Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “RIGIDITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed2004

The relative transit time of high-rigidity and low-rigidity cosmic rays through the solar system.

A study of neutron monitor count rates with vertical cut-off rigidities from 0.6 to 13 GV indicates that high-energy and low-energy galactic cosmic rays arrive at earth orbit with small time differences compared to a month. This is in contradiction to the theory of the deceleration potential which states that cosmic-ray particles with rigidities greater than 36 V arrive at earth orbit about three months before cosmic-ray particles with lesses rigidines.

Cosmic Radiation↗
PubMed2003

Rigid fixation of the calvaria in craniosynostosis without using "rigid" fixation.

Early observations of intracranial translocation of metal wires, plates, and screws used for infant skull surgery have led some surgeons to investigate alternative forms of fixation. The purpose of this study was to review a series of infants and children in whom absorbable suture fixation was used as the sole method of fixation in cranial vault remodeling. Standard osteotomies were successfully modified to permit the use of this less rigid form of fixation. Over a 6-year period, 142 cranial vault procedures were performed, primarily for craniosynostosis, using absorbable sutures (2-0 polydioxanone). Patients who did not have absorbable suture fixation, or who had a combination of absorbable sutures with another form of fixation, were excluded from this review. Records were reviewed for results (assessed by both the treating surgeon and an independent anthropologist) and for complications. The average age of patients was 2 years, 7 months (range, 1 month to 16 years). The clinical results were judged as follows: grade I (excellent), 49 percent; grade II (minor imperfections), 48 percent; grade III (small surgical procedure needed), 2 percent; and grade IV (complete reoperation required), 1 percent. Anthropologic results were similarly distributed: excellent, 36 percent; good, 56 percent; fair, 8 percent; and poor, 0 percent. Those 3 to 8 percent of patients who were found to have the poorest results were all noted to have syndromes, and it appeared that an inherent lack of growth was the primary basis for the low score. There were no deaths or major complications in this series of patients. The smaller complications identified were infections [four cases (2.8 percent)] and transient cerebrospinal fluid leak [two cases (1.4 percent)]. The most important factor in determining whether absorbable suture fixation was sufficient was the size of a preexisting calvarial defect. Although concerns have been raised about a possible link between absorbable suture fixation and subsequent poor reossification, no such association was noted in this review. The primary disadvantage of using absorbable sutures was the lack of rigidity provided. Advantages included lower costs, speed of application, and the absence of observed intracranial translocation. In conclusion, the use of absorbable suture fixation (with modifications in osteotomy design) was associated with both acceptable aesthetic outcomes and low complication rates. Craniofacial surgeons may wish to consider the use of absorbable sutures as another option for bone fixation in treatment of craniosynostosis.

Absorption↗
PubMed2000

Ultra-low wear rates for rigid-on-rigid bearings in total hip replacements.

