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PubMed1993

The effect of different fixatives and length of fixation time on subsequent AgNOR staining for frozen and paraffin-embedded tissue sections.

The AgNOR technique has been used extensively in studies investigating the possibility that the numbers and appearances of the intranuclear structures stained are markers of malignancy. The method has the advantage of being applicable to many different types of histological material, including paraffin-embedded tissue. However, it has been suggested that the visualization of AgNORs is dependent on the type and time of fixation employed. This study set out to measure this effect with the following commonly-used fixatives: acetone, absolute ethanol, methanol, Carnoy's fluid, Bouin's fluid, 4% glutaraldehyde, 10% neutral buffered formalin and 10% formol-saline. Both frozen sections and blocks of fresh tonsil were fixed for varying times, the blocks of tissue then being processed routinely. With the frozen sections AgNORs were easier to discern than in sections of paraffin-embedded tissue, and more intranucleolar AgNORs were visible when alcoholic fixatives were used than with aldehyde fixation. The effects of different fixatives on AgNOR appearance in paraffin sections is, however, more complex. Despite the variation caused by different fixatives, AgNORs could be demonstrated adequately with all the fixatives studied. It is concluded that fixation is not a limitation to the study of AgNORs provided that the time and type of fixative is controlled.

Acetates↗
PubMed1999

Early fixation of the vertically unstable pelvis: the role of iliosacral screw fixation of the posterior lesion.

OBJECTIVES: To evaluate the effectiveness of the use of iliosacral screw fixation in the management of the vertically unstable pelvis. STUDY DESIGN: Retrospective analysis with clinical follow-up of patients to assess functional outcome. METHODS: Thirty-eight vertically unstable pelvic fractures were treated using iliosacral screw fixation. Anterior fixation was by means of plating in sixteen pelves and by external fixation in fifteen pelves. Four pelves had no anterior fixation. Complications were recorded and radiographs were analyzed to classify fractures and identify screw misplacement and malunion. Twenty-six patients had a functional evaluation. RESULTS: Five patients (13 percent) suffered a pulmonary embolus in the early postoperative period, one of which was fatal, a hospital mortality of 2.6 percent. Screw misplacement occurred in five patients but there were no adverse sequelae. In thirty-four cases with radiographic follow-up, malunion was noted in fifteen cases (44 percent). A lower rate of malunion (36 percent) was noted with internal fixation of the anterior lesion. Of twenty-six patients with long-term follow-up, only four (15 percent) had no pain. Sacroiliac fusion for pain was performed in three patients (11 percent). Twelve patients (46 percent) returned to their preinjury occupation, six patients (23 percent) changed occupation, and nine patients (30 percent) had not yet returned to work by last follow-up. CONCLUSIONS: Iliosacral screw fixation is a useful method of fixation in the vertically unstable pelvis but needs to be augmented by rigid anterior fixation to minimize malunion.

Adolescent↗
PubMed1985

Fixation disparity vs. binocular fixation misalignment.

Conventional fixation disparity was compared with the corresponding foveal fixation misalignment measured by a recently developed method based on the effect of retinal eccentricity on the width of the border enhancement band. Unlike procedures using binocular nonius alignment, the method is not subject to adaptive changes in perceived direction. Forced convergence and divergence stimulation served as the independent variable. It was found that conventional fixation disparity represents only a small, constant fraction of the misalignment through the greater portion of the vergence range. However, when the misalignment is restricted to a small, central portion of the foveola, this relation changes drastically, and the fixation disparity can then be much larger than the fixation misalignment. During perfect fixation alignment of the foveal centers, there is always a significant amount of fixation disparity present. It is suggested that the large differences between fixation disparity and fixation misalignment are due to a fundamental, perceptual mechanism that is always at work during binocular vision, changing the relation between retinal location and perceived visual direction.

Convergence, Ocular↗
PubMed2000

Comparison of polyvinyl alcohol fixative with three less hazardous fixatives for detection and identification of intestinal parasites.

