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PubMed2004

The effect of fixation instability on the multifocal VEP.

In multifocal visually evoked potentials (mfVEP), we find reversals in waveform near the horizontal meridian due to convolutions in the cortex. This renders the mfVEP very sensitive to small changes in gaze position. In this study we tested the effects of very small amounts of fixation instability on the mfVEP topography under controlled conditions using four normal subjects. In order to simulate unstable fixation, subjects were instructed to move their fixation point systematically in a clockwise direction between the endpoints of a fixation cross every few seconds (two degree diameter cross = one degree fixation error). Results were compared against a control condition with stable, central fixation. The effects of 0.5 degrees fixation error are small, but 1.0 degrees fixation error can produce a large decrease in root mean square signal amplitude (e.g., 60%) in the central foveal region (i.e., within 1.4 degrees eccentricity). The size of the effect drops off rapidly with eccentricity and varies greatly between areas within a subject, and between the four subjects. Beyond 3.0 degrees eccentricity the effects are minimal. Unstable fixation with relatively small fixation errors caused a dramatic decrease in mfVEP amplitude within three degrees of eccentricity, which can be misinterpreted as loss of macular function. Fixation monitoring is essential to obtain accurate results in the macular area when recording mfVEPs.

Electroretinography↗
PubMed1988

Stability of simultaneous maxillary intrusion and mandibular advancement: a comparison of rigid and nonrigid fixation techniques.

This study examines the short-term stability of bimaxillary surgery following Le Fort I impaction with simultaneous bilateral sagittal split osteotomies and mandibular advancement using two standard techniques of postsurgical fixation. Fifteen adults had skeletal plus dental maxillomandibular fixation, and fifteen adults had rigid internal fixation using bone plates in the maxilla and bicortical bone screws between the proximal and distal segments in the mandible. The group with rigid internal fixation did not undergo maxillomandibular fixation. Radiographic cephalograms were analyzed during the postsurgical period to evaluate skeletal and dental stability. There was no statistical difference in postsurgical stability with rigid internal fixation or skeletal plus dental maxillomandibular fixation other than the vertical position of the maxillary molar; the skeletal plus dental maxillomandibular fixation group had a significant amount of postsurgical intrusion of the maxillary molar when compared with the rigid internal fixation group. Although the other measures showed no statistically significant difference between the experimental groups, the amount of variability in postsurgical stability in the group with skeletal plus dental maxillomandibular fixation was greater than that found in the group with rigid internal fixation.

Bone Plates↗
PubMed2004

Identification of fixation location with retinal photography in macular degeneration.

BACKGROUND: Identification of fixation location is an integral part of low vision assessment and subsequent rehabilitation. We performed a study to determine whether retinal photography is able to identify fixation location in eyes with age-related macular degeneration (AMD). METHODS: In a prospective, observational case series, consecutive patients with AMD attending a low-vision clinic underwent monocular fixation attempts at a fixation target of a standard ophthalmic fundus camera. Inclusion criteria included AMD with documented macular disease, low vision in both eyes and best-corrected visual acuity of 20/50 to 20/200 in the tested eye. Retinal photography was used to document retinal location of attempted fixation. Macular perimetry was used to confirm acceptable fixation maintenance behaviour. Outcome measures included acceptable fixation maintenance during retinal photography and retinal location of fixation pattern. RESULTS: Twenty-one patients (14 women and 7 men with an average age of 78 [range 53 to 86] years) met the inclusion criteria. In nine cases both eyes met the study criteria, for a total of 30 eyes. Of the 30 eyes, 24 (80%) had acceptable fixation maintenance with retinal photography (p = 0.939). In 17 (71%) of the 24 eyes the retinal fixation location was superior to the macular scar. INTERPRETATION: The results suggest that retinal photography may provide a reliable method to identify retinal location of fixation in eyes with AMD.

Aged↗
PubMed1997

Evaluation of a simple and low-cost external fixator.

