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Biomedical subjects

W T Edwards

Publications and source records attributed to W T Edwards.

At least 37 records · Page 2Linked to original sources
PubMed1993

Role of trabecular morphology in the etiology of age-related vertebral fractures.

Osteoporotic compression fractures of the spine differ from most other age-related fractures in that they usually are associated with minimal trauma and with loads no greater than those encountered during normal activities of daily living. With aging and osteoporosis, there is progressive resorption of bone, resulting in reductions in bone density, thinning of trabeculae, and loss of trabecular contiguity. These changes in trabecular bone structure are associated with losses in bone strength which are disproportionate to the reductions in bone mass alone. To explain this disproportionate loss of bone strength, the prevailing opinion is that density reductions in the vertebral centrum are accompanied by a reduction in the number of trabeculae, by preferential resorption of horizontal trabeculae, and by hypertrophy of the remaining vertical trabeculae. To evaluate this view of vertebral morphology, we performed three-dimensional stereological analysis of trabecular bone extracted from midsagittal sections of first lumbar vertebral bodies from 12 donors spanning an age of 27-81 years. We found that both the number (R2 = 0.63, P < 0.01) and thickness (R2 = 0.91, P < 0.01) of trabeculae decreased linearly with density (as expressed by bone volume fraction) whereas the spacing between the trabeculae (R2 = 0.61, P < 0.01) increased reciprocally. There were more vertical trabeculae with transverse trabeculae at all densities, and the number of vertical trabeculae changed with density at twice the rate of the number of transverse trabeculae (P < 0.001). These data do not support the prevailing view that there is preferential resorption of horizontal trabeculae or hypertrophy of the remaining vertical trabeculae.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Biomechanics of pin and screw fixation of femoral neck fractures.

Using an in vitro cadaveric femoral neck osteotomy model and a paired experimental design, we compared fixation stiffness and yield load for three- and four-pin configurations for both Knowles pins and Asnis screws and for three Asnis screws versus an AO-ASIF sliding hip screw. Repeat measure analyses of variance indicated a significant increase in stiffness (p < 0.05) with the use of three versus four pins; the yield load did not depend significantly on the number of pins. Fixation was significantly stiffer (p < 0.01) and stronger (p = 0.02) for Knowles pins if the osteotomy was oblique rather than transverse to the femoral neck; the opposite was found for Asnis screws. Femoral fixed with hip screws were significantly stiffer (p < 0.01) than the contralateral side fixed with three Asnis screws. No significant difference in yield load was observed, however. Clinically, it appears from these findings that the use of three Asnis screws or three Knowles pins provides modest increases (averaging 4%) in fixation stiffness with no degradation in strength when compared with four screws or pins. Parallel placement of Asnis screws also provides advantages over nonparallel Knowles pins by allowing controlled impaction of the femoral head. While three Asnis screws provide fixation stiffness approximately 40% less than that found with a sliding hip screw, there is no compromise in fixation strength.

Aged↗
PubMed1993

Serial intravenous doses of dezocine, morphine, and nalbuphine in the management of postoperative pain for outpatients.

Adult patients who had arthroscopic surgery under general anesthesia and requested postoperative pain relief were randomized to receive treatment in a double-blind protocol with 5 mg of intravenous dezocine (20 patients), morphine (22 patients), nalbuphine (18 patients), or saline (24 patients). At 10-min intervals, starting with the first dose of analgesic, patients could choose up to three additional doses of the primary treatment, or choose an alternative analgesic if the primary drug was unsatisfactory. One to four doses of morphine were given as the alternate treatment if the initial treatment was dezocine or nalbuphine, and one to four doses of dezocine were given if the initial treatment was saline or morphine. The proportion of patients treated successfully by the initial treatments (i.e., not requesting alternate treatment), with P value for difference from placebo treatment, were saline 25%, nalbuphine 33% (P = 0.048), morphine 54% (P = 0.04), and dezocine 75% (P = 0.003). Dezocine and morphine are more efficacious than nalbuphine in the management of early postoperative pain. As an alternate analgesic in this study, dezocine required fewer doses to achieve patient satisfaction and was thus more efficacious than morphine. The incidence of treatment-related, adverse effects was different from that of saline or other treatments only for nalbuphine-related pain or burning on injection and dezocine-related facial itching. With respect to analgesic actions and side effects, dezocine seems more like morphine than nalbuphine.

Adult↗
PubMed1993

Mechanics of anatomic reduction of thoracolumbar burst fractures. Comparison of distraction versus distraction plus lordosis, in the anatomic reduction of the thoracolumbar burst fracture.

