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PubMed2006

Biomechanical evaluation of different fixation methods for tibial eminence fractures.

BACKGROUND: Tibial eminence fractures have become more common, but the best method of fixing these fractures arthroscopically has not been elucidated. OBJECTIVE: The objective of this study is to assess the stability of different fixation methods for tibial eminence fractures. STUDY DESIGN: Controlled laboratory study. METHODS: The authors evaluated the initial fixation strength of 4 different fixation techniques for tibial eminence fractures (2 screws, 1 screw, suture fixation with 1 mm Ethibond, and suture fixation with No. 5 FiberWire) using single cycle and cyclic loading tests. The tests were performed by loading the knee with an anterior tibial shear force. RESULTS: Suture cerclage with the FiberWire showed significantly higher maximum load (599.6 N) and stiffness (36.99 N/mm) than all other fixation methods tested. The lowest maximum load in the single cycle loading test was observed in the group with 2 screws (1 screw, 371.2 N; 2 screws, 249.8 N). The lowest stiffness was found in the Ethibond group (14.5 N/mm). After 1000 cycles of loading, the maximum load of the FiberWire fixation was significantly higher than the maximum load of the Ethibond fixation (399.4 N), the fixation with 1 screw (354.2 N), and the fixation with 2 screws (301.5 N). CONCLUSION: These biomechanical data suggest that under cyclic loading conditions, suture fixation of tibial eminence fractures provides more fixation strength than screw fixation. CLINICAL RELEVANCE: A second screw has no positive effect on the biomechanical characteristics of screw fixation.

Animals↗
PubMed1997

Use of perfusion fixation for improved neuropathologic examination.

OBJECTIVE: To assess the efficacy of 10% formalin perfusion fixation as a method of rapid fixation to examine the human brain immediately following autopsy. DESIGN: Compare the histology and immunohistochemistry from human brains in which one hemisphere undergoes perfusion fixation using 10% buffered formalin, and the contralateral nonperfused hemisphere undergoes standard 14-day immersion fixation in 8 L of 10% buffered formalin. SETTING: Autopsy material in a general medical-surgical university hospital. PARTICIPANTS: Pathologists, neuropathologists, resident pathologists, and pathology assistants. INTERVENTION: Immediately following brain removal, a single hemisphere was perfused with 1 L 10% buffered formalin over a 15- to 20-minute period. The contralateral nonperfused hemisphere served as a control, undergoing standard immersion fixation for 2 weeks in 10% formalin. The perfusion-fixation hemisphere was immediately available for neuropathologic examination, and histologic sections of the brain were processed immediately with the other necropsy tissue sections. This allows completion of a final autopsy neuropathology report within 3 to 5 days in concert with the systemic section of the report. MAIN OUTCOME MEASURE: Perfusion-fixation brain sections were compared with immersion-fixation brain sections from the same brain. The effects on hematoxylin-eosin, Bielschowsky's silver, and immunohistochemical staining were evaluated by an experienced neuropathologist and a general pathologist with no prior knowledge of the fixation technique. RESULTS: Perfusion fixation revealed equal and occasionally superior histologic sections compared with traditional immersion fixation in terms of (1) technical preparation of section, (2) quality and intensity of staining with both hematoxylin-eosin and silver, and (3) immunoreactivity localization with a variety of immunohistochemical reactions. CONCLUSIONS: Immediate perfusion of the brain is an easily performed fixation technique that yields comparable or superior fixation to prolonged immersion fixation and allows an immediate complete neuropathologic examination and report within 3 to 5 days of performance of the autopsy.

Aged↗
PubMed1986

Lung deformation and macrophage displacement in smoke-exposed and normal mice (Mus musculus) following different fixation procedures.

Lung deformation (shrinkage or inflation) and displacement of pulmonary parenchymal macrophages were evaluated after immersion fixation, intratracheal instillation of fixative and lung lavage followed by intratracheal fixative instillation in cigarette smoke-exposed, sham-treated and control pallid male mice. Lung volume displacement and lung section and alveolar area analysis revealed that degree of deformation was uniform in lungs from all treatment groups fixed by immersion but not by instillation of fixative and fixative instillation following lavage. In situ pulmonary parenchymal macrophage number per lung section area of fixative-instilled lungs and lavaged lungs followed by fixative instillation was significantly greater than in those following immersion fixation in all corresponding treatment groups. A paucity of macrophages was noted in airways of fixative-instilled and lavaged followed by instillation of fixative lungs. Pulmonary macrophages were uniformly distributed throughout lung parenchyma following immersion fixation, while in fixative-instilled and lavaged prior to instillation of fixative lungs these cells tended to be concentrated in alveoli near terminal bronchioles. Lavage procedures removed an unknown portion of lung macrophages and appeared to ineffectively sample the pulmonary parenchymal macrophage population. Intratracheal instillation of fixative with or without prior lavage apparently alters the distribution of pulmonary macrophages by displacing airway phagocytes into the alveoli. Data reported suggest that fractional estimates of in situ lung parenchymal macrophage population can be obtained by counting the number of these cells per area of tissue from lungs fixed by immersion.

