Diagnostic Value of Metagenomic Next-Generation Sequencing for Pneumonia in Immunocompromised Patients.

Introduction: The diagnosis of pulmonary infection and the identification of pathogens are still clinical challenges in immunocompromised patients. Metagenomic next-generation sequencing (mNGS) has emerged as a promising infection diagnostic technique. However, its diagnostic value in immunocompromised patients needs further exploration. Purposes: This study was to evaluate the diagnostic value of mNGS compared with comprehensive conventional pathogen tests (CTs) in the etiology of pneumonia in immunocompromised patients and immunocompetent patients. Methods: We retrospectively reviewed 53 patients who were diagnosed with pneumonia from May 2019 to June 2021. There were 32 immunocompromised patients and 21 immunocompetent patients with pneumonia who received both mNGS and CTs. The diagnostic performance was compared between mNGS and CTs in immunocompromised patients, using the composite diagnosis as the reference standard. And, the diagnostic value of mNGS for mixed infections was further analyzed. Results: Compared to immunocompetent patients, the most commonly pathogens, followed by Cytomegalovirus, Pneumocystis jirovecii and Klebsiella pneumoniae in immunocompromised patients. Furthermore, more mixed infections were diagnosed, and bacterial-fungal-virus coinfection was the most frequent combination (43.8%). mNGS can detect more types of pathogenic microorganisms than CTs in both groups (78.1% vs. 62.5%, P = 0.016and 57.1% vs. 42.9%, P = 0.048). The overall diagnostic positive rate of mNGS for pathogens was higher in immunocompromised patients (P = 0.002). In immunocompromised patients, a comparable diagnostic accuracy of mNGS and CTs was found for bacterial, fungal, and viral infections and coinfection. mNGS had a much higher sensitivity for bacterial infections (92.9% vs. 50%, P < 0.001) and coinfections (68.8% vs. 48.3%, P < 0.05), and it had no significant advantage in the detection of fungal infections, mainly due to the high sensitivity for Pneumocystis jirovecii in both groups. Conclusion: mNGS is more valuable in immunocompromised patients and exhibits apparent advantages in detecting bacterial and mixed infections. It may be an alternative or complementary diagnostic method for the diagnosis of complicated infections in immunocompromised patients.

Metaraminol use during spinal anaesthesia for caesarean section: a meta-analysis of randomised controlled trials.

INTRODUCTION: During caesarean section, the use of a vasopressor is often required to achieve haemodynamic stability of the parturient. Metaraminol is a vasopressor used in this context in some countries. However, the differences between metaraminol and other vasopressors remain unclear. METHODS: A search of the PubMed, Cochrane Library, and Embase databases was performed to identify randomised controlled trials comparing the use of metaraminol with other vasopressors during spinal anaesthesia at caesarean section. The selected studies were subjected to meta-analysis and risk-of-bias assessment. RESULTS: Four randomised, controlled trials met the selection criteria and 409 parturients who underwent an elective caesarean section were included in this meta-analysis. The quality of these trials was good. Metaraminol was associated with higher umbilical arterial pH (standardised mean difference [SMD] 0.82, 95% CI 0.01 to 1.62, P=0.05); a lower incidence of fetal acidosis (RR 0.08, 95% CI 0.01 to 0.63, P=0.02); and a lower incidence of nausea or vomiting (RR 0.16, 95% CI 0.04 to 0.57, P=0.0005) than was ephedrine. Metaraminol resulted in higher umbilical arterial pH (SMD 0.42, 95% CI 0.15 to 0.68, P=0.002) but a higher incidence of reactive hypertension (RR 1.80, 95% CI 1.32 to 2.46, P=0.0002) than did phenylephrine. CONCLUSION: The results of this study showed that for spinal anaesthesia at elective caesarean section, metaraminol may be a more suitable vasopressor than ephedrine and its effects are at least not inferior to those of phenylephrine.