With the increased clinical interest in metal-on-metal and ceramic-on-ceramic total-hip replacements (THRs), the objective of this hip simulator study was to identify the relative wear ranking of three bearing systems, namely CoCr-polyethylene (M-PE), CoCr-CoCr (M-M) and ceramic-on-ceramic (C-C). Volumetric wear rates were used as the method of comparison. The seven THR groupings included one M-PE study, two M-M studies and four C-C studies. Special emphasis was given to defining the 'run-in' phase of accelerated wear that rigid-on-rigid bearings generally exhibit. The hypothesis was that characterization of the run-in and steady state wear phases would clarify not only the tribological performance in vitro but also help correlate these in vitro wear rates with the 'average' wear rates measured on retrieved implants. The implant systems were studied on multichannel hip simulators using the Paul gait cycle and bovine serum as the lubricant. With 28 mm CoCr heads, the PE (2.5 Mrad/N2) wear rates averaged 13 mm3/10(6) cycles duration. This was considered a low value compared with the clinical model of 74 mm3/year (for 28 mm heads). Our later studies established that this low laboratory value was a consequence of the serum parameters then in use. The mating CoCr heads (with PE cups) wore at the steady state rate of 0.028 mm3/10(6) cycles. The concurrently run Metasul M-M THRs wore at the steady state rate of 0.119 mm3/10(6) cycles with high-protein serum. In the second Metasul M-M study with low-protein serum, the THR run-in rate was 2.681 mm3/10(6) cycles and steady state was 0.977 mm3/10(6) cycles. At 10 years, these data would predict a 70-fold reduction in M-M wear debris compared with the clinical PE wear model. All M-M implants exhibited biphasic wear trends, with the transition point at 0.5 x 10(6) cycles between run-in and steady state phases, the latter averaging a 3-fold decrease in wear rate. White surface coatings on implants (coming from the serum solution) were a confounding factor but did not obscure the two orders of magnitude wear performance improvement for CoCr over PE cups. The liners in the alumina head-alumina cup combination wore at the steady state rate of 0.004 mm3/10(6) cycles over 14 x 10(6) cycles duration (high-protein serum). The zirconia head-alumina cup THR combination wore at 0.174 and 0.014 mm3/10(6) cycles for run-in and steady state rates respectively (low-protein serum). The zirconia head and cup THR combination wore slightly higher initially with 0.342 and 0.013 mm3/10(6) cycles for run-in and steady state rates respectively. Other wear studies have generally predicted catastrophic wear for such zirconia-ceramic combinations. It was noted that the zirconia wear trends were frequently masked by the effects of tenacious white surface coatings. It was possible that these coatings protected the zirconia surfaces somewhat in this simulator study. The experimental ceramic Crystaloy THR had the highest ceramic run-in wear at 0.681 mm3/10(6) cycles and typical 0.016 mm3/10(6) cycles for steady state. Since these implants represented the first Crystaloy THR sets made, it was likely that the surface conditions of this high-strength ceramic could be improved in the future. Overall, the ceramic THRs demonstrated three orders of magnitude wear performance improvement over PE cups. With zirconia implants, while the cup wear was sometimes measurable, head wear was seldom discernible. Therefore, we have to be cautious in interpreting such zirconia wear data. Identifying the run-in and steady state wear rates was a valuable step in processing the ceramic wear data and assessing its reliability. Thus, the M-M and C-C THRs have demonstrated two to three orders of reduction in volumetric wear in the laboratory compared with the PE wear standard, which helps to explain the excellent wear performance and minimal osteolysis seen with such implants at retrieval operations.

Aluminum Oxide↗
PubMed1995

A novel approach to measuring the wettability of rigid contact lenses. Mass measurement of the adherent liquid on the rigid lens surface (1).

A novel approach and the equilibrium sessile drop (laser assisted) method were used to determine the wettability of hydrated and unhydrated PMMA, Polycon II, Boston IV, Equalens and Boston RXD rigid contact lens materials. In the new method the ability of the contact lens surface to attract the liquid is evaluated by measuring the adhered mass of liquid on the front lens surface. The mass has a direct relationship to contact lens wettability, so the greater the lens surface hydrophilicity the more liquid adheres to the contact lens surface. In the hydrated state, Equalens and Boston IV showed the greatest hydrophilicity of all five materials, although there was no significant difference between them (P > 0.9). Boston RXD had a lower ability to attract liquid and there was a significant difference between it and the next higher material which was Boston IV (P < 0.005) and also the next lowest Polycon II (P < 0.00001). PMMA had the lowest capability to adhere liquid and there was a significant difference between PMMA and Polycon II (P < 0.00001). The new method is simple and quick to use and gives greater discrimination and repeatability than other current methods.

Adhesiveness↗
PubMed2002

Prospective comparative study of the range of movement of temporomandibular joints after mandibular fractures: rigid or non-rigid fixation.

Temporomandibular joints (TMJ) are negatively affected by trauma and disuse. In this prospective study, 103 patients with mandibular fractures were evaluated for the influence of trauma and maxillomandibular fixation on the TMJ. A total of 54 patients were treated by maxillomandibular fixation and 49 by titanium miniplate fixation. Those patients with condylar fractures and multiple mandibular fractures and malocclusion at presentation were not included in the study. The control group consisted of 44 randomly-selected healthy people with no past history of mandibular fracture or symptoms referable to the TMJ. Trauma was a major factor leading to TMJ dysfunction and maxillomandibular fixation increased the incidence and severity of TMJ dysfunction.

Adult↗