Evaluation of the role of ligaments, facets and disc nucleus in lower cervical spine under compression and sagittal moments using finite element method

Cervical spinal instability due to ligamentous injury, degenerated disc and facetectomy is a subject of great controversy. There is no analytical investigation reported on the biomechanical response of cervical spine in these respects. Parametric study on the roles of ligaments, facets, and disc nucleus of human lower cervical spine (C4-C6) was conducted for the very first time using noninvasive finite element method.A three-dimensional (3D) finite element (FE) model of the human lower cervical spine, consisted of 11,187 nodes and 7730 elements modeling the bony vertebrae, articulating facets, intervertebral disc, and associated ligaments, was developed and validated against the published data under three load configurations: axial compression; flexion; and extension. The FE model was further modified accordingly to investigate the role of disc, facets and ligaments in preserving cervical spine motion segment stability in these load configurations. The passive FE model predicted the nonlinear force displacement response of the human cervical spine, with increasing stiffness at higher loads. It also predicted that ligaments, facets or disc nucleus are crucial to maintain the cervical spine stability, in terms of sagittal rotational movement or redistribution of load. FE method of analysis is an invaluable application that can supplement experimental research in understanding the clinical biomechanics of the human cervical spine.

Nonlinear finite-element analysis of the lower cervical spine (C4-C6) under axial loading

This study was conducted to develop a detailed, nonlinear three-dimensional geometrically and mechanically accurate finite-element model of the human lower cervical spine using a high-definition digitizer. This direct digitizing process also offers an additional method in the development of the finite-element model for the human cervical spine. The biomechanical response of the finite-element model was validated and corresponded closely with the published experimental data and existing finite-element models under axial compressive loading. Furthermore, the results indicated that the cervical spine segment response is nonlinear with increasing stiffness at higher loads. As a logical step, a parametric study was conducted by evaluating the biomechanical response related to the changes in the modeling techniques of the finite-element model and the mechanical properties of the disk annulus. Variations of the predicted horizontal disk bulge were investigated under axial compressive displacements for the normal model, the model without facet articulations, and the model without nucleus. Removal of nucleus fluids causes an inward bulge of the inner annulus layers, with the displacement magnitude dependent on external loads. The result indicates that the nucleus fluid plays an important role in cervical spine mechanics. Simulated facetectomy indicates a decrease in the stiffness of the cervical spine. The study shows that, in reality, the stiffness of the lower cervical spine depends closely on factors such as the spinal geometry and physical properties, thereby resulting in various force and displacement responses.

First cervical vertebra (atlas) fracture mechanism studies using finite element method

Injury mechanisms and stress distribution patterns are important in the clinical evaluation of spinal injuries. Recognition and interpretation of the failure patterns help to determine spinal instability and consequently the choice of treatment. Although, the biomechanics responses of the atlas have received much attention, it has not been investigated using theoretical modeling. Mathematical techniques such as finite element model will provide further understanding to the injury mechanisms of the atlas, which is important for the prevention, diagnosis, and treatment of spinal injuries. In the present study, a detailed three-dimensional finite element model of the human atlas (C1) was constructed, with the geometrical data obtained using a three-dimensional digitizer. Anterior arch, superior/inferior articular processes, transverse processes, posterior arch and posterior tubercule were modeled using eight-noded brick elements. Using the material properties from literature, the 7808-finite element model was exercised under three simulated axial compressive mode of pressure loading and boundary conditions to investigate the sites of failure reported in vivo and in vitro. This report demonstrates high concentration of localized stress at the anterior and posterior archs of the atlas, which agrees well with those reported in the literature. Furthermore, under simulated hyperextension, our results agreed well with the experimental findings, which show that the groove of the posterior arch is subjected to enormous bending moment. The close agreement of the failure location provided confidence to perform further analysis and in vitro experiments. These results may be potentially used to supplement experimental research in understanding the clinical biomechanics of the atlas.