Differences in femoral morphology among the Orientals and Caucasians: a comparative study using plain radiographs.

The purpose of this study was to identify the differences in femoral dimensions among Caucasian and Oriental populations. A total of 268 femora were collected from China, Japan, Korea, Taiwan and the United States. Firstly, the dimensional parameters for measuring femur were identified. These were initially measured on bone specimens to determine the methodology, followed by measuring the same parameter on plane radiographs of the same bone specimen using a board, and digitized with the aim of verifying the repeatability and reliability of the data. Data were analyzed using ANOVA, paired students t test and Pearson's correlation analysis. The results revealed that Caucasian femora are significantly larger in maximum bone length (BL), head-neck length (HNL), lesser trochanter width and the total width of the distal epiphysis (Wdf). The Beijing femora were found to be the longest and the Japanese femora constituted the shortest bone lengths and smallest angle alpha among the Oriental populations. A strong correlation was observed between Wdf and HD, HNL, Wmc and Wlc in all the populations; however, correlation between Wdf and BL was mild. The angle alpha showed no correlation with BL. This study generated a large database of femoral geometry, which may help pharmaceutical companies to design orthopedic implants for Oriental populations.

Estudio CRONO: prevalencia del dolor irruptivo en pacientes con dolor crónico no oncológico en Andalucía, España / CRONO study: prevalence of breakthrough pain in patients with non-cancer chronic pain in Andalusia, Spain

Objetivo: El objetivo de este estudio es evaluar la prevalencia de dolor irruptivo (DI) en pacientes ambulatorios con dolor crónico de origen no oncológico y caracterizar la fisiopatología, localización, intensidad y frecuencia de los episodios de DI. Material y métodos: Estudio observacional, prospectivo y no intervencionista realizado en 16 unidades de dolor ambulatorias de hospitales de Andalucía y Ceuta. Se preguntó a los pacientes consecutivos elegibles si experimentan DI definido como "una exacerbación transitoria del dolor que ocurre espontáneamente, o en relación con un desencadenante predecible o impredecible específico, a pesar del dolor de base estable y controlado". En cada día de la encuesta, los dos primeros pacientes que confirmaron DI fueron preguntados sobre las características clínicas de su PTP (etiología, inicio, intensidad, frecuencia y tratamiento). Resultados: Se realizó un cribaje a un total de 3209 pacientes con dolor crónico no oncológico para identificar a 1118 pacientes con DI, lo que representó una prevalencia del 36 %. Se obtuvieron las características del DI de 350 pacientes: la intensidad media fue de 8,3 (± 1,4) en una Escala Analógica Visual (EVA), con una media de 2 episodios/24 horas (rango 1-5/24 h). El mecanismo del dolor fue mixto en 149 (42,6 %), neuropático en 91 (26 %) y nociceptivo en 72 (20,6 %) de los pacientes. Se encontró correlación positiva entre una mayor intensidad de DI con el nivel de dolor basal (r = 0,243, p < 0,001), y el número de crisis diarias de DI (r = 0,123, p = 0,003), ambas estadísticamente significativas. El 78 % de los pacientes estaba en tratamiento con opioides. Los más frecuentes fueron el citrato de fentanilo (52,6 %) y el tramadol (17,4 %). Conclusiones: La tasa de prevalencia del DI en pacientes con dolor crónico no oncológico es superior a un tercio de los pacientes atendidos en las unidades ambulatorias de dolor hospitalario en España. El DI provoca niveles reducidos de funcionalidad, trastornos psicológicos y un aumento del gasto asistencial. La clave del tratamiento es la individualización