Polyvinyl alcohol (PVA) containing the fixative mercuric chloride is considered the "gold standard" for the fixation of ova and parasites in the preparation of permanently stained smears of stool specimens. However, mercuric chloride is potentially hazardous to laboratory personnel and presents disposal problems. We compared three new alternative, nontoxic fixatives with PVA, analyzing ease of sample preparation and quality of smears. Sixty-eight fresh stool specimens were divided into aliquots and placed in each of four different fixatives: PARASAFE (PS) (Scientific Devices Laboratory, Inc., Des Plaines, Ill.), ECOFIX (EC) (Meridian Diagnostics, Inc., Cincinnati, Ohio), Proto-Fix (PF) (Alpha-Tec Systems, Inc., Vancouver, Wash.), and low-viscosity PVA fixative (PVA) (Meridian). Specimens were processed and stained according to each manufacturer's directions. Parasites were found in 31 of 68 slide preparations with PVA, 31 with PF, 30 with EC, and 30 with PS. Blastocystis hominis and Iodamoeba bütschlii were preserved in a readily identifiable state by all methods of fixation. However, some parasites were more easily identified with some of the fixatives because of differences in parasite distortion. For example, Entamoeba histolytica (Entamoeba dispar) was detected in 13 stools fixed with PF, 7 with PVA, and 6 with EC but none with PS. Likewise, Chilomastix mesnili was identified in 13 specimens fixed with PF, 8 with EC, and 5 with PVA but only 1 with PS, while Entamoeba coli was seen much less frequently with PS than with the other three fixatives. A dirty background was observed in 41% of specimens prepared with PS, whereas background quality was acceptable with other fixatives. Sample preparation was most rapid with PS, although the EC method involved the fewest steps. In conclusion, PVA and PF produced the least parasite distortion, while PS proved unsatisfactory for the identification of E. histolytica, E. coli, and C. mesnili. Both PF and EC appear to be acceptable, environmentally safe substitutes for PVA.

Animals↗
PubMed1984

Bone healing after metal plate fixation and external fixation of the osteotomized rabbit tibia.

Controversy still exists as to the best method of treatment of long bone fractures. The purpose of the present study was to compare the effects on the healing bone of external fixation and metal plate fixation. In an experimental model on the rabbit tibia the stiffness of the fixation corresponded intentionally to that of the same methods in human fracture treatment. A transverse midshaft osteotomy was made on one tibia, and fixed with a steel plate (45 X 5 X 1 mm) or external mini-fixation. The animals were killed after 4, 6 or 12 weeks. The bone healing was evaluated by radiography, histology and biomechanical testing in three-point bending. There were no significant differences between plate fixation and external fixation in the pattern of bone healing, as it occurred by periosteal, intramedullary and intercortical callus after both methods. The stiffness increased more rapidly than the strength, and reached normal values after about 6 weeks. No significant differences in stiffness between the two methods were found. The strength was significantly greater after plate fixation than after external fixation at 6 weeks, while no significant differences were found at either 4 or 12 weeks. It is concluded that the speed of bone healing was more rapid after plate fixation. However, in the later stages of healing the plated bones were secondarily weakened because of the stress-protecting effect of the plate.

Animals↗
PubMed2005

Biomechanical comparison: stability of lateral-approach anterior lumbar interbody fusion and lateral fixation compared with anterior-approach anterior lumbar interbody fusion and posterior fixation in the lower lumbar spine.

OBJECT: The stability of lateral lumbar interbody graft-augmented fusion and supplementary lateral plate fixation in human cadavers has not been determined. The purpose of this study was to investigate the immediate biomechanical stabilities of the following: 1) femoral ring allograft (FRA)-augmented anterior lumbar interbody fusion (ALIF) after left lateral discectomy combined with additional lateral MACS HMA plate and screw fixation; and 2) ALIF combined with posterior transpedicular fixation after anterior discectomy. METHODS: Sixteen human lumbosacral spines were loaded with six modes of motion. The intervertebral motion was measured using a video-based motion-capturing system. The range of motion (ROM) and the neutral zone (NZ) in each loading mode were compared with a maximum of 7.5 Nm. The ROM values for both stand-alone ALIF approaches were similar to those of the intact spine, whereas NZ measurements were higher in most loading modes. No significant intergroup differences were found. The ROM and NZ values for lateral fixation in all modes were significantly lower than those of intact spine, except when NZ was measured in lateral bending. All ROM and NZ values for transpedicular fixation were significantly lower than those for stand-alone anterior ALIF. Transpedicular fixation conferred better stabilization than lateral fixation in flexion, extension, and lateral bending modes. CONCLUSIONS: Neither approach to stand-alone FRA-augmented ALIF provided sufficient stabilization, but supplementary instrumentation conferred significant stabilization. The MACS HMA plate and screw fixation system, although inferior to posterior transpedicular fixation, provided adequate stability compared with the intact spine and can serve as a sound alternative to supplementary spinal stabilization.

