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PubMed2004

Enhancement of stability following anterior cervical corpectomy: a biomechanical study.

STUDY DESIGN: An in vitro biomechanical study of various reconstructive techniques following decompression of the spondylotic cervical spine. OBJECTIVE.: To evaluate the biomechanical stability of anterior cervical plate fixation following three strategies of decompression for multilevel cervical spondylosis (three levels) of the cervical spine: three level discectomy, single corpectomy and discectomy, and a two-level corpectomy. SUMMARY OF BACKGROUND DATA: The main goals of surgical treatment for cervical myelopathy include adequate decompression and stabilization while maintaining or restoring cervical lordosis. Cervical decompression is often performed through a corpectomy followed by strut-graft reconstruction. An anterior cervical plate with end-fixation (two points of fixation) is then used to span the construct. The authors propose an alternative to multilevel corpectomy and long-segment end construct plate fixation. Often times, the cervical stenosis is confined to the area of the degenerative discs. As a result, the authors feel that either multilevel discectomy or a corpectomy combined with discectomy followed by segmental plate fixation may provide adequate decompression with increased biomechanical rigidity as compared to cervical plate-constructs with end-fixation only. METHODS: Seven human cadaveric fresh-frozen cervical spines from C1-T1 were utilized. Three-dimensional motion analysis with an optical tracking device was used to determine motion following various reconstruction methods. All seven cervical spines underwent testing in a randomized order. The end construct model consisted of a corpectomy at C4 and C5 with a polymethyl methacrylate strut graft and an anterior cervical PEAK (DePuy-AcroMed) plate. The two segmental constructs also utilized the PEAK plate with one construct undergoing discectomies at C3-C4, C4-C5, and C5-C6 with polymethyl methacrylate interbody grafts and the other segmental construct undergoing a discectomy at C3-C4 and a corpectomy of C5. All specimens underwent a pure moment application of 2 Nm with regards to flexion-extension, lateral bending, and axial rotation. RESULTS.: The three-level discectomy and combined one-level discectomy and corpectomy with segmental fixation was significantly more rigid in flexion-extension and lateral bending than the two-level corpectomy with end-construct plate fixation (P < 0.05). There was no increase in stability during extension between the end construct (two-level corpectomy) reconstruction model and the un-instrumented corpectomy and grafted specimen. No difference was noted between the segmental constructs and the end-construct with regards to axial rotation. CONCLUSIONS: Cervical myelopathy is traditionally treated with a multilevel corpectomy and an end-construct plate fixation spanning the strut graft. A large moment arm is generated at the ends of the construct, potentially leading to plate migration or dislodgment. Often times, adequate decompression can be achieved with either a multilevel discectomy or a combined discectomy and corpectomy with segmental plate fixation. This study clearly demonstrates that segmental plate fixation affords a more biomechanically rigid method of reconstruction with regards to flexion-extension and lateral bending than end-construct plate fixation. The increased rigidity afforded by segmental fixation may significantly decrease the likelihood of plate dislodgement in the setting of anterior instrumentation alone following anterior alone, long segment reconstruction procedures.

Biomechanical Phenomena↗
PubMed1998

Context, composition and heterogeneity: using multilevel models in health research.

This paper considers the use of multilevel models in health research. Attention focuses on the structure and potential of such models and particular consideration is given to their use in elucidating the importance of contextual effects in relation to individual level social and demographic factors in understanding health outcomes, health-related behaviour and health service performance. Four graphical typologies are used to outline the questions that multilevel models can address and the paper illustrates their potential by drawing on published examples in a number of different research areas.

Analysis of Variance↗
PubMed1996

A work-systems analysis of compliance with universal precautions among health care workers.