Objective: The aim of this study was to evaluate the prevalence of breakthrough pain (BTP) in ambulatory patients with non-cancer chronic pain in Spain and to characterize physiopathology, location, intensity and frequency of BTP episodes. Methods: Prospective, non-interventional, observational study conducted in 16 pain units of hospitals of Andalusia and Ceuta. Eligible consecutive patients were are asked if they experience BTP defined as "a transient exacerbation of pain that occurs either spontaneously, or in relation to a specific predictable or unpredictable trigger, despite stable and controlled background pain". At each survey day, the first two patients reporting BTP were further interrogated on the clinical characteristics of their BTP (etiology, onset, intensity, frequency and treatment). Results: A total of 3,209 patients with non-cancer chronic pain were screened to identify 1,118 patients with BTP, which represented a prevalence of 36 %. BTP characteristics were retrieved from 350 patients: mean BTP intensity was 8.3 (± 1.4) on a Visual Analogue Scale (VAS), with a mean of 2 episodes/24 hour (range 1-5/24 h). Pain mechanism was mixed in 149 (42.6 %), neuropathic in 91 (26 %) and nociceptive in 72 in (20.6 %) of patients. Significant correlation was found between BTP intensity and both higher background pain (r = 0.243, p < 0.001), and daily BTP episodes frequency (r = 0.123, p = 0.003). 78 % of the patients were on opioid treatment. The most frequent were fentanyl citrate (52.6 %) and tramadol (17.4 %). Conclusions: The prevalence rate of BTP in patients with chronic non-oncologic pain is higher than one-third of the patients seen in outpatient hospital pain units in Spain. BTP causes reduced levels of functionality, psychological disorders, and an increase in health care expenditure. Individualization is the key to treatment

Fast nastic motion of plants and bioinspired structures.

The capability to sense and respond to external mechanical stimuli at various timescales is essential to many physiological aspects in plants, including self-protection, intake of nutrients and reproduction. Remarkably, some plants have evolved the ability to react to mechanical stimuli within a few seconds despite a lack of muscles and nerves. The fast movements of plants in response to mechanical stimuli have long captured the curiosity of scientists and engineers, but the mechanisms behind these rapid thigmonastic movements are still not understood completely. In this article, we provide an overview of such thigmonastic movements in several representative plants, including Dionaea, Utricularia, Aldrovanda, Drosera and Mimosa. In addition, we review a series of studies that present biomimetic structures inspired by fast-moving plants. We hope that this article will shed light on the current status of research on the fast movements of plants and bioinspired structures and also promote interdisciplinary studies on both the fundamental mechanisms of plants' fast movements and biomimetic structures for engineering applications, such as artificial muscles, multi-stable structures and bioinspired robots.

Panel-based testing for inherited colorectal cancer: a descriptive study of clinical testing performed by a US laboratory.

Next-generation sequencing enables testing for multiple genes simultaneously ('panel-based testing') as opposed to sequential testing for one inherited condition at a time ('syndrome-based testing'). This study presents results from patients who underwent hereditary colorectal cancer (CRC) panel-based testing ('ColoNext(™) '). De-identified data from a clinical testing laboratory were used to calculate (1) frequencies for patient demographic, clinical, and family history variables and (2) rates of pathogenic mutations and variants of uncertain significance (VUS). The proportion of individuals with a pathogenic mutation who met national syndrome-based testing criteria was also determined. Of 586 patients, a pathogenic mutation was identified in 10.4%, while 20.1% had at least one VUS. After removing eight patients with CHEK2 mutations and 11 MUTYH heterozygotes, the percentage of patients with 'actionable' mutations that would clearly alter cancer screening recommendations per national guidelines decreased to 7.2%. Of 42 patients with an 'actionable' result, 30 (71%) clearly met established syndrome-based testing guidelines. This descriptive study is among the first to report on a large clinical series of patients undergoing panel-based testing for inherited CRC. Results are discussed in the context of benefits and concerns that have been raised about panel-based testing implementation.

TU-E-BRA-07: Post-Operative Eye Plaque Imaging Using Tomotherapy MVCT.