The adequate reduction of vertebral burst fractures is dependent on successful application of distractive forces in combination with the restoration of normal spinal lordosis. However, the optimal sequence of distraction in comparison to distraction plus lordosis in the anatomic restoration of the fractured thoracolumbar spine has not been described. Burst fractures of the L1 vertebra were first created and the reduced in vitro using three differing reduction techniques. In six fresh human cadaver spine specimens, the mean fracture severity based on the degree of canal compromise was 31% (SD +/- 20%) after fracture. Reductions were performed using the AO Fixator Intern, the Reduction Fixation (RF) Device, and the Steffee plate systems following standard clinical techniques. The AO Fixator Intern provided independent but variable control of distraction and lordosis, the RF device provided variable distraction with independent, but preset, correction of lordosis and the Steffee system provided set distraction and stabilization. Both the AO and RF devices restored the lordosis (7.6 degrees +/- 5.2 degrees and 9.7 degrees +/- 4.5 degrees, respectively) better than the Steffee plate system (0 degrees +/- 1.6 degrees). However, the AO device provided poorest restoration of the posterior vertebral body height (92% vs 96% for the RF device and 99% for the Steffee plate). The RF device, which restored both lordosis and posterior vertebral body height to the near anatomic prefracture level, provided significantly better canal clearance (9% +/- 8%) than the other techniques, P < 0.05. The study demonstrates that instrumentation systems that provide independent correction of distraction and lordosis can best restore anatomic alignment, with indirect neurodecompression of the compromised spinal canal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Cervical injuries under flexion and compression loading.

Cervical spine segmental tests were performed to determine the specific patterns of initial cervical injury in response to loading just beyond the point of structural failure. Well-defined combinations of flexion rotation and compression translation were applied to segments with varying degrees of disc and facet degeneration. Twelve cervical spine specimens (from human cadavers ages 52-91 years), each consisting of three vertebrae (two motion segments) from the middle (C2-C5) or lower (C5-T1) regions, were subjected to pure flexion rotation (seven specimens) or to combined flexion rotation and axial compression translation (five specimens). Specimens were sectioned and dissected to determine the patterns of structural failure. Pure flexion, and combined flexion and compression produced similar patterns of injuries. The disc was the most commonly injured structure, with annular injuries noted in 8 of the 12 specimens, and with anterior herniation of the nucleus occurring in two specimens. Wedge fractures and posterior ligament injuries were noted in both specimen groups and with both modes of loading. We conclude that similar patterns of initial anterior bony compressive failure and posterior ligamentous failure can occur with both flexion and with combined flexion-compression, without axial or lateral rotation, at low rates of loading. Anterior cervical disc herniations were produced in both middle and lower cervical segments.

Aged↗
PubMed1992

In vitro hyperextension injuries in the human cadaveric cervical spine.

To investigate the relationship between the type of hyperextension injuries and the conditions producing them, nine cervical specimens (occiput to T1) were loaded to failure in tension at a fixed extension angle of 30 degrees. Under these loading conditions, specimens failed at average tensile loads and extension moments of 499 +/- 148 (SD) N and 4.0 +/- 3.1 Nm, respectively. Failure occurred at an average tensile displacement of 18.8 +/- 7.7 mm. The anterior longitudinal ligament ruptured and the intervertebral disc failed in at least one level in all specimens. In four specimens, the disc failed at an additional level, leaving the anterior longitudinal ligament intact at that site. With one exception, all injuries occurred in the lower cervical spine (C5-C6 and C6-C7), the region most often injured in vivo. The location of the injuries was associated with the degree of degeneration of the facet joints and the discs. The discs of the lower cervical spine were significantly more degenerated than those at the C2-C3 level. In addition, the degree of disc degeneration in the noninjured discs was significantly less than in the injured discs. These data help quantify the threshold of injury and the patterns of tissue damage resulting from hypertension loading of the cervical spine.

Aged↗
PubMed1992

A biomechanical study of the fatigue characteristics of thoracolumbar fixation implants in a calf spine model.

