PubMed Health⌕ Search

Biomedical subjects

S L Evans

Publications and source records attributed to S L Evans.

At least 19 recordsLinked to original sources
PubMed2006

Continuous peripheral nerve block in combat casualties receiving low-molecular weight heparin.

BACKGROUND: Continuous peripheral nerve block (CPNB) is an important therapeutic tool in the anaesthetic and analgesic management of combat casualties at Walter Reed Army Medical Center (WRAMC). We describe our experience using CPNB techniques in combat trauma patients treated with low-molecular weight heparin (LMWH). Guidelines used at our institution for managing CPNB catheters in patients being treated with LMWH are introduced. METHODS: From March 2003 to April 2005, 187 combat casualties treated by the WRAMC regional anaesthesia/acute pain section using CPNB were evaluated retrospectively by electronic chart review. Patient characteristic data, CPNB type, duration of CPNB, indication for LMWH [enoxaparin sodium injection (Lovenox-Sanofi Aventis, Bridgewater, NJ, USA)], enoxaparin dose (mg) before and after catheter insertion and removal, time from CPNB placement and removal to enoxaparin dose, and complications were recorded. RESULTS: Median enoxaparin dose and time given before catheter insertion were 30 mg and 21 h, respectively. Median enoxaparin dose was also 30 mg given a median of 12 h after peripheral nerve catheter placement. Catheters remained in situ for a median of 8 days (range 1-33 days). Catheter specific complications were infrequent and identified in 7 (3.7%) patients (two catheter malfunction-kinking, catheter tip dislodgement in situ, two superficial catheter site infections and two catheter dislocations). There were no catheter-related bleeding complications evident in this study. CONCLUSIONS: Information regarding the safety of CPNB in patients treated with LMWH for perioperative venous thromboembolism prevention is scarce. Our initial experience with CPNB and concurrent LMWH has not been complicated by catheter-related bleeding.

Adult↗
PubMed2006

Effects of porosity on the fatigue performance of polymethyl methacrylate bone cement: an analytical investigation.

Porosity has been shown to affect the fatigue life of bone cements, but, although vacuum mixing is widely used to reduce porosity in the clinical setting, results have been mixed and the effects of porosity are not well understood. The aim of this study was to investigate the effects of porosity using stress analysis and fracture mechanics techniques. The stress concentrations arising at voids in test specimens were found using analytical solutions and boundary element methods. The fatigue life of specimens containing voids of various sizes was predicted using fracture mechanics techniques. For spherical voids that do not occupy a significant proportion of the cross-section, the resulting stress concentration is independent of void size and too small to account for the observed crack initiation. Cracks must therefore initiate at additional stress raisers such as radiopacifier particles or additional voids. For large voids, the stress increases as the remaining cross-section of the specimen decreases, and this may account for much of the observed reduction in fatigue strength in hand-mixed cement. Although crack initiation may be largely independent of void size, there is an effect on crack growth rate. Cracks are predicted to grow faster around larger voids, since they remain in the stress concentration around the void for longer. This effect may account for the relationship between porosity and fatigue life that has been observed in samples without large voids. Since porosity appears to affect crack growth more than initiation, it may be less damaging in high-cycle clinical fatigue, which may be predominantly initiation controlled, than in short laboratory tests.

Bone Cements↗
PubMed2005

Three-dimensional measurement of intervertebral kinematics in vitro using optical motion analysis.

Measurement of the stiffness of spinal motion segments is widely used for evaluating the stability of spinal implant constructs. A three-dimensional motion analysis technique has been developed that allows accurate measurement of the relative movement of the vertebral bodies about a well-defined anatomical axis system. The position of marker clusters on each vertebra is tracked using digital infrared cameras (Qualisys AB, Gothenburg). Landmarks are identified using a marked pointer, and an anatomical coordinate system is defined for each vertebra. The transformation relating the upper and lower vertebrae is calculated, using the joint coordinate system approach of Grood and Suntay to find the rotations and translations in each anatomical plane. The stiffness of vertebrectomy constructs was investigated using a Synex vertebral body replacement and an anterior rod with one or two screws in each vertebral body, with or without damage to the posterior longitudinal ligament (PLL). A moment of 2 N m was applied about each anatomical axis, and the range of motion about each axis was calculated. The range of motion in flexion-extension and lateral bending was significantly greater with only one screw. When the PLL was cut, there was no significant increase in the range of motion.

