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Biomedical subjects

W T Edwards

Publications and source records attributed to W T Edwards.

At least 19 recordsLinked to original sources
PubMed2001

Peak stresses observed in the posterior lateral anulus.

STUDY DESIGN: The stress distributions within cadaveric lumbar intervertebral discs were measured for a range of loading conditions. OBJECTIVES: To examine the distribution of stress across the area of the intervertebral disc and to compare regional variations in peak stress during compression loading with various flexion angles. SUMMARY OF BACKGROUND DATA: The rate of disc degeneration and the occurrence of low back disorders increase with higher mechanical loading of the spine. The largest peak stresses occur in the anulus. METHODS: Human lumbar L2--L3 and L4--L5 cadaver functional spinal units were obtained and tested. The distribution of disc stress was measured using a pressure probe with loads applied, pure compression and compression with 5 degrees of either flexion or extension. RESULTS: Stress profiles were recorded across the intervertebral disc at a compressive force of 1000 N and each of the three flexion-extension angles. The highest values (2.99 +/- 1.31 MPa) were measured during extension-compression lateral to the midline of the disc in the posterior anulus. The pressure in the nucleus was relatively unchanged by flexion angle remaining about 1.00 MPa for a 1000-N compression. CONCLUSIONS: Pressure measurements of the cadaveric nucleus have been used to validate models of lumbar spine loading and to evaluate the risk of low back injury and disc herniation. Previous observations limited to midsagittal measurements of the nucleus did not identify the regions of highest stress. The highest values observed here within the posterolateral anulus correspond to common sites of disc degeneration and herniation.

Adult↗
PubMed2001

Structural features and thickness of the vertebral cortex in the thoracolumbar spine.

STUDY DESIGN: The thickness and structure of the vertebral body cortex were examined from sections of human cadaveric vertebrae. OBJECTIVES: The objectives were to identify the principal structural features of the cortex, to directly measure the minimum and maximum thicknesses of the cortex in the thoracolumbar spine, and to compare regional variations in the structure of the cortex. SUMMARY OF BACKGROUND DATA: The thickness of the vertebral cortical shell contributes to the compressive strength of the vertebral body. There is little consensus concerning the thickness and morphology of vertebral shell and endplate along the spine in existing data. METHODS: Human T1, T5, T9, L1, and L5 vertebral bodies (mean age 70.4 years) from 20 cadaveric spines were sectioned and photographed. The minimum and maximum cortical thickness of the shells and endplates in the midsagittal plane were measured from magnified images. RESULTS: The anterior shell thickness was significantly greater than the posterior shell and both endplates. Endplate thickness was greatest in the lower lumbar vertebrae. There was a significant decrease in cortex thickness over the central portion of endplates and shells, with a mean minimum thickness of 0.40 mm and a mean maximum thickness of 0.86 mm, with an overall mean of 0.64 +/- 0.41 mm. Increased porosity was also observed along the central regions of the cortical shells. In the lower thoracic and lumbar spine, a double-layered endplate structure was observed. CONCLUSIONS: Invasive techniques provide the only means to directly resolve the thickness and distribution of bone in the vertebral cortex. The cortex thickness and structure varies along the endplates and the anterior and posterior surfaces of the vertebral body. The implications of the so called double-layered endplate structure are unknown, but indicate the need for further study.

Aged↗
PubMed2000

Chronic phantom sensations, phantom pain, residual limb pain, and other regional pain after lower limb amputation.

OBJECTIVES: To determine the characteristics of phantom limb sensation, phantom limb pain, and residual limb pain, and to evaluate pain-related disability associated with phantom limb pain. DESIGN: Retrospective, cross-sectional survey. Six or more months after lower limb amputation, participants (n = 255) completed an amputation pain questionnaire that included several standardized pain measures. SETTING: Community-based survey from clinical databases. PARTICIPANTS: A community-based sample of persons with lower limb amputations. MAIN OUTCOME MEASURES: Frequency, duration, intensity, and quality of phantom limb and residual limb pain, and pain-related disability as measured by the Chronic Pain Grade. RESULTS: Of the respondents, 79% reported phantom limb sensations, 72% reported phantom limb pain, and 74% reported residual limb pain. Many described their phantom limb and residual limb pain as episodic and not particularly bothersome. Most participants with phantom limb pain were classified into the two low pain-related disability categories: grade I, low disability/low pain intensity (47%) or grade II, low disability/high pain intensity (28%). Many participants reported having pain in other anatomic locations, including the back (52%). CONCLUSIONS: Phantom limb and residual limb pain are common after a lower limb amputation. For most, the pain is episodic and not particularly disabling. However, for a notable subset, the pain may be quite disabling. Pain after amputation should be viewed from a broad perspective that considers other anatomic sites as well as the impact of pain on functioning.

