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At least 829 records · Page 46Linked to original sources
PubMed2003

Vessel-based non-rigid registration of MR/CT and 3D ultrasound for navigation in liver surgery.

OBJECTIVE: Computer assisted planning of liver surgery based on preoperative computed tomography (CT) or magnetic resonance imaging (MRI) data can be an important aid to operability decisions and visualization of individual patients' 3D anatomy. A navigation system based on intraoperative 3D ultrasound may help the surgeon to precisely localize vessels, vascular territories or tumors. The preoperative planning must be transferred to the intraoperative ultrasound data and thus to the patient on the operating table. Due to deformations of the liver between planning and surgery, a fast non-rigid registration method is needed. MATERIALS AND METHODS: A feature-based non-rigid registration approach based on the centerlines of the portal veins has been developed. The combination of an iterative closest point (ICP) approach and Multilevel B-Spline transformations offers a fast registration method. The vessels are segmented and their centerlines extracted from preoperative CT/MRI and intraoperative 3D Powerdoppler ultrasound data. Anatomical corresponding points on the centerlines of both modalities are determined in each iteration of the ICP algorithm. The search for corresponding points is restricted to a given search radius and the direction of the vessels is incorporated. RESULTS: The algorithm has been evaluated on two transcutaneous and one intraoperative clinical ultrasound data set from three different patients. Only a very few vessel segments were not assigned correctly compared to manual assignments. Using non-rigid transformations improved the root mean square target registration error of the vessels by approximately 3-5 mm. CONCLUSIONS: The proposed registration method is fast enough for clinical application in liver surgery. Initial accuracy results are promising and must be further evaluated, particularly in the operating room.

Algorithms↗
PubMed1976

The effects of rigidity of internal fixation plates on long bone remodeling. A biomechanical and quantitative histological study.

The effect of rigidity of internal fixation plates on long bone remodeling was studied using two types of plates with considerable differences in stiffness. The plated bones were subjected to bioengineering quantitative histological, and cortical thickness studies after 9 and 12 months. The biomechanical results, together with the quantitative histological measurements of the macroscopic architecture, showed that tissue characteristics of the plated bones were similar. However, because of the larger cortical area, the less regidly plated femora can sustain significantly higher loads and energy before failure. Cortical thickness measurements also showed that rigid plate immobilization results in thinning of the cortex of the underlying bone. The experimental results suggest that cortical bone remodels according to functional stress demands, and the osteoporosis secondary to rigid plate protection is consequent to thinking of its cortex.

Animals↗
PubMed1981

Torsional strength of cortical and cancellous bone grafts after rigid plate fixation.

Mechanical properties of cortical and cancellous interposition grafts in rabbit tibiofibular bones fixed with 6-hole DCP/ASIF plates were tested with torsional loading after intervals of 3 to 52 weeks postoperatively. In the cortical grafts maximum torque moment at fracture, energy absorption capacity and rigidity increased from 3 to 12 weeks, while the cancellous grafts were more plastic with lower rigidity, higher angular deformation and higher energy absorption. From 12 to 52 weeks maximum torque moment at fracture, energy absorption, rigidity and angular deformation decreased in grafts of both types, the respective means at 36 weeks being 39, 34, 57 and 82 per cent of the cortical grafts, and 26, 17, 42 and 58 per cent of the control values for the cancellous grafts. The differences between the torsional properties of the two graft types decreased with time.

Animals↗
PubMed1999

Biodegradable semirigid plate and miniscrew fixation compared with rigid titanium fixation in experimental calvarial osteotomy.