Simple external fixation is becoming ever more popular for the treatment of fractures. Current commercially available external fixation devices are complex and expensive, affecting management of injuries in less developed countries. In this study, a new simple and low-cost external fixator called the AG (Alinoor-Goh) fixator, is evaluated biomechanically by direct comparison with a commercially available fixator device (AO). Four modes of loading were applied to each of the fixators: axial compression, anterior-posterior bending, medial-lateral bending, and torsion. The loads were applied directly onto a fractured-bone model made of perspex, which was immobilized by the fixator through six Schanz pins. From this, stiffness values were obtained by plotting load versus displacement. The results from the mechanical testing indicated that in axial compression the AG fixator stiffness was 55.7 +/- 0.197 N/mm (AO fixator was 57.7 +/- 0.186 N/mm); for anterior-posterior bending it was 56.8 +/- 0.153 N/mm (57.4 +/- 0.134 N/mm); for medial-lateral bending it was 11.4 +/- 0.036 N/mm (11.6 +/- 0.053 N/mm); and for torsion it was 1.16 +/- 0.002 N.mm/degree (1.16+/- 0.003 N.mm/degree). No significant difference was found in the stiffness of AG and AO fixators, under all modes of loading. A further comparison in terms of overall design, versatility in application and cost shows the AG fixator to be a viable, inexpensive option for the treatment of long-bone fractures.

Costs and Cost Analysis↗
PubMed2000

Influences of fixatives on flow cytometric measurements of platelet P-selectin expression and fibrinogen binding.

Sample fixation is an important issue in flow cytometric platelet assays. However, previous reports were less than consistent regarding the influence of sample fixation on the assays. We evaluated the effects of formaldehyde and paraformaldehyde fixation on platelet P-selectin expression and fibrinogen binding using whole-blood flow cytometry and a Coulter EPICS XL-MCL cytometer. Fluorescent-labeled whole-blood samples were diluted with HEPES-buffered saline or fixed with formaldehyde (0.2, 0.5, and 1. 0%) or paraformaldehyde (0.5, 1.0, and 2.0%). Platelet P-selectin expression was 1.1+/-0.3% and 39.6+/-13.7% in unfixed resting and 10(-5) M ADP stimulated samples, respectively. Resting P-selectin expression was not significantly altered by 0.2 or 0.5% formaldehyde fixation, but was slightly decreased by 1.0% formaldehyde fixation or PFA fixation. Formaldehyde fixation caused small increases of P-selectin expression in ADP-stimulated samples. Compared to platelet fibrinogen binding of unfixed resting (4.5+/-2.1%) and ADP-stimulated (56.7+/-22.6%) samples, formaldehyde or paraformaldehyde fixation had no significant influence on resting samples, but mildly increased fibrinogen binding in stimulated samples. Unfixed samples were stable for 2 h. Fixed samples were generally stable for at least 6 h, but not thereafter. Thus, formaldehyde and paraformaldehyde have mild but complex influences on platelet P-selectin expression and fibrinogen binding measurements. To evaluate the stabilities of unfixed and fixed samples, samples were analyzed after different durations (0, 1, 2, 4, 6, 12, and 24 h) of storage at 4 degrees C in the dark. The results suggest that sample manipulation without fixation may be used when the samples are analyzed within 2 h, and that fixation with 0.5-1.0% formaldehyde or paraformaldehyde seems to be preferable when sample analysis is delayed. Effects of fixation should be carefully evaluated when establishing flow cytometric platelet assays in every laboratory.

Adenosine Diphosphate↗
PubMed2001

Detection of improper fixation in MTI photoscreening images.

PURPOSE: To determine the effect of fixation shift on photoscreening crescents, the ability of human interpreters to detect fixation shift, and the potential improvement by image processing. METHODS: MTI photoscreening (Medical Technologies & Innovations, Inc, Lancaster, PA) images, measured at 11 positions of gaze, were obtained from 10 subjects (9 with refractive error warranting spectacle correction). Photographs were taken with subjects fixating at 20, 15, 10, and 5 cm to the left and the right of the camera fixation target (1 m distant); 5 cm above and below the camera fixation target; and on-axis. Photographs were inspected by 11 experienced raters, who indicated if the subject appeared to be looking directly at the camera. The photographs were digitized, enlarged, contrast enhanced, and measured by 3 raters. For each photograph, distance from the corneal light reflex to the nasal limbus was measured and a measure of asymmetry computed. RESULTS: Raters could reliably detect off-axis fixation greater than 10 cm away from the intended fixation target. Raters correctly identified on-axis subject viewing 73% of the time. Crescents became larger when the fixation shifted off-axis for both the myopic and hyperopic subjects. Image analysis correctly classified 10 of 10 on-axis measurements and 34 of 39 off-axis measurements. CONCLUSION: Direct inspection of photoscreening images by trained raters can result in the failure to detect small but relevant errors of fixation. These fixation shifts can cause crescents to become larger than expected, resulting in false-positive classification. Image analysis offers a potential improvement in the detection of off-axis fixation in MTI photoscreening images.