Universal precautions are work practices designed to protect health care workers from occupational exposure to HIV and other bloodborne pathogens. However, despite aggressive dissemination efforts by CDC and regulatory action by OSHA, compliance remains less than satisfactory. This article argues that the minimization of risk from bloodborne pathogens requires a multilevel or work-systems perspective that considers individual, job/task, and environmental/organizational factors. The available literature on universal precautions suggests the potential of such an approach and provides insight into the limited success of current worker-focused mitigation efforts. In particular, specific opportunities exist to develop and apply engineering controls, to improve the design and organization of jobs and tasks, and to create organizations that facilitate and reinforce safe behavior.

Blood-Borne Pathogens↗
PubMed1998

Communication between the cell membrane and the nucleus: role of protein compartmentalization.

Understanding how the information is conveyed from outside to inside the cell is a critical challenge for all biologists involved in signal transduction. The flow of information initiated by cell-cell and cell-extracellular matrix contacts is mediated by the formation of adhesion complexes involving multiple proteins. Inside adhesion complexes, connective membrane skeleton (CMS) proteins are signal transducers that bind to adhesion molecules, organize the cytoskeleton, and initiate biochemical cascades. Adhesion complex-mediated signal transduction ultimately directs the formation of supramolecular structures in the cell nucleus, as illustrated by the establishment of multi complexes of DNA-bound transcription factors, and the redistribution of nuclear structural proteins to form nuclear subdomains. Recently, several CMS proteins have been observed to travel to the cell nucleus, suggesting a distinctive role for these proteins in signal transduction. This review focuses on the nuclear translocation of structural signal transducers of the membrane skeleton and also extends our analysis to possible translocation of resident nuclear proteins to the membrane skeleton. This leads us to envision the communication between spatially distant cellular compartments (i.e., membrane skeleton and cell nucleus) as a bidirectional flow of information (a dynamic reciprocity) based on subtle multilevel structural and biochemical equilibria. At one level, it is mediated by the interaction between structural signal transducers and their binding partners, at another level it may be mediated by the balance and integration of signal transducers in different cellular compartments.

Animals↗
PubMed2001

Randomized clinical trials with added rescue medication: some approaches to their analysis and interpretation.

Patients in some randomized clinical trials may start additional non-randomized medication because of an exacerbation of symptoms or insufficient therapeutic effect. Typically this rescue medication reduces the observed treatment effect in intention-to-treat analysis. We discuss methods of analysis which take account of rescue medication in order to achieve a more meaningful comparison of the randomized treatments, focusing on trials with a repeated quantitative outcome. Ignoring all data after rescue is likely to be biased because rescued patients are a highly selected group. Instead we propose using methods based on ranks or multilevel models. The rank-based methods assume that rescued patients have especially bad underlying outcomes. The multilevel regression model relates a patient's outcome to allocated treatment and rescue status at each time, and requires correct modelling of all prognostic factors which predict starting rescue medication and of the covariance between outcomes measured at different times. We also describe sensitivity analyses over a range of possible models for the effect of rescue medication. We illustrate these methods in a trial in Parkinson's disease. It appears that adjustment for rescue medication will not radically alter the randomized treatment comparison unless rescue medication is substantially imbalanced between randomized groups and has a substantial effect on the outcome.

Activities of Daily Living↗
PubMed2006

Prediction of postoperative mortality in elderly patients with colorectal cancer.

