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At least 685 records · Page 38Linked to original sources
PubMed1999

Method for safer penetrating keratoplasty in patients with low scleral rigidity.

In eyes with low scleral rigidity, penetrating keratoplasty (PKP) is a high-risk procedure because forward movement of the lens-iris diaphragm can result in prolapse of intraocular contents, expulsive choroidal hemorrhage, and damage to the crystalline lens. We developed a method for safer PKP in eyes with low scleral rigidity. In this technique, the host cornea is incompletely excised and remains attached at the 6 and 12 o'clock positions while the cardinal sutures to secure the donor button over the host are placed. Donor endothelium is protected by an intervening layer of viscoelastic material. After the first 3 cardinal sutures are placed, the host button is completely excised and removed and the donor cornea is sutured. This technique prevents the unopposed forward movement of the lens-iris diaphragm and may reduce the risk of expulsive choroidal hemorrhage and spontaneous extrusion or damage to the crystalline lens during PKP in patients with low scleral rigidity.

Cornea↗
PubMed2003

Five-year outcome and predictability of soft tissue profiles when wire or rigid fixation is used in mandibular advancement surgery.

The purpose of this study was to follow the covariation of hard and soft tissue changes in Class II malocclusion subjects who received a bilateral sagittal split osteotomy. The subjects were randomized to receive wire or rigid fixation after the surgery. Subjects in the rigid group (n = 78) received 2-mm bicortical position screws, and those in the wire group (n = 49) received inferior border wires and 6 weeks of skeletal intermaxillary fixation with 24-gauge wires. Additionally, some subjects received genioplasty in both the rigid (n = 35) and the wire groups (n = 24). Soft and hard tissue profile changes were obtained from cephalometric films immediately before surgery and at various times up to 5 years postsurgery. Soft and hard tissue profile changes were referenced to a cranial-base X-Y coordinate system. Horizontal changes in mandibular incisor, lower lip, B-point, soft tissue B-point, pogonion, and soft tissue pogonion were calculated at each time. There was considerable skeletal relapse in the wire fixation group. Bivariate correlations and ratios between the hard and soft tissue changes were calculated for each time period. Hard to soft tissue correlations were the highest at the earlier times, although the ratios varied among the 4 groups. These results provide a solid basis for both short-term and long-term prediction.

Adult↗
PubMed1999

Psychological function in orthognathic surgical patients before and after bilateral sagittal split osteotomy with rigid and wire fixation.

A multisite randomized controlled trial was conducted to compare the psychological function of patients who undergo surgical correction of a Class II malrelation with bilateral sagittal split osteotomy with either wire or rigid fixation. Subjects were 31 male and 86 female patients referred by orthodontists. Psychopathological symptoms and psychological distress were measured with the Symptom Checklist-90 Revised at the following times: before placement of orthodontic appliances, 1 to 2 weeks presurgery, and 1 week, 8 weeks, 6 months, and 2 years postsurgery. Patients' satisfaction with their surgical outcome was measured with a 3-item questionnaire. Results showed no statistically significant differences in psychological function or satisfaction between patients treated with wire or rigid fixation. Psychological function was within normal limits immediately before surgery. Psychological parameters did not determine patient satisfaction, even among patients who met an operational definition of "psychopathological caseness." Psychological symptoms and general distress increased modestly immediately after surgery for both groups and then progressively declined over the succeeding 2 years, eventually reaching levels that were significantly lower than presurgical levels. It was concluded that (1) rigid and wire fixation do not differ in their effects on psychological function and satisfaction; (2) patients who seek orthognathic surgery for a Class II malocclusion are psychologically healthy, ie, comparable to normal populations, immediately before surgery; (3) presurgical psychological function does not determine satisfaction with surgical outcome; and (4) psychological function tends to improve during the 2 years after surgery.

Adult↗
PubMed1997

Flexible (Polyactive) versus rigid (hydroxyapatite) dental implants.

