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At least 109 records · Page 6Linked to original sources
PubMed2003

Anterior occiput to axis screw fixation: part II: a biomechanical comparison with posterior fixation techniques.

STUDY DESIGN: This biomechanical study used flexibility testing on fresh-frozen human cadaveric specimens (occiput to C3) and compared the range of motion and neutral zone for three occipitocervical fixation techniques. OBJECTIVES: To contrast the stabilization provided by a new technique of anterior occipitocervical screw fixation with two other commonly used posterior occipitocervical fixation techniques. SUMMARY OF BACKGROUND DATA: There are no published reports describing this novel technique of anterior occipitocervical screw fixation. METHODS: Six human occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied a pure moment in flexion-extension, lateral bending, and axial rotation. The specimens were tested intact, after an odontoid osteotomy with capsular injury, and after each of three fixation methods: posterior wiring, posterior plate fixation with C1-C2 transarticular screws, and finally with anterior occipitocervical screws. Intervertebral motion was measured with an optoelectronic measurement system, and the range of motion and neutral zone were the kinematic variables measured and used for analysis. RESULTS: In flexion and extension testing, the posterior plate with transarticular screws provided greater stabilization than posterior wiring or anterior occipitocervical screws. In lateral bending and rotation, the anterior screws were similarly effective to the posterior plate, both of which were more effective than posterior wiring. CONCLUSION: The anterior screw fixation technique was as effective as a posterior plate with transarticular screws in stabilizing between the occiput and C2 in axial rotation and lateral bending. In extension and flexion, the anterior screw technique was not as effective as a posterior plate with transarticular screws in providing stability.

Axis, Cervical Vertebra↗
PubMed2006

Efficacy of translaminar facet screw fixation in circumferential interbody fusions as compared to pedicle screw fixation.

OBJECTIVES: Posterior lumbar fixation with translaminar facet screws is a minimally invasive technique with good success rates. Long-term follow-ups show reduced reoperation rates, a decrease in pain scores, and few complications compared with pedicle screw fixation devices. The purpose of this study was to compare the reoperation rate of translaminar facet screw fixation with that of pedicle screw fixation in 360 degrees anterior and posterior fusions for incapacitating low back pain due to lumbar disc degeneration unresponsive to at least 6 months of aggressive nonoperative treatment. METHODS: One hundred five patients underwent a combined circumferential lumbar fusion with posterior fixation for discogenic pain by one surgeon between August 1993 and February 2003. Seventeen patients were excluded from the study owing to their preoperative etiology for fusion or a prior instrumented posterior fusion. A retrospective chart review was done on all 88 remaining patients. Patients were followed in the office, by phone, or by mail to obtain functional outcome measures. Any subsequent operations by this surgeon or another were recorded. The comparison focused on the rate of reoperation on the region of posterior lumbar fixation. RESULTS: Sixty-seven patients have had at least a 2-year follow-up. Twenty-four patients had a posterior fusion with pedicle screws, and 43 had translaminar facet screw fixation. Nine patients of the pedicle screw population (37.5%) had a reoperation to remove their instrumentation. Two patients of the translaminar facet screw population (4.7%) had reoperations on their lumbar spine. There was a significant association between posterior instrumentation type and reoperation (P = 0.001). CONCLUSION: The success of translaminar facet screws in circumferential fusions is justified.

Adult↗
PubMed1991

Fixation of the macula densa with fixatives of different osmolarities in normal and diabetic rats.

