROGRESS--A total of 11 young controls were tested. Data from the first were used for structural testing of the platform using a dynamic spectrum analyzer; the rest (five females and five males) were subsequently tested during forward and backward falls.
RESULTS--The results demonstrated that the platform was marginally acceptable in the frequency range of interest (1st harmonics at 50 Hz). Both type of fall demonstrated two characteristic peaks (F1 and F2) for the hand impact force. T-tests between the two types of fall showed significant statistical differences (p<0.05) for most impact parameters. Backward falls had higher distal-proximal shear force (F1 and F2, 0.15/0.48 BW vs. 0.06/0.08 BW) and lower normal reaction forces (F1 and F2, 0.43/0.60 vs. 0.63/0.74 BW) than forward falls. Timings for each force peak (T1 and T2) after touchdown were almost the same except the normal first peak force happened more rapidly (T1, 41 vs. 56 msec) and normal second peak happened later (T2, 233 vs. 179 msec). But gender differences were not demonstrated.
FUTURE PLANS--The findings of this research will be used to conduct further experiments with specific groups, for instance, old female fallers vs. non-fallers. Future studies will identify the potential risks to fall-induced fractures, suggest protective methods of preventing associated injury to establish fall injury prevention programs, and propose protective equipment design specifications. The electromagnetic kinematic measurement system combined with force plates will be used to measure the body kinematics as well as the hand impact force.
[049] EFFECT OF GLENOHUMERAL STABILITY REQUIREMENTS ON THE LOAD ON THE SHOULDER IN MANUAL WHEELCHAIR PROPULSION
H.E.J. Veeger, PhD; L.A. Rozendaal; F.C.T. Van der
Helm
Institute for Fundamental and Clinical Human Movement
Sciences, Vrije Universiteit, 1081 BT Amsterdam; Department
of Measurement & Control, Delft University of Technology,
Delft, The Netherlands; email: h_e_j_veeger@fbw.vu.nl; web:
http://www.fbw.vu.nl/research/Lijn_A4/
Sponsor: Netherlands Organization for Scientific Research (NWO-MW)
PURPOSE--Manual wheelchair propulsion involves repetitive and high loads that lead to overuse and to pain and dysfunction, especially in the shoulder and wrist. An important factor in the etiology of shoulder complaints seems to be the requirement of active stability in the glenohumeral joint that adds to the physiological load (more muscle activity) as well as the mechanical load (higher joint compression forces). In those wheelchair users who posses control over an incomplete musculoskeletal system in the upper extremity, the demand on the remaining part of the system is likely be exponentially higher. This also applies to users with (partial) weakness there, as frequently seen in the elderly population. For those wheelchair users one or more muscles may be too weak to reach balance.
The aim of this project is to study the effect of glenohumeral stabilization on the mechanical and physiological load on the upper extremity during manual wheelchair propulsion. We hypothesize that manual wheelchair propulsion is performed in a way that prevents the glenohumeral joint from subluxating and in a manner in which energy consumption is minimized.
METHODOLOGY--To evaluate the above, manual wheelchair propulsion is modeled with a musculoskeletal model of the shoulder and arm, in which a stability constraint for the glenohumeral joint is implemented. To estimate the contribution of stability to the physiological and mechanical costs, the muscular contribution will be determined through inverse dynamic modeling with and without the stability constraint. The increase in muscle contribution and in reaction forces in the GH joint are used as indicators of the physiological and mechanical load. In addition, we intend to quantify the load on the upper extremity, resulting from propulsion with an incomplete or weak musculoskeletal system.
The model will also be used in a forward dynamic mode to predict the optimal seating position, including the position for subjects with incomplete musculoskeletal systems, both in terms of physiological load as well as mechanical load.
IMPLICATIONS--Results can be used to explain the reported high incidence of shoulder complaints in the wheelchair user population and to identify structures that are prone to overuse injury. In addition, direct modelling results can be used for the prediction of the most efficient and least injury-prone wheelchair configuration for a given wheelchair user. The results will help reduce the incidence of arm and shoulder complaints in the wheelchair user population and thus increase their mobility.
[050] DEVELOPMENT AND VALIDATION OF A MODEL TO DETERMINE THE RELATIONSHIP BETWEEN PHYSIOLOGICAL AND MECHANICAL LOAD ON THE UPPER EXTREMITY.
M. Praagman; H.E.J. Veeger, PhD; L.A. Rozendaal; F.C.T
van der Helm
Institute for Fundamental and Clinical Human Movement
Sciences, Vrije Universiteit, 1081 BT Amsterdam; Department
of Measurement & Control, Delft University of Technology,
Delft, The Netherlands; email: h_e_j_veeger@fbw.vu.nl;
m.praagman@fbw.vu.nl; web:
http://www.fbw.vu.nl/research/Lijn_A4/
Sponsor: Netherlands Organization for Scientific Research (NWO-MW)
PURPOSE--Previous studies have shown that during manual wheelchair propulsion the propulsive forces are not applied in the apparent mechanically most effective way. Possibly this is caused by a tendency of the neuromuscular system to prevent energy losses on the level of the driving muscles. It was hypothesized that the ineffective force propulsion is caused by a minimization of energy loss at the muscles. To evaluate this 'minimum energy hypothesis', it is necessary to compare the mechanical aspects of muscle function (i.e., muscle force or moment) to the physiological aspects (i.e., work or energy consumption).
