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PubMed2001

Recent advances in external skeletal fixation.

While the use of external skeletal fixation was once associated with substantial postoperative morbidity, clinical and experimental studies have led to technological advances and modifications in application techniques that have greatly improved the results obtained with this treatment modality. The past decade saw numerous advances in external skeletal fixator implants, components and instrumentation, including improvements in fixation pin design, and the development of new linear external skeletal fixation systems and economical circular external skeletal fixation systems specifically engineered for use in dogs and cats. In addition, a greater understanding of fixator biomechanics and the pathobiology of the bone-fixation pin interface have improved fixator application practices. This article reviews many of the more significant recent advances in external skeletal fixation.

Animals↗
PubMed2001

Aldehyde fixation of thiol-reactive fluorescent cytoplasmic probes for tracking cell migration.

Tracking of cell migration plays an important role in the study of morphogenesis, inflammation, and metastasis. The recent development of probes that exist as intracellular peptide-fluorescence dye adducts has offered the possibility of aldehyde fixation of these dyes for detailed anatomic studies of lymphocyte trafficking. To define the conditions for fixation of these cytoplasmic fluorescent probes, we compared fixation conditions containing formaldehyde, glutaraldehyde, paraformaldehyde, zinc formaldehyde, and glyoxylate, as well as fixation by quick-freezing in liquid nitrogen-cooled methylbutane. The efficacy of aldehyde fixation of the cell fluorescence was assessed by quantitative tissue cytometry and flow cytometry. We studied cytoplasmic fluorescent dyes with discrete emissions in the green [5-chloromethylfluorescein diacetate (CMFDA); 492 ex, 516 em] and orange [5-(and-6)-(4-chloromethyl(benzoyl)amino) tetramethylrhodamine (CMTMR); 540 ex, 566 em] spectra. The results demonstrated that aldehyde fixation preserved cell fluorescence for more than 6 months. The primary difference between the aldehyde fixatives was variability in the difference between the yield of the cell fluorescence and the relevant background fluorescence. Formaldehyde and paraformaldehyde were superior to the other fixatives in preserving cell fluorescence while limiting background fluorescence. With these fixatives, both the CMFDA and CMTMR fluorescent dyes permitted sufficient anatomic resolution for reliable localization in long-term cell tracking studies.

Aldehydes↗
PubMed2003

Effect of fibular plate fixation on rotational stability of simulated distal tibial fractures treated with intramedullary nailing.

BACKGROUND: The effect of an intact fibula on rotational stability after a distal tibial fracture has, to the best of our knowledge, not been clearly defined. We designed a cadaver study to clarify our clinical impression that fixation of the fibula with a plate increases rotational stability of distal tibial fractures fixed with a Russell-Taylor intramedullary nail. METHODS: Seven matched pairs of embalmed human cadaveric legs and sixteen fresh-frozen human cadaveric legs, including one matched pair, were tested. To simulate fractures, 5-mm transverse segmental defects were created at the same level in the tibia and fibula, 7 cm proximal to the ankle joint in each bone. The tibia was stabilized with a 9-mm Russell-Taylor intramedullary nail that was statically locked with two proximal and two distal screws. Each specimen was tested without fibular fixation as well as with fibular fixation with a six-hole semitubular plate. A biaxial mechanical testing machine was used in torque control mode with an initial axial load of 53 to 71 N applied to the tibial condyle. Angular displacement was measured in 0.56-N-m torque increments to a maximal torque of 4.52 N-m (40 in-lb). RESULTS: Initially, significantly less displacement (p < or = 0.05) was produced in the specimens with fibular plate fixation than in those without fibular plate fixation. The difference in angular displacement between the specimens treated with and without plate fixation was established at the first torque data point measured but did not increase as the torque was increased. No significant difference in the rotational stiffness was found between the specimens treated with and without plate fixation after measurement of the second torque data point (between 1.68 and 4.48 N-m). CONCLUSIONS: Fibular plate fixation increased the initial rotational stability after distal tibial fracture compared with that provided by tibial intramedullary nailing alone. However, there was no difference in rotational structural stiffness between the specimens treated with and without plate fixation as applied torque was increased.