The influence of different fixative osmolarities on the ultrastructure of the macula densa region has been studied in normal and in streptozotocin diabetic rats after 50 days' duration of diabetes. In vivo perfusion fixation of the kidneys was performed retrogradely through the aorta in five groups of controls and diabetic animals with a 1% glutaraldehyde fixative in a Tyrode solution. Between groups, the osmolarity of the fixative solution varied from 216 to 476 mosm/l. This was accomplished by variation of the NaCl concentration of the fixative vehicle. The tissue was embedded in Epon and midcortical tissue was prepared for electron microscopy. The volume density of the lateral intercellular spaces between the macula densa cells was measured applying a morphometric technique. The results confirmed that the lateral intercellular spaces are narrowed in diabetes and also showed that for all fixative osmolarities the difference is persistent between diabetic and non-diabetic animals, except at very low osmolarities. The abnormal macula densa ultrastructure has been suggested to be connected with the functional abnormalities in diabetes, i.e. the resetting of the tubuloglomerular feedback and subsequent increases in GFR. It is therefore of interest to further understand the mechanisms underlying the narrowing of the lateral intercellular spaces in diabetes. The present study has shown that the size difference in lateral intercellular spaces between diabetic and normal animals is reproducible over a wide range of fixative osmolarities, further indicating that it is an in vivo phenomenon. The diminution of the LIS in diabetes could perhaps indicate a decrease in signal function, previously reported at the MD level in diabetic animals, contributing to the increased GFR in diabetes.

Animals↗
PubMed1998

Comparison of the discharge characteristics of brain stem omnipause neurons and superior colliculus fixation neurons in monkey: implications for control of fixation and saccade behavior.

Fixation neurons (SCFNs) in the rostral pole of the superior colliculus (SC) and omnipause neurons (OPNs) in the nucleus raphe interpositus (rip) in the pons share similar discharge properties. Both types of neurons discharge tonically during periods of visual fixation and pause for saccadic eye movements, and their activation by electrical stimulation suppresses saccade generation. On the basis of these similarities and the projection from the rostral SC to the rip, it was hypothesized that SCFNs provide a major excitatory input to OPNs. We investigated the role and relationship of SCFNs and OPNs with respect to both fixation behavior and saccade generation by comparing their activity recorded in the same monkeys performing a gap saccade task. In this task, the central fixation point was extinguished 200 ms before the presentation of an eccentric saccadic target, and the discharges of OPNs and SCFNs were contrasted during visual fixation, nonvisual (gap) fixation, and saccade generation. During visual fixation, the mean discharge rate of OPNs was higher and more regular than that of SCFNs. During the gap period, SCFNs decreased their discharge rate before target appearance, whereas no change in discharge rate was observed in OPNs. For both SCFNs and OPNs, the activity level before target appearance was not correlated to saccadic reaction time. In contrast to SCFNs, several OPNs responded with a transient phasic increase in discharge immediately after the target presentation. Before their saccade-related pause, there was a gradual reduction in the activity of SCFNs, whereas OPNs had an abrupt cessation of discharge. SCFNs paused earlier than OPNs, but the OPN pause onset was better synchronized to saccade onset than the SCFN pause onset. OPNs resumed firing after their pause in activity earlier than SCFNs, and the OPN pause end was better synchronized to saccade end than the SCFN pause end. These physiological data reveal differences in the discharge properties of SCFNs and OPNs that are irreconcilable with the hypothesis that the discharge pattern of OPNs reflects simply the excitatory input from SCFNs. It is most likely that additional inputs to OPNs compensate for the reduction in discharge of SCFNs during these periods.

Animals↗
PubMed1985

A new fixative for the preservation of actin filaments: fixation of pure actin filament pellets.

Conventional fixation for thin-section microscopy is insufficient to preserve many elements of cells and tissues. Actin filaments, for example, are destroyed during post-fixation in OsO4. In our search for a better fixative, we chose pellets of pure actin filaments as a very sensitive model system. In the present study, the potential of amines for improving aldehyde fixation was explored, and the results were compared to those obtained with the use of tannic acid. Aldehyde and amine were used together as an initial fixative, followed by aldehyde alone with postfixation in 1% OsO4 in buffer at 4 degrees C for 15 min, uranyl acetate en bloc stain, acetone dehydration, and embedding in Epox 812. Some primary monoamines improved the preservation of filaments; filaments were not broken beyond recognition by OsO4, as occurs when glutaraldehyde alone is used. Excellent preservation was seen when certain primary diamines were used. The quality of this fixation was superior to that obtained with tannic acid and was without the large increase in filament diameter that is seen with concentrations of tannic acid sufficient to protect filaments against osmium damage. The effects on filaments of the amines lysine, putrescine, ammonium, and arginine have been documented in detail, as we systematically varied all the major parameters normally considered in formulating fixation protocols.