The aim of this project is to develop a model that can be used for the evaluation of the relationship between mechanical and physiological characteristics of the musculoskeletal system. Therefore, mathematical descriptions of individual muscles, based on the Distribution Moment (DM) model are incorporated in an already existing musculoskeletal model of the upper limb, the Delft Shoulder model (DSM). The DM model is a mathematical approximation of the cross-bridge theory of A.F. Huxley, from which equations can be derived that predict the rate of chemical energy release and the rate of heat production.
METHODOLOGY--Two validation phases will be performed. First the model estimations will be compared with experimentally determined local energy consumption with the help of Near Infra Red Spectroscopy (NIRS). This will be done for both an elbow flexion-extension and pro-supination task. If the model estimations of the local energy consumptions are satisfying, the second validation will be done. Full body validations will be performed with the use of oxygen consumption during cyclic movements. Kinematic, metabolic, and EMG data will be collected during submaximal arm-cranking and wheelchair exercise. During these experiments the configuration will be varied, which results in differences in efficiency between conditions. The predicted muscle force profiles will be compared with the measured EMG amplitude profiles. In addition, the muscle energy calculated by the model will be compared with experimentally obtained overall results.
IMPLICATIONS--If validation results are satisfactory, the DSM model can be used to evaluate the relationship between mechanical and physiological load during manual wheelchair propulsion. In addition, the model can be applied to other areas where the link between mechanical and physiological load on the upper extremity is of relevance.
[051] THE USE OF TIBIAL ANGLE IN DETERMINING THE AMOUNT OF VALGUS OF THE KNEE JOINT IN GIRLS AGED 9 AND 15
Mojgan Hosseini PT; Nasser Salsabili, PhD; Soghrat
Faghihzadeh, PhD
Department of Physical Therapy, Faculty of
Rehabilitation, Tehran University of Medical Sciences, Piche
Shemiran, Enghelab Ave. Tehran, Iran;
email: itok.insp@netir.net
Sponsor: Iranian Physiotherapy Association, Tehran, Iran
PURPOSE--The knee is one of the most important joints of the body. The junction between tibia and femur forms this joint, with different angles among people. The main purpose of this research is to determine and compare the deviation normality of the knee joint in 9- and 15-year-old girls by suggesting a new formula and method.
METHODOLOGY--We selected 100 9-year-old and 100 15-year-old students in the 7th province of Tehran. In this cross-sectional study 14 variables were measured. They included weight, height, distance between ASISes, femoral length, tibial length (TL), degree of plantar arc flattening, distance between greater trochanters of femurs, true length of right and left lower limbs, intercondylar distance of femurs (IDF), intermalleolar distance of tibias (IDT), Q angle, leg circumference and tibial angle (TA).
The new concept on which our discussion is formed is
the TA. This angle is made by the anatomic axis of the
tibia and the perpendicular line in the frontal plane, and
is calculated by the formula:
TA=Arc sin [(IDT-IDF)/(2*TL)]
IDT, the distance between the two medial tibial malleoli, and IDF, the distance between the two medial femoral condyles, were measured in sitting position, while the student extended her leg very slowly. Each time at least the amount of one of these two parameters had to be zero, because both lower limbs were held firmly together. TL was measured from the right medial femoral condyle to the ipsilateral medial tibial malleolus.
PROGRESS--All 14 variables have undergone primary statistical studies. Regarding the normal distribution curve of TA, amounts <1° were considered varus and >4° were considered valgus. It is noteworthy that different amounts of TA are related to positive, negative, or zero value of the numerator of the aforementioned fraction.
In order to study the relationship between variables and the TA, we used Multiple Regression Analysis.
RESULTS--Significant differences were found between the two groups in the values of weight, height, distance between the ASISes, femoral length, TL, distance between the greater trochanters of femurs, true length of right and left lower limbs, leg circumference and Q angle (all P<0.001). The IDF varied significantly between the two groups (P=0.02); the IDT did not vary significantly (P=0.37). The mean range of the TA was (1.92±2.18°) for the 9-year-olds and (1.33±1.58°) for the 15-year-olds, which had significant difference (P=0.02). This statistical difference showed that TA decreases after puberty.
Multiple regression analysis showed that in 9-year-old girls, only weight, TL, IDT, IDF, and the constant value of the multiple regression equation (R2=0.99) and in 15-year-old girls, only IDT and IDF (R2=0.85) were useful in determining TA. These, however, act with specific quotients.
IMPLICATIONS--Although the IDT and the IDF influence the amount of TA, this effect is not in direct and linear proportion. So we suggest using the stated formula in order to determine the degree of knee deformation.
[052] DIFFERENTIAL PRESSURE WALKING ASSISTANCE
Charles G. Burgar, MD; Robert Whalen, PhD; Douglas
Schwandt, MSME, James Anderson, JEM
Palo Alto VA Rehabilitation Research and Development
Center, Palo Alto, CA 94304; NASA/Ames Research Center,
Moffett Federal Airfield, CA 94035
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2070-RA)
PURPOSE--Our goal is to evaluate the safety and efficacy of a novel method for partial body weight support (BWS) during treadmill ambulation as a part of gait rehabilitation.