Animals↗
PubMed1997

Discharge patterns of neurons in the rostral superior colliculus of cat: activity related to fixation of visual and auditory targets.

Neurons in the rostral superior colliculus (SC) of alert cats exhibit quasi-sustained discharge patterns related to the fixation of visual targets. Because some SC neurons also respond to auditory stimuli, we investigated whether there is a population of neurons in the rostral SC which is active in relation to fixation of both auditory and visual targets. We identified cells which were active with visual fixation and which continued to discharge if the fixation stimulus was briefly extinguished. The population of neurons exhibited similar discharge characteristics when the fixation stimulus was auditory. Few neurons were significantly more active during fixation of visual targets than during fixation of auditory targets. Most fixation neurons showed a diminished discharge rate during spontaneous (self-generated) saccadic eye movements away from a visual fixation stimulus, regardless of the direction of the saccade. This diminished discharge rate (or pause) typically began, on average, 12.2 ms before saccade onset and the duration of the pause was longer than the duration of the saccade. These observations are consistent with the hypothesis that increased discharge of these neurons is related to active fixation and that reductions in their activity are important for the generation of saccades. However, the lack of a precise relationship between pause duration and saccade duration implies that these neurons would be unlikely to project directly to the saccadic burst generator. The mean interval from the beginning of the pauses of fixation neurons to the beginning of the saccades away from fixation targets is also shorter than has been found in brainstem omnipause neurons. By analogy with the concept of a receptive field, a gaze position error field depicts the range of gaze position error for which a cell is active. Although fixation neurons appear to encode the magnitude and direction of the error between visual targets and the visual axis, visual error fields at the end of fixating eye movements were significantly larger than those at stimulus onset. For auditory stimuli, this difference was not significant. These observations are compatible with a number of recent experiments indicating that neural signals of eye position are damped or delayed with respect to current eye position.

Acoustic Stimulation↗
PubMed2006

Hybrid femoral fixation of soft-tissue grafts in anterior cruciate ligament reconstruction using the EndoButton CL and bioabsorbable interference screws: a biomechanical study.

PURPOSE: The purpose of this study was to evaluate the effect of hybrid femoral fixation with bioabsorbable interference screws (BioRCI; Smith & Nephew Endoscopy, Andover, MA) and EndoButton CL (Smith & Nephew Endoscopy) fixation. METHODS: Biomechanical testing of 3 different fixation techniques was performed by use of porcine hind-limb distal femurs and mature bovine extremity common extensor tendons. Two independent testing sessions were examined. The first testing session (group A) compared femoral fixation via the EndoButton CL device (n = 6) with femoral fixation via the EndoButton CL device with the addition of a BioRCI screw (n = 6). The second testing session (group B) compared femoral fixation via BioRCI screws alone (n = 6) with femoral fixation via the EndoButton CL device with the addition of a BioRCI screw (n = 6). The femur-graft complex was cyclically loaded between 50 and 250 N at 1 Hz for 1,000 cycles. After cycling, the amount of graft slippage was determined by measuring the change in grip-to-grip distance. The complex was then loaded to failure at 1 mm/s, and the ultimate tensile strength, stiffness, and mode of failure were determined. RESULTS: In group A the addition of an interference screw to the EndoButton CL fixation increased the ultimate tensile strength (1,364.7 +/- 102.4 N for EndoButton CL alone v 1,449.3 +/- 94.4 N for combined technique, P = .035) and stiffness (195.5 +/- 12.1 N/mm for EndoButton CL alone v 307.3 +/- 54.9 N/mm for combined technique, P = .004) and decreased the amount of graft slippage (2.6 +/- 0.5 mm for EndoButton CL alone v 2.0 +/- 0.3 mm for combined technique, P = .017). In group B the addition of the EndoButton CL device to interference screw fixation significantly increased the ultimate tensile strength (643.5 +/- 148.4 N for BioRCI screws alone v 1,290.3 +/- 254.4 N for combined technique, P = .004) but had no effect on stiffness (315.7 +/- 38.9 N/mm for BioRCI screws alone v 341.5 +/- 64.0 N/mm for combined technique, P = .267) or graft slippage (2.7 +/- 1.0 mm for BioRCI screws alone v 2.0 +/- 0.6 mm for combined technique, P = .087). CONCLUSIONS: Our study shows that hybrid femoral fixation of double-looped gracilis-semitendinosus grafts via the EndoButton CL device and a bioabsorbable interference screw is stronger than interference or EndoButton CL fixation alone with respect to ultimate tensile strength, stiffness, and slippage. The addition of an interference screw to suspensory fixation via the EndoButton CL device increased the ultimate tensile strength from 1,360 N to 1,450 N, improved reconstruction stiffness from 200 N/mm to 300 N/mm, and decreased the amount of graft slippage resulting from cyclic loading from 2.6 mm to 2.0 mm. CLINICAL RELEVANCE: The hybrid fixation of the EndoButton CL device and an interference screw is a stronger and stiffer construct than either device alone and allows for aperture fixation, which may translate into better clinical results.