Clinical failures of internal fixation implants for the treatment of the thoracolumbar spine are generally attributed to fatigue. Few studies, however, have characterized changes in fixation rigidity with time or subjected spine-implant fixation constructs to fatigue loading until failure. Fatigue characteristics of five dorsally applied spinal fixation implants were determined using lumbosacral calf spines, with an L3 vertebrectomy, loaded cyclically in combined compression (maximum 605 N) and flexion (maximum 16 Nm) for up to 100,000 cycles. Displacement transducers monitored motion at the site of instability and at the segment above the implants. Flexibility and strain at these segments were then calculated. A one-way analysis of variance showed that there were no significant differences in flexibility of the five fixation constructs (P greater than .05). A multiple Bonferroni test revealed that the AO and Kluger fixateur interne and Steffee plates, with fixation at L2 and L4, allowed significantly more strain (P less than .01) across the site of instability than did Harrington rods and Luque plates with fixation at L1, L2, L4, and L5. There were no significant differences between fixation constructs in initial strain above the implants. After 10,000 cycles, however, there were significant increases in strain across the segment above the Luque and Harrington implants (P less than .05). Failure of the AO Schanz screw occurred in three of six constructs at a mean of 73,300 cycles. The Steffee screws failed in four of five constructs at a mean of 20,800 cycles. The rods of the Kluger fixateur interne broke in four of five constructs at a mean of 47,800 cycles, and one screw slipped at 11,000 cycles. There were no metal failures in the Harrington or Luque implants.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Vertebral burst fractures: an experimental, morphologic, and radiographic study.

Spinal burst fractures are produced by rapid compressive loading, and may result in spinal cord injury from bone fragments forced from the vertebral body into the spinal canal. This fracture is one of the most difficult injuries of the spine to successfully treat, in part because the biomechanics of reduction and the exact mechanism by which the distraction forces are transmitted to the intracanal fragments of the burst fracture have not been adequately investigated. The authors developed a reproducible technique for creating these fractures in vitro. The fractures produced were identical to those observed in clinical practice, and were used for investigating the mechanics of this fracture and its reduction. This work describes the pathologic anatomy of the burst fracture both on the gross structure and also on microtome sections of the vertebrae, and examines the biomechanics of fracture reduction. The margins of the vertebral bone fragment, which was forced posteriorly into the spinal canal during fracture, were noted to extend far laterally beyond the pedicles. The authors also found extensive damage not only to the disc above the injured level, but also to that below, explaining the clinical observation that disc degeneration frequently occurs at both levels. Examination of anatomic data provided by microtome section supported the hypothesis that the fibers that actually reduce the intracanal fragment originate in the anulus of the superior vertebra in the midportion of the endplate and insert into the lateral margins of the intracanal fragment. Investigations using magnetic resonance imaging confirmed that these obliquely directed fibers account for the indirect reduction of the fragment. The authors' studies demonstrate that the posterior longitudinal ligament provides only a minor contribution in the reduction of the fracture in comparison to the attachments of the posterior portion of the anulus fibrosus. The forces required to reduce this fragment were studied. Distraction was found to be the predominant force required for indirect posterior reduction. This was confirmed by a series of tests using devices that provided segmental fixation. The application of uniform distraction forces was most effective in the posterior reduction of the intracanal fragment.

Adult↗
PubMed1992

Effect of cervical spine motion on the neuroforaminal dimensions of human cervical spine.

A nerve root impingement within a stenotic neuroforamen is a common sequela of cervical degenerative arthritis and herniated nucleus pulposus. Understanding of the effects of cervical position on foraminal size is important in the assessment of pathology and injury, for selection of a provocative maneuver to elicit symptoms and in selecting a position of immobilization for the management of nerve root impingement syndrome. This biomechanical study of human cadaver cervical spines reports the measured variations in the sizes of neuroforamina as a function of cervical positioning. Five fresh frozen adult human cadaver cervical spines (C2-T1) were tested with combinations of flexion-extension and rotational position. Ten pounds of axial load was applied to simulate a normal loading of a cervical spine. The foramina of C5, C6, and C7 were directly measured using a set of finely graded circular probes. Compared to the foraminal diameter at the neutral position, there were statistically significant reductions in the foramen diameter of 10% and 13%, at 20 degrees and 30 degrees of extension respectively (P < 0.01). Conversely, in flexion, there were statistically significant increase of 8% and 10% at 20 degrees and 30 degrees of flexion respectively (P < 0.01). Though there was a reduction in the foraminal size with ipsilateral 20 degrees rotation, and an increase with contralateral 20 degrees rotation, these changes were not significantly different from the mean of the control. Combinations of flexion or extension position with axial rotation did not significantly change the foraminal size compared to the respective sagittal position with no axial rotation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Analgesic effect of intraarticular bupivacaine or morphine after arthroscopic knee surgery: a randomized, prospective, double-blind study.

