Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Fixatives”

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 559 records · Page 31Linked to original sources
PubMed1999

Kinetic and static fixation methods in automated threshold perimetry.

PURPOSE: Static fixation is the standard method for stabilizing the eye during automated perimetry. Kinetic fixation is an alternative for fixation control in which the eye follows a moving target. This study was conducted to evaluate the fixation accuracy of static and kinetic fixation perimetry and to determine their ability to detect the absolute scotoma of the physiologic blind spot. METHODS: The 71 patients with early glaucomatous field loss (mean age 65 years) and 45 control subjects (mean age 57 years) recruited from five clinical sites underwent threshold testing on the Dicon perimeter (kinetic fixation; Vismed, San Diego, CA) and Humphrey Field Analyzer (static fixation). The frequency of Heijl-Krakau fixation catch-trial errors was used as an indicator of fixation accuracy, and the measured sensitivity at the physiologic blind spot was used as an indicator of perimetric accuracy. RESULTS: In patients with glaucoma, the frequency of fixation errors was significantly greater for kinetic fixation (17.2%) than for static fixation (10.2%). In the control group, the frequency of fixation errors also was significantly greater for kinetic fixation (27.5%) than for static fixation (12.6%). The threshold at the presumed location of the blind spot (15 degrees temporal, 3 degrees inferior from fixation) was 14.8 dB using kinetic fixation versus 4.0 dB with static fixation in patients with glaucoma, and 18.5 dB using kinetic fixation versus 2.5 dB using static fixation in the control group. CONCLUSION: Relative to static fixation, kinetic fixation was associated with fixation inaccuracy and underestimation of the absolute scotoma at the physiologic blind spot.

Adult↗
PubMed1990

[Stability of screw fixation following sagittal splitting osteotomy of the mandibular ramus].

Recently, sagittal splitting osteotomy of the mandibular ramus is frequently performed in orthognathic surgeries of mandibular deformities. Although the surgical technique has been established. Methods for osteosynthesis following sagittal spitting of mandibular ramus still remain unestablished. Osteosynthesis is usually achieved by circumferencial wiring, interosseous wiring or screw fixation. It is unknown which of these three methods is best suited from dynamic and clinical point of view. The author carried out a simulation study of screw fixation using acrylic resin plate models and sagittally split air-dried human mandibles. The following result were obtained: 1) In the fixation experiment using an acrylic resin plate and AO cortical bone screws, a significantly smaller displacement was recorded by S3E type fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, S3D type fixation required a significantly larger stress, compared with other modes of fixation. 2) In the destruction experiment using an acrylic resin plate and AO cortical bone screws, the critical displacement measured was significantly smaller by S3E type fixation compared with other modes of fixation S3C type fixation required a significantly larger amount of stress to cause destruction. 3) In the fixation experiment using the air-dried human mandibles and alumina ceramic screws, a significantly smaller displacement was recorded by 2-alumina ceramic screw fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, 3-alumina ceramic screw fixation required a larger stress, compared with other modes of fixation. 4) In the fixation experiment using the air-dried human mandible and AO cortical bone screws, a significantly smaller displacement was recorded by 2-AO cortical bone screw fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, 3-AO cortical bone screw fixation required a larger stress, compared with the 2-AO type of fixation. The above experimental results suggest that when the sagittally split proximal cortical plate retains enough thickness for tapping, clinical application of screw fixation either with alumina ceramic or AO cortical bone screws produces an adequately high anti-displacement effect, even if only 2 screws are used. However, when stability is evaluated in terms of the resistance to stress, 3-screw fixation is considered to amply satisfy the resistance required.

Acrylic Resins↗
PubMed2001

A biomechanical comparison of modern anterior and posterior plate fixation of the cervical spine.