Aged↗
PubMed2004

[Dynamic internal fixation of the periprosthetic femoral fractures after total hip arthroplasty].

Periprosthetic fractures of the femur after total hip arthroplasty are a big orthopaedic problem, particularly in elderly patients and quite a challenge for orthopaedic surgeons. There is no universal method in treating these fractures. Rigid plates fixation can be limited and aggravated especially in the proximal part of the femur where the endoprosthesis stem does not allow for an undisturbed fixation of both femur cortexes by means of screws. Mitkovic's dynamic internal fixator is an original implant allowing for an undisturbed fixation of both femur cortexes regardless of the presence of the endoprosthesis stem. Fixation is made possible by means of movable clamps and a convergent possibility to place screws. A dynamic internal fixator can fix all types of periprosthetic femoral fractures. The paper shows the early experience in fixating periprosthetic femoral fractures after total hip arthroplasty in 14 patients, average age 69.7. According to Vancouver classification, 3 patients had the type A fracture, 9 patients had the type B fracture, and 2 patients had the type C fracture. All fractures were fixed by Mitkovic's dynamic internal fixator. The fracture occurred 2-12 years after primary total hip arthroplasty. The follow-up of the operated patients was 12 months. The method is less invasive than the methods described in books. Mechanical complications are not likely to appear due to the fracture dynamics along the femoral shaft axis, which is made possible by this implant. Our initial experience in femur fracture fixation after hip arthroplasty ahows that it is modern and effective dynamic implant which will contribute significantly to the improving of the treatment of these often very complicated fractures.

Aged↗
PubMed2003

[Biodegradable meniscus fixations: a comparative biomechanical study].

PURPOSE: Numerous new all inside meniscus repair techniques using biodegradable fixation devices have become available in the last years. Few studies have dealt with the biomechanical properties of these implants so far. The aim of this study was to analyze meniscus repairs under cyclic loading conditions for different fixation devices (Meniscus Arrow, Clearfix Meniscal Screw, Meniscal Dart, BioStinger) and to compare them to standard suture techniques. MATERIAL AND METHODS: Eighty meniscus repairs on 27 medial porcine menisci were performed. For biomechanical testing loosening, number of failures, failure modes and failure loads were evaluated under cyclic and maximum loading conditions. Testing was performed on a materials testing machine. RESULTS: During cyclic loading 10 out of 40 (25%) fixation devices failed. A gap appeared between the 2 parts of the meniscus within the first loading cycles. The failure strengths obtained with the 4 meniscus fixation devices did not differ significantly (Meniscus Arrow: 44 N; Clearfix Meniscal Screw: 35 N; Meniscal Dart: 33 N; BioStinger: 54 N). Besides for the BioStinger, the values of the sutures were significantly higher. The use of a stronger suture material (PDS 0) increased the failure load significantly. During maximum loading the fixation devices failed by both pull-out of the head or the tip of the device, except for the BioStinger showing only pull-out of the head. All sutures failed by breakage, except for the PDS 0 horizontal sutures in which 50% of complete tissue failures could be noted. CONCLUSION: This study shows that meniscal fixation devices may fail under repetitive loading conditions. A gap appeared between the meniscal margins within the first loading cycles irrespective of the suture type and fixation device used. Both gapping and failure modes of the fixation devices may be design-specific. The maximum failure loads differed significantly between the bioabsorbable devices and the sutures. Stronger suture materials increased the failure loads significantly. To allow a complete evaluation of new meniscus fixation devices not only biomechanical, but also biological and clinical parameters need to be analyzed in forthcoming studies.

Absorbable Implants↗
PubMed2003

Treatment of tibial defect and bone nonunion with limb shortening with external fixator and reconstituted bone xenograft.