Aged↗
PubMed1991

The role of supplemental lag-screw fixation for open fractures of the tibial shaft treated with external fixation.

Ninety-nine open fractures of the tibial shaft were treated with unilateral external fixation with or without supplemental lag-screw fixation. We compared the results in forty-four fractures in which only external fixation was used (control group) with those in fifty-five fractures that were stabilized with lag-screws and external fixation, and we found no statistically significant differences between the two groups with respect to the time to full weight-bearing, the time to union, or the rates of delayed union, osteomyelitis, malunion, superficial or deep pin-track infection, or loosening of the pins. The limbs in which the fracture was treated with external fixation and supplemental lag-screws had more than twice the rate of refracture of the control limbs (11 compared with 5 per cent), and the percentage of fractures having supplemental lag-screw fixation that needed bone-grafting to achieve union was more than twice that in the group treated with external fixation alone. We concluded that the routine use of supplemental lag-screw fixation is not indicated in patients who have an open fracture of the tibial shaft that has been stabilized with external fixation.

Adolescent↗
PubMed1975

The role of pH in the regulation of carbon fixation in the chloroplast stroma. Studies on CO2 fixation in the light and dark.

1. The pH in the stroma and in the thylakoid space has been measured in a number of chloroplast preparations in the dark and in the light at 20 degrees C. Illumination causes a decrease of the pH in the thylakoid space by 1.5 and an increase of the pH in the stroma by almost 1 pH unit. 2. CO2 fixation is shown to be strongly dependent on the pH in the stroma. The pH optimum was 8.1, with almost zero activity below pH 7.3.Phosphoglycerate reduction, which is a partial reaction of CO2 fixation, shows very little pH dependency. 3. Low concentrations of the uncoupler m-chlorocarbonylcyanide phenylhydrazone (CCCP) inhibit CO2 fixation without affecting phosphoglycerate reduction. This inhibition of CO2 fixation appears to be caused by reversal of light induced alkalisation in the stroma by CCCP. 4. Methylamine has a very different effect compared to CCCP. Increasing concentrations of methylamine inhibit CO2 fixation and phosphoglycerate reduction to the same extent. The light induced alkalisation of the stroma appears not to be significantly inhibited by methylamine, but the protons in the thylakoid space are neutralized. The inhibition of CO2 fixation by higher concentrations of methylamine is explained by an inhibition of photophosphorylation. It appears that methylamine does not abolish proton transport. 5. It is shown that intact chloroplasts are able to fix CO2 in the dark, yielding 3-phosphoglycerate. This requires the addition of dihydroxyacetone phosphate as precursor of ribulosemonophosphate and also to supply ATP, and the addition of oxaloacetate for reoxidation of the NADPH in the stroma. 6. Dark CO2 fixation in the presence of dihydroxyacetone phosphate and oxaloacetate has the same pH dependency as CO2 fixation in the light. This demonstrates that CO2 fixation in the dark is not possible, unless the pH in the medium is artificially raised to pH 8.8.

Adenosine Triphosphate↗
PubMed1999

Update on fixation of rigid and foldable posterior chamber intraocular lenses. Part I: Elimination of fixation-induced decentration to achieve precise optical correction and visual rehabilitation.