STUDY DESIGN: A biomechanical study was designed to assess relative rigidity provided by anterior, posterior, or combined cervical fixation using cadaveric cervical spine models for flexion-distraction injury and burst fracture. OBJECTIVES: To compare the construct stability provided by anterior plating with locked fixation screws, posterior plating with lateral mass screws, and combined anterior-posterior fixation in clinically simulated 3-column injury or corpectomy models. SUMMARY OF BACKGROUND DATA: Anterior plating with locked fixation screws is the most recent design and is found to provide better stability than the conventional unlocked anterior plating. However, there are few data on the direct comparison of biomechanical stability provided by anterior plating with locked fixation screws versus posterior plating with lateral mass screws. Biomechanical advantages of using combined anterior-posterior fixation compared with that of using either anterior or posterior fixation alone also have not been well investigated yet. METHODS: Biomechanical flexibility tests were performed using cervical spines (C2-T1) obtained from 10 fresh human cadavers. In group I (5 specimens), one-level, 3-column injury was created at C4-C5 by removing the ligamentum flavum and bilateral facet capsules, the posterior longitudinal ligament, and the posterior half of the intervertebral disc. In group II (5 specimens), complete corpectomy of C5 was performed to simulate burst injury. In each specimen, the intact spine underwent flexibility tests, and the following constructs were tested: (1) posterior lateral mass screw fixation (Axis plate) after injury; (2) polymethylmethacrylate anterior fusion block plus posterior fixation; (3) polymethylmethacrylate block plus anterior (Orion plate) and posterior plate fixation; and (4) polymethylmethacrylate block plus anterior fixation. Rotational angles of the C4-C5 (or C4-C6) segment were measured and normalized by the corresponding angles of the intact specimen to study the overall stabilizing effects. RESULTS: Posterior plating with an interbody graft showed effective stabilization of the unstable cervical segments in all loading modes in all cases. There was no significant stability improvement by the use of combined fixation compared with the posterior fixation with interbody grafting, although combined anterior-posterior fixation tended to provide greater stability than both anterior and posterior fixation alone. Anterior fixation alone was found to fail in stabilizing the cervical spine, particularly in the flexion-distraction injury model in which no contribution of posterior ligaments is available. Anterior plating fixation provided much greater fixation in the corpectomy model than in the flexion-distraction injury model. This finding suggests that preservation of the posterior ligaments may be an important factor in anterior plating fixation. CONCLUSIONS: This study showed that the posterior plating with interbody grafting is biomechanically superior to anterior plating with locked fixation screws for stabilizing the one-level flexion-distraction injury or burst injury. More rigid postoperative external orthoses should be considered if the anterior plating is used alone for the treatment of unstable cervical injuries. It was also found that combined anterior and posterior fixation may not improve the stability significantly as compared with posterior grafting with lateral mass screws and interbody grafting.

Aged↗
PubMed1999

[Replacement of the anterior cruciate ligament. Biomechanical studies for patellar and semitendinosus tendon fixation with a poly(D,L-lactide) interference screw].

Anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendons are being performed more frequently and satisfactory results have been reported. Advantages such as low donor site morbidity and ease of harvest as well as disadvantages like low initial construct stiffness have been described. Recently, it has been demonstrated that graft fixation close to the original ACL insertion sites increases anterior knee stability and graft isometry. Hamstring tendon fixation techniques using interference screws offer this possibility. To reduce the risk of graft laceration, a round threaded titanium interference screw (RCI) was developed. To improve initial fixation strength, fixation techniques for hamstring tendons with separate or attached tibial bone plugs were introduced. However, data on fixation strength do not yet exist. With respect to the proposed advantages of biodegradable implants, like undistorted magnetic resonance imaging, uncompromised revision surgery and a decreased potential of graft laceration during screw insertion, we performed pullout tests of round threaded biodegradable and round threaded titanium interference screw fixation of semitendinosus (ST) grafts with and without distally attached tibial bone plugs. Data were compared with bone-tendon-bone (BTB) graft fixation using biodegradable and conventional titanium interference screws. We used 56 proximal calf tibiae to compare maximum pullout force, screw insertion torque, and stiffness of fixation for biodegradable direct ST tendon and bone plug fixation (group I: without bone plug, group II: with bone plug) versus titanium interference screw fixation (group III: without bone plug, group IV: with bone plug). A round threaded biodegradable poly-(D, L-lactide) (Sysorb) and a round threaded titanium interference screw (RCI) were used. As a control calf bone-tendon-bone (BTB) grafts fixed with either poly-(D, L-lactide) (group V) or conventional titanium (group VI) interference screws were used. ST tendons were harvested either with or without their distally attached tibial bone plugs from human cadavers and were folded to a three-stranded graft. Specimen were loaded in a material testing machine with the applied load parallel to the long axis of the bone tunnel. Maximum pullout force of ST bone plug (group III: 717 N +/- 90, group IV: 602 N +/- 117) fixation was significantly higher than that of direct tendon (group I: 507 N +/- 93, group III: 419 N +/- 77) fixation. Maximum pullout force of biodegradable screw ST fixation was higher than that of titanium screw fixation in both settings. There was no significant difference in pullout force between biodegradable (713 N +/- 210) and titanium (822 N +/- 130) BTB graft fixation or between ST fixation with bone plug and biodegradable screw with BTB fixation. Pullout force of hamstring tendon interference screw fixation can be improved by using a biodegradable implant. In addition, initial pullout force can be greatly improved by harvesting the hamstring tendon graft with its distally attached tibial bone plug. This may be important, especially in improving tibial graft fixation. This study encourages further research in tendon-bone healing with direct interference screw fixation to confirm the potential of this advanced method.