PURPOSE: This study was designed to develop a model for predicting postoperative mortality in elderly patients undergoing surgery for colorectal cancer. METHODS: This multicenter study was conducted by using routinely collected clinical data, assessing patients older than aged 80 years, with 30-day operative mortality as the primary end point. Data were collected from The Association of Coloproctology of Great Britain and Ireland database, encompassing 8,077 newly diagnosed colorectal cancer patients undergoing resectional surgery in 79 hospitals between April 2000 to March 2002, The Association of Coloproctology Malignant Bowel Obstruction Study, encompassing 1,046 patients with malignant bowel obstruction in 148 hospitals, between April 1998 to March 1999, and The Wales-Trent audit, encompassing 3,522 newly diagnosed colorectal cancer patients, between July 1992 to June 1993. A multilevel logistic regression model was developed to adjust for case-mix and to accommodate the variability of outcomes between the three study populations. The model was internally validated using a Bayesian resampling technique and tested using measures of discrimination, calibration, and subgroup analysis. RESULTS: A total of 2,533 patients satisfied the inclusion criteria, with a 30-day mortality of 15.6 percent. Multivariate analysis identified the following independent risk factors: age (odds ratio for 85-90, 90-95, >95 vs. 80-85 = 1.1, 1.8, 2.9), American Society of Anesthesiology grade (odds ratio for Grade III, IV vs. I-II = 2.7, 6.1), operative urgency (odds ratio for emergency vs. elective = 1.9), no cancer excision vs. resection (odds ratio = 1.2), and metastatic disease (odds ratio for metastases vs. no metastases = 1.9). The model offered adequate discrimination (area under receiver operator curve = 0.732) and excellent agreement between observed and predicted outcomes during eight colorectal procedures (P = 0.885). CONCLUSIONS: The elderly colorectal cancer model can accurately estimate 30-day mortality in patients older than aged 80 years undergoing surgery for colorectal cancer. Because the mortality can be considerable, this may have important implications when determining management for this group of patients.

Age Factors↗
PubMed2005

Contemporary results of angioplasty-based infrainguinal percutaneous interventions.

INTRODUCTION: Although lower-extremity bypass grafting has been the gold standard for infrainguinal revascularization, endovascular therapies have been increasingly applied to avoid operative morbidities. This study addresses the initial results of an implementation of infrainguinal percutaneous transluminal angioplasty (PTA) performed by vascular surgeons to treat lower-extremity ischemia. METHODS: From January 2002 to July 2003, 95 consecutive patients presenting with the spectrum of lower-extremity ischemic manifestations, in whom infrainguinal PTA was the initial choice of treatment, were assessed for treatment efficacy by clinical and noninvasive evaluation. Study end points of angiographic, hemodynamic, and clinical successes (Society of Vascular Surgery reporting standards) were recorded, and variables associated with ischemic category improvement were analyzed by univariate and multivariate analysis. During the same study interval, 87 patients underwent bypass grafting (not further considered). RESULTS: PTA was used to treat 100 limbs in 95 consecutive patients: 63 limbs (63%) had femoropopliteal PTA, 17 limbs (17%) had tibioperoneal PTA, and 20 limbs (20%) had multilevel PTA. Tissue-threatening ischemia was present in 47% of patients, and 53% were treated for claudication. Complications (no mortality) included one myocardial infarction (1%) and two access site hematomas (2%). Angiographic and hemodynamic success (a .10 increase in ankle-brachial index) was obtained in 97% and 90% of the treated limbs, respectively. With a mean follow-up of 14 months, clinical success was obtained in 85% of the treated limbs, and limb salvage for critical ischemia was achieved in 75% (30/40 limbs). Of the PTA failures, five patients (5%) underwent bypass grafting, and five patients (5%) underwent major amputation because of no further reconstructive options or extensive necrosis. Insulin-dependent diabetes mellitus (risk ratio [RR], 3.1; 95% confidence interval [CI], 1.1 to 8.7, P = .02), poor runoff into the foot (RR, 3.7; 95% CI, 1.6 to 8.6, P = .001), and renal insufficiency (serum creatinine >1.5 mg/dL) (RR, 3.7; 95% CI, 1.8 to 7.6, P = .001) were predictive of PTA failure. CONCLUSION: Infrainguinal percutaneous transluminal angioplasty for lower-extremity ischemia is feasible, safe and provides acceptable hemodynamic and clinical results. PTA will become the initial treatment for most patients requiring lower-extremity revascularization.

Aged↗
PubMed2001

Application of microbial enumeration technique to evaluate the occurrence of natural bioremediation.