Animals↗
PubMed2003

Morphological determinants of femoral strength in growth hormone-deficient transgenic growth-retarded (Tgr) rats.

UNLABELLED: The extent to which childhood GHD affects adult fracture risk is unclear. We measured femoral strength in adult transgenic growth-retarded rats as a model of GHD. Long-term, moderate GHD was accompanied by endocrine and morphometric changes consistent with a significant reduction in femoral strength. INTRODUCTION: Childhood growth hormone deficiency (GHD) is associated with osteopenia, but little is known about its effects on subsequent adult bone strength and fracture risk. MATERIALS AND METHODS: We have therefore measured femoral strength (failure load measured by three-point bending) in a new model of moderate GHD, the transgenic growth-retarded (Tgr) rat at 15, 22-23, and 52 weeks of age, and have quantified potential morphological and endocrine determinants of bone strength. RESULTS: Skeletal growth retardation in Tgr rats was accompanied by a sustained reduction in the anterior-posterior diameter of the femoral cortex, whereas mid-diaphyseal cortical wall thicknesses were largely unaltered. Total femoral strength was significantly impaired in Tgr rats (p < 0.01), and this impairment was more pronounced in males than females. Compromised bone strength in Tgr rats could not be accounted for by the reduction in mechanical load (body weight) and was not caused by impairment of the material properties of the calcified tissue (ultimate tensile stress), despite marked reductions in femoral mineral density (areal bone mineral density; p < 0.001). Microcomputerized tomographical analysis revealed significant modification of the architecture of trabecular bone in Tgr rats, with reductions in the number and thickness of trabeculae (p < 0.05) and in the degree of anisotropy (p < 0.01). The marked reduction in plasma insulin-like growth factor-1 in Tgr rats was accompanied by the development of high circulating leptin levels (p < 0.01). CONCLUSION: These results show that the changes in endocrinology and bone morphology associated with long-term moderate GHD in Tgr rats are accompanied by changes consistent with a significant reduction in the threshold for femoral fracture.

Age Factors↗
PubMed2002

Bone cement or bone substitute augmentation of pedicle screws improves pullout strength in posterior spinal fixation.

Pedicle screws are widely used to fix posterior spinal implants. However, in some situations, such as at the ends of long constructs in scoliosis correction, the screws may pull out of the pedicles. This limits the use of pedicle screw fixation where bone quality is poor. The aim of this study was to investigate the effect of using either a low-viscosity bone cement (Palacos LV) or a bone augmentation material (Cortoss) on the pullout strength of typical pedicle screws (5 mm USS Schanz screws). Ten lumbar calf vertebrae were implanted with pedicle screws. One screw was inserted as normal, and the contralateral screw was augmented with Palacos LV or Cortoss. A plate was then cemented to the posterior surface of each pedicle and the screws were pulled out using a tensile testing machine. The pullout strength of the non-augmented screws was 1203+/-260 N, while the pullout strength of the augmented screws was 1970+/-220 N (Palacos LV) and 2021+/-342 N (Cortoss). Both Palacos LV and Cortoss significantly increased the pullout strength (p=0.0213 and p=0.0029, respectively). There was no significant difference between the Palacos LV and Cortoss groups (p=0.79).

Journal Article↗
PubMed2001

A biomechanical reconstruction of a wound caused by a glass shard--a case report.

During the course of a criminal trial, an investigating pathologist is commonly asked how much force was required to produce an injury. This subjective opinion is based on the pathologist's previous experience of dealing with wounds inflicted with similar weapons. However, in the case of stab wounds inflicted by broken glass, it is unlikely that two glass fragments would be physically similar. In the case studied, two theories were examined: that a wound resulted from a thrown glass fragment or that it had been caused as a stab injury by the glass held in the bare hand. The investigation involved quantifying the energy required for human tissue penetration, comparison of sharpness, a biomechanical analysis of throwing actions and testing of the hypothesis that if the glass shard were used as a stabbing implement it would result in a cut to the hand.The investigation utilised a scientific methodology that reduced the need for speculative (though informed) opinion from the pathologist by producing quantitative results.

Biomechanical Phenomena↗
PubMed2001

Failure strengths of suture vs. biodegradable arrow and staple for meniscal repair: an in vitro study.