OBJECT: To determine the biocompatibility and suitability of resorbable plates and miniscrews, consolidation of symmetrical, bilateral frontal bone craniotomies that had been closed using various methods was studied in 20 growing lambs. METHODS: Bone fixation with a flexible, punched polylactide plate and four slowly degradable, self-reinforced poly-levolactide (SR-PLLA) or rapidly degradable, self-reinforced polyglycolide (SR-PGA) miniscrews (10 animals in each group) was compared intraindividually with rigid fixation by using a titanium miniplate and four miniscrews. Plain x-ray films, magnetic resonance images, histological studies, and histomorphometric studies were obtained at 4 to 104 weeks. CONCLUSIONS: No dislocation, instability, clinical foreign body reactions, infections, or loss of fixation were observed. Bone consolidation of the 2.35-mm-wide craniotomy lines was incomplete; connective tissue-filled defects through the bone were observed in 13 of 28 lines at 26 to 52 weeks. Statistical analyses based on histomorphometric studies showed no difference in consolidation with SR-PLLA miniscrew and titanium plate/screw fixation or between the two resorbable fixation methods. Fixation with rapidly degradable SR-PGA miniscrews resulted in less effective consolidation than on the contralateral titanium-treated side (p<0.05), but the bone segment was thicker (p<0.005). The SR-PGA miniscrews had disappeared by 6 weeks, the polyactide plate by 104 weeks, and the SR-PLLA miniscrews had been mostly resorbed at 104 weeks. Passive translocation of the titanium plates and screws into the bone tissue was seen at 52 and 104 weeks. In rapidly growing lamb frontal bone, comparable consolidation results, without complications, can be achieved with semi-rigid resorbable fixation compared with rigid metallic fixation.

Absorbable Implants↗
PubMed2005

Translaminar rigid screw fixation of the axis. Technical note.

Rigid fixation of the axis with C1-2 transarticular screws or C-2 pedicle screws results in high fusion rates but remains technically demanding because of the risk of injury to the vertebral artery (VA) and the limitations imposed by anatomical variability. Translaminar fixation of the axis with crossing bilateral screws provides rigid fixation and is technically simple, is not affected by variations in individual anatomy, and does not place the VA at risk. The long-term results in 20 patients treated with translaminar fixation for craniocervical, atlantoaxial, and axial-subaxial instability are presented, with 100% fusion rates and no neurological or vascular complications. Translaminar screws may be a good option for rigid fixation of the axis for surgeons not proficient in the more technically demanding methods of stabilization.

Adolescent↗
PubMed2001

Rigidity of circulating lymphocytes is primarily conferred by vimentin intermediate filaments.

Lymphocytes need rigidity while in circulation, but must abruptly become deformable to undergo transmigration into tissue. Previously, the control of leukocyte deformability has been attributed to microfilaments or microtubules, but the present studies demonstrate the greater importance of vimentin intermediate filaments (IFs). In circulating T lymphocytes, IFs form a distinctive spherical cage that undergoes a rapid condensation into a juxtanuclear aggregate during chemokine-induced polarization. Measurements of the resistance of peripheral blood T lymphocytes to global deformation demonstrate that their rigidity is primarily dependent on intact vimentin filaments. Microtubules, in contrast, are not sufficient to maintain rigidity. Thus, vimentin IFs are a primary source of structural support in circulating human lymphocytes, and their regulated collapse is likely to be an essential element in chemokine-induced transendothelial migration.

Animals↗
PubMed2002

Bivalent ligands with rigid double-stranded DNA spacers reveal structural constraints on signaling by Fc epsilon RI.

Degranulation of mast cells and basophils during the allergic response is initiated by Ag-induced cross-linking of cell surface IgE-Fc epsilon RI receptor complexes. To investigate how separation distances between cross-linked receptors affect the competency of signal transduction, we synthesized and characterized bivalent dinitrophenyl (DNP)-modified dsDNA oligomers with rigid spacing lengths of approximately 40-100 A. All of these bivalent ligands effectively bind and cross-link anti-DNP IgE with similar affinities in the nanomolar range. The 13-mer (dsDNA length of 44 A), 15-mer (51 A), and flexible 30-mer ligands stimulate similar amounts of cellular degranulation, about one-third of that with multivalent Ag, whereas the 20-mer (68 A) ligand is less effective and the rigid 30-mer (102 A) ligand is ineffective. Surprisingly, all stimulate tyrosine phosphorylation of Fc epsilon RI beta, Syk, and linker for activation of T cells to similar extents as multivalent Ag at optimal ligand concentrations. The magnitudes of Ca(2+) responses stimulated by these bivalent DNP-dsDNA ligands are small, implicating activation of Ca(2+) mobilization by stimulated tyrosine phosphorylation as a limiting process. The results indicate that structural constraints on cross-linked IgE-Fc epsilon RI complexes imposed by these rigid DNP-dsDNA ligands prevent robust activation of signaling immediately downstream of early tyrosine phosphorylation events. To account for these results, we propose that activation of a key downstream target is limited by the spacing between cross-linked, phosphorylated receptors and their associated components.