Near fatal drug interactions with methotrexate given for psoriasis

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An axisymmetric contact model of ultra high molecular weight polyethylene cups against metallic femoral heads for artificial hip joint replacements

Contact mechanics of ultra high molecular weight polyethylene (UHMWPE) cups against metallic femoral heads for artificial hip joints is considered in this study. Both the experimental measurement of the contact area and the finite element prediction of the contact radius, maximum contact pressure and maximum Von Mises stress have been carried out for a wide range of contemporary artificial hip joints. Good agreement of the contact radius has been found between the experimental measurements and the finite element predictions based upon an elastic modulus of 1000 MPa and a Poisson's ratio of 0.4 for UHMWPE material under various loads up to 2.5 kN. It has been shown that the half contact angle for all the cup/head combinations considered in this study is between 40 degrees and 50 degrees under a load of 2.5 kN. The importance of this result has been discussed with respect to the anatomical position of the cup when placed in the body and the selection of a simple wear-screening test for artificial hip joints. The predicted contact radius and maximum contact pressure from the finite element model have also been compared with a simple elasticity analysis. It has been shown that the difference in the predicted contact radius between the two methods is reduced for more conforming contacts between the femoral head and the acetabular cup and smaller UHMWPE cup thickness. However, good agreement of the predicted maximum contact pressure has been found for all the combinations of the femoral head and the acetabular cup considered in this study. The importance of contact mechanics on the clinical performance of artificial hip joint replacements has also been discussed.

The Biomechanics of Lumbar Graded Facetectomy Under Anterior-Shear Load

In this paper, an anatomically accurate three-dimensional finite-element (FE) model of the human lumbar spine (L2-L3) was used to study the biomechanical effects of graded bilateral and unilateral facetectomies of L3 under anterior shear. The intact L2-L3 FE model was validated under compression, tension, and shear loading and the predicted responses matched well with experimental data. The gross external (translational and coupled) responses, flexibilities, and facet load were delineated for these iatrogenic changes. Results indicted that unilateral facetectomy of greater than 75% and bilateral facetectomy of 75% or more resection markedly alter the translational displacement and flexibilities of the motion segment. This study suggests that fixation or fusion to restore strength and stability of the lumbar spine may be required for surgical intervention of greater than 75% facetectomy.

Finite-Element Analysis for Lumbar Interbody Fusion Under Axial Loading

A parametric study was conducted to evaluate axial stiffness of the interbody fusion, compressive stress, and bulging in the endplate due to changes in the spacer position with/without fusion bone using an anatomically accurate and validated L2-L3 finite-element model exercised under physiological axial compression. The results show that the spacer plays an important role in initial stability for fusion, and high compressive force is predicted at the ventral endplate for the models with the spacer and fusion bone together. By varying the positioning of the spacer anteriorly along anteroposterior axis, no significant change in terms of axial stiffness, compressive stress, and bulging of the endplate are predicted for the implant model. The findings suggest that varying the spacer position in surgical situations does not affect the mechanical behavior of the lumbar spine after interbody fusion.

Statistical factorial analysis on the material property sensitivity of the mechanical responses of the C4–C6 under compression, anterior and posterior shear

A systematic approach using factorial analysis was conducted on the C4-C6 finite element model to analyse the influence of six spinal components (cortical shell, vertebral body, posterior elements, endplate, disc annulus and disc nucleus) on the internal stresses and external biomechanical responses under compression, anterior and posterior shear. Results indicated that the material properties variation of the disc annulus has a significant influence on both the external biomechanical responses and internal stress of the disc annulus and its neighboring hard bones. The study reveals for the first time, the significant influence of the cancellous bone under compression, while variation in the cortical shell modulus has a high influence under anterior and posterior shear. The study also reveals that the effects of interaction between two main components are insignificant.

Comparison and reproducibility of transthoracic bioimpedance and dual beam Doppler ultrasound measurement of cardiac function in healthy volunteers

1. We compared the ease of use and reproducibility of two noninvasive methods, transthoracic electrical bioimpedance (TEB) (BoMed NCCOM3-R7) and non-imaging dual beam Doppler ultrasound (Quantascope--Vital Science), in cardiac output (CO) and stroke volume (SV) measurement in healthy volunteers at rest and during physiological stress, both short term and from day to day. 2. The TEB method was easier to use and not dependent on the operator. The TEB method was more reproducible both in the short term and from day to day. Both devices were able to detect CO and SV changes under physiological stress, but were less reproducible day to day during exercise. 3. At supine rest, the within subject coefficient of variation between time point for TEB was 4.6% for CO and 6.1% for SV, and 7.9% for CO and 7.4% for SV with Doppler. 4. The results from each device showed a linear correlation coefficient (r) of 0.69 for CO (P less than 0.0005) and 0.64 for SV (P less than 0.0005). The correlation coefficient improved to 0.76 (P less than 0.0005) when only changes in CO and SV were considered. There was no systematic difference in the changes detected by the two methods, but the individual variation was wide.