METHODOLOGY--By creating a difference in air pressure on body segments above and below the waist, a buoyant force acting near the body's center of mass can be created during treadmill ambulation. The force reduction on the lower limbs is similar to that experienced while wading in waist-deep water. Unlike aquatic therapy, the lifting force is continuously variable from 0 to 100 percent of body weight, is under computer control, and there is no appreciable viscous drag. The Palo Alto VA Rehab R&D Center, in collaboration with the Gravitational Research Branch of NASA-Ames Research Center, has developed a clinical prototype differential pressure walking assistance (DPWA) apparatus that consists of an inflatable bag equipped with a waist seal and enclosing a treadmill.
Evaluation of DPWA is proceeding in three phases. In the first, we shall measure the cardiovascular response of subjects walking with, and without, DPWA. Because we envision DPWA as having utility in a wide range of rehabilitation diagnoses, we shall include subjects with medical conditions typical of older rehabilitation patients. The differential pressure across the waist and the workload will be systematically varied to document the absence of adverse cardiovascular effects, even if rapid pressure changes occur. Any precautions for the application of the technique in a rehabilitation clinic will be sought.
In the second phase, we shall identify key factors relating body shape and size, pressure difference, and hardware configuration to subject performance. We will measure changes in gait parameters and reaction forces in subjects selected for a wide range of body size and weight. A model for predicting limb forces and torques as a function of pressure and treadmill velocity during normal gait will be generated. Applicability of the model to subjects who have gait impairment from amputation, hip and knee joint surgery, and stroke will be investigated.
Finally, we shall evaluate treadmill training with and without DPWA in patients with gait deficits. Gait parameters, adherence to prescribed loading limitations, and functional gait changes will be compared.
PROGRESS--Safety tests have been conducted using subjects with, and without neurological deficits. Clinical trials are in progress.
PRELIMINARY RESULTS--To date, no adverse physiological effects have been observed during treadmill ambulation with DPWA.
FUTURE PLANS--Clinical trials will be completed and data analyzed. In future studies, the clinical utility of gait training with DPWA in additional patient populations will be investigated.
[053] THE EFFICACY OF ANKLE ORTHOSES IN PREVENTING FALLS IN THE ELDERLY
Michael L. Boninger, MD; Charles J. Robinson, DSc; Susan
Whitney, PhD; Mark S. Redfern, PhD
Rehabilitation Neuroscience Laboratories, Pittsburgh VA
Medical Center, 7180 Highland Drive MS 151R Pittsburgh, PA
15206; The Division of Physical Medicine and Rehabilitation
and the Department of Otolaryngology of the School of
Medicine, Department of Rehabilitation Science and
Technology and of Physical Therapy of the School of Health
and Rehabilitation Sciences, and the Department of
Bioengineering, School of Engineering, University of
Pittsburgh, Pittsburgh, PA 15261; email:
mlboning+@pitt.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2831-2RA)
PURPOSE--Almost one-third of all ambulatory people over the age of 65 and not in nursing homes fall each year. Such falls are a major source of serious injury, morbidity, and mortality in the elderly population. Even in cases that do not cause injury, the fall itself may result in an increased sense of fear, reduced independence, curtailed activity, and a higher morbidity rate associated with inactivity. In previous studies, peripheral neuropathy, decreased proprioception, increased reaction time, and decreased strength have all been independently associated with an increased risk of falling. In addition, separate but related research has shown that taping the ankle can improve reaction time and strength in young athletic subjects with a history of ankle sprain. The aim of the present study is to determine the efficacy of two different ankle wrapping techniques as interventions to falling.
METHODOLOGY--A commercially available elastic ankle wrap, and a common method of ankle taping were used on two different groups of elderly subjects: fallers (those who have fallen two or more times during the 6-mo period prior to testing) and nonfallers. The neuromuscular condition of the legs was evaluated for each subject prior to testing. This evaluation consisted of a nerve conduction study as well as a physical examination. Subjects performed a series of tests designed to allow measurement of physical parameters that have been correlated to falling, including:
Measures of sway were made using a commercially available platform equipped with force transducers, designed to monitor center of pressure data. Muscle responses were measured for the gastroc, peroneus longus, anterior tibialis, and gluteus minimus muscles, and recorded through a series of four surface electrodes placed accordingly. Comparisons of the measured parameters were made between the ankle wrap, the tape, and the control (no ankle support at all) groups to determine which of these wrapping techniques, if either, may act as an effective intervention to falling in the tested population.
PROGRESS--Thirty-nine subjects have been tested. The protocol was modified after testing the first subject, and again after testing the second. As such, these two persons were considered trial subjects, and have therefore been excluded from the main testing groups. Of the remaining 37, there are 17 fallers and 20 nonfallers; all completed the entire testing procedure.
PRELIMINARY RESULTS--Preliminary analysis shows a greater incidence of nerve conduction abnormalities in the falling group when compared to the nonfallers. Although not unexpected, if this finding proves to be statistically significant it will be the first time it has been shown in a prospective fashion. Analysis conducted to date indicates that taping the ankle had no effect on measures of sway, functional reach, proprioception, or muscle response time. This was true in both groups.