Adult↗
PubMed1999

Cervical flexion, extension, protrusion, and retraction. A radiographic segmental analysis.

STUDY DESIGN: A lateral radiographic analysis of the cervical spine was performed on 20 asymptomatic volunteers. OBJECTIVES: To quantify the contribution of each cervical segment to each of four sagittal cervical end-range positions: full-length flexion, full-length extension, protrusion, and retraction. SUMMARY OF BACKGROUND DATA: Recent clinical research supports the relevance of cervical protrusion and retraction in symptomatic patients. Currently, few quantitative studies are available regarding cervical protrusion and retraction. METHODS: Lateral cervical radiographs of 20 asymptomatic volunteers for four test positions and a neutral position were collected. Mean angular measurements and available ranges of motion were calculated from the occiput to C7. RESULTS: Retraction consists of lower cervical extension and upper cervical flexion, whereas protrusion consists of lower cervical flexion and upper cervical extension. Full-length cervical flexion produced more flexion at lower segments than did protrusion, and full-length cervical extension produced more extension at lower segments than did retraction. With both full-length flexion and retraction, upper cervical segments are positioned in the flexion portion of their total range, but only retraction takes Occ-C1 and C1-C2 to their full end-range of flexion. Similarly, with both full-length extension and protrusion, upper cervical segments are positioned in the extension portion of their total range, but only protrusion takes Occ-C1 and C1-C2 to their end-range of extension. CONCLUSION: A greater range of motion at Occ-C1 and C1-C2 was found for the protruded and retracted positions compared with the full-length flexion and full-length extension positions. Effects on cervical symptoms reported to occur in response to flexion, extension, protrusion, and retraction test movements may correspond with the position of lower cervical segments.

Adult↗
PubMed1999

Management of pain in intensive care settings.

An organized treatment plan for providing analgesia in ICU settings can make a significant difference in patient comfort and outcome. Advanced analgesic techniques are available for use at each level of the "pain pathway." These include agents and methods that act at the periphery, at the spinal cord level, and through a systemic approach. Consultation with specialists in pain management can help achieve optimum therapy for patients in the ICU setting.

Analgesia↗
PubMed1998

Optimal short forms of the Spanish WAIS (EIWA).

Although the Spanish version of the WAIS (Escala de Inteligencia Wechsler para Adultos, EIWA) is widely used as a measure of intelligence in Spanish-speaking populations, little is known about the psychometric characteristics of the test beyond the information given in the test manual. Despite this, users have assumed that the test functions clinically and statistically as does the original WAIS. This assumption has been applied to the area of short test forms which are assumed to be as valid as those used with the WAIS. The present study is an attempt to determine the optimal two-, three-, four-, and five-test short forms for estimation of Full Scale IQ based on the EIWA standardization test data. In addition, the relative amount of common and specific variance in the EIWA subtests was determined, along with the degree of measurement error. The study emphasizes the limitations of using the EIWA arising from its out-of-date norms, use of a restricted Spanish-speaking population, and failure to make updates since its introduction. These cautions suggest that the EIWA (long and short forms) should not be used for determining IQs; instead its use should be limited to research and to tracking cognitive changes over time.

Adolescent↗
PubMed1997

Cervical sagittal range-of-motion analysis using three methods. Cervical range-of-motion device, 3space, and radiography.