2,4-Dinitrophenol↗
PubMedDate not supplied

Rigid bronchoscopic dilatation of postintubation tracheal stenosis.

BACKGROUND: Postintubation tracheal stenosis (PITS) occurs due to excessive pressure on the trachea by the cuff of the endotracheal tube which leads to local ischaemic necrosis of the tracheal cartilage and excessive growth of granulation tissue. The recognition of its aetiology and modifications in the design and management of endotracheal tubes have led to a diminished incidence of PITS. The management modalities that have been employed for the management of PITS include stenting, surgical resection and reconstruction, percutaneous dilatation, rigid bronchoscopic dilatation, fibreoptic assisted balloon dilatation and Nd:YAG (neodymium: yttritium-aluminum garnet) laser therapy with or without stenting. METHODS: Three female patients with a history of varying periods of endotracheal intubation after a period of acute respiratory failure who developed symptoms of tracheal stenosis 1-2 weeks post-extubationare presented. The mean age was 24 +/- 12.49 years (range = 14-38 years). RESULTS: All the three patients were successfully managed by frequent, rigid bronchoscopy and gradual dilatation until the resolution of the tracheal stenosis and the return of pulmonary function tests (PFT) to normal. CONCLUSIONS: Rigid bronchoscopic dilation in patients with PITS provides safe, effective tracheal dilatation and improved pulmonary function in the medium term.

Adolescent↗
PubMed2001

5: Movement disorders I: parkinsonism and the akinetic-rigid syndromes.

The major features of akinetic-rigid syndromes are bradykinesia (small, slow movements), rigidity and tremor, often summarised as "parkinsonism". Approximately 80% of akinetic-rigid syndromes are due to Parkinson's disease. Treatment of Parkinson's disease should be determined by level of disability and handicap. The combination of levodopa and peripheral dopadecarboxylase inhibitor is the most efficacious symptomatic treatment for Parkinson's disease. Motor fluctuations appear after 2-3 years of levodopa treatment, and affect at least 50% of patients after five years. Surgery can relieve refractory tremor and dyskinesias, but does not alter disease progression or need for drug therapy.

Aged↗
PubMed1993

[Transurethral ureterolithotripsy with rigid ureteroscope--efficacy of balloon dilation of ureteral orifice and intramural ureter].

In order to minimize the late complications of transurethral ureterolithotripsy with a rigid ureteroscope such as distal ureteral stricture or vesicoureteral reflux, we have performed a balloon dilation of the ureteral orifice and the intramural ureter prior to insertion of a rigid ureteroscope in 62 cases with ureteral calculi between October 1986 and December 1991. A 7F balloon dilator (Bard Co. USA) was cystoscopically inserted into the ureter over a 0.038 inches Radifocus guide wire (Terumo Co., Japan) and then, a balloon was inflated to 15F size with saline using a 10 ml disposal syringe. Thereafter, an 11.5F rigid ureteroscope (Wolf Co., Germany) was inserted instead of a balloon dilator. The stone was disintegrated and removed by ultrasonic lithotripter, electrohydraulic lithotripter and/or basket forceps. The stone was removed completely in 45 cases (72.6%) and incompletely in 10 (16.1%). In 7 cases (11.3%), the stone removal was failed. Long-term follow up with an excretory urography obtained at 6 months or later in 31 cases showed no distal ureteral stricture. Voiding cystography was performed in 33 cases at a mean 2.8 months postoperatively and no vesicoureteral reflux was observed. In control group, 309 cases were treated with transurethral ureterolithotripsy without dilation of the ureteral orifice and the intramural ureter between the same period. A complete removal was achieved in 262 cases (84.8%) and an incomplete removal in 16 (5.2%). 31 (10%) was failed. Distal ureteral stricture due to this procedure was found in 3 cases (2.1%) in 141 long term followed up cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1975

Oxidative injury to erythrocytes, cell rigidity, and splenic hemolysis in hemodialyzed uremic patients.