FUTURE PLANS--We plan on completing the analysis of all of our data. We expect to learn more about nerve function in fallers and the effect of nerve function on measures of balance. We also expect to complete the analysis of the effects the orthoses have on measures of sway, functional reach, proprioception, or muscle response time.
[054] EFFECT OF AN INDUCED LEG-LENGTH DISCREPANCY ON GAIT BIOMECHANICS
Alberto Esquenazi, MD; Mukul Talaty, MS, BME; Mike
Hatzakis, MD
Gait & Motion Analysis Laboratory, MossRehab Hospital,
Philadelphia, PA 19141; Thomas Jefferson University
Hospital; Philadelphia, PA 19107; email:
aesquena@aehn2.einstein.edu;
mtalaty@aehn2.einstein.edu
Sponsor: Department of the Army, The Pentagon, VA 20310
PURPOSE--Our major goal is to better understand the physiologic factors involved in the compensation for the inequality of lengths in the lower limbs. It is desired to document at what levels of inequality does compensation at the hip occur, and what overall changes occur in the mechanics of gait. With this information, pathologic changes that occur in the hips, lower back, and lower limbs due to compensation for leg length inequality may be better understood. This may facilitate inferences on effective treatment options.
METHODOLOGY--Six to 10 nonimpaired control subjects with documented normal leg length (using both the ASIS-to-floor and the ASIS-to-medial-malleolus methods to assure no structural or functional pre-existing pathology) will be tested by completion of the study. Many have studied the clinical assessment of degree of leg-length discrepancy, and we choose the ASIS-to-medial-malleolus because it seems to be the most rigorously tested; although some claim that ASIS-to-lateral-malleolus can detect functional leg-length inequalities, this technique has not been as well demonstrated in the literature. Two mechanisms of leg length discrepancy are used: a tapered heel (variable thickness with maximum thickness of 1.2 cm at the heel) lift is placed in one shoe, or a full shoe, constant thickness of 1.2 cm lift is placed on one foot. Each subject is given a chance to accommodate to the test condition before data is recorded. The subject is tested without any orthotic mechanisms as well. Temporo-spatial foot-fall parameters (such as stride lengths and times, stance/swing lengths and times, step lengths, walking velocity) as well as ipsilateral hip, knee, and ankle kinematics and kinetics are recorded. Upon completion of the test session, the subject is given the partial lift to wear during all activities for 2-3 wk. Each subject is then re-tested as outlined above in just the heel lift and no lift conditions.
PROGRESS--Several subjects have been tested to date; testing and analysis are ongoing.
PRELIMINARY RESULTS--Statistically significant differences in lower-limb kinematics and kinetics of the longer limb are noted. Differences between the lengthened and normal limb, as well as between the lengthened limb before and after the accommodation period, are seen. Changes in the first few subjects are noted in pelvic obliquity and range of motion, pelvic rotation, hip flexion, hip adduction and range of motion, hip rotation, and various forces. Some of the changes seem to correlate with the expected responses to a lift (such increased ipsilateral hip flexion and pelvic obliquity), while others do not. A complex series of interactions give rise to the mechanisms that individuals use to compensate for the intervention. An insufficient number of subjects have been tested so far to be able to speculate about trends in the methods of compensation.
FUTURE PLANS--Differences between short- and long-term changes in the biomechanics of gait in compensation of leg length discrepancy and characteristics of leg length discrepancy that leads to pathologic changes in the hip and back will be our areas of focus.
[055] TRUNK MOTION OF PATHOLOGICAL GAIT IN DIFFERENT WALKING SPEED
Fumio Ochi, MD; Alberto Esquenazi, MD; Shigenobu
Ishigami, MD
Moss Rehab Hospital, Gait Analysis Laboratory,
Philadelphia, PA 19141; Department of Rehabilitation,
National Defense Medical College, Saitama Japan; email:
fochi@aehn2.einstein.edu
PURPOSE--Kinematics of the trunk (head, thorax, and pelvis) are important in gait studies because their movement patterns are closely related to gait efficiency and smoothness of locomotion. One of the goals of rehabilitation treatment is to improve gait efficiency, which would include the minimization of trunk movement. Trunk motion is dependent on walking velocity. The purpose of this study is to identify features of the normal gait pattern and patterns from stroke and traumatic brain injury populations across the velocity range.
METHODOLOGY--Control subjects, and subjects with hemiplegic stroke and traumatic brain injury (TBI), able to walk over a level surface and on a treadmill at least 0.27 m/s, were tested. Those with a history of cardiopulmonary disease or pain in lower limbs or the back were excluded. The mini gyro sensor is a 3.5 cm cube and includes 3 gyro sensors and 3 accelerometers capable of measuring the angle of motion in 3 dimensions. Roll is the motion in the frontal plane, pitch is sagittal plane motion, and yaw is horizontal (coronal) motion. Three gyro sensors were placed on the top of head, spinous process of T1 vertebra, and spinous process of S1. Each sensor measures the motion of the head, the thorax, and the pelvis, respectively. Foot switches are attached under the bilateral heel and toe to measure the gait cycle. The normal subjects walked on the treadmill from 0.44 m/s to 1.33 m/s in steps of 0.22 m/s, holding the treadmill rail with their dominant hands. Those with stroke and traumatic brain injury walked 0.27 m/s and 0.44 m/s; after that the velocity was increased at 0.22 m/s increments until the subject could no longer safely and easily sustain the required velocity. The subjects held the treadmill rail with their "good" hand. Ten strides at each velocity were recorded. The amplitude of motion in three directions at the three trunk locations was compared to the normal data to determine patterns within and across the various walking velocities.