Actins↗
PubMed1984

An ethanol-acetic acid-formol saline fixative for routine use with special application to the fixation of non-perfused rat lung.

An ethanol-acetic acid-formol saline fixative (40 : 5 : 10 : 45 v/v) has been developed which gives good results with non-perfused rat lung and which may be used routinely for the fixation of a wide range of rat tissues. The special qualities of the fixative include good penetration, good fixation of nuclei and mitotic chromosomes, and little shrinkage after paraffin embedding. The fixative is also easy to use and has a flexible fixation period (nominally 48 h). Although several fixative mixtures containing alcohol, acetic acid and formalin have previously been reported, none are identical to the present mixture, which was developed independently and systematically in accordance with specific listed requirements.

Acetates↗
PubMed1977

Comparison of immediate polyvinyl alcohol (PVA) fixation with delayed Schaudinn's fixation for the demonstration of protozoa in stool specimens.

Immediate fixation of stool specimens in polyvinyl alcohol fixative (PVA) was compared with Schaudinn's fixation delayed until the specimens were received in the laboratory, in a series of 100 consecutive positive stool specimens. More specimens were found positive following PVA fixation, and the numbers of organisms present on the slides were greater in specimens processed by this technique than after Schaudinn's fixation. It is concluded that immediate fixation results in the preservation of larger numbers of organisms in a recognizable state. The routine use of PVA fixation prior to transportation of the specimen to the laboratory is recommended.

Amebiasis↗
PubMed1999

External fixator for war purposes: the CMC fixator.

More than 75% of all injuries in modern wars are localized on the extremities, and more than one-third of these injuries are accompanied by bone fracture. Application of an external fixator is one of the basic procedures in the treatment of war fractures. In this article, we present an external fixator for war purposes of our own construction called the CMC (Croatian Medical Corps) fixator. Although designed as a transport fixator, because of good biomechanical properties it has been widely used for definitive osteosynthesis of war injuries. The CMC fixator is manufactured as a sterile set, ready to use, with all necessary parts for application. On the battlefields of Croatia and Bosnia and Herzegovina during the war from 1991 to 1995, more than 2,500 CMC fixators were applied. The fixator has satisfied all required conditions and considerably contributed to diminishing the consequences of war fractures.

Biomechanical Phenomena↗
PubMed2005

Comparison of fixation disparity curve parameters obtained with the Wesson and Saladin fixation disparity cards.

PURPOSE: This study compared fixation curve parameters with two commercially available fixation disparity cards, one that has been available for several years, the Wesson card, and a new one, the Saladin card. METHODS: Fixation disparity curves were measured on 50 subjects with the Wesson fixation disparity card and the Saladin fixation disparity card. RESULTS: The x intercepts were on average more in the base-in direction with the Wesson card than with the Saladin card. The y intercepts were shifted in the exo direction with the Wesson card compared with the Saladin card. The slope with the Wesson card was steeper than the slope obtained with the Saladin card. The distribution of curve types was also different with the two different instruments. CONCLUSION: Fixation disparity curves measured with these two instruments are different, and separate norms should be used for each fixation disparity measurement method.

Adult↗
PubMed1984

The influence of mode of fixation, type of fixative and vehicles on the same rat liver: a morphometric/stereologic study by light and electron microscopy.

