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At least 649 records · Page 36Linked to original sources
PubMed2006

Effect of a posterior dynamic implant adjacent to a rigid spinal fixator.

BACKGROUND: A slightly degenerated disc adjacent to a segment that has to be fused is sometimes instrumented with a dynamic fixator. The dynamic implant is assumed to reduce disc loads at that level and to preserve disc function, thus inhibiting the progression of degeneration. METHODS: A three-dimensional finite element model of the lumbar spine was used to study the effect of a dynamic implant on the mechanical behavior at the corresponding level. After studying a healthy lumbar spine for comparison, a rigid fixator and a bone graft were inserted at L2/L3. Healthy and degenerated discs were assumed at the adjacent level, i.e. L3/L4. An additional paired dynamic posterior fixator was then implemented at level L3/L4. Finally, the segment with the dynamic fixator was distracted to the height of a healthy disc. The loading cases of walking, extension, flexion and axial rotation were simulated. FINDINGS: A dynamic implant reduces intersegmental rotation for walking, extension and flexion as well as facet joint forces for axial rotation at its insertion level. Intradiscal pressure is not markedly reduced by a dynamic implant. Moreover, there are no substantial differences between the mechanical behavior of rigid and dynamic fixators. INTERPRETATION: Our model does not predict major differences in the mechanical effects between rigid and dynamic fixators despite the extreme assumption that a dynamic implant does not transfer moments. The results do not support the assumption that disc loads are significantly reduced by a dynamic implant. For axial rotation, however, dynamic fixation devices do reduce the force in the facet joint.

Back↗
PubMed2005

Rigid internal fixation with titanium versus bioresorbable miniplates in the repair of mandibular fractures in rabbits.

The purpose of this study was to compare by qualitative histology the efficacy of rigid internal fixation with titanium system and the Lacto Sorb system in mandibular fractures in rabbits. Thirty male adult rabbits Oryctolagus cuniculus were used. Unilateral mandibular osteotomies were performed between the canine and first premolar. The animals were divided into two groups: for Group I-rigid internal fixation was performed with titanium system 1.5 mm (Synthes, Oberdorf, Switzerland), with two screws of 6 mm (bicortical) on each side of the osteotomy. For Group II-rigid internal fixation was performed with PLLA/PGA system 1.5 mm (Lacto Sorb, WLorenz, Jacksonville, FL, USA). The histological analysis evaluated the presence of inflammatory reaction, degree of bone healing and degree of resorption of the Lacto Sorb screws. The results of both fixation systems were similar, only with a small difference after 15 and 30 days. In Group I a faster bony healing was noted. But after 60 days, bony healing was similar in both groups. It is concluded that both PLLA/PGA and titanium plates and screws provide sufficient strength to permit mandibular bone healing. The resorption process of PLLA/PGA osteosynthesis material did not cause acute or chronic inflammatory reaction or foreign body reaction during the studied period.

Absorbable Implants↗
PubMed2006

Rigid tracheobronchoscopy in the management of airway foreign bodies: 10 years experience in Kosovo.

OBJECTIVES: To review the incidence of tracheobronchial foreign body aspiration in the population of Kosovo and to evaluate the clinical features and management of tracheobronchial foreign body aspiration during a 10-year period. SETTING: Tertiary medical institution, ENT/Head and Neck Surgery Clinic, University Clinical Center, Prishtina, Kosovo. METHODS: We retrospectively reviewed the medical records of patients with tracheobronchial foreign body aspiration who underwent rigid tracheobronchoscopy between January 1994 and December 2003. RESULTS: During a 10-year period, 244 rigid tracheobronchoscopy procedures were performed when foreign body aspiration was suspected. In 182 patients (75%), a foreign body was found and extirpated. Of these, 107 (59%) were male and 75 (41%) were female; 124 patients (68%) were aged 0-3 years and 36 (20%) were aged 4-7 years. The most commonly extirpated foreign bodies were peanuts (30% of cases) followed by beans (22.5%) and corn kernels (9%). Of 176 plain chest radiographs, 65% showed no signs of foreign bodies. Two patients (1.1%) died as result of complications related to foreign body aspiration. CONCLUSION: Rigid bronchoscopy represents a safe and effective tool in the management of foreign body aspiration. However, the high percentage of false-negative results on chest radiography in our series warrants further investigation.