PROGRESS--Five controls, 9 subjects with hemiplegic stroke, and 11 with TBI were measured.
RESULTS--In controls, the amplitude of pitch at thorax, and roll and pitch at pelvis were increased with increasing walking velocity. In the persons with TBI, roll and pitch at the pelvis increased with increasing walking velocity as seen in the controls. But thorax motion decreased with increasing walking velocity. In those with stroke, there is slight tendency toward increasing amplitude of roll at the pelvis. The other variables were not changed as walking velocity. In those with TBI, head motion and pitch at pelvis were larger than that in controls or persons with stroke.
IMPLICATIONS--Fewer persons with stroke could walk at faster speeds than those with TBI. There is some difference in trunk motion across the different walking speeds between the two. No difference of thorax motion was found between groups. We will analyze foot switch data and the timing of the peak movement to compare the groups.
[056] THE DEVELOPMENT OF A DIRECT ULTRASOUND RANGING SYSTEM FOR THE QUANTIFICATION OF AMBULATION
Dudley S. Childress, PhD; Richard F. ff. Weir,
PhD
Northwestern University, Rehabilitation Engineering
Program, 345 East Superior Street, Room 1441, Chicago,
Illinois 60611; email: d-childress@nwu.edu; web:
http://www.repoc.nwu.edu/
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 22202
PURPOSE--Full gait analysis capabilities for comprehensive studies of walking tend to be costly to develop and maintain. There is a wealth of data that can be obtained by recording the 3-dimensional (3-D) position of a single marker at the approximate level of the body center of mass (BCOM) during walking. We are currently involved in the process of evolving the design of a previous 1-D single-marker gait system into a portable, easy-to-use, real-time system that will measure in 3-D the position of the BCOM during walking, not only its instantaneous anterior-posterior (A-P), but also its medial-lateral (M-L), and vertical displacements.
METHODOLOGY--A transponder worn by the subject at the approximate level of the BCOM is triggered by an infra-red pulse from a base unit to emit an ultrasound pulse. The time-of-flight of the ultrasound pulse is then measured simultaneously by at least three ultrasound receivers of known position. Through triangulation, the measured distances, along with the known positions of the receivers, can be used to compute instantaneous M-L and vertical displacements as well as the instantaneous A-P velocity. These data are saved and displayed onscreen. By calibrating for the speed of sound in air, the time taken for the ultrasound pulse to travel from the transponder to each receiver is converted into a measurement of the distance between each receiver and the transponder. Since a distance measurement is taken at a rate of 22 Hz, a measure of how the distance changes with time (i.e., velocity) can then be obtained.
During a walking trial, the transponder is placed posteriorly on the midline of the body at approximately S-2 level. When instructed to do so, the subject walks away from the base unit until told to stop. Samples are stored by the computer for further processing immediately following the trial. Gait parameters such as the average walking speed, cadence, stride time, stride length, step lengths and times for each leg, maximum and minimum instantaneous velocity, peak-to-peak fluctuation of the instantaneous velocity, time to reach steady-state walking, and an estimate of the vertical displacement can all be obtained from the instantaneous A-P velocity. Measurement of M-L displacement allows the amount of sway to be measured. The amount of sway is an important indicator of stability, particularly in prosthetics alignment. Measurement of the vertical displacement in conjunction with M-L displacement allows a Lissajous plot of the coronal plane trunk motions to be created. The lobes of this plot correspond to the phase relationship of the two displacements. Two in-phase signals create a U-shaped plot, while out-of-phase signals create a figure-of-eight plot. The size of the lobes on the figure-of-eight are indicative of out-of-plane rotations (in the case of gait, the amount of pelvic rotation). The power of this device lies in its ability to provide gait data in real time, enabling an iterative approach to experiments to be performed. Ideas or changes can be tried out immediately.
PROGRESS--A prototype, 3-D, single-active-marker, gait analysis system has been designed and patent applied for. The additional dimensional data will allow the more commonly used M-L and vertical displacements to be found. The system is portable, easy to use, and all data are generated in real time.
[057] BALANCE CONTROL WHEN STEPPING OVER OBSTACLES OF DIFFERENT HEIGHTS
Li-Shan Chou, PhD; Robert H. Brey, PhD; Kenton R.
Kaufman, PhD
Biomechanics Laboratory, Department of Orthopedics and
the Vestibular/Balance Laboratory, Department of
Otorhinolaryngology, Mayo Clinic and Mayo Foundation,
Rochester, MN 55905; email: Chou.Lishan@Mayo.edu
PURPOSE--Imbalance during gait has been reported to contribute to falls in the elderly. Biomechanical studies have demonstrated that postural sway during quiet stance is greater in healthy elderly adults (EA) than in young adults (YA), and greater in elderly adults with a history of falls (BP), than in those without. EAs were also reported to adopt a more conservative strategy when crossing obstacles, with slower crossing speed and shorter step length, than YAs. However, studies of balance control of the whole body when stepping over obstacles during gait have not been reported. The purpose of this study is to understand the effects of obstacle height, age, and sensory function disorder on the control of the body's center of mass (COM) when stepping over obstacles of different heights.