PURPOSE: Realizing that precise posterior chamber intraocular lens (PC-IOL) centration is needed to consistently achieve good optical results and visual rehabilitation after modern cataract surgery, the authors assessed the status and success rate of lens haptic fixation and its correlation with lens optic centration-decentration in a large series of eyes with PC-IOLs obtained postmortem. DESIGN: Prospective analysis of pseudophakic eyes obtained postmortem. PARTICIPANTS: A total of 3493 human eyes obtained postmortem, the largest database of such specimens available to date. METHODS: Miyake-Apple posterior photographic technique. MAIN OUTCOME MEASURES: The amount of decentration of rigid PC-IOLs and small-incision foldable PC-IOLs was analyzed, and the results were correlated with the type of fixation that had been achieved in each case. RESULTS: Determination of mean values revealed that capsular bag fixation was achieved in 52.05% of eyes, asymmetric bag-sulcus fixation in 34.21 % of eyes, and sulcus-sulcus fixation in 13.74% of eyes. Asymmetrically fixed lenses consistently showed significant decentration. During the past 5 years (1993-98), the overall rate of in-the-bag fixation increased to 59.2%; by 1998 it had increased to 64%. Most significantly, success in achieving bag-bag fixation of foldable IOLs implanted in association with modern capsular surgery with small incisions has surged to 90% over the past 4 years. CONCLUSIONS: The authors found a direct correlation of decentration in eyes with asymmetric fixation, and the results underscore the need for careful in-the-bag haptic placement. Although few surgeons today would dispute the goal to implanting haptics in the capsular bag, these findings show that the overall success rate over the years has, while improving, remained surprisingly low. The overall success rate of about 60% seen with all lens designs is probably as good as can be expected with classic large-incision extracapsular techniques. However, and most important and encouraging, the success rate of haptic fixation in cases with foldable lenses has improved dramatically during the past 4 years (up to the 90% range). This coincides with the present emphasis on modern capsular surgery and small-incision techniques used to insert these lenses.

Acrylic Resins↗
PubMed2002

Inadequate formalin fixation decreases reliability of p27 immunohistochemical staining: probing optimal fixation time using high-density tissue microarrays.

Immunohistochemical analysis of molecular targets in clinical tissues is increasingly becoming central to our ability to render diagnoses, to predict prognosis, to select patients for appropriate therapies, and to provide surrogate end points for therapeutic monitoring. For example, reduction of immunohistochemical staining for the cyclin-dependent kinase inhibitor p27(Kip1) has been proposed as a potential prognostic biomarker in prostate, breast, and gastrointestinal tumors. We observed that with our standard formalin fixation in rapidly processed (same-day) radical prostatectomy specimens, there is often a gradient of p27(Kip1) staining in normal prostate epithelium, with more staining near the periphery and less staining toward the center of the sample. This raised the hypothesis that the reliability of staining for p27(Kip1) is decreased in inadequately fixed tissues. The implications of this, if true, are that many studies using p27(Kip1) for prognostic purposes may be subject to unpredictable artifacts, and hence unreliable results, if the fixation of the specimens is not well controlled. The objectives of the present study were (1) to formally test the hypothesis that inadequate fixation time is responsible for apparent loss of p27(Kip1) nuclear staining and (2) to test a recently proposed method for improving the uniformity of immmunohistochemical staining using formalin injection. Prostate tissue sections from radical prostatectomy specimens were either processed immediately (zero time fixation) or fixed for 1, 2, 3, or 8 days in 10% neutral buffered formalin before processing into paraffin. To assure identical antigen retrieval and immunohistochemical staining conditions for specimens fixed for different lengths of time, 2 high-density tissue microarrays (TMAs), containing 564 tissue samples (0.6 mm in diameter) were constructed. Based on an estimate of the percentage of nuclei in normal prostatic epithelial secretory cells with strong staining, quality of p27(Kip1) staining was graded in a blinded fashion with respect to fixation time. There was a significant increase in the percentage of cores that were scored as "strong" as fixation time increased from 0 (same-day processing) to 1 or more days (P <.0001). Interestingly, even at 8 days of fixation, there was excellent staining that was superior to the same-day processing. Based on these results, we conclude the following: (1) for large clinical specimens that have been fixed briefly to decrease diagnostic turn-around time, the reliability of interpretation of immunohistochemical staining may be quite limited; (2) for p27(Kip1), decreased antigen staining as a result of the widely held concept of "overfixation" is much less of a problem than "underfixation"; (3) formalin injection produces a marked improvement in staining for several markers, including p27(Kip1); and (4) high-density TMAs, which assure identical test conditions, provide an excellent platform on which to evaluate the effects of tissue fixation on immunohistochemical staining.