Adult↗
PubMed1999

Comparative biomechanics of hybrid external fixation.

OBJECTIVE: To compare the elastic stiffness, in several loading modes, of commercially available hybrid external fixation systems. DESIGN: Laboratory investigation using a polyvinylchloride pipe periarticular tibia fracture model. SETTING: Simulated periarticular fractures were created in an in vitro tibia fracture model. Instrumented specimens and intact controls were elastically tested in a biomaterials testing system. INTERVENTION: Groups of simulated periarticular tibia fractures were stabilized with one of six different hybrid external fixator designs. MAIN OUTCOME MEASUREMENTS: Elastic stiffness of each specimen was measured in compression, torsion, flexion bending, extension bending, and varus/valgus bending. RESULTS: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. Specifically, the EBI Ring Connector fixator was stiffer than all others in all modes of testing. The Ace, Synthes, Smith & Nephew Richards, and How medica fixators were mechanically similar. The Zimmer Torus fixator was the least stiff fixator tested. CONCLUSIONS: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. The choice of which hybrid external fixator to use should be made based not only on stiffness but also on ease of clinical application, patient comfort, customer support from the manufacturer, and cost. Clinical investigation of the efficacy of each of these devices is warranted.

Analysis of Variance↗
PubMed2003

Vertically unstable pelvic fractures fixed with percutaneous iliosacral screws: does posterior injury pattern predict fixation failure?

OBJECTIVE: To measure the failure rate of percutaneous iliosacral screw fixation of vertically unstable pelvic fractures and particularly to test the hypothesis that fixations in which the posterior injury is a vertical fracture of the sacrum are more likely to fail than fixations with dislocations or fracture-dislocations of the sacroiliac joint. DESIGN: Retrospective review. SETTING: Level 1 trauma center. METHODS: All patients with pelvic fractures admitted between January 1, 1993, and December 31, 1998, were identified from the trauma registry. Hospital records were used to identify patients treated with iliosacral screws. Radiologic studies were examined to identify patients who had unequivocally vertically unstable pelvic fractures. Immediate postoperative and follow-up anteroposterior, inlet, and outlet radiographs from a minimum of 12 months postinjury were examined. Position, length, and numbers of iliosacral screws and any evidence of screw failure (eg, bending or breakage) were recorded. Residual postoperative displacement and late displacement of the posterior pelvis were measured. The main outcome measure was failure, defined as at least 1cm of combined vertical displacement of the posterior pelvis compared with immediate postoperative position. The main analysis was for association between fracture pattern and failure. Patient demographic data, iliosacral screw position, and anterior pelvic fixation method also were studied. RESULTS: The study group comprised 62 patients with unequivocally vertically unstable pelvic fractures in whom the posterior injury was treated with closed reduction and percutaneous iliosacral screw fixation. Of patients, 32 had dislocations or fracture-dislocations of the sacroiliac joint, and 30 had vertical fractures of the sacrum. Fixation failed in four patients, all with vertical sacral fractures and all within the first 3 weeks after surgery. These four patients required revision fixation. In two further cases with vertical sacral fractures, there was evidence that the fracture had only barely been held by the fixation, but these fractures healed, and follow-up radiographs did not meet the displacement criteria for failure. A vertical sacral fracture pattern was associated significantly with failure (Fisher exact test, P = 0.04); the excess risk of failure compared with sacroiliac joint injury was 13% (95% confidence interval 1% to 25%). There was no significant association between failure and anterior fixation method, iliosacral screw arrangement or length, or any demographic or injury variable. CONCLUSIONS: Percutaneous iliosacral screw fixation is a useful technique in the management of vertically unstable pelvic fractures, but a vertical sacral fracture should make the surgeon more wary of fixation failure and loss of reduction.

Adolescent↗
PubMed1991

Impact of the use of absorbable fracture fixation implants on consumption of hospital resources and economic costs.