In a beagle dog study, the peri-implant bone changes around flexible (Polyactive) and rigid hydroxyapatite (HA) implants were investigated radiographically by quantitative digital subtraction analysis and by assessment of marginal bone height, with the aid of a computerized method. A loss of approximately 1 mm of marginal bone height was observed for both the dense Polyactive and the HA implants, after 6 months of loading. This value appeared to be stable from 12 weeks of loading onward. Along the total length of the implant during the first 6 weeks of loading, both the flexible (dense Polyactive) and the rigid (HA) implants showed a decrease in density. However, after this 6-week period, the bone density around the implants increased, and after 18 weeks the original bone density was reached. The flexible Polyactive implants provoked less decrease in density than the rigid HA implants, although not to a statistically significant level. This finding sustains the hypothesis that flexible implant materials may transfer stresses to the surrounding bone more favorably.

Alveolar Bone Loss↗
PubMed1989

Stress shielding effect of rigid internal fixation plates on mandibular bone grafts. A photon absorption densitometry and quantitative computerized tomographic evaluation.

The use of rigid internal fixation reconstruction plates in combination with bone grafts provides many advantages in mandibular reconstruction. These advantages include ease of adaptability at the time of surgery as well as immediate postoperative function for the patient. Disadvantages may include a "stress shielding" or disuse osteoporosis effect on the underlying bone graft as a result of the rigidity of the reconstruction plate. This study evaluated the stress shielding effects on bone grafts in primate mandibles. Bilateral bone grafts stabilized with rigid fixation plates were performed in 4 Macaca fascicularis monkeys. Three months after the bone grafting procedure one plate was removed from each monkey. The monkeys were then killed 1, 4, 6 and 8 months after plate removal. Photon absorption densitometry and computerized tomography were used to evaluate stress shielding. The results of this study indicate that the stress shielding effect occurs if the plate is not removed from the area of bone grafting postoperatively.

Absorptiometry, Photon↗
PubMed1996

A simple method for verifying activity of iodine-125 seeds in rigid absorbable suture.

A simple system which facilitates the verification of the calibration of iodine-125 sources in rigid absorbable suture, on the remote traceability basis, was developed. It consists of a plastic jig accommodating a sterile closed-end 16 gauge plastic catheter. The iodine-125 source in rigid absorbable suture is placed into the sterile closed-end 16 gauge plastic catheter. The jig fits in a standard dose calibrator. The sterility of the strand is maintained while a reasonable number of seeds used for an actual implant can be easily measured. This is an improvement over the current recommended practice of assaying just one separate seed of the same strength designation. This system brings the calibration procedure for the rigid sterile seed strands in line with the AAPM TG-40 recommendation for the rest of radioactive seed products.

Brachytherapy↗
PubMed1995

Comparison of screw placement patterns on the rigidity of the sagittal split ramus osteotomy: technical note.

Various screw placement patterns have been described for fixation of the sagittal split ramus osteotomy. This study is a comparative evaluation of 3 different screw placement patterns on the rigidity of the sagittal split ramus osteotomy. Twenty cadaver mandibles were used to compare the load strength of triangular pattern, oblique linear pattern versus linear pattern. Internal fixation with screws placed in a triangular pattern were significantly more rigid than those fixed with screws placed in the other patterns. Also, internal fixation with an oblique linear pattern was more rigid than that with a linear pattern.

Bone Screws↗
PubMed2003

Choice of opioid supplementation for day-case rigid bronchoscopy:a randomized placebo-controlled comparison of a bolus of remifentanil and alfentanil.