Absorbable Implants↗
PubMedDate not supplied

Primary stability with tibial press-fit fixation of patellar ligament graft: An experimental study in ovine knees.

PURPOSE: To investigate the initial fixation strength and to assess the value of tibial press-fit fixation of the bone-tendon-bone graft in anterior cruciate ligament reconstruction. TYPE OF STUDY: Nonrandomized control trial. METHODS: For tibial press-fit fixation, the tibial bone block of the bone-tendon-bone graft is countersunk in a bony groove at the distal tunnel outlet and fixed over a bone bridge with 2 No. 6 Ethibond sutures. The bone cylinder harvested from the tibial tunnel using an oscillating hollow saw is plugged into the tibial tunnel parallel to the graft, thus providing for additional anchoring of the graft by tibial press-fit fixation. In a comparative experimental study in 46 ovine knees, this fixation method was assessed for its value in anterior cruciate ligament reconstruction. A tibial bone tunnel was placed in routine manner in each ovine tibia using a target drill unit and an oscillating hollow saw. The complete patellar ligament, proximally attached to the patella and distally to a cylindrical bone block (20 x 8.4 mm), served as graft. Tibial fixation in group A (n = 10) was done using a titanium interference screw (20 x 8 mm), in group B (n = 10) using a titanium staple, in group C (n = 12) using suture fixation over a bone bridge, and in group D (n = 14) using the press-fit fixation described above. In a materials testing machine, all specimens were subjected to continuously increasing load until failure at a velocity of 1 mm/second. Ultimate failure load, stiffness, stress-strain characteristics, and failure mode were evaluated. RESULTS: Ultimate load to failure was 572 N (range, 473 to 680 N) in group A, corresponding to a fixation stiffness of 17.68 N/mm. For group B, ultimate load to failure was 608.4 N (range, 511 to 727 N) and stiffness of 19.92 N/mm. Bone block dislocation was the failure mode in groups A and B. Group C with exclusive suture fixation showed an ultimate load to failure of 304.5 N (range, 120 to 327 N) and a stiffness of only 6.96 N/mm. The mode of failure was suture cutout caused by the bone block in 9 of the cases and untying of the suture knot in 3 cases. Group D with press-fit fixation showed a significantly higher primary stability of 758 N (range, 513 to 993 N) relative to group C, with a corresponding stiffness of 25.12 N/mm (P <.02). In this group, the mode of failure was ligamentous rupture from the bone block. Regarding mechanical properties, no significant differences were seen between groups A, B, and D. CONCLUSIONS: Tibial press-fit fixation allows for metal-free fixation with high primary stability. By refilling the bone tunnel, the ligament (with a rather small cross-sectional diameter compared with hamstrings) is safely fixed within the bone tunnel to prevent potential postoperative tunnel enlargement due to movement of the graft within the tunnel. Anchoring the graft at the entrance into the joint, it provides for reduced graft length and adequate elasticity and accomplishes the requirements of fixation at the correct anatomic insertion site.

Animals↗
PubMed1964

MEASUREMENTS OF SOME CELLULAR CHANGES DURING THE FIXATION OF AMPHIBIAN ERYTHROCYTES WITH OSMIUM TETROXIDE SOLUTIONS.