STUDY DESIGN: Cervical flexion, extension, protrusion, and retraction were comparatively measured in volunteers using a cervical range-of-motion device (Performance Attainment Associates, Roseville, MN), a 3space system (Polhemus, Colchester, VT), and lateral radiographs. OBJECTIVES: To compare the outcomes of three methods of measurement of cervical flexion, extension, protrusion, and retraction. SUMMARY OF BACKGROUND DATA: Few studies compare cervical range-of-motion measurement devices with radiographic measurements, and no studies have compared methods of measurement for cervical protrusion and retraction measurement. METHODS: In 20 asymptomatic volunteers, four end-range sagittal cervical positions (flexion, extension, protrusion, and retraction) were measured simultaneously using a cervical range-of-motion device, a 3Space and lateral cervical radiographs. Measurements were compared, and differences were analyzed. RESULTS: There were no significant differences for flexion and extension measurements between the cervical range-of-motion device and that radiographic angle determined by an occipital line and the vertical, nor were there any between the 3Space and that radiographic angle between this same occipital line and C7. The cervical range-of-motion device and the 3Space measurements for flexion and extension, however, differed significantly from one another (P < 0.05). For protrusion and retraction, there was no significant difference between the 3Space and radiographic measurements, but these two both differed significantly from the cervical range-of-motion device (P < 0.05). CONCLUSIONS: Available methods of measurement differ as to whether the cervical spine is isolated or includes upper thoracic motion. Protrusion and retraction can be measured reliably with all three methods studied, but without measurement consistency between devices. Because end-range cervical flexion and extension-cannot occur in isolation from upper thoracic motion, true cervical motion can be measured only with an internally referenced, or landmark-based, methodology such as the 3Space. Even though the cervical range-of-motion device cannot measure isolated cervical flexion and extension, it is nevertheless a reliable clinical tool in measuring flexion and extension as well as protrusion and retraction as long as patient thoracic positioning is standardized to minimize the upper thoracic contribution.

Adult↗
PubMed1997

The effect of pulsed electromagnetic fields on instrumented posterolateral spinal fusion and device-related stress shielding.

STUDY DESIGN: This study was designed to examine stress-shielding effects on the spine caused by rigid implants and to investigate the effects of pulsed electromagnetic fields on the instrumented spine. OBJECTIVES: To investigate the effects of pulsed electromagnetic fields on posterolateral spinal fusion, and to determine if osteopenia induced by rigid instrumentation can be diminished by pulsed electromagnetic fields. SUMMARY OF BACKGROUND DATA: Although device-related osteopenia on vertebral bodies is of a great clinical importance, no method for preventing bone mineral loss in vertebrae by stiff spinal implants has been effective. METHODS: Twenty-eight adult beagles underwent L5-L6 destabilization followed by posterolateral spinal fusion. The study was divided into four groups: 1) Group CNTL: without instrumentation, without pulsed electromagnetic fields, 2) Group PEMF: without Steffee, with pulsed electromagnetic fields, 3) Group INST: with Steffee, without pulsed electromagnetic fields, 4) Group PEMF + INST: with Steffee, with pulsed electromagnetic fields. At the end of 24 weeks, the dogs were killed, and L4-L7 segments were tested biomechanically without instrumentation. Radiographs and quantitative computed tomography assessed the condition of the fusion mass. RESULTS: Stress shielding was induced in the anterior vertebral bodies of L6 with the Steffee plates; bone mineral density was increased with the addition of pulsed electromagnetic fields, regardless of the presence or absence of fixation. A decrease in flexion and bending stiffness was observed in the Group INST; pulsed electromagnetic fields did increase the flexion stiffness regardless of the presence or absence of fixation, although this was not statistically significant. CONCLUSIONS: Use of pulsed electromagnetic fields has the potential to minimize device-related vertebral-bone mineral loss.

Animals↗
PubMed1996

Hypnosis as an adjunct to medical care in the management of Burger's disease: a case report.

Burger's disease is a peripheral vascular disorder characterized by constricted blood flow, ischemic pain, and necrotizing tissue processes. This report describes the application of a brief hypnosis intervention in conjunction with standard medical procedures to increase peripheral blood flow in a patient with advanced Burger's disease. Using suggestions for foot warming and increased blood flow, substantial increases in surface foot temperature were obtained prior to and following an epidural sympathectomy. As a result, the procedure contributed to keeping necrotic tissue loss to a minimum, decreasing ischemic pain, and hopefully preventing the need for amputation. Treatment gains were maintained through discharge and at two month follow up. The results suggest that hypnosis may serve as a parsimonious, yet efficacious adjunct to standard medical care in the management of reduced peripheral blood flow in patients with Burger's disease. Further, it illustrates the feasibility of hypnosis as an adjunct treatment in busy, inpatient hospital settings.

Humans↗
PubMed1995

Biomechanical testing of the spine. Load-controlled versus displacement-controlled analysis.

Mechanical testing of the spine can be carried out in either a load-controlled or a displacement-controlled manner. Each method requires certain assumptions and offers different advantages. Dr. W. Thomas Edwards believes that displacement-controlled testing most accurately reflects the in vivo environment, while Drs. Vijay Goel, David Wilder, and Malcolm Pope support the use of the load-controlled method as most logical and easily standardized.

Biomechanical Phenomena↗
PubMed1995

Increasing neuroforaminal volume by anterior interbody distraction in degenerative lumbar spine.