Cell Cycle Proteins↗
PubMed2006

Conversion from temporary external fixation to definitive fixation: shaft fractures.

Temporary external fixation is the most common method of initial stabilization of diaphyseal fractures in forward surgical hospitals. Once the patient arrives at a stable environment, usually the United States, the fracture is managed with intramedullary nailing, small-pin external fixation, or a modified external fixator. Future research should be directed toward improving methods of care. It is not precisely known when is the best time to convert to definitive fixation without increasing the risk of infection. The risk factors leading to infection and nonunion are not well-established, making that determination even more difficult. Clinical studies of a suitable size should provide insight into these problems. Although temporary external fixation is commonly used, an optimal construct has not been determined. Data from studies of in vivo fracture-site motion after application of the temporary external fixator should be compared with biomechanical testing of similar constructs. These data could be used to recommend optimal temporary external fixation constructs of tibia, femur, and humerus fractures using currently available devices as well as to provide groundwork for the next generation of fixators.

External Fixators↗
PubMed2005

Trans-sacral fixation for failed posterior fixation of the pelvic ring.

INTRODUCTION: In the treatment of certain pelvic ring pathologies (non-unions and failure of ilio-sacral screw fixation) trans-sacral fixation (i.e. fixation from iliac wing to the other traversing the body of S1) may be necessary. The purpose of our study was to describe our early experience and describe the surgical technique. MATERIALS AND METHODS: Seven cases of trans-sacral fixation were identified with a mean patient age of 49-years-old with four females and three males. The diagnosis at the time of trans-sacral fixation was failure of posterior ring fixation in four (three of which had vertical sacral fractures), mal-position of iliosacral (IS) screw in one, failure of fusion of sacroiliac (SI) joint in two. All these cases were augmented with a 4.5 mm reconstruction plate placed in tension posteriorly. RESULTS: At average follow up of 39 months (range 24-75), all patients achieved union. There were no neurological or vascular complications. Two patients required reoperations prior to union. Our current use for this technique is with a 8.0 mm screw (16 mm thread). CONCLUSIONS: Initial experience with trans-sacral fixation has proven to be very effective technique to solve the most difficult problems in posterior pelvic ring fixation. We reserve its use to the following indications: nonunion/malunion of the pelvic ring, and sacral fractures.

Aged↗
PubMed2001

Fixation location effects on fixation durations during reading: an inverted optimal viewing position effect.

Previous research has found that words are identified most quickly when the eyes are near their center (the Optimal Viewing Position effect). A study was conducted to determine whether this same phenomenon is observed during reading, as revealed by a relationship between fixation position in a word and the duration of the fixation. An analysis of three large existing corpora of eye movement data, two from adults and one from children, showed a surprising inverted Optimal Viewing Position curve: mean fixation duration is greatest, rather than lowest, when the eyes were at the centers of words. From this phenomenon, we suggest an alternative explanation to the fixation duration trade-off effect in word refixations [O'Regan & Lévy-Schoen, Attention and performance XII: the psychology of reading (1987)]; the phenomenon also contradicts expectations of both oculomotor and cognitive theories of eye movement control. Attempts to test alternative explanations led to the discovery of another phenomenon, the Saccade Distance effect: mean fixation durations vary with the distance of the prior fixation from the currently-fixated word, being longer with greater distances. The durations of fixations in reading are complexly determined, with influences both from language and perceptual/oculomotor levels.

Adult↗
PubMed2006

Gene expression during fracture healing in rats comparing intramedullary fixation to plate fixation by DNA microarray.