OBJECTIVE: To explore the effect of external fixator and reconstituted bone xenograft (RBX) in the treatment of tibial bone defect, tibial bone nonunion and congenital pseudarthrosis of the tibia with limb shortening. METHODS: Twenty patients (13 males and 7 females) with tibial bone defect, tibial bone nonunion or congenital pseudarthrosis of the tibia with limb shortening were treated with external fixation. Two kinds of external fixators were used: a half ring sulcated external fixator used in 13 patients and a combined external fixator in 7 patients. Foot-drop was corrected at the same time with external fixation in 4 patients. The shortened length of the tibia was in the range of 2-9 cm, with an average of 4.8 cm. For bone grafting, RBX was used in 12 patients, autogenous ilium was used in 3 patients and autogenous fibula was implanted as a bone plug into the medullary canal in 1 case, and no bone graft was used in 4 patients. RESULTS: All the 20 patients were followed-up for 8 months to 7 years, averaging 51 months. Satisfactory function of the affected extremities was obtained. All the shortened extremities were lengthened to the expected length. For all the lengthening area and the fracture sites, bone union was obtained at the last. The average healing time of 12 patients treated with RBX was 4.8 months. CONCLUSIONS: Both the half ring sulcated external fixator and the combined external fixator have the advantages of small trauma, simple operation, elastic fixation without stress shielding and non-limitation from local soft tissue conditions, and there is satisfactory functional recovery of affected extremities in the treatment of tibial bone defects, tibial bone nonunion and congenital pseudarthrosis of the tibia combined with limb shortening. RBX has good biocompatibility and does not cause immunological rejections. It can also be safely used in treatment of bone nonunion and has reliable effect to promote bone healing.

Adolescent↗
PubMed2004

External fixation with or without supplementary intramedullary Kirschner wires in the treatment of distal radial fractures.

OBJECTIVES: To determine radiographic outcomes in the fracture of distal radius treated by close reduction and external fixation, with or without supplementary intramedullary Kirschner wires.. METHODS: At the Orthopedic Department of National Taiwan University Hospital, we carried out a retrospective study of distal radial fractures treated with close reduction and external fixation. A consecutive series of 20 fractures were treated (from March 1995 to June 1998) with external fixation only; later (from January 1999 to December 2001), 36 distal radius fractures were treated with external fixation supplemented with intramedullary wires. The fractures were evaluated via good-quality posteroanterior and lateral radiographs. In both groups, the radial height, radial inclination and volar tilting were measured on initial (preoperative) and immediate postoperative radiographs and on others taken immediately after the removal of external fixation. Overall results were based on objective radiographic and functional data as well as on subjective assessments with demerit-point scoring. Data were analyzed with a 2-tailed t test. RESULTS: Radial height and radial inclination improved significantly immediately after surgery, but volar tilting of distal-radius deformity was little improved by treatment with external fixation alone. When external fixation was supplemented with intramedullary Kirschner wires, improvement in all 3 measurements was statistically significant. Clinical examination likewise found significantly better functional results in patients treated with the Kirschner wires. CONCLUSION: External fixation is a popular method too reduce osseous deformity of the distal radius, but can not assure maintenance of the reduction. Supplementing external fixation with intramedullary Kirschner wires can improve retention of fracture reduction during healing, resulting in better functional results.

Bone Wires↗
PubMed1989

A biomechanical analysis of the Ilizarov external fixator.

Five configurations of the Ilizarov fixator were analyzed in vitro. The overall stiffness, shear stiffness, and axial motion of the fracture site were determined. The data were compared with the results of eight conventional one-half frame fixators previously tested in the same manner. The Ilizarov fixator allowed significantly more axial motion at the fracture site during axial compression than the other fixators tested. The overall stiffness and shear rigidity of the Ilizarov external fixator were similar to those of the one-half pin fixators in bending and torsion. The stability of the Ilizarov fixator was a function of bone position within the fixator rings and fixation wire tension. The use of olive stop wires increased the shear resistance of the Ilizarov system.

Biomechanical Phenomena↗
PubMed1987

An evaluation of the bending stiffness of various tibial fixation methods.