In 23 hemodialyzed patients the metabolic defect of erythrocytes related to uremia and potentiated by dialysis was studied to establish a possible link with the shortened erythrocyte survival. A highly significant correlation was found between sulfhemoglobin provoked by oxidative stress and erythrocyte rigidity measured by filterability. Impaired filterability also correlated with the degree of splenic sequestration. Both sulfhemoglobin and impaired filterability correlated with the degree of hemolysis. Finally, erythrocyte survival showed a highly significant correlation with the degree of anemia. From osmotic fragility, plasma trapping, erythrocyte ATP and 2,3-diphosphoglycerate (DPG), and serum phosphorus, calcium, and magnesium measurements it seems unlikely that either spheric transformation or sol-gel transformation of the membrane is causing the increased erythrocyte rigidity. In view of the impaired erythrocyte defense capacity against oxidative injury, cell content rigidity as mediated by reduced hemoglobin solubility is a more likely explanation. Our results give a rational basis for a trial of splenectomy in severely anemia hemodialyzed patients.

Anemia, Hemolytic↗
PubMed1993

Reduction of plantar pressure with the rigid relief orthosis.

The rigid relief orthosis was developed to protect vulnerable sites on the plantar surface of the insensitive foot against reulceration by providing both a nonyielding relief under the healed lesion site and a total contact fit. Clinically, the rigid relief orthosis has been effective in protecting the foot against the trauma induced by the repetitive mechanical stress of walking. This study used both the Hercules and F-Scan pressure transducer systems to measure pressure at the first metatarsal head in three orthotic treatments. Both measurement systems recorded significant reductions in pressure at the first metatarsal head with the rigid relief orthosis, establishing a quantitative rationale explaining its clinical effectiveness. Significant pressure differences were also recorded at the secondary sites of the heel, midfoot, and third metatarsal head.

Adult↗
PubMed1999

The role of bilateral talectomy in the management of bilateral rigid clubfeet.

Severe clubfoot is a common sequela of arthrogryposis multiplex congenita and myelomeningocele. Talectomy is a practical surgical procedure to assist in the correction of severe, rigid equinovarus foot deformity. However, the results of talectomy may be less predictable in rigid bilateral equinovarus foot deformity than in the treatment of unilateral clubfoot. To determine the outcome of talectomy in the treatment of bilateral rigid clubfoot, we reviewed the cases of all patients at our center who underwent bilateral talectomy. Seven children were treated for bilateral talipes equinovarus with talectomy. The patient group consisted of 3 children with arthrogryposis, 3 with myelomeningocele, and 1 with Duchenne muscular dystrophy. The age at surgery averaged 6 years and ranged from 1 year and 10 months to 15 years and 7 months. The length of follow-up averaged 5 years and 6 months and ranged from 3 years to 12 years and 6 months. Three feet had a good and 7 feet a satisfactory correction of the deformity. Four feet had poor results. Bilateral talectomy was found overall to be a successful and predictable procedure, with low morbidity for the attainment of functional feet.

Adolescent↗
PubMed2000

Gastroenterology-urology devices: reclassification of the penile rigidity implant. Food and Drug Administration, HHS. Final rule.

The Food and Drug Administration (FDA) is reclassifying the penile rigidity implant from class III to class II when intended to provide penile rigidity in men diagnosed as having erectile dysfunction. The special control is the FDA guidance document entitled "Guidance for the Content of Premarket Notifications for Penile Rigidity Implants." This action is taken on FDA's own initiative based on new information. This action is being taken under the Federal Food, Drug, and Cosmetic Act (the act), as amended by the Medical Device Amendments of 1976, the Safe Medical Devices Act of 1990, and the FDA Modernization Act of 1997.