The influence on cellular and subcellular structure was studied by comparing perfusion versus immersion fixation with cacodylate buffered glutaraldehyde, osmium or glutaraldehyde immersion fixation with two vehicles, phosphate and cacodylate buffer. The study was performed in the same animal using the left liver lobe for the four immersion fixation experiments and the remaining lobes for perfusion. The preparative steps were done under identical conditions in one operation. The mode of fixation was the most influential factor with clear (15%) increases for the volume of hepatocytes (mainly their cytoplasm), and the mitochondria (30%), when comparing immersion to perfusion fixation. This mitochondrial enlargement was particularly displayed in the organelles' average profile area, being more than doubled (211%) in immersion fixation. Similarly high profile enlargements (150%) were also found after osmium immersion fixation. Changes in nuclei were minor compared to the cytoplasm. There was a good correlation between the volume changes of the hepatocyte cytoplasm and the mitochondria (r = 0.85, p less than 0.01). Qualitative results revealed that there exists a zone of good electron microscopic preservation 2-3 cell layers beneath the block edge in immersion fixed material, whereas perfusion fixed tissue displays a homogeneous fine structure.

Animals↗
PubMed1994

Assessment of condylar position following bilateral sagittal split ramus osteotomy with wire fixation or rigid fixation.

In this study, 53 patients who underwent a bilateral sagittal split ramus osteotomy to advance the mandible were examined radiographically to assess condylar position presurgically, postsurgically, and posttreatment. Subjects were separated into two groups, 29 patients who received wire fixation and 24 who received rigid internal fixation. Condylar position changes were measured on tracings of submentovertex and transcranial radiographs at the time periods mentioned. Differences in condylar position were evaluated in two defined time intervals--T1, presurgical to postsurgical, and T2, postsurgical to posttreatment. Right and left sides were evaluated independently. No correlation between amount of advancement and condylar position change was identified within or between the fixation groups at T1 and T2. No correlation between change in mandibular plane angle and change in condylar position was identified within or between the groups at T1 and T2. Statistically significant differences were identified between the fixation groups in the degree of condylar change measured on the tracings of both submentovertex and transcranial radiographs both right and left sides, at time T1. There was also a significant difference in the change in mandibular plane angle at T1 between the fixation groups. It appears from this study that use of rigid internal fixation following bilateral sagittal split ramus osteotomy results in a statistically significantly greater condylar displacement than does wire fixation. Further research is required to determine whether these changes in condylar position are clinically significant.

Adult↗
PubMed1998

Fragment reconstruction and bone plate fixation versus bridging plate fixation for treating highly comminuted femoral fractures in dogs: 35 cases (1987-1997).

OBJECTIVE: To compare fragment reconstruction and bone plate fixation versus bridging plate fixation for treating highly comminuted (> 4 fragments) femoral fractures in dogs. DESIGN: Retrospective study. ANIMALS: 35 dogs with highly comminuted fractures of the femur. PROCEDURE: Medical records of all dogs included in this study were reviewed. Dogs had been treated with fragment reconstruction and bone plate application (n = 20) or major fragment alignment and bridging plate fixation (15). Postoperative and follow-up radiographs were evaluated. Operating and hospitalization times, bone alignment, bone healing, and complications were considered. RESULTS: There were no differences in hospitalization times, limb alignment, and complications between dogs with fractures treated with fragment reconstruction and dogs with fractures treated with bridging plate fixation. Dogs with fractures treated with bridging plate fixation had shorter operative times and faster times to radiographic evidence of bone healing. CLINICAL IMPLICATIONS: Bridging plate fixation is quicker to perform and results in faster healing than fragment reconstruction and bone plate fixation when used to treat comminuted femoral fractures.

Age Factors↗
PubMed2003

Analysis of initial fixation strength of press-fit fixation technique in anterior cruciate ligament reconstruction. A comparative study with titanium and bioabsorbable interference screw using porcine lower limb.