Within a 6-year period (1984-1989) absorbable pins, rods, and screws made of polyglycolide, polylactide, or lactide-glycolide copolymer were used in the internal fixation of 881 fractures, 73.1% of which were displaced malleolar fractures of the ankle. During the last 3 years the patients treated using absorbable fracture fixation constituted 19.6% of all fracture patients managed by internal fixation at the department. The number of hardware removal procedures avoided during the 6-year period as a result of the use of the absorbable implants was estimated at approximately 700. By determining all direct and indirect costs associated with internal fracture fixation and the influence of the percentage of hardware removal, a cost coefficient was calculated for certain fracture types when treated using absorbable versus metallic internal fixation. In bimalleolar fractures, an optimal indication for absorbable fixation, the coefficient was 1.04 (cost of absorbable fixation 4% higher than that of metallic fixation) if the removal percentage with metallic fixation was zero and 0.91 (cost of absorbable fixation 9% lower than that of metallic fixation) if the removal percentage was 100%. The breakeven point was a removal rate of 31%.

Absorption↗
PubMed1998

Reuse of external skeletal fixator components: effects on costs and complications.

BACKGROUND: Although many community hospitals and trauma centers reuse external fixator components, no published studies have examined the cost-effectiveness or the effect on the rate of complications of reuse. This study reports the preliminary results of a program for the reuse of selected components of external fixators at a trauma center. METHODS: After removal from the patient, fixators were cleaned and examined by a single nurse responsible for the program. Components in good repair were returned to the operating room stock for reuse, whereas those showing specific signs of wear were discarded. No component was used more than three times. The medical center charged patients a loaner fee equal to the hospital's cost for reusable components of external fixators. Data were collected for all fixators applied in the 15 months before and after institution of the program (69 and 65 fixators, respectively). RESULTS: The overall mean hospital charge for a fixator decreased 32% as a result of the reuse program (from $4,067 to $2,791). For the two fractures most commonly treated with external fixation, the distal radius and tibial plafond fractures, the mean charge decreased 44 and 29%, respectively. The mean hospital cost for a fixator decreased 34% as a result of the program (from $1,864 to $1,238). There were no differences in the rates of reoperation or complications before and after institution of the reuse program. No patient had mechanical failure of a new or reused fixator body. CONCLUSION: The preliminary results of this program are encouraging. We recommend that institutions reusing these devices develop specific programs outlining criteria for reuse and guidelines for reprocessing devices for reuse. The results of this study represent an important first step in the validation of the efficacy and safety of reuse of external fixator components.

Cost Savings↗
PubMed2003

Errors of binocular fixation are common in normal subjects during natural conditions.

PURPOSE: To investigate the accuracy of fixation after symmetrical vergence eye movements along the midline during natural full-field viewing conditions using a video method of eye position measurement. METHODS: The accuracy of binocular fixation after symmetrical vergence eye movements during natural conditions was measured on 29 young adults using a precise head-mounted video eye movement measuring system. All subjects had normal binocular vision and good visual acuity. Measurements were taken for both near and far fixation after vergence changes of 5 degrees, 10 degrees, and 15 degrees using three rates of change, approximately 0.25, 0.5, and 1 Hz. RESULTS: The amplitude of the vergence movement tended to be hypometric, resulting in underconvergence for near fixations, and overconvergence for distance fixation. For far fixations, most errors (82%) were from -120 to +120 min arc, and for near, most errors (85%) were from -30 to +120 min arc. For far fixations, there was a significant effect of the size of vergence change (F1,28 = 61.8; p < 0.001), the rate of change (F1,28 = 7.08; p = 0.013), and the interaction between these two factors (F1,28 = 7.17; p = 0.012) on resulting errors, with the eyes showing greater overconvergence on the target for the larger and faster fixation changes. For near fixations, there was a significant effect (F1,28 = 15.9; p < 0.001) for the angle of change with the faster vergence changes producing relatively more convergence, thus reducing the mean vergence error. No subject reported diplopia during any conditions despite our measures showing vergence errors of up to 5 degrees. CONCLUSIONS: Vergence errors of up to +/-2 degrees, without diplopia, were common in subjects with normal binocular single vision. Errors of 5 degrees were rare but present. In all, the largest number of errors occurred as a failure of divergence for far fixations, consistent with previous studies that have suggested differences in the neural control of pathways for convergence and divergence, or possibly caused by differences in the anatomical properties of the medial and lateral rectus muscles and their associated fascia. The absence of diplopia during the period of fixation could only be partly associated with the visual suppression associated with vergence eye movements that has been reported by others because it was still present after the vergence movement was completed. The natural viewing conditions in this study that included a full visual field and multiple disparities may have contributed to this effect.