Anterior Cruciate Ligament↗
PubMed2006

The importance of iliac fixation in prevention of stent graft migration.

OBJECTIVE: Secure proximal fixation of endografts to the infrarenal aortic neck is known to be important in the short- and long-term success of endovascular aneurysm repair. We sought to determine the relative importance of distal iliac fixation in preventing endograft migration and adverse clinical events after endovascular aneurysm repair. METHODS: We reviewed the outcome of 173 patients treated from 1996 to 2003 at Stanford University Medical Center with an externally supported stent graft. Quantitative image analysis of the postimplantation computed tomography scan was performed to determine the proximal aortic and distal iliac fixation lengths and the proximity the distal end of the stent graft to the iliac bifurcation. Subsequent follow-up computed tomography scans were reviewed for evidence of stent graft migration. Patients were grouped according to good (>15 mm), intermediate, or bad (<10 mm) aortic fixation and good (iliac fixation length > or =25 mm and iliac limbs <10 mm from iliac bifurcation), intermediate, or bad (<25-mm fixation length) iliac fixation. RESULTS: Stent graft migration of 10 mm or more was seen in 17 patients (10%) during the 23 +/- 19-month follow-up period. Patients with no migration had a greater iliac fixation length (30 +/- 12 mm) than those with migration (22 +/- 8 mm; P = .01), and the distal ends of the iliac limbs were closer to the iliac bifurcation (15 +/- 12 mm) than in patients with migration (25 +/- 10 mm; P < .001). Patients with no migration also had a greater proximal aortic fixation length (23 +/- 12 mm) than migration patients (13 +/- 7 mm; P = .001). There were no migrations among patients with good iliac fixation whether aortic fixation was good, intermediate, or bad (0/63; 0%). Among patients with bad/intermediate iliac and good aortic fixation, there were 5 (9%) of 58 patients had migrations. Patients with both bad/intermediate iliac and bad/intermediate aortic fixation had the highest migration rate (12/52; 23%). Cox proportional hazards regression modeling revealed that the significant factors predicting migration were poor proximity of the distal end of the iliac limbs to the iliac bifurcation (odds ratio 17.2; P = .01) and aortic fixation length (odds ratio 2.0; p = 0.007 for each centimeter). Iliac extender modules were placed in 9 patients with bad iliac fixation and migration, with no further migration during a mean follow-up of 12 months. Patients with good iliac and aortic fixation and no endoleak on the initial postprocedure computed tomography scan (n = 43) had no migrations, secondary procedures, or adverse clinical events over a 2-year follow-up period. CONCLUSIONS: Iliac fixation, along with proximal aortic fixation, is an important factor in preventing the migration of stent grafts that have longitudinal columnar support. Patients with good iliac fixation did not experience migration even in the presence of suboptimal proximal aortic fixation. Close proximity of the distal end of the stent graft to the iliac bifurcation seems to provide stability against migration.

Aged↗
PubMed2002

Biomechanical comparison of lumbosacral fixation techniques in a calf spine model.