The effect of 20 mL of intraarticular bupivacaine (0.25%, with or without 1:200,000 epinephrine), morphine (0.03%, with or without 1:200,000 epinephrine), or normal saline on postoperative analgesia after arthroscopic knee surgery was studied in a randomized, prospective, double-blind trial in ASA I-III outpatients receiving general anesthesia (n = 112) or regional anesthesia (n = 27 [spinal (n = 25) or epidural (n = 2)]). The visual analogue pain scores in the postanesthesia care unit and 3, 6, 12, and 24 h after surgery, time to first analgesic use, and total 24-h analgesic requirements were recorded. In those who received general anesthesia, the visual analogue scores were significantly lower in the bupivacaine group compared with both the morphine- and placebo-treated patients (P less than 0.05). The time to first analgesic use was longer in both the bupivacaine and morphine groups when compared with the control group (P less than 0.05). No significant differences were detected in total 24-h analgesic requirements among the groups. Patients who had received regional anesthesia had lower visual analogue scores compared with patients who had received general anesthesia irrespective of the intraarticular treatment (P less than 0.05). Our results indicate that intraarticular injection of bupivacaine after arthroscopic knee surgery provides prolonged analgesia but that there is no significant prolonged analgesia provided by intraarticular morphine.

Adult↗
PubMed1992

Ethnic variations in the chronic pain experience.

Although ethnic identity has been found to have an important influence on experimental and acute pain intensity and response, little work has been directed to understanding how ethnicity affects the chronic pain experience. We report the results of a quantitative study of 372 chronic pain patients, in six ethnic groups, who were under treatment at a multidisciplinary pain management center in New England. The study used questionnaires and standardized instruments for assessing pain intensity to determine whether ethnic background was significantly related to interethnic or intraethnic group variation in pain intensity and response when other significant medical, sociodemographic, and psychological variables were controlled. In this study population, the most frequent statistically significant intergroup differences in pain intensity and in behavioral, psychological, and attitudinal responses to pain are related to differences in ethnic identity and psychological coping style according to locus of control. In addition, in this population, ethnic identity is a predictor of locus-of-control coping style. The major statistically significant intragroup differences in pain intensity and response are related to differences in generation, degree of heritage consistency, and locus-of-control style. We suggest that treatment programs for multiethnic populations should include a thorough cultural assessment and that providers need to be aware of the potential effect of ethnic background on chronic pain patients' communications, concerns, and coping styles related to the chronic pain experience.

Adaptation, Psychological↗
PubMed1991

Variations of stiffness and strength along the human cervical spine.

The load-displacement response and strength of the mid (C2-C5) and lower (C5-T1) cervical regions were determined for combinations of sagittal loads, in vitro. In unpaired t-test comparisons, the mid cervical region was significantly stiffer in compression and extension than the lower region. In tests to failure, failure in six out of seven mid cervical specimens resulted from flexion alone, while combined compression-flexion was required to fail five of the eight lower cervical specimens. Post-test dissections revealed no regional differences in the pattern of failure. In addition to sagittal tests, the load-displacement responses of three-vertebrae cervical specimens were measured with the upper body axially rotated with respect to the lower body. The effect of this pre-torsion was to diminish the zone of low slope near zero load for axial, shear, and flexion motion. Three of the four axially rotated specimens failed in flexion without added compression. These controlled load-displacement measurements of cervical spine specimens describe for the first time the continuous flexion-compression response up to failure, and suggest that consideration of the biomechanics of three apparently distinct mobile regions of the cervical spine (C1-C2, C2-C5, C5-T1) may facilitate the interpretation of hazardous conditions and the diagnosis of injury. These data also provide basic information for the in vitro investigation of passive cervical spine protection such as helmets and head-rests, suggesting that the head should be kept in a non-rotated position to reduce risk of injury.

Biomechanical Phenomena↗
PubMed1991

Interference screw fixation of cervical grafts: a biomechanical study of a new method of cervical fixation.

The dislodgement of 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 pull-out strength of the construct and decrease the rate of these complications. Mechanical tests were conducted to compare interference screw fixation methods for enhancing the fixation between the bone graft and the adjacent vertebra. The anterior pull-out strengths of cervical bone grafts were compared using fixation with and without the addition of interference screws. Both discectomy and corpectomy graft models were examined in vitro. The mean pull-out force 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); for the graft with four 3.5 mm screws, 217.1 N (SD +/- 69.9 N). The pull-out strengths of the two and four 3.5 mm screw constructs were significantly greater than the strength of the graft alone (p less than 0.05). Similarly placed 2.7 mm cortical screws of the same length provided increased pull-out strength (123.7 N +/- 38.6 N and 142.5 N +/- 38.2 N for two and four screws, 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 different.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Three-dimensional load displacement properties of posterior lumbar fixation.