The relative stiffness of human tibial fixation by plaster casts, intramedullary rods, external fixators, and dynamic compression plates was compared to the stiffness of the intact tibia. Four-point bending was performed on each specimen, first intact, and then after sequential instrumentation, thus allowing each specimen to serve as its own control. The mean stiffnesses obtained for the bone-device complexes, as a percentage of the intact tibial stiffness, were 113 +/- 9% for the delta frame fixator, 57 +/- 14% for the dynamic compression plate, 28 +/- 2% for the unilateral external fixator (UEF) with stainless steel sidebar, 18 +/- 1% for the UEF with aluminum sidebar, 7 +/- 2% for the flexible intramedullary (IM) rods, and 6 +/- 2% for the cast. Even relatively flexible unilateral external fixators are much stiffer than cast or IM rod fixation, methods that usually lead to satisfactory union by secondary healing. If secondary union with callus formation is desirable, modifications of the external fixator may be necessary to provide more flexible fixation. This study may be one of the first attempts to quantitate the stiffness of tibial fixation in a standard cast and compare it with other devices.

Biomechanical Phenomena↗
PubMed1999

Fixation technique influences osteogenesis of comminuted fractures.

Comminuted fractures most often are associated with compromised soft tissue conditions and diminished vascularization leading to a reduced osteogenesis. In contrast to stable fixation by compression plating with lag screws, the less stable but also less invasive techniques of external fixation, unreamed nailing, or bridging plates have become increasingly popular. The aim of this study was to compare the bone healing and osteogenesis of these fixation techniques. A triple wedge osteotomy of the sheep tibia was used as a bone healing model. Internal compression plate fixation of all fragments with lag screws was used in one group. In the other three groups, only the main proximal and distal fragments were fixed by external fixation, unreamed interlocking nail, or bridging plate. The sheep with compression plate fixation and lag screws showed the worst results after 12 weeks. The periosteal and endosteal osteogenesis and the apparent density of the newly formed bone in the fracture gaps were significantly lower than those seen in the sheep in the other three technique groups. The best results were found for the bridging plate and external fixator. From these results, it can be concluded that compression plate fixation should be avoided for treatment of comminuted fractures.

Animals↗
PubMed1995

Fixation switch diplopia.

OBJECTIVE: To present guidelines for the diagnosis and management of fixation switch diplopia. BACKGROUND: Adults with a history of strabismus since childhood may experience acquired diplopia if a change in their refractive error or use of spectacles encourages fixation with their nondominant eye. This is referred to as "fixation switch diplopia." If correctly diagnosed, this seldom-recognized cause of acquired diplopia in adults can almost always be successfully treated with the proper optical management. PATIENTS: A retrospective review was carried out for all patients with the diagnosis of fixation switch diplopia who were seen in my private practice. RESULTS: A review of patient records identified 16 patients with fixation switch diplopia. In four patients, the switch in fixation was spontaneous owing to the development of myopia in the previously preferred eye in patients with mild contralateral amblyopia. Six patients developed diplopia owing to their "monovision" (one eye optically corrected for distance and the other eye presbyopic). In six patients, fixation switch diplopia occurred because a noncycloplegic subjective refraction was performed in the presence of amblyopia, resulting in an unbalanced refractive correction. In all 16 patients, symptoms were eliminated when proper optical correction was instituted to encourage fixation with the dominant eye. CONCLUSIONS: Fixation switch diplopia is a cause of acquired diplopia in adults with a history of strabismus since childhood. It can usually be successfully treated with proper optical management.

Adult↗
PubMed1997

A solvent-based fixative for electron microscopy to improve retention and visualization of the intestinal mucus blanket for probiotics studies.