PURPOSE: Intra-operative ultrasound is used to verify the positioning of episcleral eye plaques used to treat ocular melanoma. Ultrasound can be ambiguous because of image artifacts, and plaques may shift position after surgery. Ultrasound verification is particularly challenging for anterior tumors. Post-operative imaging could be used to trigger interventions that would prevent local treatment failure. We investigated if, and under what conditions, the Tomotherapy megavoltage computed tomography (MVCT) system could be used to perform post-implantation verification of eye plaque positioning. METHODS: Plaques were placed on a preserved cow's eye, and imaged with the megavoltage CT of a Tomotherapy linear accelerator (Accuray, Sunnyvale, CA). The images were visually and quantitatively assessed to determine if they were of sufficient quality to verify tumor coverage and plaque tilt with respect to the sclera. We used the visibility of the lens as a proxy for visibility of a tumor. To test the utility of hypothetical higher beam current Tomotherapy images, we averaged sequential images of the same setup. RESULTS: The plaque, the lens of the eye, and the globe are visible in the images. The CNR of the lens with respect to the vitreous was 5.6 for a single image. For 10 images averaged, the CNR was 9.2. Estimated dose from a single image was 1.3 cGy (body CTDIvol); even 10 times this dose would be an acceptable image-guidance dose for radiotherapy patients. One limitation of the imaging procedure is the long scan time (up to 240 seconds), during which time any significant patient motion would lead to image artifacts. Human trials on eye plaque patients are planned. CONCLUSIONS: Tomotherapy MVCT imaging could be used to verify tumor coverage and plaque tilt after episcleral plaque implantation. Tumors should be visible in standard Tomotherapy images but higher beam current images would be preferred if available.

TU-E-BRA-06: Evaluation of a New MV X-Ray Detector Designed for the TomoTherapy® System.

PURPOSE: To evaluate the performance of a new MV X-ray detector prototype specifically designed for use on the TomoTherapy® System. METHODS: A gas-filled detector array, similar in concept to existing TomoTherapy detector arrays, has been designed and fabricated for the TomoTherapy System. Unlike existing detector arrays, the prototype detector array has a radius of curvature that matches the source-to-detector distance. Also, the internal structure of the detector such as the septa material and geometry has been optimized for MV X-rays. The prototype detector performance was assessed by measuring the signal properties of each of the detector channel signals. Signal, noise, and signal-to-noise ratios (SNR) were measured. Finally, the resulting MVCT image quality was assessed. RESULTS: The signal profile across the prototype detector more closely matches the incident X-ray beam intensity and, in particular, is missing the characteristic trough in the center of signal profiles from existing TomoTherapy detector arrays. Compared to an existing detector, the mean signal is approximately equal outside the central region. Inside the 100 central channels (out of 576 total channels), the prototype detector signal is substantially larger than the existing detector. The variation in the pulse-to-pulse signal (noise), after accounting for output fluctuations, is substantially lower with the new detector. The resulting SNR is an average of 18% higher across all channels, with an improvement of up to 36% for the central channels. The prototype detector yielded MVCT images that, compared to one typical system with an existing detector array, had 7% lower image noise in the periphery and 36% lower noise at the center of the image. CONCLUSIONS: This evaluation indicates that the performance of a new MV X-ray detector array prototype exceeds the performance of an existing detector array in terms of signal-to-noise ratio and resulting MVCT image quality.

Problemas éticos en relación a la nutrición y a la hidratación: aspectos básicos / Ethical questions related to nutrition and hidration: basic aspects

Las situaciones que plantean problemas éticos en relación con la nutrición y la hidratación son muy frecuentes hoy día, principalmente a nivel hospitalario tanto en pacientes terminales como en otro tipo de pacientes que precisen de hidronutrición. En este artículo se pretende analizar las sencillas en sus fundamentos, a la luz de valores éticos ampliamente aceptados, para intentar enunciar un modo de actuación claro que ayude en su resolución a los clínicos que han de tomar estas difíciles decisiones. Las situaciones problema analizadas incluyen, entre otras, si la hidratación y la nutrición deben considerarse medidas terapéuticas o cuidados básicos, y si presentan iguales aspectos éticos la nutrición enteral y la parenteral (AU)