A study was performed to determine the in vitro biomechanical behaviour of two 'all inside' meniscal repair techniques (Meniscal Arrow [Bionx Implants Inc.] and Meniscal Staple [Surgical Dynamics Inc.]) and compare these directly with both a horizontal and vertical suture repair. Using 30 fresh bovine medial menisci, vertical 'bucket handle' tears were created 4 mm from the meniscus periphery. Repairs were subsequently performed, using four techniques, with 15 repairs in each group, a horizontally placed 3-metric Ethibond suture, a vertically placed 3-metric Ethibond suture, a single 13-mm arrow and a single 7-mm staple. A tensile test was performed to determine the force at failure for each technique. The mean force at failure of the horizontal and vertical suture groups was 63.2 and 73.9 N, respectively, 44.3 N for the arrow group and 17.8 N for the staple group. The mean forces at failure were significantly different (P < 0.005). The mean tensile strength of the meniscal staple was significantly lower than that of both suture and arrow groups. The 7-mm staple design may not allow adequate interdigitation between the barbed legs and the semicircular collagen fibres of the meniscus.

Absorbable Implants↗
PubMed2000

Prolonged use of heat and moisture exchangers does not affect device efficiency or frequency rate of nosocomial pneumonia.

OBJECTIVE: To determine whether use of a single heat and moisture exchanger (HME) for < or =120 hrs affects efficiency, resistance, level of bacterial colonization, frequency rate of nosocomial pneumonia, and cost compared with changing the HME every 24 hrs. DESIGN: Prospective, controlled, randomized, unblinded study. SETTING: Surgical intensive care unit at a university teaching hospital. PATIENTS: A total of 220 consecutive patients requiring mechanical ventilation for >48 hrs. INTERVENTIONS: Patients were randomized to one of three groups: a) hygroscopic HME (Aqua+) changed every 24 hrs (HHME-24); b) hydrophobic HME (Duration HME) changed every 120 hrs (HME-120); and c) hygroscopic HME (Aqua+) changed every 120 hrs (HHME-120). Devices in all groups could be changed at the discretion of the staff when signs of occlusion or increased resistance were identified. MEASUREMENTS AND MAIN RESULTS: Daily measurements of inspired gas temperature, inspired relative humidity, and device resistance were made. Additionally, daily cultures of the patient side of the device were accomplished. The frequency rate of nosocomial pneumonia was made by using clinical criteria. Ventilatory support variables, airway care, device costs, and clinical indicators of humidification efficiency (sputum volume, sputum efficiency) were also recorded. Prolonged use of both hygroscopic and hydrophobic devices did not diminish efficiency or increase resistance. There was no difference in the number of colony-forming units from device cultures over the 5-day period and no difference between colony-forming units in devices changed every 24 hrs compared with devices changed after 120 hrs. The average duration of use was 23+/-4 hrs in the HHME-24 group, 73+/-13 hrs in the HME-120 group, and 74+/-9 hrs in the HHME-120 group. Mean absolute humidity was greater for the hygroscopic devices (30.4+/-1.1 mg of H2O/L) compared with the hydrophobic devices (27.8+/-1.3 mg of H2O/L). The frequency rate of nosocomial pneumonia was 8% (8:100) in the HHME-24 group, 8.3% (5:60) in the HME-120 group, and 6.6% (4:60) in the HHME-120 group. Pneumonia rates per 1000 ventilatory support days were 20:1000 in the HHME-24 group, 20.8:1000 in the HME-120 group, and 16.6:1000 in the HHME-120 group. Costs per day were $3.24 for the HHME-24 group, $2.98 for the HME-120 group, and $1.65 for the HHME-120 group. CONCLUSIONS: Changing the hydrophobic or hygroscopic HME after 3 days does not diminish efficiency, increase resistance, or alter bacterial colonization. The frequency rate of nosocomial pneumonia was also unchanged. Use of HMEs for >24 hrs, up to 72 hrs, is safe and cost effective.

Adult↗
PubMed2000

Subjective assessment of blunt impacts.

An important role of an eyewitness to an assault is to effectively quantify the degree of force used; yet evidence of this form is often subjective and relies on personal opinion. Twelve subjects were asked to strike a load cell with a wooden bat, using varying degrees of force. The strikes were recorded by video camera and 50 people observed the video and were asked to grade the strikes. On average 44% accurately assessed the severity of the strikes, whilst 26% over-estimated. Results suggest that the evidence of eyewitnesses should be treated with caution.