OBJECTIVE: To compare the efficacy of different bolus doses of remifentanil, alfentanil, and saline at controlling the hemodynamic responses to day-case rigid bronchoscopy under general anesthesia. DESIGN: Prospective, randomized, double-blind, placebo-controlled study. SETTING: Tertiary referral cardiothoracic hospital, single center. PARTICIPANTS: Eighty consenting adults scheduled for elective day-case rigid bronchoscopy under general anesthesia. INTERVENTIONS: Patients were randomized to receive a bolus of 10 micro g/kg of alfentanil, 1 micro g/kg of remifentanil, 2 micro g/kg of remifentanil or saline. After this, anesthesia was induced and maintained with a target-controlled propofol infusion (TCI) and succinylcholine was used for muscle relaxation. Heart rate and noninvasive arterial pressure were measured at 1-minute intervals throughout. MEASUREMENTS AND MAIN RESULTS: Patients' characteristics were similar in all 4 groups. There were no differences in time to return of spontaneous ventilation, wake-up times, or use of rescue vasopressors, and no patients complained of postoperative nausea. Remifentanil provided greater hemodynamic stability than alfentanil and a bolus of remifentanil of 2 micro g/kg significantly attenuated the rise in heart rate and was the most effective in preventing a rise in blood pressure. CONCLUSIONS: A bolus of 2 micro g/kg of remifentanil successfully attenuated the hemodynamic response to rigid bronchoscopy without delaying recovery.

Aged↗
PubMed2000

Technical factors accounting for stability of a bilateral sagittal split osteotomy advancement: wire osteosynthesis versus rigid fixation.

OBJECTIVE: Relapse after bilateral sagittal split osteotomy has been attributed to various technical factors that are inherent in the surgical procedure. The purpose of this article was to analyze technical factors that predispose to relapse when wire or rigid fixation is used. STUDY DESIGN: Patients were randomized to either rigid or wire osteosynthesis. Cephalometric radiographs were obtained and digitized at multiple time periods before and after surgery. Data were analyzed through use of 2-sample t tests and stepwise regression analyses. RESULTS: Multivariate analysis indicated that the following factors correlated with relapse: initial advancement, change in ramus in inclination, change in the mandibular plane, and fixation type. CONCLUSIONS: Relapse increased with the amount of initial advancement and, to a lesser extent, with control of the proximal segment and change in the mandibular plane. These factors are similar for wire osteosynthesis and rigid fixation.

Adolescent↗
PubMed1995

Comparison of the morbidity associated with maxillary fractures treated by maxillomandibular and rigid internal fixation.

OBJECTIVE: To compare the type and incidence of morbidity encountered by two groups of patients with maxillary fractures, one treated by closed reduction and maxillomandibular fixation and the other by open reduction and rigid internal fixation. STUDY DESIGN: This was a retrospective review of records for all patients with maxillary fractures treated over a 10-year period. Age, sex, mechanism of injury, anatomic location of fracture, treatment modality, and complications were identified. Two populations of patients, those treated with closed reduction and maxillomandibular fixation and those treated with open reduction and rigid internal fixation, that were similar in size (n = 50), age, sex, and anatomic distribution of fractures were compared. RESULTS AND CONCLUSIONS: This study indicates that patients with maxillary fractures treated with either closed reduction and maxillomandibular fixation or open reduction and rigid internal fixation will encounter postoperative problems with a near equal frequency (60% to 64%). Regardless of the technique used, no relationship could be established between age, sex, or cause of injury. The more superior the level of the fracture, the higher the rate of adverse sequelae.

Adolescent↗
PubMed2000

Physical model-based non-rigid registration incorporating statistical shape information.

This paper describes two new atlas-based methods of 2D single modality non-rigid registration using the combined power of physical and statistical shape models. The transformations are constrained to be consistent with the physical properties of deformable elastic solids in the first method and those of viscous fluids in the second, to maintain smoothness and continuity. A Bayesian formulation, based on each physical model, an intensity similarity measure, and statistical shape information embedded in corresponding boundary points, is employed to derive more accurate and robust approaches to non-rigid registration. A dense set of forces arises from the intensity similarity measure to accommodate complex anatomical details. A sparse set of forces constrains consistency with statistical shape models derived from a training set. A number of experiments were performed on both synthetic and real medical images of the brain and heart to evaluate the approaches. It is shown that statistical boundary shape information significantly augments and improves physical model-based non-rigid registration and the two methods we present each have advantages under different conditions.

Brain↗
PubMed1999

The parameter stability of a high dk rigid lens material.