METHODOLOGY--Three groups of subjects were tested in this study: YAs (aged 18-40 yr), EAs (aged 65-85 yr), and BPs (aged 65-85 yr). All were tested with the computerized dynamic posturography (CDP) platform. Both the sensory organization test (SOT) and the motor coordination test (MCT) were performed. The SOT accesses the three sensory components of balance under six altered visual and support surface conditions, and the MCT evaluates the automatic motor reactions provoked by unexpected support surface perturbations. Next, a set of 27 reflective markers was placed on bony landmarks before the gait trials were begun. Subjects were then instructed to perform unobstructed level walking and to step over obstacles of heights corresponding to 2.5, 5, 10, and 15 percent of their height, all at a comfortable self-selected speed while barefoot. The order of obstacle height was randomly selected. A six-camera ExpertVison system was used to collect 3-D marker trajectory. Ground reaction forces of the trailing and leading feet were collected from two force plates. A 13-link biomechanical model of the human body, consisting of six links for the lower extremities, four links for the upper extremities, one for the pelvis, one for the trunk, and one for the head, was used to compute the kinematics of the whole body's COM from the weighted sum of the COM of every segment of the body.
PRELIMINARY RESULTS--The data from three YAs (mean age: 31±4 yr), three EAs (mean age: 72±7 yr), and three BPs (mean age: 75±5 yr) were collected and analyzed. In gait and obstacle crossing, the anterior-posterior distances traveled by the COM during the crossing stride were greater for the YAs than for the EAs. Greater range of motion of the COM in medial-lateral direction was found in the YAs during unobstructed level walking and stepping over lower obstacles, as was a greater range of motion of the COM in vertical direction. Compared to the EAs, the BPs demonstrated greater ranges of motion of the COM in both medial-lateral and vertical directions, as well as a shorter anterior-posterior displacement of the COM during the crossing stride.
IMPLICATIONS--Greater excursion of the COM during gait requires greater muscle strength and faster neuromuscular response. EAs were able to limit the excursion of the COM by adopting a slower crossing speed and shorter step when crossing an obstacle. However, the BPs failed to limit the excursion of the COM by adopting the same strategy. This inability to control the position of the body COM may contribute to an increased falling risk.
[058] WHEELCHAIR PROPULSION PERFORMANCE IN YOUNG, MIDDLE-AGED, AND ELDERLY
Mary M. Rodgers, PT, PhD; Peter H. Gorman, MD; Randall
E. Keyser, PhD; Pamela J. Russell, PhD; Elizabeth R.
Gardner, MS
VA Maryland Health Care System, Research & Development
and Physical Medicine and Rehabilitation Services,
Baltimore, MD 20201; University of Maryland School of
Medicine, Departments of Physical Therapy and Neurology,
Baltimore, MD 21201; Bridgewater State College, Department
of Movement Arts, Bridgewater, MA 02325; email:
mrodgers@physio.umaryland.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #B764-2RA)
PURPOSE--The purpose of this research program was twofold: we seek to investigate how age affects wheelchair performance for manual wheelchair users (MWU) and to test a specific exercise intervention for its effectiveness in reducing potentially harmful biomechanical and physiologic stresses.
METHODOLOGY--After medical screening, 20 MWUs without upper limb involvement participated in the study. Anthropometric and muscle-strength measurements, neuromuscular assessments, and wheelchair-propulsion testing were performed before and after 6 wk of supervised exercise training. With the assumption that propulsion muscles were overdeveloped and shortened from constant use and antagonists were concomitantly stretched and weakened, training included stretching of propulsion muscles and strengthening/aerobic training of antagonists. Wheelchair-propulsion testing included maximal and submaximal exercise tests performed on an instrumented wheelchair ergometer at a velocity of 3 km/hr. Handrim kinetics, joint kinematics, propulsion temporal characteristics, and EMG data were collected when subjects were fresh and when fatigued. Cardiorespiratory indices were collected continuously. Joint kinetics were calculated from 3-D motion and handrim data. For investigation of the age effect, correlation analyses were performed to determine the relationship between age, propulsion mechanics, and oxygen uptake during propulsion. When significant, an ANCOVA (covariate=age) was used (p<0.05). To examine the exercise intervention, we tested changes with training using repeated measures ANOVAs (p<0.05).
PROGRESS--In total, 40 subjects met selection criteria and signed consents. Of those subjects, 23 completed pretesting and 20 completed the entire study. In addition to the MWU, 10 nonusers of wheelchairs (age 31±7 yrs; 7 male, 3 female) were tested for database comparisons.