STUDY DESIGN: This study quantified changes in the size of the stenotic neuroforamen in degenerative lumbar spines. The volume and area of the neuroforamen were measured before and after the application of anterior distraction using the BAK interbody fusion system. OBJECTIVE: To quantitatively assess the neuroforaminal area and volume when the BAK interbody fusion system is applied to lumbar spines with neuroforaminal stenosis. SUMMARY OF BACKGROUND DATA: The spatial relationship between the nerve root and the osseous and nonosseous elements of the neuroforamen is clinically important. Few studies have focused on changes in neuroforaminal size in the lumbar spine after anterior interbody distraction. No previous study has assessed the neuroforaminal volume. METHODS: The BAK instrumentation system was applied anteriorly at L4-L5 and L5-S1 intervertebral discs in nine degenerative cadaver lumbar spines. The neuroforaminal volumes of L4-L5 and L5-S1 were measured from silicon molds taken of the neuroforamen. In addition, computed tomography and circular blunt probes were used to determine the neuroforaminal areas. The disc height was recorded from lateral radiographs. RESULTS: After the BAK instrumentation, the volume of the neuroforamen increased significantly--by 22.9% for L4-L5 and 21.5% for L5-S1. The posterior disc height increased by 37.1% at L4-L5 and 45.1% at L5-S1. The neuroforaminal areas significantly increased--by 29.0% at L4-L5 and 33.8% at L5-S1. There was good correlation between the volume and the posterior disc height (R2 = 0.50) and the volume and the area of the narrowest portion of neuroforamen (R2 = 0.56). CONCLUSIONS: The results indicated that anterior systems such as the BAK system, which increase disc heights, can significantly increase neuroforaminal volume and area, providing adequate space for the nerve root and improving neuroforaminal stenosis.

Aged↗
PubMed1995

Optimization technique for the calculation of in vitro three-dimensional vertebral motion.

A method for the calculation of translations and Eulerian rotations of an orthogonal axis system with respect to a fixed reference is described with application to the measurement of position in a vertebral motion segment. Kinematic equations were derived to compute the three-dimensional motion of a moving vertebra relative to an adjacent fixed body, without the requirement of a direct physical link between the two bodies. For this calculation, the quadratic error of the lengths of six position vectors was minimized to obtain a mathematically optimal estimate of the translations and rotations. Tests with a rigid model resulted in mean maximum overall system errors of 2.8 percent for the measurement of translation (translations less than 3.5 mm) and 6.1 percent for the measurement of rotations (rotations less than 10 deg) limited by transducer accuracy. The mathematical techniques presented for the quantitative description of rigid body motion, based on the measurement of three reference vectors, may be extended to a broad range of kinematic problems.

Biomechanical Phenomena↗
PubMed1994

Cortical and trabecular bone contribute strength to the osteopenic distal radius.

Fractures of the distal radius are common, especially in postmenopausal women, and their prevalence increases with age. Knowledge of the factors that increase the risk of fracture in this metaphyseal region would have predictive and therapeutic implications. Of particular interest in this study were (a) the relative contributions of cortical and trabecular bone to the strength of the distal radius and (b) the best radiographic features to use as strength indicators. In 21 forearms from fresh cadavera (median age at the time of death, 75 years), single photon absorptiometry and quantitative computed tomography were used to determine bone mineral content (BMC), density (BMC/W), and cross-sectional properties of the radius at distal and midshaft sites. Mechanical testing of the forearms then was used to determine the ultimate force and energy to cause the type of fracture that might be caused by a fall on the outstretched hand. Twelve of the 17 tested specimens sustained a fracture of the distal radius, and five sustained a fracture of the scaphoid. In the group of fractures of the distal radius, we found the cross-sectional area and moment of inertia of the cortical shell at the metaphyseal site to be better correlates of strength than the trabecular area and trabecular moment. In contrast, strength correlated much better with trabecular density than with cortical density. Overall, the best correlates of strength were the BMC and BMC/W at either the distal or proximal site. On balance, these results suggest that the thin cortical shell contributes substantially more to the mechanical strength of the distal radius than has been commonly appreciated.

Aged↗
PubMed1994

Continuous regional analgesia by intraneural block: effect on postoperative opioid requirements and phantom limb pain following amputation.