Samples of pig small intestine, cecum, and large intestine were prepared for scanning electron microscopy (SEM), concentrating on mucus blanket retention and visualization. Samples were fixed using three aqueous-based fixatives which included a standard glutaraldehyde fixative alone as the control and the standard fixative formulation with either ruthenium red or alcian blue added and using one solvent-based fixative, osmium tetroxide dissolved in FC-72 (a degreasing fluorocarbon solvent produced by 3M Canada, Inc.), which had been successfully used by Sims et al. [(1991) Biotech. Histochem., 66:173-180] to preserve tracheal mucus of nonhuman mammals. Pig intestine samples prepared using the solvent-based fixative retained a contiguous mucus blanket, while the aqueous-based treatments retained only patchy or fibrous remnants to a degree depending on fixative composition and intestinal site. We conclude that preparation of the pig intestinal mucus layer using the solvent-based fixative suggested by Sims et al. (1991) preserves the mucus blanket in its entirety and gives superior results to aqueous-based fixatives containing the standard additives ruthenium red and alcian blue. We recommend that this anhydrous fixation, which requires only a slight modification from standard conditions, be adopted when mucus layer retention and visualization is important, as in the field of probiotics. Overcoming this major technical obstacle will now allow electron microscopy (EM) to once again provide new in situ information in this reemerging field.

Animals↗
PubMed1996

Crosslinking characteristics of an epoxy-fixed porcine tendon: effects of pH, temperature, and fixative concentration.

Injury to the anterior cruciate ligament (ACL) often results in functional instability within the knee joint and may induce a severe articular deterioration. Clinically, these patients may require an ACL reconstruction. In an attempt to develop an improved ligament prosthesis, a prototype xenograft--an epoxy-fixed porcine Achilles tendon--was developed. The study was intended to investigate the crosslinking characteristics of the epoxy-fixed porcine tendons fixed at different pHs (4.0, 7.4, 9.0, and 10.5), temperatures (4, 25, and 37 degrees C), and fixative concentrations (1, 2, or 4%). Samples of each group were taken out at various elapsed fixation periods. The crosslinking characteristics-fixation index, denaturation temperature, and moisture content-of each sample were determined. Additionally, the stiffness of the epoxy-fixed tendons under various fixation conditions was qualitatively compared. In the study it was noted that the color of porcine Achilles tendons remained natural after epoxy fixation. With increasing pH, temperature, or fixative concentration, the fixation indices and denaturation temperatures of the epoxy-fixed tendons increased. However, the fixed porcine tendons tended to be stiffer at a higher pH, temperature, or fixative concentration. The moisture contents of the epoxy-fixed tendons were relatively lower than the fresh ones, while they were approximately the same at different pHs, temperatures, and fixative concentrations. The implications of these findings for the epoxy-fixed porcine tendons in ACL reconstruction require further investigation.

Animals↗
PubMed1996

Augmentation of femoral neck fracture fixation with an injectable calcium-phosphate bone mineral cement.

The first goal of this study was to determine if augmentation with an injectable, in situ setting, calcium-phosphate cement that is capable of being remodeled and was designed to mimic bone mineral significantly improved the strength and stiffness of fixation in a cadaveric femoral neck fracture model. The second goal was to determine if greater increases in fixation strength were achieved as the bone density of the specimen decreased. Sixteen pairs of fresh cadaveric human femora with a mean age of 70.9 years (SD = 17.2 years) were utilized. The bone density of the femoral neck was measured with dual-energy x-ray absorptiometry. The femoral head was impacted vertically with the femoral shaft fixed in 12 degrees of adduction using a materials testing machine to create a fully displaced fracture. Following fracture, 30% inferior comminution was created in each specimen. One randomly chosen femur from each pair underwent anatomic reduction and fixation with three cannulated cancellous bone screws, 7 mm in diameter, in an inverted triangle configuration. The contralateral femur underwent the same fixation augmented with calcium-phosphate cement. Specimens were preconditioned followed by 1.000 cycles to one body weight (611.6 N) at 0.5 Hz to simulate single-limb stance loading. The stiffness in the first cycle was observed to be significantly greater in cement-augmented specimens compared with unaugmented controls (p < 0.05). After cycling, each specimen was loaded at 10 mm/min until complete displacement of the fracture surface and failure of fixation occurred. Specimens augmented with bone mineral cement failed at a mean of 4,573 N (SD = 1,243 N); this was significantly greater (p < 0.01) than the mean for controls (3,092 N, SD = 1,258 N). The relative improvement in fixation strength (augmented/control x 100%) was not inversely correlated to femoral neck bone density (p = 0.25, R2 = 0.09), was weakly correlated to the volume of cement injected (p = 0.07, R2 = 0.22), and was inversely related to the fixation failure load of the control specimen (p = 0.001, R2 = 0.54). There was a mean relative improvement in fixation strength of 169.6% (SD = 77.5). These findings suggest that calcium-phosphate cement provides initial beneficial augmentation to fixation of femoral neck fractures.