Adult↗
PubMed1999

In vivo biocompatibility and mechanical study of novel bone-bioactive materials for prosthetic implantation.

Two epoxy materials with or without adhesively bonded hydroxyapatite (HA) coatings were studied for their biocompatibility and mechanical pushout strength using in vivo implantation in the rabbit lower femur for a duration of 10 days to 6 months. Both were two-part epoxies cured at room temperature for 24 h, with material 1 (Ampreg 26; SP Systems Limited, Cowes, UK) postcured at 110 degrees C (Tg approximately 80 degrees C) and Material 2 (CG5052; Ciba Geigy Limited, Cambridge, UK) at 125 degrees C (Tg approximately 120 degrees C). Implantation in dead rabbit bone was performed to provide mechanical baseline levels. Polymethylmethacrylate (PMMA) and conventionally HA-coated titanium alloy (Ti-6Al-4V) were used as control materials. In the biological study, different fluorescent dyes were used to label newly formed bone. After 6 weeks of implantation, results from mechanical pushout tests showed that the interfacial shear strength (ISS) values were significantly higher than for dead bones with each of the different implants (p < .01-.001). HA-coated material 2 showed a significantly higher ISS value than the uncoated material (p < .05) after 6 weeks' implantation. However, the ISS value for the uncoated material 2 was significantly higher than for PMMA controls (p < .05). No significant differences in the ISS values were shown between HA-coated materials 1 and 2 and Ti-6Al-4V on in vivo implantation for 6 weeks. Failure points of the pushout test from the three HA-coated materials were defined by scanning electron microscopy. Specimens implanted with both HA-coated epoxies were fractured within the HA-coatings or the bone, while with HA-coated Ti-6Al-4V cracked between the coating and metal implant. The percentage of bone in contact with the implant surface was obtained by image analysis which showed that there were no significant differences between different materials after short time implantation (up to 6 week). Long-term implantation of the HA-coated material 2 showed that the percentage of bone contact had increased from 52.8+/-1.1% (6 week) to 80.0+/-0.3% (3 months) (p < .01) and remained at 81.0+/-0.8% (6 months). Measurements of bone mineralization rate (BMR) showed that after 3 weeks of implantation, there were no significant differences between PMMA and uncoated materials 1 and 2. After 6 weeks, the BMRs in animals implanted with either HA-coated material 1 or 2 were significantly higher than with HA-coated Ti-6Al-4V (p < .05-.0001 in both cases), but with HA-coated material 2 was lower than with this material uncoated (p < .05-.001). No significant differences were found between the two HA-coated epoxy materials. In addition, there were always lower BMRs during the third week of implantation than other periods regardless of biomaterial implanted. The study indicated that the adhesively bonded HA-coated novel epoxy materials were superior to conventional plasma-sprayed Ti-6Al-4V implants with respect to both BMR and bone integration with the implant surfaces. Adhesively bonded HA-coated epoxy materials had similar ISS values to HA-coated Ti-6Al-4V, but the former failed within the bone and coating, while the latter showed splitting between coating and metal.

Algorithms↗
PubMed1998

Composite technology in load-bearing orthopaedic implants.

Composite materials have been widely promoted as possible orthopaedic biomaterials but to date have found few successful commercial applications, due to the many challenging problems presented by their design, fabrication and testing. The range of possible composite biomaterials is reviewed, together with the possible methods of fabrication and the limitations that these place on the design of composite components. The use of composite materials allows many new design possibilities, but this freedom of design requires a clearer understanding of the objectives and constraints on the design process. The testing of composite components also presents many challenging problems, which are not adequately addressed by existing standards developed for testing conventional monolithic materials. The interaction of composite materials with the body is more complex than that of the component materials, and the prediction of their long-term mechanical performance also presents many intractable difficulties. However, despite these challenges composite materials are likely to prove invaluable in the future development of orthopaedics.

Biocompatible Materials↗
PubMed1998

Development of fatigue lifetime predictive test methods for hip implants: part I. Test methodology.

