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PubMed2002

N-isotope effects on the Raman spectra of Fe(2)S(2) ferredoxin and Rieske ferredoxin: evidence for structural rigidity of metal sites.

The diiron ferredoxins have a common diamond-core structure with two bridging sulfides, but differ in the nature of their terminal ligands: either four cysteine thiolates in the Fe(2)S(2) ferredoxins or two cysteine thiolates and two histidine imidazoles in the Rieske ferredoxins. Contributions of the bridging (b) and terminal (t) ligands to the resonance Raman spectra of the Fe(2)S(2) ferredoxins have been distinguished previously by isotopic substitution of the bridging sulfides. We now find that uniform (15)N-labeling of Anabaena Fe(2)S(2) ferredoxin results in shifts of -1 cm(-1) in the Fe-S(t) stretching modes at 282, 340, and 357 cm(-1). The (15)N dependence is ascribed to kinematic coupling of the Fe-S(Cys) stretch with deformations of the cysteine backbone, including the amide nitrogen. No (15)N dependence occurs for the nu(Fe-S(b)) modes at 395 and 426 cm(-1). Similar effects are observed for the Rieske center in T4MOC ferredoxin from the toluene-4-monooxygenase system of Pseudomonas mendocina. Upon selective (15)N-labeling of the alpha-amino group of cysteine, the vibrational modes at 321, 332, 350, and 362 cm(-1) all undergo shifts of -1 to -2 cm(-1), thereby identifying them as combinations of nu(Fe-S(t)) and delta(Cys). These same four modes undergo similar isotope shifts when T4MOC ferredoxin is selectively labeled with (15)N-histidine ((15)N in either the alpha1,delta1 or delta1,epsilon2 positions). Thus, the Fe-S(Cys) stretch must also be undergoing kinematic coupling with vibrations of the Fe-His moiety. The extensive kinematic coupling of iron ligand vibrations observed in both the Fe(2)S(2) and Rieske ferredoxins presumably arises from the rigidity of the protein framework and is reminiscent of the behavior of cupredoxins. In both cases, the structural rigidity is likely to play a role in minimizing the reorganization energy for electron transfer.

Anabaena↗
PubMed1980

On the elastic and rigid forms of constrictive pericarditis.

This article discusses a thesis regarding the pathophysiology of constrictive pericarditis. The thesis is that there are two forms of constriction, one being elastic and the other more analogous to a rigid shell. The two forms of constriction are considered to cause different patterns of the diagnostic signs of constriction. The elastic form is similar to cardiac tamponade, and is associated with prominent paradoxical pulse and systolic descent in the venous pressure waveform. The rigid shell type has less prominent paradoxical pulse and a more conspicuous diastolic descent in the venous pressure waveform, often associated with an early diastolic sound (pericardial knock). Recognition of these two types of constriction may be helpful in clinical diagnosis and in understanding the pathophysiology of pericardial disease.

Acute Disease↗
PubMed1979

Appraisal of "rigid" blood glucose control during pregnancy in the overtly diabetic woman.

The degree of maternal glucose control achieved during the third trimester of pregnancy was evaluated for 120 overtly diabetic women hospitalized on a high-risk pregnancy ward. "Rigid" blood glucose control, defined as a mean preprandial plasma glucose concentration less than 115 mg/dl was achieved in only 14% of these women. Although mean preprandial plasmal glucose concentrations ranged between 115 and 172 mg/dl in 66% of women and exceeded 172 mg/dl in 20%, the perinatal salvage rate was greater than 95%. Pregnancies of those women whose mean plasma glucose levels exceeded 172 mg/dl required earlier intervention for signs of fetal jeopardy, but the degree of glucose control was not significantly related to either perinatal death or neonatal morbidity. These results suggest that maternal hyperglycemia exceeding a mean preprandial glucose concentration of 172 mg/dl is to be avoided, whereas, at the other extreme, mean glucose levels less than 115 mg/dl or "rigid" control is unnecessary for a successful perinatal outcome.

Adult↗
PubMed1991

The healing sternum: a comparison of osseous healing with wire versus rigid fixation.