Adolescent↗
PubMed2006

The impact of object size and rigidity on infant reaching.

Although the changes in kinematics of infant reaching have been studied, few researchers have investigated the improvement of reaching regarding objects of distinct physical properties. The aim of this longitudinal study was to verify the impact of object size and rigidity on the development of reaching in 4-6-month-old infants. Four infants were observed with a motion capture system during trials with four objects of distinct sizes and rigidity. A total of 188 reaches were analyzed by using the 3D movement reconstruction. Our results showed that reaching frequency, mean velocity, and straightness index increased with age. The number of movement units decreased with age and increased for small objects. Rigidity was not shown to affect reaching trajectories. These findings suggest that infants are capable of perceiving the more relevant object properties, thus using their available motor capabilities to modify the essential variables so that they can reach the target more accurately.

Distance Perception↗
PubMed2004

Shape equations and curvature bifurcations induced by inhomogeneous rigidities in cell membranes.

This article aims at two objectives: one is the shape equation for the equilibrium configurations of biomembranes with heterogeneous rigidities; another is the possible mechanism for curvature bifurcations in various biomembranes such as human red blood cells (RBC). The shape equation is established by treating the inhomogeneous biomembrane as a lipid bilayer vesicle containing inclusions or impurities. After careful investigation of the equation, the rigidity gradient is found to be an initial "driving force" that may destabilize the biomembrane and stimulate shape transitions, and the concept (or mechanism) termed "curvature bifurcations induced by rigidity gradients" is suggested. Various post-bifurcation modes recording the new equilibrium configurations are disclosed. A few post-bifurcation modes are found to coincide well with some practical shape transitions in cells such as the cup-like shape (stomatocyte) transition and spiculated shape (echinocyte) transition in RBC.

Anisotropy↗
PubMed2006

Abeta42 is more rigid than Abeta40 at the C terminus: implications for Abeta aggregation and toxicity.

Abeta40 and Abeta42 are the major forms of amyloid beta peptides (Abeta) in the brain. Although Abeta42 differs from Abeta40 by only two residues, Abeta42 is much more prone to aggregation and more toxic to neurons than Abeta40. To probe whether dynamics contribute to such dramatic difference in function, backbone ps-ns dynamics of native Abeta monomers were characterized by 15N spin relaxation at 273.3 K and 800 MHz. Abeta42 aggregates much faster than Abeta40 in the NMR tube. The effect of Abeta aggregation was removed from the relaxation measurement by interleaved data collection. R1, R2 and nuclear Overhauser enhancement (NOE) values are similar in Abeta40 and Abeta42, except at the C terminus, indicating Abeta42 and Abeta40 monomers have identical global motions. Comparisons of the spectral density function J(0.87omegaH) and order parameters (S2) indicate that the Abeta42 C terminus is more rigid than the Abeta40 C terminus. At 280.4 K and 287.6 K, the Abeta42 C terminus remains more rigid than the Abeta40 C terminus, suggesting such a dynamical difference is likely present at the physiological temperature. The Abeta42 monomer likely has less configurational entropy due to restricted motion in the C terminus and may pay a smaller entropic price to form fibrils than the Abeta40 monomer. We hypothesize that the entropic difference between Abeta40 and Abeta42 monomers might partly account for the fact that Abeta42 is the major Abeta species in parenchymal senile plaques in most Alzheimer's diseased brains in spite of the predominance of Abeta40 in plasma. The increased rigidity of the Abeta42 C terminus is likely due to its pre-ordering for beta-conformation present in soluble oligomers and fibrils. The Abeta42 C terminus may therefore serve as an internal seed for aggregation.

Amyloid beta-Peptides↗
PubMed2006

How different are structurally flexible and rigid binding sites? Sequence and structural features discriminating proteins that do and do not undergo conformational change upon ligand binding.