A case of systemic lupus erythematosus with sideroblastic anaemia terminating in erythroleukaemia

A case of systemic lupus erythematosus is described in which for 10 years the only significant findings were erythema multiforme and vasculitis. Gross hepatosplenomegaly with persistent pancytopenia developed, and bone marrow examination revealed the presence of sideroblasts. The patient's condition deteriorated, and subsequently she developed a severe bleeding tendency, terminating in erythroleukaemia.

Experimental investigation of failure load and fracture patterns of C2 (axis)

The injury mechanism and magnitude of failure load of C2 fractures are important in the clinical treatment of its fixation. The magnitudes of the failure load of C2 and the mechanism of injury in vivo are uncertain. Accordingly, nine C2 vertebrae obtained from cadaver spines, ranging in age from 51 to 80 years, were used for the study. Special restraint conditions were applied to yield specific fracture of C2. With the posterior element potted postero-anteriorly up to one-quarter of the inferior facet, posterior shear force ranging from 840 to 1220N was required to cause fracture across the pars interarticularis. For odontoid fracture study, a special rig was fabricated to encapsulate the body of C2 in a cell using ISOPON, and a thin layer of ISOPON sandwiched between the inferior facets and two lateral plates. The assembled rig permits slight sagittal movement of C2 about the cup lateral pivot supports. Failure load of between 900 and 1500N was recorded for odontoid fracture. These values are in agreement with published data. The experiment carried out under these two different restraint conditions had specifically resulted in different fractures of C2. In reality, depending on factors such as the inclination of this force vector applied to the head, the precise posture at the time of trauma, the spinal geometry, and the physical properties, different types of fracture patterns of C2 may be produced. This additional data will be useful in the biomechanical study of C2 vertebra using analytical approaches, and in surgical anterior/posterior fixation using screws.

T-cell lymphoma in Singapore: pathology, clinical findings and association with HTLV-1 antibodies

Of 128 cases of malignant lymphomas studied in Singapore between 1986 and 1988, 28 were identified as peripheral T-cell lymphomas. Sera from two of the 128 cases were positive for HTLV-1 antibodies and both cases had the clinical and pathological features of adult T-cell leukaemia/lymphoma. The pathological and clinical features of the 28 cases of peripheral T-cell lymphoma are presented in detail. Survival data indicated no significant difference between the low grade and high grade histological types. Three of the patients had previous or concomitant malignancies. The percentage of T-cell lymphomas associated with HTLV-1 infection in Singapore is low compared to those areas in which HTLV-1 is endemic.

Quality control metrics improve repeatability and reproducibility of single-nucleotide variants derived from whole-genome sequencing

Although many quality control (QC) methods have been developed to improve the quality of single-nucleotide variants (SNVs) in SNV-calling, QC methods for use subsequent to single-nucleotide polymorphism-calling have not been reported. We developed five QC metrics to improve the quality of SNVs using the whole-genome-sequencing data of a monozygotic twin pair from the Korean Personal Genome Project. The QC metrics improved both repeatability between the monozygotic twin pair and reproducibility between SNV-calling pipelines. We demonstrated the QC metrics improve reproducibility of SNVs derived from not only whole-genome-sequencing data but also whole-exome-sequencing data. The QC metrics are calculated based on the reference genome used in the alignment without accessing the raw and intermediate data or knowing the SNV-calling details. Therefore, the QC metrics can be easily adopted in downstream association analysis.

A Retrospective Survey on the Clinical Presentation of Ketamine Abusers in a Hong Kong Emergency Department

Objective

Ketamine is one of the commonest abusing agents in Hong Kong. Our study aims to identify their clinical pattern of presentations to emergency departments.

Method

This is a retrospective survey study. The studied group was ketamine abusers being referred to us from a source out of emergency department (ED). Control group was randomly selected from patients attending our ED. The electronic records of the ketamine abusers and the controls in the past 3 years (1st April 2004-31st March 2007) were reviewed and analysed.