Although median sternotomy is used for most cardiac procedures, postoperative dehiscence remains a serious and persistent problem. This investigation was designed to assess new bone formation and sternal healing across the linear osteotomy of the sternum and to determine if rigid fixation would enhance bony healing and thus decrease unfavorable sequelae. To test this hypothesis, 14 skeletally mature baboons (Papio anubis) underwent standard median sternotomy; seven sternotomies were closed with interrupted 24-gauge cerclage wires, and seven, with thin Vitallium compression miniplates and transverse lag screws. The sterna from each group were harvested en bloc at 4 and 8 weeks, radiographed, processed, and serially sectioned and stained for histomorphometry to assess the quantity of new bone across the linear osteotomy. Clinical stability was superior with the plated and lag screw group at 4 weeks; however, by 8 weeks, no clinical difference between treatments was apparent. Histomorphometric analysis indicated that the linear osteotomy gap treated with plates and screws was less than the gap associated with the wire group. Rigid fixation of the sternum resulted in earlier union with primary osseous healing, suggesting greater inherent stability. these factors may decrease adverse sequelae for this procedure.

Animals↗
PubMed1994

Nasotracheal jet ventilation for rigid endoscopy.

Providing adequate ventilation and unencumbered access for manipulation of the airway or esophagus during rigid endoscopic procedures can be problematic. We describe a method of nasotracheal high-frequency jet ventilation that is ideally suited for many patients requiring rigid upper endoscopy.

Bronchoscopy↗
PubMed1983

NMR analyses on the molecular mechanism of the conformational rigidity of 2-thioribothymidine, a modified nucleoside in extreme thermophile tRNAs.

1H-NMR analyses have been made on the conformations of 2-thioribothymidine (s2T), 2-thiodeoxyribothymidine (s2dT), as well as ribothymidine (T) and deoxyribothymidine (dT). s2T and s2dT exclusively take the anti form rather than the syn form. The C3'-endo-gg form of the sugar moiety is remarkably stabilized on modification of T to s2T, but not on modification of dT to s2dT. The steric effects of the 2-thiocarbonyl group and the 2'-hydroxyl group cause the rigidity of the C3'-endo-gg form of s2T. Such rigidity of s2T probably contributes to the thermostability of 2-thiopyrimidine polyribonucleotides and extreme thermophile tRNAs.

Eubacterium↗
PubMed1975

Tibial shaft fractures treated by rigid internal fixation: the early results in a 4-year series.

Ninety-nine fractures of the shaft of the tibia in 98 patients were treated by rigid internal fixation over 4 years. One patient died after operation from myocardial infarction; and one patient went abroad. The healing course of the remaining 97 fractures is described, classified according to the type of fracture and the accuracy of operative reduction. Seventy-five fractures had a normal time to union, defined as the lasting achievement of full weight-bearing within 4 months. In 7 fractures the healing period was moderately delayed (full weight-bearing being achieved in 4-6 months) and in 5 it was seriously delayed, requiring 6-11 months after injury. Nonunion occurred in 4 cases and refracture in 6 cases. Osteitis developed in 2 cases and was successfully treated with antibiotics within 6 weeks. A second internal fixation was necessary in 12 patients. In 5 patients a plaster cast was applied to treat delayed union. Amputation was necessary in a 75-year-old man with senile dementia who developed infection after a second operation for refracture. One patient still has a pseudarthrosis after 2 years and 2 further operations. In the other 95 fractures union was the end-result. Of the 21 comminuted and open fractures only 13 healed within 4 months. We recommend a different approach in the treatment of badly comminuted and open 'high-energy' fractures. With this reservation, we find that the method of rigid internal fixation which we employ has given satisfactory early results. The frequency of both delayed healing and infection is reasonably low compared to the results in similar series.

Adolescent↗
PubMed1983

The stability of the tibio-fibular syndesmosis following rigid internal fixation for type C malleolar fractures: an experimental and clinical study.