Proteins are dynamic molecules and often undergo conformational change upon ligand binding. It is widely accepted that flexible loop regions have a critical functional role in enzymes. Lack of consideration of binding site flexibility has led to failures in predicting protein functions and in successfully docking ligands with protein receptors. Here we address the question: which sequence and structural features distinguish the structurally flexible and rigid binding sites? We analyze high-resolution crystal structures of ligand bound (holo) and free (apo) forms of 41 proteins where no conformational change takes place upon ligand binding, 35 examples with moderate conformational change, and 22 cases where a large conformational change has been observed. We find that the number of residue-residue contacts observed per-residue (contact density) does not distinguish flexible and rigid binding sites, suggesting a role for specific interactions and amino acids in modulating the conformational changes. Examination of hydrogen bonding and hydrophobic interactions reveals that cases that do not undergo conformational change have high polar interactions constituting the binding pockets. Intriguingly, the large, aromatic amino acid tryptophan has a high propensity to occur at the binding sites of examples where a large conformational change has been noted. Further, in large conformational change examples, hydrophobic-hydrophobic, aromatic-aromatic, and hydrophobic-polar residue pair interactions are dominant. Further analysis of the Ramachandran dihedral angles (phi, psi) reveals that the residues adopting disallowed conformations are found in both rigid and flexible cases. More importantly, the binding site residues adopting disallowed conformations clustered narrowly into two specific regions of the L-Ala Ramachandran map. Examination of the dihedral angles changes upon ligand binding shows that the magnitude of phi, psi changes are in general minimal, although some large changes particularly between right-handed alpha-helical and extended conformations are seen. Our work further provides an account of conformational changes in the dihedral angles space. The findings reported here are expected to assist in providing a framework for predicting protein-ligand complexes and for template-based prediction of protein function.

Amino Acids↗
PubMed2006

Juvenile onset acid maltase deficiency presenting as a rigid spine syndrome.

The rigid spine syndrome is a disorder characterized by proximal muscle weakness and limitation in flexion of the cervical and dorsolumbar spine. Such phenotype may be caused by a variety of hereditary myopathies. We present the case of a 15-years-old boy with rigid spine syndrome and severe restrictive respiratory changes. Muscle biopsy revealed vacuolar myopathy with excessive deposition of PAS-positive material. Lysosomal acid maltase activity in cultured skin fibroblasts was reduced to 6% of control values. DNA analysis demonstrated novel mutation E888X of acid alpha-glucosidase gene with compound heterozygosity IVS1/E888X, confirming diagnosis of Pompe disease. We conclude that acid maltase deficiency should be considered in the diagnosis of rigid spine syndrome.

Adolescent↗
PubMed2006

A pedicle subtraction osteotomy as an adjunctive tool in the surgical treatment of a rigid thoracolumbar hyperkyphosis; a preliminary report.

BACKGROUND CONTEXT: A pedicle subtraction osteotomy can be considered as part of the surgical treatment of a symptomatic sagittal imbalance. The literature on the use of this technique is limited and thus far not applied to a rigid thoracolumbar hyperkyphosis. PURPOSE: To evaluate our preliminary results of a pedicle subtraction osteotomy as an adjunctive tool in the surgical treatment of thoracolumbar kyphotic deformities. STUDY DESIGN/SETTING: Case series METHODS: Eleven patients with a symptomatic kyphotic deformity were treated with a thoracolumbar pedicle subtraction osteotomy in combination with a multilevel correction. The mean follow-up was 42.8 months (range 26-105). The clinical outcome, radiographic correction, and perioperative complications were analyzed. The results in six more traditional indications (ankylosing spondylitis, kyphoscoliosis, congenital and posttraumatic deformity), were compared with the results in a subgroup of five cases with a rigid thoracolumbar hyperkyphosis. RESULTS: All patients had a kyphotic thoracolumbar junction. An average of 5.8 levels was involved in the corrective fusion. A pedicle subtraction was always performed between the level Th10 and L2 to correct the sagittal balance. A lordotic correction of 38.8 (range 25-49) degrees was established with this fusion. The osteotomy contributed 66% (26.9 degrees) of the correction, whereas the remaining correction came from multilevel facetectomies. The visual analogue scale for both pain and impairment improved significantly (p<.005) for the entire group. Statistical analysis on the results for both subgroups separately was inappropriate because of the small number of patients available; however, overall both subgroups appeared to do equally well. All patients were very satisfied with the result and would choose surgical treatment again. No major complications were encountered. CONCLUSIONS: A pedicle subtraction osteotomy is a technically demanding but well tolerated operative procedure for the correction of a kyphotic deformity. This technique can also be considered as an adjunctive tool in the surgical treatment of a rigid thoracolumbar (Scheuermann's) kyphosis.