Natural bioremediation is believed to be the major processes that account for both containment of the petroleum-hydrocarbon plume and reduction of the contaminant concentrations. In this study, the feasibility of applying the microbial enumeration technique was assessed for natural biodegradation evaluation at three selected gasoline spill sites. At each site, two monitor wells were installed along the groundwater flow, and one multilevel sampler (MLS) was installed to delineate the vertical distribution of the contaminant plume. Two continuous soil cores were collected at each site to evaluate the horizontal distribution of the microbial activity. Soil samples were used for microbial enumeration, grain-size distribution analysis, and sediment extraction. In situ tracer study was performed using 1,2,4-trimethylbenzene (1,2,4-TMB) as the tracer to study the efficiency of contaminant biodegradation. Investigation results demonstrate the agreement between microbial enumeration and other evaluation techniques for natural bioremediation (e.g., geochemical indicator analysis, tracer study). Results suggest that the microbial enumeration is useful in assessing the occurrence, efficiency, and status of the bioremediation. Because this technique provides insight into factors controlling contaminant biodegradation, it could be performed as the supplemental method for natural bioremediation evaluation at petroleum-hydrocarbon spill sites.

Benzene Derivatives↗
PubMed1993

Analyzing individual status and change with hierarchical linear models: illustration with depression in college students.

A recently developed class of multilevel or hierarchical linear models (HLM) provides an intuitive and efficient way to estimate individual growth or change curves. The approach also models the between-subjects variation of the individual change curves with treatment factors and individual attributes. Unlike other repeated measures analysis methods common in the behavioral sciences, HLM allows the fit of data with unequal numbers of repeated observations for each subject, variable timing of observations, and missing data, features which are often characteristic of data from field studies. The application of HLM for the analysis of repeated psychological measures is discussed and illustrated here with depression data for college students. Strengths and limitations of the approach are discussed.

Adaptation, Psychological↗
PubMedDate not supplied

Mesh simplification with hierarchical shape analysis and iterative edge contraction.

This paper presents a novel mesh simplification algorithm. It decouples the simplification process into two phases: shape analysis and edge contraction. In the analysis phase, it imposes a hierarchical structure on a surface mesh by uniform hierarchical partitioning, marks the importance of each vertex in the hierarchical structure, and determines the affected regions of each vertex at the hierarchical levels. In the contraction phase, it also divides the simplification procedure into two steps: half-edge contraction and optimization. In the first step, memoryless quadric metric error and the importance of vertices in the hierarchical structure are combined to determine one operation of half-edge contraction. In the second step, it repositions the vertices in the half-edge simplified mesh by minimizing the multilevel synthesized quadric error on the corresponding affected regions from the immediately local to the more global. The experiments illustrate the competitive results.

Algorithms↗
PubMedDate not supplied

Multilevel models and health economics.

Multilevel analyses have become an accepted statistical technique in the field of education where over the past decade or so the methods have been developed to explore the relationships between pupil characteristics and the characteristics of the schools they attend. More recently, widespread use has extended to other social sciences and health research. However, to date, little use has been made of these techniques within the health economics literature. This paper presents an introductory account of multilevel models and describes some of the areas of health economics research that may benefit from their use.

Adult↗
PubMed1999

Variation in the provision of chemotherapy for colorectal cancer.

OBJECTIVE: To quantify the impact of patient, area and hospital characteristics on variations in the provision of chemotherapy for colorectal cancer. SUBJECTS: Incident cases of colorectal cancer (ICD 153-154), aged under 75 years and resident in Scotland, derived from linked hospital discharge records and death records for the period January 1990 to June 1994. The final analysis was carried out on 7852 patients resident in 823 areas and first admitted to one of 59 hospitals. MAIN OUTCOME MEASURE: Whether a patient received chemotherapy (OPCS4 procedure code X35.2) during any hospital episode in the six months after their first admission. METHODS: Multilevel logistic regression to separate effects of patients, areas and hospitals. RESULTS: During the study period, 8% (n = 626) of the study population received chemotherapy within six months of their first admission. Adjusting for comorbidities and emergency admissions, both age and deprivation were significantly associated with the treatment. The odds ratios (OR) of chemotherapy relative to patients aged 65-74 were 2.13 and 4.50 for patients aged 55-64 and under 55 respectively. Relative to patients resident in the most affluent areas, the OR of chemotherapy for patients resident in the most deprived areas was 0.73. Area level availability of the treatment was not significantly associated with a patient's odds of receiving the treatment while on site provision of chemotherapy at the hospital of first admission was (OR = 4.32). There was significant unexplained variation between hospitals of first admission but not between areas of residence; between hospital variation decreased by 22% during the study period. CONCLUSION: Differences according to age may reflect both clinical and patient decisions regarding the benefits of the treatment relative to its toxicity. Lower treatment rates in deprived areas may indicate inequitable access to services. Hospital differences may reflect consultant effects and it would be expected that these should decrease now that the efficacy of the treatment has been recognised and guidelines have been issued.