RESULTS--The 20 MWUs (age 44±11 yrs; 16 male, 4 female; users for 16±10 yrs) who completed the study had diagnoses that included spinal cord injury (ranging from T2-L5), multi-trauma, and spinabifida. Age was found to covary significantly with two variables: maximum elbow extension angle and concentric shoulder external rotation strength. These relationships do not appear to reflect a meaningful influence of age on wheelchair propulsion performance. Anthropometric, temporal, and cardiorespiratory measures were unaffected by training. However, eccentric isokinetic strength increased significantly after training for wrist flexors (38.5 percent), extensors (27.8 percent), radial (30.1 percent) and ulnar deviators (32.5 percent). Significant joint kinematic changes after training included a 3.2 percent increase in maximum elbow extension and a 6.5 percent increase in maximum trunk flexion during the entire propulsion cycle. The increase in trunk forward flexion was evident during both contact (6.1 percent) and release (6.9 percent), and increased 8.9 percent in the fatigued condition at the posttest compared to the pretest. Following training, significant handrim kinetic changes included an increase in the maximum propulsion moment (1.1 percent) and the resultant moment (1.2 percent). Joint kinetic changes included a significant increase in shoulder flexion moment (Mz) of 16.2 percent and shoulder anteroposterior shear force of 16.4 percent. The timing of muscle activity as determined from EMG changed significantly for the middle trapezius which came on 16.1 percent later in the cycle, reached peak activity 13.1 percent later, and shut off 10.9 percent later.
IMPLICATIONS--These results indicate that as subjects fatigue during wheelchair propulsion, they lean forward. This adaptation to fatigue is more pronounced following training. In combination with our other findings suggesting that a propulsion style of trunk flexion may indicate fatigue of muscles critical to propulsion, it appears that the training regimen applied in this study could be improved. Even though modest gains in handrim propulsive moment (Mz) and shoulder flexion moment occurred across subjects as a result training, more specific training of muscles critical to propulsion appears to be warranted for certain individuals. Further study in this area is needed.
[059] PHYSICAL PERFORMANCE MEASURES FOR YOUNG, MIDDLE-AGED, AND ELDERLY MANUAL WHEELCHAIR USERS
Mary M. Rodgers, PT, PhD; Peter H. Gorman, MD; Randall
E. Keyser, PhD; Elizabeth R. Gardner, MS
VA Maryland Health Care System, Research & Development
and Physical Medicine and Rehabilitation Services,
Baltimore, MD 20201; University of Maryland School of
Medicine, Departments of Physical Therapy and Neurology,
Baltimore, MD 21201; email:
mrodgers@physio.umaryland.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #B2168-RA)
PURPOSE--The purpose of this 3-year research program is twofold: we seek to develop a clinical tool to evaluate functional independence specifically in young, middle-aged, and elderly manual wheelchair users (MWUs), and we want to determine the relationship between functional independence and physical fitness in these individuals.
METHODOLOGY--Fourteen subjects (12 male, 2 female) who use manual wheelchairs for greater than 80 percent of their home and community mobility have participated in the development of a clinical tool of functional independence for MWUs. Since there was no gold standard for a functional outcome measure specific to MWUs, the tool (FIMWC) was developed by a panel of experts in Phase I. Using the FIM as a model, indicators for each task were identified, and agreement was made on scoring and timing requirements for each task. Using videotapes of subjects performing the FIMWC tasks, six raters assessed five subjects, and then repeated this process 1 mo later. Phase II included evaluation of the subjects with the FIM, FIMWC, expert assessment, and each subject's self-perceived level of independence scores. Phase I FIMWC scores were analyzed for interrater and intrarater reliability with a two-way ANOVA and ICC. For phase II, scores from the FIM, FIMWC, expert, and self-assessments were compared using a Spearman rho rank correlation.
Fitness of MWUs is being evaluated through wheelchair propulsion testing on a stationary, instrumented wheelchair ergometer. Maximal and submaximal exercise tests are performed before, at the mid-point, and after a 12-wk home exercise program that includes stretching, strengthening, and aerobic training performed three times per week. Handrim kinetics, joint kinematics, propulsion temporal characteristics, and EMG data are collected when subjects are fresh and when they are fatigued. Cardiorespiratory indices are collected continuously. Shoulder, elbow, and wrist joint kinetics are calculated from motion and handrim data.
PROGRESS--Development of the assessment tool of functional independence for MWU, called the FIMWC, has been completed in addition to the MWU self-assessment questionnaire. To date, 16 subjects have completed FIM and FIMWC testing, and the results from 14 of them are reported here: 4 have completed pretesting on the ergometer and are currently performing the home exercise program, 1 has completed interim testing, and 2 additional participants are scheduled to begin testing.
PRELIMINARY RESULTS--FIMWC Reliability (Phase I): There was no significant difference between repeated tests (p=0.14, ICC of 0.78 indicates a high correlation). There was no significant difference between raters (p=0.15, an ICC of 0.96 indicated a very high correlation). FIMWC Validity (Phase II): All correlations between the FIM, FIMWC, self-reported, and expert-assessment scores were significant; however, the FIMWC demonstrated a higher correlation with both self-reported scores and expert-assessment scores than the FIM. The correlation of the FIMWC with expert assessment and the self-reported scores were 0.95 and 0.81, respectively; the FIM correlates were 0.80 and 0.71 respectively.
FUTURE PLANS/IMPLICATIONS--Preliminary results suggest that the FIMWC is reliable, valid, and able to predict level independence more accurately than the FIM for MWUs. This is important since the FIM, the most widely used functional assessment tool for tracking outcomes in neurologic rehabilitation, has limitations when applied to MWUs. Future plans include continuation of subject recruitment and data collection on the FIM and FIMWC as well as wheelchair propulsion performance.