Adult↗
PubMed2001

[Treatment of ureteral calculi with rigid ureteroscopy. Report of 67 cases].

PURPOSE: To evaluate the results obtained by rigid ureteroscopy to treat ureteral calculi. MATERIALS AND METHODS: Between May 1998 and September 2000, 63 patients underwent 67 rigid ureteroscopies (URS) with three endoscopic retreatments and one bilateral URS, for 48 distal, ten mid and nine proximal ureteral calculi. RESULTS: After URS 77.6% of the patients were free of the stones. Success rate was respectively 85.4%, 60% and 55.5% in distal, mid and proximal uretero. Morbidity was 10.4% and there have been one stricture treated by endoscopy. CONCLUSION: Our series demonstrates that rigid URS is safe and effective procedure to treat distal, ureteral calculi. Thus, it should be considered a treatment of choice for distal ureteral calculi.

Adult↗
PubMed2001

Perceptual illusions in eating disorders: rigid and fluctuating styles.

This study investigated perceptual styles in anorexia nervosa (AN) and bulimia nervosa (BN) using a perceptual set task. We hypothesised that, consistent with personality style research. AN patients might be more rigid in style than those with BN or no eating disorder. We found that once an illusion had been established, participants with AN and BN showed more illusions than non-ED women. However, while AN patients responded rigidly, giving the same response repeatedly, BN patients were more likely to change their responses. The study suggests interesting differences to be followed up in future research. Differences in rigid and fluctuating perceptual styles may have implications for understanding the phenomenology of eating disorders, and have implications for treatment.

Adult↗
PubMed2000

Cell movement is guided by the rigidity of the substrate.

Directional cell locomotion is critical in many physiological processes, including morphogenesis, the immune response, and wound healing. It is well known that in these processes cell movements can be guided by gradients of various chemical signals. In this study, we demonstrate that cell movement can also be guided by purely physical interactions at the cell-substrate interface. We cultured National Institutes of Health 3T3 fibroblasts on flexible polyacrylamide sheets coated with type I collagen. A transition in rigidity was introduced in the central region of the sheet by a discontinuity in the concentration of the bis-acrylamide cross-linker. Cells approaching the transition region from the soft side could easily migrate across the boundary, with a concurrent increase in spreading area and traction forces. In contrast, cells migrating from the stiff side turned around or retracted as they reached the boundary. We call this apparent preference for a stiff substrate "durotaxis." In addition to substrate rigidity, we discovered that cell movement could also be guided by manipulating the flexible substrate to produce mechanical strains in the front or rear of a polarized cell. We conclude that changes in tissue rigidity and strain could play an important controlling role in a number of normal and pathological processes involving cell locomotion.

3T3 Cells↗
PubMed2003

Intrasequence GFP in class I MHC molecules, a rigid probe for fluorescence anisotropy measurements of the membrane environment.

Fluorescence anisotropy measurements can elucidate the microenvironment of a membrane protein in terms of its rotational diffusion, interactions, and proximity to other proteins. However, use of this approach requires a fluorescent probe that is rigidly attached to the protein of interest. Here we describe the use of one such probe, a green fluorescent protein (GFP) expressed and rigidly held within the amino acid sequence of a major histocompatibility complex (MHC) class I molecule, H2L(d). We contrast the anisotropy of this GFP-tagged MHC molecule, H2L(d)GFPout, with that of an H2L(d) that was GFP-tagged at its C-terminus, H2L(d)GFPin. Both molecules fold properly, reach the cell surface, and are recognized by specific antibodies and T-cell receptors. We found that polarized fluorescence images of H2L(d)GFPout in plasma membrane blebs show intensity variations that depend on the relative orientation of the polarizers and the membrane normal, thus demonstrating that the GFP is oriented with respect to the membrane. These variations were not seen for H2L(d)GFPin. Before transport to the membrane surface, MHC class I associates with the transporter associated with antigen processing complex in the endoplasmic reticulum. The intensity-dependent steady-state anisotropy in the ER of H2L(d)GFPout was consistent with FRET homotransfer, which indicates that a significant fraction of these molecules were clustered. After MCMV-peptide loading, which supplies antigenic peptide to the MHC class I releasing it from the antigen processing complex, the anisotropy of H2L(d)GFPout was independent of intensity, suggesting that the MHC proteins were no longer clustered. These results demonstrate the feasibility and usefulness of a GFP moiety rigidly attached to the protein of interest as a probe for molecular motion and proximity in cell membranes.