Adolescent↗
PubMed1994

Allocating resources to health authorities: development of method for small area analysis of use of inpatient services.

Every year about 22 billion pounds is allocated to health authorities for hospital and community services in England. The distribution of most of these funds is based on a formula developed to reflect the population's needs, but the existing formula has been criticised on several grounds. This paper describes the development of a method to determine the health needs for small geographical areas. Data from the hospital episodes statistics and 1991 census together with information on vital statistics and supply of health care facilities were used in the model. Two stage least squares regression was used to identify true indicators of need, and these were entered into a multilevel model to take account of variations in practice in different health authorities. The resulting formula should be more statistically robust and more sensitive to needs than previous approaches.

Health Care Rationing↗
PubMed2007

Pain and negative mood during rehabilitation after anterior cruciate ligament reconstruction: a daily process analysis.

Daily diary methods were used to examine changes in pain and negative mood over the first 6 weeks of rehabilitation after surgical reconstruction of the anterior cruciate ligament (ACL). Participants (58 men and 33 women) completed measures of personal factors (i.e., age, athletic identity, neuroticism, optimism) before surgery and indices of daily pain, negative mood, and stress for 42 days after surgery. Multilevel modeling revealed that, as would be expected, daily pain ratings decreased significantly over the course of the study and that the rate of decline in pain ratings decreased over time. Age and daily negative mood were positively associated with daily pain ratings. Daily negative mood also decreased significantly over the course of the study and was positively associated with neuroticism, daily pain, and daily stress. Athletic identity and optimism interacted with time since surgery in predicting daily negative mood such that participants with high levels of athletic identity and low levels of optimism reported greater decreases in daily negative mood over time. Overall, the findings reveal a pattern of improved psychological functioning over the early stages of post-operative ACL rehabilitation.

Adolescent↗
PubMed2007

Multivariable modelling for meta-epidemiological assessment of the association between trial quality and treatment effects estimated in randomized clinical trials.

Methodological deficiencies are known to affect the results of randomized trials. There are several components of trial quality, which, when inadequately attended to, may bias the treatment effect under study. The extent of this bias, so far only vaguely known, is currently being investigated by 'meta-epidemiological' re-analysis of data collected as part of systematic reviews. As inadequate quality components often co-occur, we maintain that the suspected biases must be evaluated simultaneously. Furthermore, the biases cannot safely be assumed to be homogeneous across systematic reviews. Therefore, a stable multivariable method that allows for heterogeneity is needed for assessing the 'bias coefficients'. We present two general statistical models for analysis of a study of 523 randomized trials from 48 meta-analyses in a random sample of Cochrane reviews: a logistic regression model uses the design of the trials as such to give estimates; a weighted regression model incorporates between-trial variation and thus gives wider confidence intervals, but is computationally lighter and can be used with trials of more general design. In both models, heterogeneity in the bias coefficients can be incorporated in two ways. A stratification approach pools the estimates from models estimated on subgroups of the data. We explore stratification by reviews and by broad trial types, the latter of which gives larger subgroups of the data, circumventing instabilities. A multilevel approach also avoids instabilities and addresses the more fundamental problem of interpretation of the pooled multivariable effect in the presence of heterogeneity.