Conditions that pose ethical problems related to nutrition and hydration are very common now days, particularly within Hospitals among terminally ill patients and other patients who require nutrition and hydration. In this article we intend to analyze some circumstances, according to widely accepted ethical values, in order to outline a clear action model to help clinicians in making such difficult decisions. The problematic situations analyzed include: should hydration and nutrition be considered basic care or therapeutic measures?, and the ethical aspects of enteral versus parenteral nutrition (AU)

[Ethical questions related to nutrition and hidration: basic aspects]. / Problemas éticos en relación a la nutrición y a la hidratación: aspectos básicos.

Conditions that pose ethical problems related to nutrition and hydration are very common nowdays, particularly within Hospitals among terminally ill patients and other patients who require nutrition and hydration. In this article we intend to analyze some circumstances, according to widely accepted ethical values, in order to outline a clear action model to help clinicians in making such difficult decisions. The problematic situations analyzed include: should hydration and nutrition be considered basic care or therapeutic measures?, and the ethical aspects of enteral versus parenteral nutrition.

Discrete element analysis in musculoskeletal biomechanics.

This paper is written to honor Professor Y. C. Fung, the applied mechanician who has made seminal contributions in biomechanics. His work has generated great spin-off utility in the field of musculoskeletal biomechanics. Following the concept of the Rigid Body-Spring Model theory by T. Kawai (1978) for non-linear analysis of beam, plate, and shell structures and the soil-gravel mixture foundation, we have derived a generalized Discrete Element Analysis (DEA) method to determine human articular joint contact pressure, constraining ligament tension and bone-implant interface stresses. The basic formulation of DEA to solve linear problems is reviewed. The derivation of non-linear springs for the cartilage in normal diarthrodial joint contact problem was briefly summarized. Numerical implementation of the DEA method for both linear and non-linear springs is presented. This method was able to generate comparable results to the classic contact stress problem (the Hertzian solution) and the use of Finite Element Modeling (FEM) technique on selected models. Selected applications in human knee and hip joints are demonstrated. In addition, the femoral joint prosthesis stem/bone interface stresses in a non-cemented fixation were analyzed using a 2D plane-strain approach. The DEA method has the advantages of ease in creating the model and reducing computational time for joints of irregular geometry. However, for the analysis of joint tissue stresses, the FEA technique remains the method of choice.

Effects of intensive insulin therapy alone and with added pioglitazone on renal salt/water balance and fluid compartment shifts in type 2 diabetes.

OBJECTIVE: To evaluate the effects of intensive insulin therapy alone or with added pioglitazone on renal salt/water balance and body fluid compartment shifts in type 2 diabetes. METHODS: A total of 25 insulin-treated, obese patients with type 2 diabetes were randomized to pioglitazone 45 mg (n = 12) or placebo (n = 13) and treated intensively for 12-16 weeks to achieve equivalent glycaemic control. We measured total body water (TBW) and extracellular/intracellular fluid by bioimpedance analysis; plasma/RBC volume with I(131)albumin; sodium handling by fractional excretion of sodium/lithium (FeNa/FeLi) and other renal/hormonal parameters. RESULTS: Intensification of insulin therapy and the addition of pioglitazone significantly improved glycaemia (HbA1C 7.8-7.2% and 7.6-7.1%) and increased body weight (1.7 and 4.9 kg) respectively. TBW increased 1.7 l with insulin alone (65% intracellular) and 1.6 l with added pioglitazone (75% extracellular) (p = 0.06 and 0.09 respectively). Plasma volume increased 0.2 +/- 0.1 l with insulin alone (p = 0.05) and 0.4 +/- 0.1 l with added pioglitazone (p < 0.05). Extravascular, extracellular (interstitial) fluid increased significantly and more with added pioglitazone (0.8 +/- 0.2 l, p < 0.01) than with insulin alone (0.4 +/- 0.2 l, p = ns). At steady-state, FeLi (marker of proximal-tubular sodium delivery to the distal nephron) increased significantly with added pioglitazone (12.4 +/- 1.3 to 18.0 +/- 3.2%) vs. no significant change with insulin alone (15.4 +/- 1.2 to 14.5 +/- 2.3%). There were no significant changes in the other parameters. CONCLUSION: In intensively insulin-treated obese type 2 diabetic patients, at equivalent glycaemic control, the addition of pioglitazone causes greater weight gain, but a similar increase in body water that is mainly extracellular and interstitial compared with intracellular increase with insulin therapy alone. Pioglitazone also increases the filtered load of sodium reabsorbed at the distal nephron with no net change in FeNa.