Pedicular fixation devices for the posterior treatment of segmental spinal instability are thought to offer enhanced stabilization compared with sublaminar wire systems, while avoiding the immobilization of multiple normal motion segments. We compared the performance of three dissimilar stabilization systems: the Hartshill rectangle, the Acromed/Steffee interpedicular screw and plate, and the Synthes/Dick fixateur interne. Human cadaveric lumbosacral specimens were first tested intact, then after a laminectomy and a facetectomy at the L3/L4 level, and finally after the fixation devices were sequentially attached. Constructs spanning two to four vertebral levels were compared for stabilization of the resected lumbar spine segments. When tested in compression, the Acromed/Steffee system with pedicular screws at L2-L5 allowed significantly less intersegmental distraction than the Synthes/Dick construct with screws at L2 and L5 only, and less than the intact and the destabilized uninstrumented spine. When sagittally rotated, the Acromed/Steffee construct with screws at L2-L5, or at L2 and L5, allowed significantly less distraction than the intact or destabilized segments, and the construct with screws at L2 through L5 allowed less distraction than the Synthes/Dick constructs with screws at L3/L4 or L2/L5. With the exception of the Acromed/Steffee system with screws at four levels, there were no significant differences in distraction allowed between the Synthes/Dick and Acromed/Steffee constructs, or between the multisegment and single segment constructs. There were no significant differences in stiffness across levels L3/L4 with the various implants. Results indicate that the use of posterior spine constructs significantly augment the stability of posterior segmental defects. Pedicular fixation immediately cephalad and caudad to the defect provided stable fixation in this application.

Bone Plates↗
PubMed1991

Biomechanics of spinal fixation and fusion.

Recent experiments have shown that in the sheep spine a displacement of 5.2 mm and a strain of 36% was present at the lumbosacral joint, where fusion almost never occurred when multiple, small (5 mm x 14 mm) cancellous and corticocancellous bone grafts were placed in an interlocking fashion across the decorticated lamina of the lumbar spine and sacrum. A displacement of 1.2 mm and a strain of 10% was found at the L5-L6 joint, where fusion always occurred when the same type of bone grafts were applied in the same manner (described above) over the decorticated lamina of L5 and L6. Firm fixation of the lumbosacral spine and bone graft has brought about an arthrodesis in this model, presumably because the displacement and strain had been limited to acceptable levels. Data are presented to support the concept that, because the spine is composed of bony elements separated by a disc with viscoelastic properties, the biomechanics of spinal fixation and fusion are different than the biomechanics of long bone fixation and fracture healing. These differences should be considered in the design and use of spinal fixation devices.

Animals↗
PubMed1991

Biomechanics of posterior lumbar fixation. Analysis of testing methodologies.

A variety of biomechanical methods have been used for the experimental evaluation of spine instrumentation in vitro. Consensus has not been reached for criteria to compare the performance of dissimilar devices. The range of load-displacement conditions currently used for in vitro testing of spine instrumentation was reviewed, and compared to calculated estimates for flexion, lateral bending, and torsion loads. It is recommended that future studies simulate combinations of loads or displacements associated with common patterns of motion, and that the distraction across the region of injury be measured. For cyclic testing, input frequencies of 4-5 cycles/sec are within physiologic range, and offer advantages over tests at lower frequencies. The development of consistent protocols based on physiologic conditions should facilitate the biomechanical assessment of techniques for stabilizing the human spine.

Biomechanical Phenomena↗
PubMed1990

Optimizing opioid treatment of postoperative pain.

The problem of undertreatment of acute postoperative pain has been documented in many studies. This article reviews this evidence and defines the problem of undertreatment as a group of attitudes about pain treatment that originate with deficiencies in knowledge and skills and lead to the development of inappropriate behaviors on the part of health care professionals, patients, and health care system administrators. The correction of these attitudinal barriers to appropriate pain management will require education about opioid pharmacology, newer techniques of opioid administration, and the value of appropriate treatment to the individual patients and the health care system as a whole. Emerging Comprehensive Acute Pain Management Services will play a role in this education and in the standardization of postoperative pain treatment.

Analgesics, Opioid↗