Adolescent↗
PubMed1999

Experimental external fixation combined with percutaneous discectomy in the management of scoliosis.

STUDY DESIGN: An assessment of the value of external fixation with or without percutaneous discectomy for the management of scoliosis in young rabbits with induced progressive thoracic scoliosis. OBJECTIVES: To investigate in an experimental setting the effect of external fixation with or without percutaneous discectomy for the management of scoliosis, as a preliminary study to precede clinical consideration. SUMMARY OF BACKGROUND DATA: External fixation of the spine using percutaneous transpedicular screws has been used clinically for cases of traumatic spinal injury, infectious spine, or chronic low back pain caused by a disc lesion. Percutaneous discectomy for the management of scoliosis has been reported. METHODS: Thirty-two young rabbits underwent partial resection of the right lower ribs. Nine rabbits were not treated after production of scoliosis and were followed as controls. At 4-6 weeks after production of scoliosis, in 23 animals, Kirschner wires were inserted percutaneously into the T9-T10 and L1-L2 disc space, and both ends were attached to an external fixator after correction of the scoliosis. In 8 of those 23 animals, percutaneous discectomy was also performed at the apex of the caudal compensatory curvature. RESULTS: In these 23 animals, the initial correction by fixation on of the caudal vertebrae was accompanied by a derotation in the apex. Five animals treated with external fixation only and four treated with combined percutaneous discectomy survived with external fixation until the age of 17 weeks and were followed to the natural cessation of the curve progression, at which the fixation was removed and a final assessment was made. The mean progression of curvature was 15.8 degrees in the group of five animals with external fixation only, and 33.8 degrees in the controls. In the group of four animals treated with supplementary percutaneous discectomy, however, the treated disc space became rigid, and the mean progression of curvature after removal of the fixation was only 5.3 degrees. CONCLUSIONS: The results of the current study suggest the potential for external fixation to allow for derotation and, when combined with percutaneous discectomy, to offer a feasible method of managing scoliosis in the human adolescent. This study was a preliminary experimental study; further experimental studies are planned to develop this novel technique.

Animals↗
PubMed2001

Biomechanical comparison of posterior cervical fixation.

STUDY DESIGN: Biomechanical stability using four different posterior cervical fixation techniques was evaluated in human cadaveric spine. OBJECTIVES: To introduce an alternative interspinous fixation technique using wavy-shaped rods, and to compare its in vitro biomechanical stability with that of other posterior cervical fixation techniques. SUMMARY OF BACKGROUND DATA: Fixation of the posterior cervical spine with interspinous wiring is well known as Rogers' or Bohlman's technique. Recently, several plate fixation techniques have been used for posterior cervical stabilization. Since 1983, the authors have developed the wavy-shaped rod system as an alternative to the interspinous fixation technique. This unique technique has been proven clinically useful in Japan. However, the authors are not aware of any prior biomechanical studies. METHODS: Seven fresh frozen cervical human spines were tested at the C5-C6 motion segment. Nondestructive static biomechanical testing was performed with flexion-extension, lateral bending, and axial rotation for the following stabilization techniques: intact spine, creation of a Stage 3 distractive-flexion injury followed by fixation with the wavy-shaped rods bounded by three multistrand cables, interspinous wiring with a multistrand cable, triple wiring technique using multistrand cables with a pair of unicortical grafts from the ilium, and lateral mass plate fixation with Magerl's screw technique. Testing was performed on a material testing machine (MTS 858 Bionix test system, MTS, Minneapolis, MN), and load displacement curves were obtained using four linear extensometers and one rotatory extensometer across the C5-C6 motion segment. RESULTS: In axial compression loading, the reconstructed specimens showed significant differences in range of motion measured at the anterior and posterior positions, and statistical analysis was performed using one-way analysis of variance. In a comparison of the four fixation techniques, the construct with the wavy-shaped rod indicated significantly less motion both anteriorly and posteriorly than with the other fixation techniques. Also in flexion-extension loading, all the techniques significantly limited the intervertebral motion below the level of the intact motion segment. Particularly, the construct with the wavy-shaped rod showed the smallest mobility, 49.9% anteriorly and 9.3% posteriorly, compared with that of the intact spine. In lateral bending, the lateral mass plate provided the greatest stability, which was superior to the intact segment, but the difference was not statistically significant. In axial rotation, all the reconstruction techniques limited the angular motion below the intact level (wavy rod, 68.0%; Rogers' wiring, 75.2%; Bohlman's triple wiring, 59.8%; lateral mass plate, 71.7%), but no significant differences were observed using one-way analysis of variance, as compared with the intact segment. CONCLUSIONS: All four reconstruction techniques restored the stability of the cervical motion segment to at least the level of the intact motion segment before destabilization. An alternative cervical posterior fixation technique, the Wavy Rod system, was considered the most effective technique in stabilizing a cervical motion segment, particularly in axial compression and flexion extension loading.