Adult↗
PubMed1994

The importance of fixation procedures on DNA template and its suitability for solution-phase polymerase chain reaction and PCR in situ hybridization.

Conventional solution-phase polymerase chain reaction (PCR) and in situ PCR/PCR in situ hybridization are powerful tools for retrospective analysis of fixed paraffin wax-embedded material. Amplification failure using these techniques is now encountered in some centres using archival fixed tissues. Such 'failures' may not only be due to absent target DNA sequences in the tissues, but may be a direct effect of the type of fixative, fixation time and/or fixation temperature used. The type of nucleic acid extraction procedure applied will also influence amplification results. This is particularly true with in situ PCR/PCR in situ hybridization. To examine these effects in solution-phase PCR, beta-globin gene was amplified in 100 mg pieces of tonsillar tissue fixed in Formal saline, 10% formalin, neutral buffered formaldehyde, Carnoy's Bouin's, buffered formaldehyde sublimate, Zenker's, Helly's and glutaraldehyde at 0 to 4 degrees C, room temperature and 37 degrees C fixation temperatures and for fixation periods of 6, 24, 48 and 72 hours and 1 week. DNA extraction procedures used were simple boiling and 5 days' proteinase K digestion at 37 degrees C. Amplified product was visible primarily yet variably from tissue fixed in neutral buffered formaldehyde and Carnoy's, whereas fixation in mercuric chloride-based fixatives produced consistently negative results. Room temperature and 37 degrees C fixation temperature appeared most conducive to yielding amplifiable DNA template. Fixation times of 24 and 48 hours in neutral buffered formaldehyde and Carnoy's again favoured amplification.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1996

Morphological changes in rat submandibular gland mucous cells during fixation with 10% formalin.

The features of mucous cells in 10% formalin (FA)-fixed submandibular glands differ markedly from those fixed in glutaraldehyde (GA). We therefore studied morphological changes in mucous cells during 10% FA fixation. Mucous cells were fixed in either 10% FA, neutral sodium-phosphate-buffered (Na-PBed) 10% FA, ice-cold 10% FA or an ice-cold fixative mixture of 2.0% paraformaldehyde (PA) and 0.5% GA. Two different methods were used: immersion fixation and venous perfusion fixation. The 10% FA-fixed tissues had elliptical or flattened nuclei, a clear cytoplasm and no secretory granules. Tissues fixed with the fixative mixture displayed almost round nuclei, a broad endoplasmic reticulum and abundant secretory granules in the cytoplasm. Tissues immersion-fixed with neutral Na-PBed 10% FA or perfusion-fixed with ice-cold 10% FA had almost the same light microscopic appearance as that of the mixture-fixed tissues. To elucidate the process of morphological changes during 10% FA fixation at room temperature, samples immersed in 10% FA for varying periods of time were postfixed immediately in the fixative mixture and exposed to microwave irradiation. This method produced a variety of findings, even within the same section. There was a significant difference in the findings seen in the center of the section and at the periphery. The initial changes caused by 10% FA were rupture of the secretory granules located in the perinuclear region and destruction of the perinuclear organelles such as Golgi apparatus, mitochondria and endoplasmic reticulum. Absorption of the endoplasmic reticulum progressed so that the perinuclear region became translucent. To obtain a better structure in mucous cells from the fixed submandibular gland tissues, an appropriate fixative such as GA should be used and the fixative should infiltrate into the tissues as quickly as possible.