Amino Acid Sequence↗
PubMed1991

Time-correlation analysis of simulated water motion in flexible and rigid gramicidin channels.

Molecular dynamics simulations have been done on a system consisting of the polypeptide membrane channel former gramicidin, plus water molecules in the channel and caps of waters at the two ends of the channel. In the absence of explicit simulation of the surrounding membrane, the helical form of the channel was maintained by artificial restraints on the peptide motion. The characteristic time constant of the artificial restraint was varied to assess the effect of the restraints on the channel structure and water motions. Time-correlation analysis was done on the motions of individual channel waters and on the motions of the center of mass of the channel waters. It is found that individual water molecules confined in the channel execute higher frequency motions than bulk water, for all degrees of channel peptide restraint. The center-of-mass motion of the chain of channel waters (which is the motion that is critical for transmembrane transport, due to the mandatory single filing of water in the channel) does not exhibit these higher frequency motions. The mobility of the water chain is dramatically reduced by holding the channel rigid. Thus permeation through the channel is not like flow through a rigid pipe; rather permeation is facilitated by peptide motion. For the looser restraints we used, the mobility of the water chain was not very much affected by the degree of restraint. Depending on which set of experiments is considered, the computed mobility of our water chain in the flexible channel is four to twenty times too high to account for the experimentally measured resistance of the gramicidin channel to water flow. From this result it appears likely that the peptide motions of an actual gramicidin channel embedded in a lipid membrane may be more restrained than in our flexible channel model, and that these restraints may be a significant modulator of channel permeability. For the completely rigid channel model the "trapping" of the water molecules in preferred positions throughout the molecular dynamics run precludes a reasonable assessment of mobility, but it seems to be quite low.

Gramicidin↗
PubMed1997

Histological markers of neuronal, axonal and astrocytic changes after lateral rigid impact traumatic brain injury.

The model of lateral, rigid impact traumatic brain injury is widely used but remains relatively poorly characterized by comparison with fluid percussion injury models. Thus, whilst the gross morphological changes that occur over the short- and long-term post-injury have been described, more subtle measures of neuronal injury and activation, and markers of axonal and glial reactions have not been investigated, complicating interpretation of data from this model. To address this issue, a variety of neurohistological markers were examined in adult male rats which had been subjected to open brain, lateral rigid impact injury. A piston device was unilaterally driven 3.0 mm into the somatosensory cortex at a speed of 3.2 m/s. Neuronal activation evidenced by Fos-like immunoreactivity showed a complex pattern at 3 h after injury which appeared to be related both to proximity to the impact site and cortical efferent connectivity. At 24 h after injury, acid fuchsin staining demonstrated dying neurons in the margin of the injury and in ipsilateral hippocampus and dorsal thalamus. Injured cells identified by heat-shock protein immunoreactivity showed a similar distribution. Axonal injury demonstrated with 68 kDa neurofilament immunoreactivity was more widely distributed. Less axonal damage was found with increasing distance from the injury site. At 7 days post-injury, glial fibrillary acidic protein immunoreactive astrocytes were prolific in the ipsilateral thalamus, hippocampus and striatum and throughout the injured cortex. In general, controlled, lateral rigid impact injury provides a more focused injury than is seen with lateral fluid percussion which may have implications for the behavioral deficits seen in this injury model.