Erectile Dysfunction↗
PubMedDate not supplied

Rigidity and retention of ceramic root canal posts.

Ceramic root-canal posts offer potential advantages over other types with respect to aesthetics and biocompatibility. Any post must be sufficiently rigid and retentive to withstand functional forces. Ceraposts (1.2 mm coronal diameter, ceramic, tapering, smooth posts) and Paraposts (1.25 mm, stainless-steel, parallel, serrated posts) were tested for rigidity by means of a three-point bending test. To test retention in roots, ceramic posts were cemented using one of three protocols: (1) glass-ionomer cement, (2) silane coupling agent and resin cement, or (3) sandblasted post surface, silane coupling agent, and resin cement. Stainless-steel posts were cemented with resin. The tensile force required to dislodge the posts, following four weeks of storage in water, was recorded. Data were compared using Student's t-test and Mann-Whitney U analysis. Ceraposts were significantly more rigid than Paraposts (p < 0.001). Paraposts cemented with resin were significantly more strongly retained than Ceraposts following any cementation protocol (p < 0.001). Retention of the ceramic posts was significantly greater with a silane coupling agent and resin cement than with glass-ionomer cement (p < 0.001). Sandblasting the ceramic posts produced variable results and needs further investigation before it could be recommended.

Acid Etching, Dental↗
PubMed2000

Case report: a non-rigid connector for a resin bonded bridge.

The use of rigid connectors between pontics and retainers is common for conventional bridges. Restoration of two missing teeth and an intermediate pier abutment with a rigid bridge is not an ideal treatment. In this report a resin bonded bridge with a non-rigid connector within the pontic distal to the pier abutment was constructed and remained in place without debonding for seven years.

Bicuspid↗
PubMed2001

Fire and ecotoxicological aspects of polyurethane rigid foam.

The main characteristics of fire effluents from polyurethane (PUR) foams are comparable to those from natural materials like wood, cork, or wool. This similarity has been demonstrated by comparative data from analytical and toxicological studies. It is therefore presumed that effluents of these materials present similar hazards to human beings and the environment. In almost all fires, dioxins can be found in the smoke and residues. In fires involving PURs, relevant quantities of halogenated dioxins or furans are not to be expected; this has been confirmed by investigations under controlled laboratory conditions. The insulation properties of rigid PUR foam contribute significantly to environmental protection and the conservation of resources. A number of methods for reusing and recycling PUR rigid foam waste have been developed and realized in practise. The possibilities range from reusing the material itself, generating liquid raw materials, and thermal recycling, even for (H)CFC-containing PUR rigid foams, by cocombustion in suitable plants.

Conservation of Natural Resources↗
PubMed2001

Modulation of A-NK cell rigidity: In vitro characterization and in vivo implications for cell delivery.

The delivery of cells to specific regions of the vasculature is a critical step in many therapeutic strategies. These include the packaging of DNA or RNA in cell "vehicles" for delivery to tissues, the reconstitution of differentiated cells to an organ using embryonic stem cells, and the enhancement of the immune response using effector lymphocytes. In most cases, these cells must be injected systemically. Unfortunately, ex vivo manipulation or activation can affect cell visco-elastic properties, making it difficult for the injected cells to traverse capillary beds. Compounding the problem is the fact that common agents used in the laboratory for increasing cell deformability generally have adverse side effects on the therapeutic potential of the cells. Using micropipet aspiration techniques, cytotoxicity assays and in vivo trafficking studies we show that: (1) the rigidity of injected effector cells directly affects resistance to passage through tissue; (2) modulation of cytoskeletal organization can be used to decrease cell rigidity, but can also compromise therapeutic efficacy; and (3) thioglycollate, an agent which does not influence effector lymphocyte cytotoxic activity, reduces cell rigidity and entrapment in the lungs.

Animals↗