Biomechanical Phenomena↗
PubMedDate not supplied

Biomechanical comparison of flexible stainless steel and titanium nails with external fixation using a femur fracture model.

There are several options available for surgical stabilization of pediatric femoral shaft fractures. The purpose of this study was to compare the stability afforded by Ender stainless steel nails, titanium elastic nails, and one-plane unilateral external fixators for the fixation using a synthetic adolescent midshaft femur fracture model. The anterior-posterior (sagittal plane) bending, lateral (coronal plane) bending, torsional, and axial stiffness values were calculated using 6 different fixation configurations. These included pairs of 3.5-mm-diameter Ender nails with and without distal locking, 3.5- and 4.0-mm-diameter titanium elastic nails as well as single- and double-stacked monolateral external fixators. Eight synthetic femur models, 4 each with simulated transverse and comminuted fracture patterns, were sequentially tested for stability afforded by the various fracture fixation configurations. External fixation exhibited significantly greater control of anterior-posterior angulation compared with all flexible-nailing systems. Although Ender nails were slightly superior to titanium nails in control of sagittal plane angulation, this was not statistically significant. Compared with the external fixation constructs, all 4 flexible nail constructs demonstrated higher torsional stability. For prevention of axial shortening, all fixation methods were similar for the transverse fracture pattern, whereas external fixation was superior to flexible nails in the comminuted fracture model. No significant benefit was demonstrated with double stacking of external fixators. These findings may help guide clinicians choose the optimal fixation method for treatment of pediatric femoral shaft fractures.

Biomechanical Phenomena↗
PubMed2005

Biomechanical analysis of posterior fixation techniques in a 360 degrees arthrodesis model.

STUDY DESIGN: A biomechanical study to assess the ability of posterior fixation techniques to stabilize a functional spine unit (FSU) after insertion of an anterior load-sharing device. OBJECTIVE: The objective of this study is to compare various posterior fixation techniques in combination with an anterior load-sharing implant. SUMMARY OF BACKGROUND DATA: Pedicle screws and translaminar facet screws have been shown to improve the stiffness of an FSU in combination with an anterior load-sharing device. No published studies, to our knowledge, have compared translaminar facet screw fixation versus bilateral and unilateral pedicle screw fixation used with an anterior load-sharing device. METHODS: Ten cadaveric FSUs were potted using methylmethacrylate and attached to a spine simulator mounted to an MTS Mini-Bionix testing machine. The simulator was configured to control compressive loading, axial torque, flexion, extension, and lateral bending. Each specimen was tested in the intact state and following the application of each of four stabilization techniques: custom cage alone, cage plus translaminar facet screw fixation, cage plus unilateral pedicle screw and plate fixation, and cage plus bilateral pedicle screw and rod fixation with transverse coupling. Compressive stiffness and total range of motion (ROM) between +/-8 Nm of torque were extracted from the raw data. RESULTS: Each fixation method decreased ROM in torsion, flexion-extension, and lateral bending compared with the intact state. Unilateral pedicle fixation offered less stability than either of the other posterior fixations in all modes of testing except axial loading, where it was equivalent. Translaminar facet screw fixation was equivalent to bilateral pedicle screws in all modes tested. CONCLUSIONS: Using a load-sharing interbody implant, translaminar facet screws are equivalent to bilateral pedicle screws in resisting motion in all three planes. Translaminar facet screws and bilateral pedicle screws offer greater stabilization in all three planes compared with unilateral pedicle screws and a single plate.

Aged↗
PubMed2005

Treatment of zygomatic fractures without inferior orbital rim fixation.