We performed a controlled laboratory study to evaluate the initial fixation strength of press-fit technique. Forty porcine lower limbs were used and divided into four groups according to the method of fixation; group 1 (press-fit+1.4 mm), in which the diameter difference between the bone plug and the femoral tunnel was 1.4 mm; group 2 (press-fit+1.4 mm, 30 degrees), in which the diameter difference was the same with group 1, but the tensile loading axis was 30 degrees away from the long axis of the femoral tunnel; group 3 (titanium), in which a titanium interference screw was used for fixation; group 4 (bioabsorbable), in which a bioabsorbable interference screw was used for fixation. The graft in the press-fit group was harvested with a hollow oscillating saw with inner diameter of 9.4 mm to obtain consistent and completely circular shape of the bone plug. The femoral tunnel with diameter of 8 mm was drilled at the original ACL insertion. Following the bone plug insertion into the femoral tunnel and applying a preload of 20 N, the specimen underwent 500 loading cycles between 0 and 2 mm of displacement. Thereafter the specimen was loaded to failure. There was no fixation site failure during the cyclic loading test. Significant differences in the stiffness, linear load, or failure mode among the groups were not found. The average ultimate failure load of group 1 and group 2 were not significantly different from those of group 3 and group 4. The press-fit groups demonstrated sufficient fixation strength for the rehabilitation and interference screw groups. The completely circular shape of the bone plug and increased diameter difference between the bone plug and the femoral tunnel seemed to contribute to the strong fixation.

Animals↗
PubMed2003

Tendon transfer fixation: comparing a tendon to tendon technique vs. bioabsorbable interference-fit screw fixation.

Tendon transfer techniques in the foot and ankle are used for tendon ruptures, deformities, and instabilities. This fresh cadaver study compares the tendon fixation strength in 10 paired specimens by performing a tendon to tendon fixation technique or using 7 x 20-25 mm bioabsorbable interference-fit screw tendon fixation technique. Load at failure of the tendon to tendon fixation method averaged 279N (Standard Deviation 81N) and the bioabsorbable screw 148N (Standard Deviation 72N) [p = 0.0008]. Bioabsorbable interference-fit screws in these specimens show decreased fixation strength relative to the traditional fixation technique. However, the mean bioabsorbable screw fixation strength of 148N provides physiologic strength at the tendon-bone interface.

Absorbable Implants↗
PubMed2005

Cemented tibial component fixation performs better than cementless fixation: a randomized radiostereometric study comparing porous-coated, hydroxyapatite-coated and cemented tibial components over 5 years.

BACKGROUND: The question whether the tibial component of a total knee arthroplasty should be fixed to bone with or without bone cement has not yet been definitely answered. We studied movements between the tibial component and bone by radiostereometry (RSA) in total knee replacement (TKR) for 3 different types of fixation: cemented fixation (C-F), uncemented porous fixation (UC-F) and uncemented porous hydroxyapatite fixation (UCHA-F). PATIENTS: 116 patients with osteoarthrosis, who had 146 TKRs, were included in 2 randomized series. The first series included 86 unilateral TKRs stratified into 1 of the 3 types of fixation. The second series included 30 patients who had simultaneous bilateral TKR surgery, and who were stratified into 3 subgroups of pairwise comparisons of the 3 types of fixation. RESULTS: After 5 years 2 knees had been revised, neither of which were due to loosening. 1 UCHA-F knee in the unilateral series showed a large and continuous migration and a poor clinical result, and is a pending failure. The C-F knees rotated and migrated less than UC-F and UCHA-F knees over 5 years. UCHA-F migrated less than UC-F after 1 year. INTERPRETATION: Cementing of the tibial component offers more stable bone-implant contact for 5 years compared to uncemented fixation. When using uncemented components, however, there is evidence that augmenting a porous surface with hydroxyapatite may mean less motion between implant and bone after the initial postoperative year.

Aged↗
PubMed1993

A preliminary study of the fixation mechanism of collagen reaction with a polyepoxy fixative.