OBJECTIVE: This study was designed to compare mRNA gene expression in healing diaphyseal femoral fractures between those injuries treated with intramedullary nails and those treated with internal plate fixation. DESIGN: RNA gene expression was measured at 1 day, 3 days, and 1, 2, 4, and 6 weeks after surgery in the fracture callus of rats randomized to femoral shaft fracture with intramedullary nail fixation, rigid plate fixation, or sham fracture. SETTING: AAALAC-accredited vivarium of an independent academic medical center. ANIMALS: Fifty-seven, adult, female, Sprague-Dawley rats at 16 weeks of age. INTERVENTION: Femoral fracture with intramedullary nail fixation, femoral fracture with plate and screw fixation, or sham surgery with no fracture. MAIN OUTCOME MEASUREMENTS: RNA expression for 8700 genes was measured with 19 Affymetrix U34A microarrays. The fracture callus was significantly larger with intramedullary nail fixation than with plate fixation. Most genes responded to fracture with a change in mRNA expression. Most of the responding genes followed the same time course for both fixation methods. This included genes related to growth factors, bone matrix, mast cells, most nerve factors, and hematopoiesis. The intramedullary nail group had significantly greater up-regulation for transcripts related to cartilage, cell division, inflammation, and the acetylcholine receptor. There was significantly greater up-regulation in the plate group for genes related to macrophage activity. CONCLUSIONS: There were differentially expressed genes present between the 2 surgical groups that may give insight into the control of fracture repair.

Animals↗
PubMed2004

Can fixation instability improve text perception during eccentric fixation in patients with central scotomas?

BACKGROUND: Oculomotor behaviour was investigated in 14 patients with central scotomas from age related macular degeneration (AMD) or Stargardt's disease. A scanning laser ophthalmoscope (SLO) was used to project letters and words onto the retina and to assess fixation behaviour. Five patients reported while deciphering letters that they needed to "move their eye" to prevent the image from vanishing. The observation of the SLO fundus images revealed that the gradual disappearance of the stimulus did not result from a transient projection of the word in the lesion. This prompted the authors to investigate, in an experimental setting, whether purposeful changes in fixation position could improve the perception of an eccentrically fixated text stimulus. METHODS: Twenty normal subjects were asked to alternate fixation, every three to four seconds, between two vertically aligned dots, spaced 10 degrees apart, and to report any changes in the perception of a laterally located letter, 1.5 degrees in height, 7 degrees apart and equidistant between the two fixation spots. RESULTS: Nineteen subjects reported a transient refreshment of the letter image immediately after the realisation of a saccade. Improved perception lasted approximately a second. With persistent fixation, they noted a rapid fading effect that reduced letter recognition. CONCLUSION: These observations suggest that ocular instability during eccentric viewing can have a functional advantage, probably related to counteracting Troxler's phenomenon. In addition to alternating between PRLs, it appears that saccades related to fixation instability might be valuable and improve text perception in individuals with a central scotoma and eccentric fixation. This possibility should be taken into consideration when conducting visual rehabilitation procedures.

Adult↗
PubMed2006

Comparison of plate and screw fixation and screw fixation alone in a comminuted talar neck fracture model.

BACKGROUND: Talar neck fracture fixation has been studied in noncomminuted fracture models, but no large clinical series of comminuted fracture patterns have been published and no biomechanical studies have compared plate fixation with screw fixation in comminuted talar neck fractures. METHODS: Nine matched pairs of fresh frozen talar specimens were stripped of soft tissue and mounted in a cylindrical jig. The talar neck was fractured using a dorsally directed shear force at a rate of 200 mm/min, and dorsal comminution was simulated by removing a 2-mm section of bone from the distal fracture fragment. One specimen from each pair was fixed with either two solid 4.0-mm partially threaded cancellous screws posterior-to-anterior just lateral to the posterior process of the talus or with a four-hole 2.0-mm minifragment plate contoured to the lateral surface of the talar neck and secured with 2.7-mm screws. A 2.7-mm fully threaded cortical screw was placed medially using a lag technique. The specimens were then loaded to failure with a dorsally directed force at a rate of 200 mm/min. Failure was defined as the load producing 2 mm of displacement. A Student's t-test analysis was used with significance set at p < or = 0.05. RESULTS: Posterior-to-anterior screw fixation had a statistically significant higher load to failure than plate fixation (p < 0.05). Mean load to failure for the screw group was 120.7 +/- 68.5 N and 89.7 +/- 46.6 N for the plating group. CONCLUSIONS: Plate fixation may offer substantial advantages in the ability to control the anatomic alignment of comminuted talar neck fractures, but it does not provide any biomechanical advantage compared with axial screw fixation. Further, the fixation strength of both methods was an order of magnitude lower than those found in previous studies of noncomminuted fractures.

Bone Plates↗