The objective of this study was to assess the effectiveness of a previously described technique of regional analgesia (continuous infusion of local anesthetic through a catheter placed at the time of amputation within the exposed sciatic or posterior tibial nerve) on relieving the postoperative pain in a heterogeneous group of patients who underwent lower extremity amputations. A second objective was to determine the effect of such treatment on the incidence and characteristics of phantom limb pain 6 months or more after surgery in the same patients. The study design was retrospective, unblinded, controlled (postoperative pain), and unblinded questionnaire and interview (phantom pain) were utilized. Subjects were inpatients at Harborview Medical Center, University of Washington, Seattle, WA. Nineteen bupivacaine-treated and 40 nonbupivacaine-treated patients who underwent lower extremity amputation subsequent to trauma, infection, long-standing injury (poor or no function), congenital deformity, or burns were evaluated in the postoperative pain management assessment. Nine treated and 12 untreated patients were interviewed in the phantom pain assessment. Bupivacaine 0.5% 2-6 ml/h was infused through a polyamide 20-gauge catheter inserted into the sciatic or posterior tibial nerve sheath under direct vision at the time of surgery. All patients, treated and control, received opioid analgesics systemically during the 72-hour period of study. The postoperative opioid analgesic requirement of treated patients was compared with that of control patients who received opioid analgesics alone. A questionnaire was administered to assess presence, severity, and character of phantom pain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Management of pain in mechanically ventilated patients.

Acute pain management in critically ill ICU patients is an area that needs increased attention. Modern techniques exist that can help speed recovery and reduce duration of ICU and, potentially, hospital stay. Application of contemporary knowledge in this area benefits both clinician and patient.

Analgesia↗
PubMed1993

Finite-element stress analysis of the normal and osteoporotic lumbar vertebral body.

A finite-element model of an isolated elderly human L3 vertebral body was developed to study how material properties and loading conditions influence end-plate and cortical-shell displacements and stresses. The model consisted of an idealized geometric representation of an isolated vertebral body, with a 1-mm-thick end plate and cortical shell. For uniform compression, large tensile stresses occurred all around the cortical shell just below the end plate as a result of bending of the cortical shell as it supported the end plate. Large tensile bending stresses also developed in the inferior surface of the end plate. Equal reductions in both trabecular and cortical bone moduli increased displacements but did not affect peak stresses. A 50% reduction in trabecular bone modulus alone increased peak stresses in the end plate by 74%. Elimination of the cortical shell reduced peak stresses in the end plate by approximately 20%. For nonuniform, anteriorly eccentric compression, peak stresses everywhere changed by less than 11% but moved to the anterior aspect. When material properties were adjusted to represent osteoporosis with disproportionate reductions in trabecular (50% decrease) and cortical (25% decrease) bone moduli, anterior compression increased peak stresses by up to 250% compared to uniform compression. If fractures are initiated in regions of large tensile stresses, the results from this relatively simple model may explain how central end-plate and transverse fractures initiate from uniform compression of the end plate. Furthermore, for anterior compression, disproportionate modulus reductions in trabecular and cortical bone may substantially increase end plate and cortical shell stresses, suggesting a cause of age-related spine fractures.

Aged↗
PubMed1993

Interference screw fixation of cervical grafts. A combined in vitro biomechanical and in vivo animal study.

The dislodgement of an anterior bone graft in the cervical spine is a frequent complication of attempted fusion following discectomy or corpectomy. It has been hypothesized that fixation augmented with interference screws may increase the pullout strength of the construct and decrease the rate of these complications. In vitro mechanical tests and in vivo sheep studies were conducted to compare interference screw fixation methods for enhancing the fixation between the bone graft and the adjacent vertebra. Using human cadaver cervical spines, the anterior pullout strengths of cervical bone grafts were compared using fixation with and without the addition of interference screws for the in vitro mechanical testing. The mean pullout forces for a Smith-Robinson type bone graft alone was 58.1 N (SD 11.4 N); for the graft augmented with two 3.5 mm cancellous bone screws, 153.9 N (58.9 N); and for the graft with four 3.5 mm screws, 217.1 N (SD 69.9 N). The pullout strengths of the two- and four-3.5 mm screw constructs were significantly greater than the strength of the graft alone (P < 0.05). Similarly placed 2.7 mm cortical screws of the same length provided increased pullout strength (123.7 N 38.6 N and 142.5 N 38.2 N for two- and four-screw constructs, respectively); however, in comparison to the graft alone, these differences were not statistically significant. For both screw types, the four-screw fixations were stronger than the two-screw fixations, although these differences were not statistically significant. For the in vivo portion of the study, a single-level anterior cervical discectomy and fusion were performed on 20 sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