Animals↗
PubMed1994

Gaze shifts evoked by stimulation of the superior colliculus in the head-free cat conform to the motor map but also depend on stimulus strength and fixation activity.

In our previous paper we demonstrated that electrical microstimulation of the fixation area at the rostral pole of the cat superior colliculus (SC) elicits no gaze movement but, rather, transiently suppresses eye-head gaze saccades. In this paper, we investigated the more caudal region of the SC and its interaction with the fixation area. In the alert head-free cat, suprathreshold stimulation in the anterior portion of the SC but outside the fixation area evoked small saccadic shifts of gaze consisting mainly of an eye movement, the head's contribution being small. Stimulating more posteriorly elicited large gaze saccades consisting of an ocular saccade combined with a rapid head movement. At these latter stimulation sites, craniocentric (goal-directed) eye movements were evoked when the cat's head was restrained. The amplitude of eye-head gaze saccades elicited at a particular stimulation site increased with stimulus duration, current strength, and pulse rate, until a constant or "unit" value was reached. The peak velocity of gaze shifts depended on both pulse rate and current strength. The movement direction was not affected by stimulus parameters. The unit gaze vector evoked, in the head-free condition, by stimulating one collicular site was similar to that coded by efferent neurons recorded at that site, thereby indicating a retinotopically coded gaze error representation on the collicular motor map which is not revealed by stimulating the head-fixed animal. Evoked gaze saccades were found to be influenced by fixation behavior. The amplitude of evoked gaze shifts was reduced if stimulation occurred when the hungry animal fixated a food target. Electrical activation of the collicular fixation area was found to mimic well the effects of natural fixation on evoked gaze shifts. Taken together, our results support the view that the overall distribution and level of collicular activity contributes to the encoding of the metrics of gaze saccades. We suggest that the combined levels of activity at the site being stimulated and at the fixation area influence the amplitude of evoked gaze saccades through competition. When stimulation is at low intensities, fixation-related activity reduces the amplitude of evoked gaze saccades. At high activation levels, the site being stimulated dominates and the gaze vector is specified only by that site's collicular output neurons, from which arises the close correspondence between the unit-evoked gaze saccades and the neurally coded gaze vector at that site.

Animals↗
PubMed1981

Effects of ocular fixation on perrotatory nystagmus in damped pendular rotation test.

Effects of ocular fixation on pendular rotation nystagmus were investigated in 65 patients. There were 25 with peripheral vestibular or vestibulo-cochlear disorders, 17 with central vestibular disorders, five with congenital nystagmus, 16 patients over 60 years old with vertigo in whom peripheral vestibular disorders were ruled out, however, the causes were unknown. Damped pendular rotation test (DPRT) was performed both under darkness and employing mental arithmetic and under ocular fixation. These findings were related to those of caloric vestibular suppression test (VST) by Takemori and those of optokinetic pattern test (OKP), eye tracking test (ETT), and spontaneous nystagmus. Thirteen of 17 patients with central vestibular disorders and five with congenital nystagmus showed loss of visual suppression during ocular fixation in DPRT, whereas in cases of peripheral lesions, visual suppression was observed. Loss of visual suppression during ocular fixation in DPRT was often seen in cases of brainstem and cerebellar lesions. In brainstem lesions, perrotatory nystagmus was evoked during ocular fixation, whereas no nystagmus was seen in darkness with eyes open. In cerebellar lesions, perrotatory nystagmus was partly suppressed or decreased during ocular fixation. Relationships between the direction of the visual suppression during ocular fixation in DPRT and the side of the lesion were not apparent. Ocular fixation test in DPRT has a diagnostic value not only for central lesions, but for differentiating brainstem lesion from cerebellar lesion with the findings in DPRT under darkness. The findings under ocular fixation in DPRT are closely related to those of VST in cases of caloric nystagmus.

Adult↗