The use of rigid materials with high oxygen permeability (Dk) is on the increase, their major benefit being the reduction of hypoxia. However, there is a reluctance to use these materials possibly due to increased surface scratching, reduced wettability, increased deposition, reduced life expectancy and parameter instability. Considering parameter stability, various studies have demonstrated contradictory results or used high Dk materials based on the silicone acrylate polymer. This study was designed to investigate whether the parameters of a high Dk rigid fluorocarbon contact lens material changed during daily wear and extended wear schedules. Thirty five subjects, divided into group groups, Group I wore the lens on a daily wear basis, whereas those in Group II wore the lens on a monthly extended wear basis. The parameters and integrity of the lenses were monitored in both groups every 3 months. For lens integrity a statistically significant increase in surface scratching was demonstrated for the lenses worn by the subjects of both groups over the time of the study (Group I, F=7.990, P <0.0001 [ANCOVA]; Group II, F=6.241, P=0.003 [ANCOVA]). The only parameter to show a statistically significant variation over the study period was that of centre thickness for the lenses worn by the subjects in Group I (F=3.976, P=0.0063 [ANCOVA]), with a mean reduction in centre thickness of 0.022 mm at the 12 month visit. No change was noted for either group or between groups for the other parameters measured. This study demonstrates that the parameters of rigid contact lenses manufactured from high Dk fluorocarbons are stable with only a non-clinically significant reduction in centre thickness for the contact lenses worn by the subjects in Group I.

Journal Article↗
PubMed2005

Rigid endoscopy in globus pharyngeus: how valuable is it?

The aim of this study was to assess the value of rigid endoscopy in patients presenting with globus symptoms. We conducted a retrospective analysis of 250 patients who underwent rigid endoscopy for globus symptoms over a 12-month period. In 217 patients (86.8 per cent) the examination of the larynx, pharynx and upper oesophagus was entirely normal. Abnormal findings included cricopharyngeal spasm in 12 patients (4.8 per cent), reflux in 11 (4.4 per cent), pharyngitis in two (0.8 per cent), web in two (0.8 per cent), and retention cyst in three (1.2 per cent). The 95 per cent confidence interval (CI) for the mean number of persons with malignancy based on the Poisson distribution is 0 and 3.7 (0 and 14.8 as rates per 1000). The relationship between the clinical diagnosis and endoscopic findings was examined using the chi-square test, with a p value of 0.0001. These results suggest that patients presenting with globus sensation are unlikely to harbour neoplastic lesions and therefore rigid endoscopy may well be an inappropriate investigation in this group. The risks, costs and discomfort associated with this intervention can often be avoided.

Adolescent↗
PubMed2003

Increased rigidity of eglin c at acidic pH: evidence from NMR spin relaxation and MD simulations.

To gain physical insights into how proteins respond to changes in pH, the picosecond to nanosecond time scale dynamics of the small serine protease inhibitor eglin c have been studied by NMR spin relaxation experiments and MD simulations under two pH solution conditions, pH 7 and 3. Like many proteins, eglin c is destabilized by a lowering of the pH, although it retains enough stability to maintain its native conformation at pH 3. Backbone (15)N relaxation results show comparable global tumbling times (tau(m)) and model-free order parameters (S(2)) under the two pH conditions, indicating that the molecule maintains its overall molecular shape and structure at low pH, although the backbone rigidity is slightly increased ( / = 0.6%). In contrast, the side-chain methyl dynamics, as measured from (2)H relaxation experiments, show a substantial increase in rigidity at lower pH ( / = 14.8%). Molecular dynamics simulations performed at these pH states produce results consistent with NMR measurements, showing that the two methods are in qualitative agreement. Although a full accounting of the physical basis for the concurrent conformational rigidification and destabilization at low pH requires further investigation, the high level of detail in the MD simulations provides a potential molecular mechanism: the breaking of the hydrogen bond between the side chains of Asp46 and Arg53, and changes in electrostatic interactions, appear to allow the binding loop to move closer to the core part of the protein, resulting in a more compact structure at low pH. This more compact structure may be responsible for the increased level of restriction of molecular motion. As these findings show, the stability of a molecular structure is distinct from its conformational rigidity, and the two can even change in opposite directions, against naïve expectation.