Clinical Trials as Topic↗
PubMed2003

Raltitrexed-induced hepatotoxicity: multivariate analysis of predictive factors.

Raltitrexed (Tomudex; TOM) hepatotoxicity is usually characterized by a transient and self-limiting increase in transaminase levels. How this may condition daily clinical practice is still unclear. The aim of this study was to investigate predictive factors of TOM hepatotoxicity. In total, 130 patients were treated at two medical oncology institutions with TOM (3 mg/m2) (52 patients) or TOM plus oxaliplatin (TOMOX) (100 mg/m2 day 1 or 70 mg/m2 day 1, 8) (78 patients). A multinomial logistic regression (adjusted for multilevel data) was performed (on all administered chemotherapy courses) to assess the dependence of hepatic toxicity on a set of clinical factors correlated with patient, disease and treatment characteristics. Creatinine clearance was calculated by the Cockcroft formula before each chemotherapy course. Most of the patients presented colorectal cancer (95%) and metastatic disease (93%). Out of the 130 patients, 41 were aged 70 or more, while 119 (91.5%) had a good performance status (PS) (ECOG 0 or 1). Before chemotherapy, liver metastases were present in 78 (60%) patients and elevated transaminase in 25 (19%). A total of 584 courses were administered (252 TOM and 332 TOMOX). National Cancer Institute Common Toxicity Criteria grade 1/2 and 3/4 transaminase toxicity was observed in 62 and 20% of patients, respectively. To control transaminase increase, glutathione (GSH) or ademethionine (SAMe) was administered in 96 and 129 cycles, respectively. Hepatotoxicity conditioned delays (a week or more) in 60 (10%) chemotherapy cycles and was the reason for the discontinuation of chemotherapy in eight (6%) patients. Among the factors evaluated with multivariate analysis, sex, age, PS, creatinine clearance, previous chemotherapy treatment, presence of liver metastases and oncology centre were not significantly associated with TOM hepatotoxicity. Elevated baseline transaminase levels (p=0.001), number of chemotherapy cycles (p<0.001), TOM cumulative dose (p=0.018), unprolonged intervals between courses (p<0.001) and TOMOX regimen (p<0.001) emerged as factors predictive of hepatotoxicity. In the same analysis, GSH (p<0.001) and SAMe (p<0.001) were hepatoprotective agents. This study confirmed TOM-based hepatotoxicity as a clinical relevant side-effect and a major factor for treatment delays or discontinuation. Predictive and protective factors listed above could assist the management of this toxicity that has probably been underestimated until now.

Adult↗
PubMed1979

Multilevel care. A Veterans Administration initiative in health care cost control.

The Veterans Administration's (VA) Department of Medicine and Surgery, the largest of the civilian federal health care systems, is under continuous White House, congressional, and public pressure to provide greater accountability and increased cost-effectiveness for its $5 billion-plus annual budget. Responding to these pressures, the VA is evaluating in ten of its 172 medical centers a new system of resource allocation and financial management known as a multilevel care system. This is a major VA intiative with highly important implications for both the VA and the private health care sector.

Cost-Benefit Analysis↗
PubMed1992

A customized non-axial external beam technique for treatment of prostate carcinomas.

A nonaxial four-field technique for primary and boost treatment of prostate carcinoma has been developed in an effort to minimize dose to rectum and bladder. Using a treatment planning CT scan, prostate, rectal and bladder volumes are outlined and corresponding three-dimensional structures are created. An oblique CT image, which bisects the prostate volume and excludes rectum and bladder, is reconstructed. Four beams, consisting of direct laterals and two anterior, inferior obliques, are designed, which lie in the plane of the generated image. Utilizing a beam's-eye-view display and multilevel dose calculations, blocks are designed for each port, which encompass the target volume within a minimum isodose surface. These customized angles result in oblique ports with rectal and bladder sparing that can be comparable to that of direct lateral ports. Dose-volume histogram analysis is used to evaluate the merits of this nonaxial method with other approaches.

Humans↗