In 5 cadavers, type C malleolar fractures of the pronation-eversion rotation type, were produced. The stability of the ankle mortice under stress was tested before and after rigid internal fixation of the fracture in the fibula. The intact interosseous membrane above the fracture in combination with the internal fixation of the fibula was sufficient to keep the lateral malleolus in place. A clinical series of 8 equivalent fractures treated with rigid internal fixation without suture of the syndesmodesis was collected and evaluated clinically and radiologically 3 years after the injury. None of the patients had significant complaints and all ankle joints were stable.

Adult↗
PubMed1986

Ankle fractures treated with non-rigid internal fixation.

Two hundred and thirty-seven fractures of the ankle treated with non-rigid internal fixation were reviewed with regard to classification, congruency of joint surface, range of motion and the patients' subjective symptoms. The fractures were divided into either severe fractures consisting of two or more skeletal injuries or simple fractures consisting of only one skeletal injury. Successful operation, i.e. congruency of the joint, was seen in 50 per cent of the severe and in 73 per cent of the simple fractures (significant, P less than 0.001). Disability was significantly more frequent after severe fractures and with incongruent joints. This study shows that the operative technique using non-rigid internal fixation is not sufficient for treating severe fractures, as exact anatomical reconstruction of the joint was not obtained.

Adolescent↗
PubMed1982

Rigidity and stress analyses of external fracture fixation devices--a theoretical approach.

The rigidity and stresses in external fracture fixation devices were studied by means of the finite element method. Different geometries and material parameters were simulated using a beam element model. Axial, bending and torsional loads were applied through the bone ends and the displacement obtained at the fracture sites was used to calculate the fracture fixation stiffness. The key parameters which increased fixation rigidity were identified. High pin stresses were predicted under certain application conditions. Possible clinical implications for the use of such apparatus are discussed in the light of bone fracture healing. The present results are expected to have a significant impact on future design modifications and clinical applications of this popular instrument in orthopedic surgery and traumatology.

Biomechanical Phenomena↗
PubMed1989

Simulation of quadrupedal locomotion using a rigid body model.

Locomotion of the horse is simulated using a mathematical model based on rigid body dynamics. A general method to generate the equations of motion for a two-dimensional rigid body model with an arbitrary number of hinge joints is presented and a numerical solution method, restricted to tree-structured models, is described. Joint movements originating from muscular forces or moments are simulated, but the method also allows that parts of the model follow strictly the pattern of kinematic data. Moment-generators with first-order linear feedback were used as a rotational muscle-equivalent. Ground-hoof interaction forces are approximated by a viscoelastic model and pseudo-Coulomb friction in vertical and horizontal directions respectively. Results of model simulations are compared to experimentally recorded data. Subsequently, adjustments are made to improve the agreement between simulation and experimental results.

Animals↗
PubMed1990

Mineral and matrix contributions to rigidity in fracture healing.

The purpose of this study was to investigate the relationships among selected properties of fracture callus: bending rigidity, tissue density, mineral density, matrix density and mineral-to-matrix ratio. The experimental model was an osteotomized canine radius in which the development of the fracture callus was modified by electrical stimulation with various levels of direct current. This resulted in a range of values for the selected properties of the callus, determined post mortem at 7 weeks after osteotomy. We found that the rigidity (R) of the bone-callus combination obeyed relationships of the form R = axb, where x is the tissue density, mineral density, matrix density or the mineral-to-matrix ratio of the repair tissue. These are analogous to power-law relationships found in studies of compact and cancellous bone. The results suggest that fracture callus at 7 weeks after osteotomy in canine radius behaves more like immature compact bone than cancellous bone in its mechanical and physicochemical properties. The present study demonstrates the feasibility of developing non-invasive in vivo densitometric methods to monitor fracture healing, since models may be developed that can predict mechanical properties from densitometric data. Further studies are needed to develop a refined model based on experimental data on the mechanical and physicochemical properties and microstructure of fracture callus at different stages of healing.

Animals↗
PubMed1995

Two-dimensional rigid-body kinematics using image contour registration.