Animals↗
PubMed1999

The active site of Paracoccus denitrificans aromatic amino acid aminotransferase has contrary properties: flexibility and rigidity.

Paracoccus denitrificans aromatic amino acid aminotransferase (EC 2. 6.1.57; pdAroAT) binds with a series of aliphatic monocarboxylates attached to the bulky hydrophobic groups. To analyze the properties of the active site in this enzyme, we determined the tertiary structures of pdAroAT complexed with nine different inhibitors. Comparison of these active site structures showed that the active site of pdAroAT consists of two parts with contrary properties: rigidity and flexibility. The regions that interact with the carboxylates and methylene chains of the inhibitors gave essentially the same structures among these complexes, exhibiting the rigid property, which would involve fixing the substrate at the proper orientation for efficient catalysis. The region that interacts with the terminal hydrophobic groups of the inhibitors gave versatile structures according to the structures of the terminal groups, showing that this region is structurally flexible. This is mainly achieved by the conformational versatility of the side chains of Asp15, Lys16, Asn142, Arg292, and Ser296. These residues formed in the active site hydrogen bond networks, which were adaptable for the structures of the terminal hydrophobic groups of the inhibitors, with a small deformation or partial destruction according to the shapes and sizes of the inhibitors. These observations illustrate how the flexibility and rigidity in the active site can be used for the substrate binding and recognition.

Acids, Acyclic↗
PubMed2004

Powder diffraction study of a coordination polymer comprised of rigid building blocks: [Rh2(O2CCH3)4.mu2-Se2C5H8-Se,Se']infinity.

The crystal structure of a new hybrid product comprised of two rigid building blocks, namely dirhodium(II) tetraacetate, [Rh(2)(O(2)CCH(3))(4)] (1), and 2,6-diselenaspiro[3.3]heptane, Se(2)C(5)H(8) (2), has been solved ab initio using laboratory source X-ray powder diffraction (XRPD) data. The rigid body refinement approach has been applied to assist in finding an adequate model and to reduce the number of the refined parameters. Complex [Rh(2)(O(2)CCH(3))(4).mu(2)-Se(2)C(5)H(8)-Se,Se'] (3) conforms to the triclinic unit cell with lattice parameters of a = 8.1357(4), b = 8.7736(4), and c = 15.2183(8) A, alpha = 77.417(3), beta = 88.837(3), and gamma = 69.276(4) degrees, V = 989.66(8) A(3), and Z = 2. The centrosymmetric P space group was selected for calculations. The final values of the reduced wR(p), R(p), and chi(2) were calculated at 0.0579, 0.0433, and 5.95, respectively. The structure of 3 is a one-dimensional zigzag polymer built on axial Rh...Se interactions at 2.632(6) A. The 2,6-diselenaspiro[3.3]heptane ligand acts as a bidentate linker bridging dirhodium units via both selenium atoms. The geometrical parameters of individual groups for rigid body refinement have been obtained from X-ray powder data for dirhodium(II) tetraacetate (1) and from single-crystal X-ray diffraction for diselenium molecule 2. The crystal structures of 1 and 2 are reported here for the first time. For 1 indexing based on XRPD data has resulted in the triclinic unit cell P with lattice parameters of a = 8.3392(7), b = 5.2216(5), and c = 7.5264(6) A, alpha = 95.547(10), beta = 78.101(6), and gamma = 104.714(13) degrees, V = 309.51(5) A(3), and Z = 1. The final values were wR(p) = 0.0452, R(p) = 0.0340, and chi(2) = 1.99. The 1D polymeric motif built on axial Rh.O interactions of the centrosymmetric dirhodium units has been confirmed for the solid-state structure of 1. Compound 2,6-diselenaspiro[3.3]heptane (2) conforms to the monoclinic space group P2(1)/c with the unit cell parameters of a = 5.9123(4), b = 19.6400(13), and c = 5.8877(4) A, beta = 108.5500(10) degrees, V = 648.15(8) A(3), and Z = 4.