Result

Total 91 subjects (48 in ketamine group, 43 in control group) were included. The mean age of ketamine abusers and control group are 21 and 22.2 year-old respectively. Most of them (97.9%) did not declare their background of ketamine abuse. The mean 3-year attendance rate for the ketamine group was 2.38 and for control group was 0.91, with a difference of 1.47 (95% CI 0.54-2.41, p=0.003). Most of their illnesses were diagnosed as epigastric pain (25%), followed by upper respiratory tract infection (18.8%), head injury (10.4%) and urinary tract infection (10.4%). Significantly higher number of ketamine abusers presented with epigastric pain compared with control group (odds ratio 143, p<0.001).

Conclusion

Most teenage ketamine abusers do not declare their background of drug abuse when they present to emergency departments. They tend to have a higher frequency of attendances. Most of their presenting problems are related to gastrointestinal system.

A Volunteer Study on the Blood Salicylate Level of Excessive Use of Topical Methylsalicylate

Objective

The purpose of this study was to evaluate the serum level of salicylate after topical application of methylsalicylate (analgesic balm), and to determine the safety of its use in our population.

Methods

This was a human volunteer study involving six volunteers. Each of them applied 10 grams of analgesic balm (containing 5 grams of methylsalicylate) on the limbs, and serial serum salicylate levels were measured just before the trial, and 1, 2, 4 and 8 hours after application. The time required to reach the maximum blood level after application was recorded.

Results

The serum salicylate level ranged from non-detectable level up to near therapeutic level in different subjects. The maximum salicylate level measured was 130 mg/L in one of the volunteers 8 hours after application. The calculated systemic bioavailability of dermal methylsalicylate in our study was 19-45%, which was comparable to previous studies.

Conclusions

Dermal application of massive amount of analgesic balm may cause unpredictable absorption of methylsalicylate. Patients and physicians should be aware of its potential risk.

Material versatility using replica molding for large-scale fabrication of high aspect-ratio, high density arrays of nano-pillars

Arrays of high aspect-ratio (AR) nano-pillars have attracted a lot of interest for various applications, such as for use in solar cells, surface acoustic sensors, tissue engineering, bio-inspired adhesives and anti-reflective surfaces. Each application may require a different structural material, which can vary in the required chemical composition and mechanical properties. In this paper, a low cost fabrication procedure is proposed for large scale, high AR and high density arrays of nano-pillars. The proposed method enables the replication of a master with high fidelity, using the subsequent replica molds multiple times, and preparing arrays of nano-pillars in a variety of different materials. As an example applied to bio-inspired dry adhesion, polymeric arrays of nano-pillars are prepared in this work. Thermoset and thermoplastic nano-pillar arrays are examined using an atomic force microscope to assess their adhesion strength and its uniformity. Results indicate the proposed method is robust and can be used to reliably prepare nano-structures with a high AR.

Overwhelming Postsplenectomy Sepsis Presenting as Purpura Fulminans due to Streptococcus Suis Infection

Splenectomised patients are more likely to suffer from severe infections, such as sepsis and meningitis. This condition is called overwhelming postsplenectomy infection (OPSI) syndrome. The risk of OPSI is greatest in the early months, and even years, after the operation, but never disappears entirely. The course of OSPI is rapid, the clinical presentations serious, and the prognosis poor. We present here a case of OPSI in a posttraumatic splenectomised adult who had features of fulminant sepsis such as hypotension, renal and liver failure, coagulopathy, and generalised skin rash presented as purpura fulminans. The culprit was found to be Streptococcus suis by the polymerase chain reaction technique. By reporting this case, we hope to emphasize the importance of preventive strategies: vaccination, antibiotic prophylaxis, and patient education. The management of Streptococcus suis infection and the use of 16S rRNA gene sequencing for bacterial identification were also highlighted.

Confusion in Patients with Shingles and Renal Failure: Acyclovir Neurotoxicity or Herpes Encephalitis

It is not uncommon for patients with shingles and renal failure who develop confusion during the course of therapy. The patient may have suffered from the adverse reaction of acyclovir or have the neurologic complication related to the dermatological herpes zoster. Acyclovir induced neurotoxicity and herpes encephalitis have similar clinical feature but their treatments are completely different. Often, doctors face challenges in differentiating the two conditions and the dilemma of whether to continue or stop acyclovir. We reported two cases of renal impairment patient who developed altered mental state after receiving oral acyclovir for the herpes skin lesion. One suffered from varicella encephalitis and the other had acyclovir-induced neurotoxicity. The difference in clinical features among the two conditions and the management of acyclovir-induced neurotoxicity was highlighted.