A method for calculating two-dimensional rigid-body kinematic parameters using shape features is presented. Proposed applications include the noninvasive quantification of planar joint motion in vivo. By using digitized images (computed tomographs, radiographs, etc.) of a bone contour at two positions, the contour curvatures can be 'best-fit' to obtain a one-to-one mapping or registration of the bone images. This produces a dense field of displacement vectors from which planar rigid-body kinematic parameters can be estimated. Accuracy was studied using radiographic images of cadaveric femoral bone. The two motions of pure rotation with a fixed center of rotation and of pure translation were simulated. For pure rotation, error in rotation was independent of the rotation magnitude, with an average (n = 10) error of 0.3 +/- 0.8 degrees. The translation error averaged 0.9 +/- 0.5 mm. For pure translation, the error in rotation was -0.01 +/- 0.69 degrees and the error in translation was -0.62 +/- 0.98 mm (n = 10). This novel method has broad applications in the field of planar kinematics, especially in cases for which marker fixation is neither possible nor practical.

Algorithms↗
PubMed1980

A photoelastic analysis of the stress distribution in bone supporting fixed partial dentures of rigid and nonrigid design.

Within the limitations of the experiment, the following conclusions can be made from this investigation: 1. Under conditions of vertical loading, the rigid fixed partial denture design does not permit independent response by either abutment. The nonrigid fixed partial denture design allows the abutments some independence in response to vertical loading 2. The stress distributions and concentrations produced in the supporting bone are favorably altered by the placement of a fixed partial denture of rigid or nonrigid design. 3. The distribution of stresses in the supporting bone varies with the number and location of the loading sites. 4. Under conditions of vertical loading, the Ney and Stern nonrigid fixed partial denture designs exhibit no significant differences in stress distribution or concentration.

Alveolar Process↗
PubMed1983

Rate theory models for ion transport through rigid pores. I. Time-dependent analysis in the case of vanishing interactions.

In this first of a series of papers concerning the theoretical analysis of rate theory models for ion transport through rigid pores, the case of vanishing interactions is investigated. "Rigidity" means that ions crossing membranes through pores see a fixed structure of the pores, not changing in time. A single pore is considered to be a sequence of (n + 1) activation barriers separated by n energy minima. The explicit analytical treatment is restricted to pores with regular internal barrier structure, including the nonequilibrium situation of an applied electric field. In this case the connection with continuum diffusion models is demonstrated by performing in the limit n leads to infinity (n = number of binding sites within the pores) the transition to continuum. Thus, from diffusion equations describing a discrete number of jumps, the corresponding diffusion-like partial differential equations and boundary conditions are generated. For regular pores, from the time dependent solutions of the discrete equations, the corresponding solutions of the continuum equations are explicitly generated. The time-dependent relaxation behaviour of the discrete model is in good agreement with the continuum model if one assumes more than two binding sites in the pores.

Binding Sites↗
PubMed1988

Rigid fixation: a review of concepts and treatment of fractures.

Rigid fixation has been given considerable attention in the current literature. The concepts of treatment and the philosophies of the different systems vary, as do the results reported by different authors. This article reviews the basic tenets of rigid fixation and points out where systems are similar or diverge. Advantages and disadvantages of each system are covered.

Bone Screws↗
PubMed1989

Passive rigid fixation of sagittal split osteotomy.

To provide increased stability and to decrease intermaxillary fixation time after sagittal split osteotomy, we have used passive rigid fixation. Our method has not only achieved a diminution of intermaxillary fixation time, but it has also resulted in excellent stability and retention. A total of 72 sagittal split osteotomies were performed on 36 patients from July 1985 through December 1986. Rigid fixation was accomplished with two superior border 2.7 mm bicortical screws.

Adolescent↗
PubMed1990

Simultaneous maxillary and mandibular orthognathic surgery stabilized by rigid internal fixation.

Rigid internal fixation was used successfully in 111 consecutive cases in which both the maxilla and the mandible were mobilized simultaneously. The use of rigid fixation allowed for early mobilization of the mandible, which facilitated resumption of orthodontic therapy after surgery. The favorable short-term results achieved indicate the need to study the long-term stability of the technique.

Bone Plates↗