Animals↗
PubMed1997

S6 permutein shows that the unusual target topology is not responsible for the absence of rigid tertiary structure in de novo protein albebetin.

Ribosomal protein S6 from Thermus thermophilus was modified to form the unusual unique topology designed earlier for a de novo protein albebetin. The S6 gene was cloned, sequenced and circularly permutated by means of genetic engineering methods. The permutated gene was expressed in Escherichia coli and the permutein was isolated and investigated by means of circular dichroism, fluorescence spectroscopy and scanning microcalorimetry. The permutated protein revealed a pronounced secondary structure close to that of the wild type S6 protein and a rigid tertiary structure possessing cooperative temperature melting. It means that the unusual new topology of albebetin is compatible with a rigid tertiary structure, it may be realized in natural proteins and it is not responsible for the absence of rigid structure in albebetin.

Circular Dichroism↗
PubMed1988

Carbon dioxide laser laparoscopy by means of a 3.0-mm diameter rigid wave guide.

Rigid carbon dioxide wave guides measuring 300 to 500 mm in length and 3.0 mm in diameter were evaluated in rabbits and humans. The wave guide provided an effective laser delivery system for operative laparoscopy. The tested guide was introduced into the abdominal cavity alternatively via the operating channel of a 9-mm operating laparoscope, through the central channel of a smoke evacuation/irrigation cannula, or via a 3.25-mm second puncture trocar. In contrast to previously tested flexible guides, the rigid device transmitted a visible helium-neon aiming beam, power up to 50 watts, and a beam diameter of less than 1 mm. The hollow guide was kept free of smoke by-products by continuous purging with carbon dioxide gas flowing at 800 to 1000 cc per minute. All wave guides could be sterilized by ethylene oxide gas or Cidex (Surgikos, Arlington, TX) soaking. Fourteen women with a variety of reproductive disorders underwent laser laparoscopy. The rigid wave guide was fired at distances ranging from less than 1 mm to 30 mm from the target and performed with maximal impact at distances of 3 to 5 mm. Perhaps the greatest advantage of this system is its ability to focus-defocus while directly coupling to the handpiece of standard lasers and requiring no special alignment procedures.

Animals↗
PubMed2000

Effect of plate position relative to bending direction on the rigidity of a plate osteosynthesis. A theoretical analysis.

Mechanical unloading of the plated bone segment is observed after plate osteosynthesis because the implant takes over a part of the physiological loading. Strain reduction in the bony tissue depends on the rigidity of the plate (cross-sectional area, geometrical form, and modulus of elasticity). The aim of the present study was to calculate theoretically the effect of plate position relative to bending direction on the overall bending stiffness of the composite system plate-bone. To calculate the rigidity, a cylindrical bone model with mechanical characteristics similar to a sheep tibia and a rectangular plate cross-section corresponding to a DC-plate with either a modulus of elasticity of steel or titanium was used. Calculations under different bending directions were performed according to the laws of the linear bending theory and the composite beam theory. The bending stiffness of a plate osteosynthesis reaches a minimum and a maximum respectively, in cases in which the bending moment acts in the direction of the main axis of the area moment of inertia of the plate. The minimum is present with the plate bent vertically, the maximum with the plate bent horizontally, e.g. on the tension side of the composite system--on the assumption that the bone structure opposite the plate is capable of withstanding compressive loading. For steel and titanium plates, factors of 2 and 2.25 respectively were calculated between the minimum and the maximum bending stiffnesses of the osteosynthesis. The bending rigidity of the plate alone has only a minimal effect on the total stiffness of the osteosynthesis. With a plate bent vertically, the difference between steel and titanium plates was 18%, with the plate bent horizontally (situated on the tension side), it was only 7%. The bending stiffness of a plate osteosynthesis depends on the cross-section, the geometrical form, and the modulus of elasticity of the plate, as well as on the plate position relative to the bending direction of the composite system. The modulus of elasticity of the plate is relatively unimportant, while with a given plate the individual plate position relative to the bending direction is of crucial importance. Thus, changing the modulus of elasticity of the plate cannot solve the problem of implant induced unloading of the bone cortex because the bending stiffness of the composite system depends much more on the plate position relative to the bending direction.

Animals↗