[060] BIOMECHANICS OF THE UPPER LIMB IN WHEELCHAIR PROPULSION
Michelle B. Sabick, PhD; Hong-Wen Wu, PhD; Fong-Chin
Su, PhD; Kai-Nan An, PhD
Orthopedic Biomechanics Laboratory, Department of
Orthopedics, Mayo Clinic, Rochester, MN 55905; Institute of
Biomedical Engineering, National Cheng Kung University,
Tainan, Taiwan; email: Sabick.Michelle@mayo.edu
Sponsor: National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
PURPOSE--The forces applied to the wheelchair handrim during propulsion may be a cause of overuse injuries in wheelchair users. However, quantifying wheelchair propulsion kinematics and kinetics is difficult due to the three-dimensional nature of the motions and forces involved. Many techniques for measuring the kinetics and kinematics of wheelchair propulsion have been used, but few have been carefully validated. The purpose of this project is to develop and test methods to accurately collect such data in realistic situations, and to use the new methods to study the effects of propulsion technique and ramp grade on the joint forces and moments generated during propulsion.
METHODOLOGY--Subjects propel their own wheelchair up a 3.66 m ramp that can be adjusted to provide three different grades. Custom wheels are mounted to the subject's wheelchair to record the three-dimensional forces and moments applied to the handrim. Force data are collected with a commercially available load cell (JR3 Inc., Woodland, CA) at a sampling frequency of 100 Hz using a portable data logger. The ramp can be configured to provide 20:1, 12:1 and 8:1 (run:rise) grades. These grades represent the maximum outdoor and indoor ramp grades according to the Americans with Disabilities Act (20:1 and 12:1, respectively) and the maximum grade for non-wheelchair accessible ramps under the building code of the State of Minnesota (8:1).
Subjects propel the wheelchair on level ground using two different propulsion techniques, and up each ramp grade five times in random order. Angular orientation of the wheel and the locations of 13 bony landmarks on the subject's upper limb are recorded at 60 Hz using a video based motion analysis system. A three-dimensional model of the upper limb is used to compute the joint angles and resultant joint moments at the wrist, elbow, and shoulder during wheelchair propulsion.
PROGRESS--Both the kinetic and kinematic data measurement techniques developed for this project have been carefully validated. Data were collected from twelve ambulatory physical therapists with wheelchair experience and nine wheelchair users with spinal cord injuries (1) while propelling a wheelchair on level ground using two different propulsion styles and (2) while propelling up the three ramp grades. Handrim force and moment components for the two propulsion techniques and three ramp grades were compared. Both kinematics and kinetics of groups with different levels of spinal cord injury, different propulsion techniques, and different ramp grades will be compared.
PRELIMINARY RESULTS--Increasing ramp slope causes corresponding increases in the tangential force needed to traverse the ramp, even though the wheelchair velocity is not significantly different. Both the radial and normal force components also increase with ramp slope. These force components do not aid in propulsion of the wheelchair, but may be needed to create sufficient friction with the handrim. They also may increase the compressive force in upper limb joints, which is implicated in overuse injuries such as carpal tunnel syndrome. We also showed that the radial force component is larger in normal push-pull-style wheelchair propulsion than in pumping style propulsion, although the tangential and normal force components are not different. Therefore, the pumping style may be recommended to reduce the likelihood of upper extremity overuse injury.
FUTURE PLANS--We are currently collecting data from additional wheelchair users and modifying the force transducer so that kinetic data may be collected outside of the laboratory. We will collect handrim force data while subjects are performing activities of daily living and maneuvers that are common in wheelchair propulsion. In addition, a pilot study is underway to monitor the changes in propulsion style and upper limb strength as new wheelchair users become accustomed to wheelchair propulsion.
[061] BILATERAL DEFICIT DURING KNEE EXTENSION
J. R. Sexsmith, PhD; Brian Woods; Heather
Jardine
Institute of Biomedical Engineering, University of New
Brunswick, Fredericton, NB CANADA E3B 5A3; email:
sexs@unb.ca
Sponsor: University of New Brunswick Research Fund, Fredericton, NB CANADA E3B 5A3
PURPOSE--The project studied the reproducibility, reliability, effect of contraction velocity, and neuromuscular control of bilateral and unilateral maximal voluntary contractions.
METHODOLOGY--In order to understand the coordinated functioning of the neuromuscular system, we need to know how it functions during a multitude of specific conditions, such as when a coordinated task involves one limb (unilateral) as compared to the same task performed with both limbs simultaneously (bilateral). To quantify the relative contributions of the unilateral and bilateral performances, Bilateral Ratios (BLR) are calculated.
RESULTS--The reproducibility, reliability, and the effect of contraction velocity on BLRs during dynamic omnikinetic maximal knee extensions were assessed. In summary, the peak torque BLRs and knee angle BLRs were similar to previous literature which employed isometric contractions. In addition the intra- and intertest reliability of all BLRs was extremely high (r>0.95). Contraction velocity caused BLR to decrease; that is, the force generated during bilateral contractions decreased more than during unilateral contractions. Furthermore the relationship between knee angle and BLR was perturbed by contraction. Investigation is ongoing to determine the muscular control differences between bilateral and unilateral contractions by recording and analyzing myoelectric signals.
FUTURE PLANS--Future work will extend these studies to other muscles and will apply the results in rehabilitation-related activities.
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