Copper↗
PubMed1996

Photoinduced Electron and Energy Transfer in Rigidly Bridged Ru(II)-Rh(III) Binuclear Complexes.

A series of binuclear Ru(II)-Rh(III) complexes of general formula (ttpy)Ru-tpy-(ph)(n)-tpy-Rh(ttpy)(5+) (n = 0-2) have been synthesized, where ttpy = 4'-p-tolyl-2,2':6,2"-terpyridine and tpy-(ph)(n)-tpy represents a bridging ligand where two 2,2':6',2"-terpyridine units are either directly linked together (n = 0) or connected through one (n = 1) or two (n = 2) phenyl spacers in the 4'-position. This series of complexes is characterized by (i) rigid bridge structures and (ii) variable metal-metal distances (11 Å for n = 0, 15.5 Å for n = 1, 20 Å for n = 2). The photophysics of these binuclear complexes has been investigated in 4:1 methanol/ethanol at 77 K (rigid glass) and 150 K (fluid solution) and compared with that of mononuclear [Ru(ttpy)(2)(2+) and Rh(ttpy)(2)(3+)] or binuclear [(ttpy)Ru-tpy-tpy-Ru(ttpy)(4+)] model compounds. At 77 K, no quenching of the Ru(II)-based excited state is observed, whereas energy transfer from excited Rh(III) to Ru(II) is observed for all complexes. At 150 K, energy transfer from excited Rh(III) to Ru(II) is again observed for all complexes, while quenching of excited Ru(II) by electron transfer to Rh(III) is observed, but only in the complex with n = 0. The reasons for the observed behavior can be qualitatively understood in terms of standard electron and energy transfer theory. The different behavior between n = 0 and n = 1, 2 can be rationalized in terms of better electronic factors and smaller reorganizational energies for the former species. The freezing of electron transfer quenching but not of energy transfer, in rigid glasses reflects the different reorganizational energies involved in the two processes. Unusual results arising from multiphotonic and conformational effects have also been observed with these systems.

Journal Article↗
PubMed2000

A new class of conformationally rigid analogues of 4-amino-5-halopentanoic acids, potent inactivators of gamma-aminobutyric acid aminotransferase.

Recently, we found (Qiu, J.; Pingsterhaus, J. M.; Silverman, R. B. J. Med. Chem. 1999, 42, 4725-4728) that conformationally rigid analogues of the GABA aminotransferase (GABA-AT) inactivator vigabatrin were not inactivators of GABA-AT. To determine if this is a general phenomenon of GABA-AT inactivators, several mono- and di-halogen-substituted conformationally rigid analogues (7-15) of other GABA-AT inactivators, 4-amino-5-halopentanoic acids, were synthesized as potential inactivators of GABA-AT. Four of them, (+)-7, (-)-9, (+)-10, and (+)-15, were inactivators, although not as potent as the corresponding open-chain analogues. The maximal inactivation rate constants, k(inact), for the fluoro- and bromo-substituted analogues were comparable, indicating that cleavage of the C-X bond is not rate determining. Consistent with that observation is the finding that [3-(2)H]-10 exhibits a deuterium isotope effect on inactivation of 3.3, suggesting that C-H bond cleavage is the rate-determining step. The rate of inactivation of GABA-AT by the fluorinated analogue 7 is 1/15 that of inactivation by the corresponding open-chain analogue, 4-amino-5-fluoropentanoic acid (3a). Whereas inactivation by 3a releases only one fluoride ion, inactivation by 7 releases 148 fluoride ions, accounting for the less efficient inactivation rate. Inactivation leads to covalent attachment of 2 equiv of inactivator after gel filtration; upon urea denaturation, 1 equiv of radioactivity remains bound to the enzyme. This suggests that, unlike the open-chain anlogue, the conformationally rigid analogue becomes, at least partially, attached to an active-site residue. It appears that the conformational constraint has a larger effect on inactivators that inactivate by a Michael addition mechanism than by an enamine mechanism.

4-Aminobutyrate Transaminase↗