Efectividad de la acupuntura en el alivio del dolor refractario al tratamiento farmacológico convencional / Effectiveness of acupuncture in relieving pain refractory to conventional pharmacological therapy

Objetivos: Valorar la efectividad global de la acupuntura como terapia complementaria en la reducción del dolor crónico en grupos apareados (antes-después) de pacientes en condiciones de práctica clínica real. Conocer en qué proporción disminuye el consumo de analgésicos en estos pacientes tras un ciclo de acupuntura. Determinar las reacciones adversas debidas a acupuntura. Distinguir la efectividad de la acupuntura en la reducción del dolor en diversas patologías para averiguar en cuáles es más efectiva. Material y métodos: Estudio cuasi experimental en 225 pacientes ambulatorios con dolor refractario a tratamiento farmacológico convencional. Medición con una escala múltiple de valoración del dolor antes de iniciar el ciclo de tratamiento con acupuntura, después de realizar diagnóstico según la medicina tradicional china y al terminar el ciclo de tratamiento. Resultados: Se ha obtenido un nivel de significación p < 0,001 para el valor total de la escala de dolor y para cada una de sus variables (intensidad, frecuencia, consumo de analgésicos, discapacidad y sueño) antes y después del tratamiento con acupuntura. Tras la aplicación de un ciclo de acupuntura, el total de la escala de dolor disminuyó en un 60,6%; la intensidad en un 55,5%; la frecuencia en un 51,2%; el consumo de analgésicos en un 68,2%; la discapacidad en un 59,9%; el sueño mejoró en un 74,1%. Las patologías más frecuentes fueron lumbalgia, fibromialgia y cefalea. No se observaron efectos adversos de la acupuntura. El 11% de los sujetos presentaba intolerancia a fármacos. Conclusiones: La acupuntura es un procedimiento que consume escasos recursos y es altamente efectiva en el tratamiento complementario del dolor crónico. La reducción en la ingesta de fármacos en pacientes con dolor se traduce además en un incremento de la calidad de vida, disminución de efectos secundarios, reducción del coste para el sistema sanitario y aumento de la satisfacción del usuario (...) (AU)

Objectives: To evaluate the overall effectiveness of acupuncture as a complementary therapy in relieving chronic pain in paired groups (before-after) of patients in a real life clinical setting. To determine the extent to which analgesic consumption is reduced in these patients after an acupuncture cycle. To determine the adverse reactions due to acupuncture. To evaluate the effectiveness of acupuncture in reducing pain in distinct clinical entities in order to identify those in which this therapeutic modality is most effective. Material and methods: We performed a quasi-experimental study in 225 outpatients with pain refractory to conventional pharmacological therapy. Pain was measured with a multiple-item pain scale before the acupuncture cycle was started, after the traditional Chinese medicine diagnosis was made, and when the treatment cycle was complete. Results: Significant differences (p < 0.001) before and after acupuncture treatment were obtained for the overall pain score and for each of its variables (intensity, frequency, analgesic consumption, disability, and sleep). After the acupuncture cycle, the total pain score decreased by 60.6%, intensity by 55.5%, frequency by 51.2%, analgesic consumption by 68.2%, disability by 59.9%, and sleep improved by 74.1%. The most frequent disorders were low back pain, fibromyalgia, and headache. No adverse effects of acupuncture were observed. Eleven percent of the patients showed drug intolerance. Conclusions: Acupuncture consumes few resources and is highly effective in the complementary treatment of chronic pain. The reduction in analgesic consumption in patients with pain increases quality of life and patient satisfaction and reduces adverse effects and healthcare costs. Larger studies are required to identify the disorders in which acupuncture should be considered a first-line option (AU)