Timolol Eye Drops Induced Bradycardia

We report a 25-year-old man with bradycardia after administration of ophthalmic timolol. The patient was asymptomatic, and his bradycardia resolved after stopping the eye drop. He was discharged after a four-hour observation. This case demonstrated that topical timolol eye drop may cause systemic adverse reaction. The use of timolol and its possible side-effects are discussed.

Oral Mucosal Irritating Plant Ingestion in Hong Kong: Epidemiology and Its Clinical Presentation

Objective

To study the local epidemiology and clinical presentation after ingestion of oral mucosal irritating plants.

Methodology

Cases presenting with immediate oral mucosal irritation after plant product ingestion from July 2005 to June 2009 were retrieved from the Hong Kong Poison Information Centre's clinical database. Their clinical features and management were reviewed.

Results

Thirty cases were retrieved and analysed, including 14 males and 16 females. Poisoning occurred all year round with no seasonal predilection. Vomiting and dysphagia were the two most common symptoms other than immediate oral mucosal irritation. Half of the cases could be managed with symptomatic treatment and discharged after a few hours of observation. Six patients presented with angioedema and were managed initially with the use of intravenous steroid, antihistamine and with or without adrenaline. Urgent airway assessment with laryngoscope was performed in 3 patients. No patient required endotracheal intubation.

Conclusion

Oral mucosal irritating plant ingestion is not uncommon in Hong Kong. Its clinical feature can mimic angioedema on presentation. Immediate and localized oral mucosal symptoms after plant product ingestion are the key to diagnosis.

Graft-versus-host disease following sibling allogeneic bone marrow transplantation--the Singapore experience

Fourteen patients with haematological malignancies received allogeneic bone marrow transplantation from Major Histocompatility Complex compatible siblings. Five (35.7%) patients developed mild and 4 (28.6%) severe graft-versus-host disease (GVHD). There were correlations between the age of recipient (p less than 0.05), the degree of haematological support (p less than 0.1) and GVHD. The effects of the Mixed Lymphocyte Culture reactivity, donor/recipient sex match, cyclosporin A levels and the use of Total Parenteral Nutrition were not apparent. Two patients had relapses of their initial diseases. One of them did not develop any GVHD and the other only mild GVHD post bone marrow transplantation.

Comparison of bioimpedance and Doppler ultrasound cardiac output in CAPD patients

The reproducibility and reliability of cardiac output (CO) measurement by transthoracic electrical bioimpedance (TEB) and dual beam Doppler ultrasound methods were compared in 9 uremic patients during treatment with continuous ambulatory peritoneal dialysis (CAPD). CO was measured simultaneously by each method during supine rest and 70 degree passive head-up tilt on two separate days. The effect on CO after the infusion of dialysate was also studied on day 1. CO, stroke volume (SV) and heart rate (HR) measurements were reproducible by each method. The median day to day differences (95% confidence intervals) in CO and SV were 0.6 (-0.3, 1.8) l/min and 10 (-1.5, 24.5) ml for TEB and 0.7 (-0.5, 2.2) l/min and 13 (-1.0, 30.5) ml for Doppler at supine rest; 0.4 (-0.2, 0.9) l/min and 11 (-0.5, 19.0) ml for TEB and 0.5 (-0.3, 1.2) l/min and 8 (-5.0, 16.0) ml for Doppler during tilt (p > 0.05 in each case). Data were unobtainable by TEB at five time points while none were lost by Doppler. This is due to incorrect HR or poor quality signals detected by TEB. CO and SV measured by Doppler were higher than that by TEB during supine rest (p < or = 0.01) but not during passive tilt. As a result, there was significant change (p < or = 0.01) in CO and SV from supine to tilt measured by Doppler but not by TEB. Neither TEB nor Doppler detected significant change (p > 0.05) in CO or SV after the infusion of dialysate, in either the supine or tilt positions.(ABSTRACT TRUNCATED AT 250 WORDS)