Zygomatic fractures can be associated with functional and esthetic problems. Recent improvements in surgical techniques and materials have enabled stable fixation of zygmomatic fractures. Multiple-point fixation is most commonly used for internal fixation. Generally, reduction and fixation are performed through lateral brow, subciliary, temporal, or intraoral incisions (three-point fixation). Our experience indicates that postoperative scarring and sensory disturbances are caused by a subciliary incision with inferior orbital rim fixation. It is thus recommended that inferior orbital rim fixation with mini- or microplates be avoided. In patients in whom the fracture does not involve the orbital floor, reduction of the zygoma and zygomatic arch through a temporal incision is performed at this institution. Fixation of the lateral zygomaticomaxillary buttress and anterior wall of the maxilla with miniplates through an intraoral incision is also performed. If necessary, zygomaticofrontal suture fixation with a miniplate or wire is performed through a lateral brow incision. The status of inferior orbital rim reduction is confirmed by palpitation. Inferior orbital rim fixation with mini- or microplates is recommended for reduction of comminuted fractures and orbital floor fractures with herniation of internal orbit components. Patients who did not undergo inferior orbital rim fixation were free of inferior orbital rim deformity, diplopia, and postreduction rotation.

Adolescent↗
PubMed1989

Visual responses of neurones in cat superior colliculus in relation to fixation of targets.

1. Visually elicited discharges were recorded from single cells in the intermediate and deep layers of the superior colliculus of alert, trained cats. With the behavioural protocols used, vigorous and consistent visual responses to the onset and offset of small, stationary targets were encountered in all layers of the colliculus. In addition, the responses of many cells depended on the behavioural context in which the response occurred. Specifically, thirty-nine cells were encountered in which discharge was contingent upon prolonged fixation of the visual stimulus. Thirty of these were located in the intermediate and deep layers and comprised 22% of the 134 isolated cells which were not related to saccadic eye movement. 2. Fixation-related cells showed sustained increases or decreases in firing during fixation of a visual target. Responses to presentation of a visual target at the same retinal location, without active fixation by the animal, were either absent, much weaker, or had extremely variable latencies. 3. Changes in activity were well established by the end of the fixation saccade. The neuronal response was sustained if fixation was sustained. Moreover, the neuronal response began to decrease before the onset of the saccade which broke fixation even though the receptive field location of the target had not yet changed. 4. In these neurones, the discharge rate was not a function of the position of the eye in the orbit. 5. Neurones in which the discharge rate was suppressed during fixation had larger receptive fields than cells in which the discharge rate was enhanced during fixation. There were fewer fixation-suppressed cells (n = 7, 5%) than fixation-activated cells (n = 23, 17%).

Animals↗
PubMed2005

Knee stability after articulated external fixation.

BACKGROUND: Articulated external fixation has been proposed as a method to protect ligament reconstructions while allowing aggressive and early postoperative rehabilitation after knee dislocation. However, the ability of these fixators to protect and stabilize the knee joint has not been clearly determined. HYPOTHESIS: Articulated external fixation can reduce anteroposterior translation in the cruciate-deficient knee and reduce cruciate ligament strain in cases of intact or reconstructed ligaments. STUDY DESIGN: Controlled laboratory study. METHODS: Knee stability was assessed by 3 standard clinical stability tests (Lachman, anterior drawer, and posterior drawer) on 7 human cadaveric lower extremities. Instrumented forces of 100 N were applied to the tibia to measure cruciate ligament forces and tibiofemoral displacement in intact and cruciate-deficient specimens with and without articulated external fixation to determine the degree to which a fixator can protect cruciate ligaments and stabilize the knee. Articulated external fixation was applied using monolateral and bilateral fixators to comparatively analyze the effectiveness of each construct. Statistical analysis was performed using 2-tailed, paired Student t tests. RESULTS: Application of the monolateral articulated external fixator to specimens with intact ligaments significantly reduced cruciate ligament forces by 1.0 N (P = .011), 1.7 N (P = .046), and 1.4 N (P = .009) for Lachman, anterior drawer, and posterior drawer tests, respectively. In the cruciate ligament-deficient knees, the application of a monolateral fixator significantly reduced tibiofemoral translation by 49%, 70%, and 46% for Lachman, anterior drawer, and posterior drawer tests, respectively. No significant differences between the monolateral and bilateral fixator frames, in terms of ligament protection and joint stabilization, were observed. CONCLUSION AND CLINICAL RELEVANCE: Articulated external fixation of the knee can reduce stress in the cruciate ligaments after multiligament reconstructions and can decrease anteroposterior translation in the cruciate-deficient knee.

Aged↗