On foundations of discrete element analysis of contact in diarthrodial joints.

Information about the stress distribution on contact surfaces of adjacent bones is indispensable for analysis of arthritis, bone fracture and remodeling. Numerical solution of the contact problem based on the classical approaches of solid mechanics is sophisticated and time-consuming. However, the solution can be essentially simplified on the following physical grounds. The bone contact surfaces are covered with a layer of articular cartilage, which is a soft tissue as compared to the hard bone. The latter allows ignoring the bone compliance in analysis of the contact problem, i.e. rigid bones are considered to interact through a compliant cartilage. Moreover, cartilage shear stresses and strains can be ignored because of the negligible friction between contacting cartilage layers. Thus, the cartilage can be approximated by a set of unilateral compressive springs normal to the bone surface. The forces in the springs can be computed from the equilibrium equations iteratively accounting for the changing contact area. This is the essence of the discrete element analysis (DEA). Despite the success in applications of DEA to various bone contact problems, its classical formulation required experimental validation because the springs approximating the cartilage were assumed linear while the real articular cartilage exhibited non-linear mechanical response in reported tests. Recent experimental results of Ateshian and his co-workers allow for revisiting the classical DEA formulation and establishing the limits of its applicability. In the present work, it is shown that the linear spring model is remarkably valid within a wide range of large deformations of the cartilage. It is also shown how to extend the classical DEA to the case of strong nonlinearity if necessary.

Prediction of femoral head collapse in osteonecrosis.

The femoral head deteriorates in osteonecrosis. As a consequence of that, the cortical shell of the femoral head can buckle into the cancellous bone supporting it. In order to examine the buckling scenario we performed numerical analysis of a realistic femoral head model. The analysis included a solution of the hip contact problem, which provided the contact pressure distribution, and subsequent buckling simulation based on the given contact pressure. The contact problem was solved iteratively by approximating the cartilage by a discrete set of unilateral linear springs. The buckling calculations were based on a finite element mesh with brick elements for the cancellous bone and shell elements for the cortical shell. Results of 144 simulations for a variety of geometrical, material, and loading parameters strengthen the buckling scenario. They, particularly, show that the normal cancellous bone serves as a strong supporting foundation for the cortical shell and prevents it from buckling. However, under the development of osteonecrosis the deteriorating cancellous bone is unable to prevent the cortical shell from buckling and the critical pressure decreases with the decreasing Young modulus of the cancellous bone. The local buckling of the cortical shell seems to be the driving force of the progressive fracturing of the femoral head leading to its entire collapse. The buckling analysis provides an additional criterion of the femoral head collapse, the critical contact pressure. The buckling scenario also suggests a new argument in speculating on the femoral head reinforcement. If the entire collapse of the femoral head starts with the buckling of the cortical shell then it is reasonable to place the reinforcement as close to the cortical shell as possible.

Development and validation of a new approach for computer-aided long bone fracture reduction using unilateral external fixator.