STUDY DESIGN: biomechanical testing of the strength and stability of lumbosacral fixation constructs. OBJECTIVES: The purpose of this study was to quantify and compare the biomechanical properties of five different lumbosacral fixation constructs and determine the benefit of adding supplementary fixation to S1 screws. SUMMARY OF BACKGROUND DATA: Extension of long fusions to the sacrum remains a difficult clinical challenge. Only a limited number of biomechanical studies have evaluated the different fixation methods available, and none has included both nondestructive and load to failure testing of these fixation methods. METHODS: Six fresh-frozen calf spines were prepared and tested for each construct. The five constructs tested included the following: S1 screws alone, S1 screws and S2 proximally directed screws, S1 screws and S2 distally directed screws, S1 screws and intrasacral rods, and S1 screws and iliac screws. Nondestructive, multidirectional flexibility analyses included four loading methods followed by a destructive flexural load to failure. Lumbosacral peak range of motion (millimeters or degrees) and ultimate failure load (Nm) of the five reconstruction techniques were statistically compared using a one-way analysis of variance combined with a Student-Newman-Keuls post hoc test. RESULTS: S1 screw strain tested in flexion-extension was significantly reduced by the addition of any second point of distal fixation. There was no significant difference between any of the different sacral fixation constructs (P > 0.05). In axial compression, only the addition of iliac screws significantly reduced S1 screw strain. In destructive testing under flexion loading, only iliac screws statistically increased the load at failure (P = 0.005). CONCLUSION: This study demonstrates the effectiveness of adding a second fixation point distal to the S1 screws in reducing S1 screw strain. Iliac fixation is more effective than secondary sacral fixation points but may not be necessary in all clinical situations. Only iliac fixation effectively increased the load to failure under catastrophic loading conditions. Supplementary sacral fixation failed to significantly protect against catastrophic failure. These findings support the clinical observation that iliac fixation is least likely to fail in high-risk, long fusions. Whether testing range of motion, screw strain, or load to failure, no benefit could be demonstrated for intrasacral rod placement when compared with other supplementary sacral fixation techniques. Intrasacral rod placement was equal to a second sacral screw in reducing S1 screw strain during flexion-extension loading. It was not as effective as iliac fixation in reducing screw strain or preventing catastrophic failure. When choosing fixation methods in long fusions to the sacrum, this study supports the use of iliac fixation as the method least likely to loosen or pull out. A second point of sacral fixation also offers biomechanical advantages when compared with S1 fixation alone and may be an appropriate choice in less "high risk" fusions to the sacrum.

Animals↗
PubMed2006

Effects of unsteady fixation on multifocal electroretinogram (mfERG).

PURPOSE: To investigate the effect of unsteady fixation on the multifocal electroretinogram (mfERG) measurement in normal subjects. METHODS: The mfERGs of 20 subjects with normal vision (mean age=23.5 years) were recorded with different levels of voluntary eye movements made to mimic unsteady fixation. Subjects were required to move their fixation regularly every 2 s between the center and the ends of a fixation cross, so that 51.2% of the time fixation was at the center and 12.2% of the time it was at each end of the fixation cross. Four different conditions were performed: central fixation (without voluntary eye movements) and with 2 degrees, 4 degrees and 6 degrees magnitude of unsteady fixation. First-order kernel mfERG findings are presented. RESULTS: Analysis of the ring responses indicated that the central mfERG amplitude was most affected by unsteady fixation. There was significantly reduced amplitude for 4 degrees unsteady fixation and as expected, this reduction became larger with 6 degrees unstable fixation. However, there was no significant effect on the center hexagon amplitude for 2 degrees unsteady fixation. The amplitudes of the ring-2 responses were only affected in the 6 degrees unsteady fixation condition. No significant change in implicit time was found for any level of unsteady fixation. CONCLUSION: These results suggest that mfERG amplitude is not substantially affected if fixation is maintained within the central stimulus hexagon. We conclude that, for patients with poor fixation, the accuracy of mfERG results may be difficult to interpret and the use of a fixation-monitoring system is desirable for ideal measurement. The depth of depression at the blind spot area may be another useful parameter to interpret the accuracy of mfERG results in patients with poor fixation.

Adult↗
PubMed2003

Stiffness characteristics and inter-fragmentary displacements with different hybrid external fixators.

OBJECTIVES: To determine how the different approaches of constructing a hybrid external skeletal fixator affect the mechanical environment at the fracture site. DESIGN: A comparative biomechanical analysis of external fixators that represent a spectrum of designs from unilateral to circular fixators. BACKGROUND: The most pertinent parameter that affects fracture healing is the inter-fragmentary displacement. Most studies on the mechanical performance of external fixators have concentrated on the overall stiffness of the fixators. METHODS: Mechanical testing was performed on four types of hybrid fixators in which the overall stiffness of the fixator as well as the axial, transverse shear and angular displacements at the fracture site were measured. RESULTS: The Ilizarov hybrid fixator with one wire and one screw on each ring behaved more like a unilateral fixator than a circular fixator. The bar-ring hybrid fixator that simply connected a unilateral fixator body to a wire/ring assembly was too flexible. Reinforcing the bar-ring hybrid system with diagonally placed struts eliminated the deformation associated with the unilateral body and the resulting construct performed considerably better. The two-ring hybrid fixator most closely resembled the Ilizarov fixator. CONCLUSIONS: Depending on the construction characteristics hybrid fixators possess a spectrum of mechanical characteristics of both unilateral and circular fixators. The constructions using two rings in which at least one bone segment is supported entirely by wires appears to have the best mechanical characteristics. RELEVANCE: Understanding how the different approaches of constructing a hybrid fixator affect the mechanical environment at the fracture site will enable surgeons to chose or build the most appropriate fixator for each clinical situation.

Bone Screws↗