A new biomaterial has been developed by fixing native collagens with a polyepoxy compound (PC) fixative. Prior studies have shown that this biomaterial has comparable properties as compared to collagen fixed with glutaraldehyde (GA) and thus has a great promise for use as an implantable bioprosthesis. The purpose of this study was to understand the mechanism of the amino acids-PC reactions in the fixation process. Bovine arteries were fixed with PC under various pH, concentration and temperature conditions as a function of fixation time. Individual amino acid components in the fresh and the fixed arteries were assayed using a Beckman amino acid analyzer to determine the degree of tanning. The denaturation temperature (Td) was also measured on each sample. Since the denaturation temperature is a direct indication of cross-linking of individual amino acids with the fixative, the difference in the degree of tanning for the same increase in Td may be indicative of the quantity of the masked, non-cross-linked amino acids. The fixation reaction data indicated that not all amino acids were cross-linked upon contacting the PC fixative. Masking appeared to be more substantial with a fixation at higher pH values.

Amino Acids↗
PubMed1995

Fixation of whole eyes: the role of fixative osmolarity in the production of tissue artifact.

BACKGROUND: Whole eyes fixed in 4% buffered formaldehyde (10% neutral buffered formalin) demonstrate a variety of artifacts, including separation of the neurosensory retina from the retinal pigment epithelium. We postulate that the osmolarity of 4% buffered formaldehyde causes contraction of the internal compartments of the eye leading to several artifactual changes commonly observed in routine histologic sections. METHODS: In part I of the study, enucleated animal eyes were examined histologically after immersion in different concentrations of formaldehyde. The variables of fixation and processing were kept constant except for the concentration and osmolarity of formaldehyde. In part II, enucleated animal eyes were used to empirically determine the optimal mixture of formaldehyde and glutaraldehyde for fixation based on subjective assessment of histologic sections. RESULTS: In the first part of the study, the post-fixed volume of the anterior chamber and vitreous increased as the concentration (and osmolarity) of formaldehyde decreased. In part II of the study, fixation of whole eyes was optimal with a mixture of 1% buffered formaldehyde and 1.25% glutaraldehyde. The neurosensory retina was less likely to detach from the retinal pigment epithelium, and the anterior chamber retained a more normal shape with this fixative. CONCLUSIONS: Volume contraction of whole eyes fixed in 4% buffered formaldehyde is caused by the relatively high osmolarity of the fixative. Immersion fixation of whole eyes for 36 h (or longer) in 1% buffered formaldehyde/1.25% glutaraldehyde reduces tissue distortion without compromising cellular preservation.

Animals↗
PubMed1995

The importance of tissue fixation for light microscopic immunohistochemical localization of peroxisomal proteins: the superiority of Carnoy's fixative over Baker's formalin and Bouin's solution.

We have compared the effects of fixation with three commonly used fixatives upon preservation of the antigenicity of six peroxisomal proteins in rat liver using both immunohistochemical staining and Western blotting of fixed tissue extracts. The immunoreactivity of all six peroxisomal proteins was well preserved and peroxisomes were clearly identified in material fixed in Carnoy's fixative. Moreover, the corresponding proteins stained well in Western blots prepared from extracts of Carnoy-fixed material. The intensity of the immunohistochemical staining was reduced at different rates for individual peroxisomal proteins after fixation in Baker's formalin, but peroxisomes were still well visualized with antibodies to catalase and some beta-oxidation enzymes. No evidence of immunohistochemical staining for any peroxisomal antigens was obtained after fixation in Bouin's fluid. For detection of the antibody binding sites in Carnoy's fixed material, the avidin-biotin-peroxidase complex (ABC) with aminoethyl carbazole as chromogen was found to be superior to the methods of peroxidase-antiperoxidase/diaminobenzidine and protein A-gold with silver intensification. Using Carnoy-fixative and the ABC-method, we demonstrate light microscopic immunohistochemical localization of peroxisomal antigens in several rat tissues as well as in human post-mortem liver.

Acetates↗