An innovative computer-aided method to plan and execute long bone fracture reduction using Dynafix unilateral external fixator (EF) is presented and validated. A matrix equation, which represents a sequential transformation from proximal to distal ends, was derived and solved for the amount of rotation and translation required at each EF joint to correct for a displaced fracture using a non-linear least square optimization method. Six polyurethane-foam models of displaced fracture tibiae were used to validate the method. The reduction accuracy was quantified by calculating the residual translations (xr, yr, zr), the residual displacement (dr), and the residual angulations (alphar, betar, gammar) based on the X-Y-Z Euler angle convention. The experiment showed that the mean+/-S.D. of alphar, betar, gammar, xr, yr, zr and dr were 1.57+/-1.14 degrees, 1.33+/-0.90 degrees, 0.71+/-0.70 degrees, 0.98+/-1.85, 0.80+/-0.67, 0.30+/-0.27, and 0.50+/-0.77 mm, respectively, which demonstrated the accuracy and reliability of the method. Instead of adjusting the fixator joints in-situ, our method allows for off-site adjustment of the fixator joints and employs the adjusted EF as a template to guide the surgeons to manipulate the fracture fragments to complete the reduction process. Success of this method would allow surgeons to perform fracture reduction more objectively, efficiently and accurately yet reduce the radiation exposure to both the involved clinicians and patients and lessen the extent of periosteum and soft tissue disruption around the fracture site.

Fixation stiffness of Dynafix unilateral external fixator in neutral and non-neutral configurations.

A primary function of external fixator is to stabilize the fracture site after fracture reduction. Conventional fracture reduction method would result in fixator configurations deviated from its neutral configuration. How the non-neutral configurations would affect the biomechanical performance of unilateral external fixators is still not well-documented. We developed a finite element model to predict the fixation stiffness of the Dynafix unilateral external fixator at arbitrary configurations under compression, torsion, three-point, and four-point bending. Experimental testing was done to validate the model using six Dynafix unilateral external fixators in neutral and particular non-neutral configurations. Effects of loading directions on bending stiffness were also studied. It appeared that the model succeeded in revealing the relative stiffness of the neutral and non-neutral configuration in all the loading conditions. Our results also demonstrated that bending stiffness could vary substantially for different loading directions and the principle loading directions could be very different for different fixator configurations. Therefore, a more logical way to compare the bending stiffness is to identify the principle loading directions of each fixator configuration and used their maximum and minimum bending stiffness as comparison criteria. Given that fixator configurations could substantially change the stiffness properties of the bone-fixator system, computer simulation with finite element modeling of this kind will provide useful clinical information on the rigidity of certain configurations in stabilizing the fracture site for bone healing.

The effect of recombinant human osteogenic protein-1 on allograft incorporation.

We used a canine intercalary bone defect model to determine the effects of recombinant human osteogenic protein 1 (rhOP-1) on allograft incorporation. The allograft was treated with an implant made up of rhOP-1 and type I collagen or with type I collagen alone. Radiographic analysis showed an increased volume of periosteal callus in both test groups compared with the control group at weeks 4, 6, 8 and 10. Mechanical testing after 12 weeks revealed increased maximal torque and stiffness in the rhOP-1 treated groups compared with the control group. These results indicate a benefit from the use of an rhOP-1 implant in the healing of bone allografts. The effect was independent of the position of the implant. There may be a beneficial clinical application for this treatment.

A novel reconstruction algorithm to extend the CT scan field-of-view.

For various reasons, a projection dataset acquired on a computed tomography (CT) scanner can be truncated. That is, a portion of the scanned object is positioned outside the scan field-of-view (SFOV) and the line integrals corresponding to those regions are not measured. A projection truncation problem causes imaging artifacts that lead to suboptimal image quality. In this paper, we propose a reconstruction algorithm that enables an adequate estimation of the projection outside the SFOV. We make use of the fact that the total attenuation of each ideal projection in a parallel sampling geometry remains constant over views. We use the magnitudes and slopes of the projection samples at the location of truncation to estimate water cylinders that can best fit to the projection data outside the SFOV. To improve the robustness of the algorithm, continuity constraints are placed on the fitting parameters. Extensive phantom and patient experiments were conducted to test the robustness and accuracy of the proposed algorithm.