The fatigue failure of hip joint prostheses will be expected to assume more importance in second generation implants aimed at younger, more active patients. Furthermore, new designs and material combinations including coatings (e.g. hydroxyapatite) may introduce fatigue problems that as yet have not been considered. The current research makes an initial attempt to develop accelerated fatigue testing procedures to enhance the methodology of hip implant lifetime prediction. Tests conducted on a 'model' four point bendbar testpiece (mill-annealed Ti-6A1-4V) highlighted that the accelerated test must be conducted in a physiological solution such as Ringer's at 37 degrees C. The introduction of superimposed block overloads (50 cycles) to signify stair ascent/descent or fast walking and single overloads to signify sit/stand movements or stumbling were found to reduce fatigue life by > 50%. The findings of this fatigue study were combined with biomechanics studies to construct a variable amplitude 'in-service' load spectrum for testing hip implants. Using ambulatory trial data, a simple load sequence was designed containing 4 single (sit/stand movements) and 3 block (stair ascent/descent) overloads that repeated ten times gave one days activity; single overloads repeated every 110 base cycles (normal walking) and block overloads 80, 110 (morning/evening) and 250 (daytime) base cycles.

Alloys↗
PubMed1996

Phenylacetic acid halides inhibit estrogen receptor (ER)-positive MCF-7 cells, but not ER-negative human breast cancer cells or normal breast epithelial cells.

Phenylacetic acid (PA) derivatives and conjugates have been reported to have antiproliferative and antitumor properties against various types of cancers. Based on these findings, recent in vitro experiments were devised to examine the antiproliferative properties of a series of para substituted (Br, Cl, F, H, NO2 and OCH3) PAs. The in vitro screening protocal involved the plating of MCF-7 cells in a 96-well plate assay. After 1 day, the cells were exposed to the PA derivatives for 2 days (log phase of MCF-7 growth curve). Cells growth was determined by the Alamar blue dye reagent. The optical density data was analyzed and IC50 concentration values determined. The results showed that PA halide derivatives caused a significant decrease in proliferation of the MCF-7 cells. The order of antiproliferative activity was BR > Cl > or = F, with IC50 values (nM) of 10 +/- 0.005, 100 +/- 0.02 and 100 +/- 0.04, respectively. The OCH3, H and NO2 compounds showed no significant antiproliferative activity. PA halide derivatives may have similar actions as tamoxifen because they show specificity for estrogen receptor-positive cells.

Antimetabolites, Antineoplastic↗
PubMed1996

Adiposity and regional body fat distribution in physically active young and middle-aged women.

OBJECTIVE: To test the hypothesis that age does not directly influence body composition or regional body fat distribution throughout middle age in women. DESIGN: Cross-sectional. SUBJECTS: Thirty female endurance athletes of similar competitive ranking ranging in age from 23-56 years. MEASUREMENTS: Body composition (hydrodensitometry and skinfolds) and regional body fat distribution (waist and hip circumference and tricep, subscapular, suprailiac, abdomen and thigh skinfolds); maximal oxygen uptake. RESULTS: In contrast to the age-related increases in total and regional body fat levels and decreases in fat-free mass in the general population of women, there were no significant trends for changes in body composition or regional body fat distribution in our cross-section of highly physically active subjects with age. CONCLUSION: These findings suggest that age-related increases in total body fat and decreases in fat-free mass may be a result of reduced chronic physical activity levels with age rather than an inevitable consequence of the aging process.

Adipose Tissue↗
PubMed1995

The growth inhibitory properties of a dopamine agonist (SKF 38393) on MCF-7 cells.

Dopamine agonists have been indicated as treatment for disorders such as Parkinson's disease, cardiogenic shock and dopamine insufficiency. A unique relationship exists between dopamine and carcinogenicity. Chronic prolactin stimulation has been identified as a promoter of carcinogenicity. Prolactin secretion is regulated through dopamine receptor activation. Dopaminergic agonists inhibit prolactin release and antagonists increase release. High levels of prolactin have been shown to suppress production of estrogen and progesterone. As a result of these findings, a series of experiments were designed to examine the effects of a specific dopamine agonist, SKF 38393, against MCF-7 cells. MDA-MB231 and MCF-10 cells were used as negative controls. The breast cancer in vitro screening procedure involved the plating of MCF-7, MDA-MB231 and MCF-10 cells in a 96-well plate assay. After 1 day, the cells were exposed to SKF 38393 for 2 days and cell growth was determined by the Alamar blue dye reagent method. The optical density data was analyzed and IC50 values determined. The results indicated that SKF 38393 caused a significant decrease in proliferation of MCF-7 cells. The IC50 value was 0.1 +/- 0.03 microM. The results also indicated no significant effect on MDA-MB231 and MCF-10 cells.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