On average, 15 per cent of the total haemoglobin present in the blood of the newt Triturus cristatus was extracted during 45 minutes of fixation in Palade-Caulfield fixative. This extraction was reduced with fixatives buffered at pH 6.2 instead of pH 7.4. The addition of Ca(++) ions to a final concentration of 0.01 M in the fixative completely suppressed haemoglobin extraction. The effect of the pH, and the presence or absence of Ca(++) ions in the fixative, on the rate of haemoglobin extraction has been determined. During Palade-Caulfield fixation the average projected area of newt erythrocytes increased by 37 per cent, and after dehydration and embedding in Epon the average area was 25 per cent greater than that of the unfixed cell. Fixatives buffered at pH 6.2 and containing 0.01 M Ca(++) ions caused cellular shrinkage, with the average projected area decreasing by 10 per cent in the fixative. This shrinkage continued during dehydration, and the final average area of the erythrocytes in Epon was 26 per cent less than that of the unfixed cells. Similar measurements with erythrocytes of Amphiuma tridactylum showed that after Palade-Caulfield fixation the average cellular area was increased by 45 per cent, and after dehydration and embedding in Araldite it was 36 per cent greater than that of the unfixed cell. The average nuclear area increased by 35 per cent during fixation but after embedding it was 26 per cent greater than that of the unfixed nuclei. With a fixative at pH 6.2 containing 0.01 M Ca(++) ions, both the nucleus and the whole cell shrank during fixation. The nuclear area decreased by 20 per cent and the cellular area by 22 per cent. After dehydration and embedding in Araldite, the average nuclear area had decreased by 35 per cent and the cellular area by 40 per cent. It has been shown that OsO(4) fixation lowers the isoelectric points of haemoglobins and other proteins. This finding has been used in the interpretation of the observed cellular changes resulting from fixation.

Animals↗
PubMed1997

Atrial pacing leads following open heart surgery: active or passive fixation?

The right atrial appendage is often amputated at the time of cardiopulmonary bypass. Because of concerns regarding lead displacement, use of active fixation atrial leads has been recommended in patients who require permanent atrial or dual chamber pacing after open heart surgery. We evaluated the acute and chronic performance of active and passive fixation atrial leads implanted at our institution between 1985 and 1993 in patients with previous open heart surgery. Of 78 consecutive patients, 38 had an active fixation atrial lead, 28 had a passive fixation steroid-eluting lead, and 12 had a passive fixation lead without steroid-eluting properties. At implantation, sensed P wave amplitudes were similar in the three groups, but lead impedance and threshold were significantly higher for active fixation leads compared to all passive fixation leads. During follow-up, atrial pacing thresholds were significantly higher, and sensed P wave amplitudes significantly lower, in the patients with active fixation leads compared to those with passive fixation leads. Loss of sensing occurred in 6 of 38 (16%) patients with active fixation leads and 1 of 40 (2.5%) patients with a passive fixation lead (P = 0.027). Atrial lead displacement occurred in two patients with active fixation leads and one with a passive fixation lead. Comparison with a parallel group of patients without previous open heart surgery demonstrated that atrial lead performance was similar in the two groups. We conclude that, when permanent atrial or dual chamber pacing is necessary in patients with prior open heart surgery, it is appropriate to implant a passive fixation atrial lead except on the infrequent occasions when a stable atrial position cannot be obtained.

Aged↗
PubMed1984

[Effect of fixation on immunolocalization of transferrin and albumin in the liver of the adult rat].

The influence of the fixation procedure on the localization of albumin and transferrin in adult rat liver has been carried out using an indirect immunoperoxidase technique at the light and electron microscopic levels. Perfusion and immersion fixations with different concentrations of paraformaldehyde (with or without addition of glutaraldehyde) have been investigated. According to the mode of fixation (perfusion versus immersion) and the concentration of the fixative, the number of albumin and transferrin containing hepatocytes could vary from 10% to 100%, and different labeling patterns could be observed at the electron microscopic level. For the same concentration of fixative, a perfusion fixation induces a less intense labeling than an immersion fixation. Thus similar results are obtained after immersion fixation in 6% paraformaldehyde + 0.25% glutaraldehyde or after perfusion fixation in 4% paraformaldehyde + 0.025% glutaraldehyde. Similar data are noticed after immersion fixation in 4% paraformaldehyde or after perfusion fixation in 1% paraformaldehyde + 0.025% glutaraldehyde. Moreover, perfusion fixation induced a more fine cell structure preservation than immersion fixations and avoided the appearance of zones of fixation.

Albumins↗
PubMed2006

A biomechanic comparison of an internal radiocarpal-spanning 2.4-mm locking plate and external fixation in a model of distal radius fractures.

PURPOSE: To compare the biomechanic stability of distal radius fracture fixation with a new internal radiocarpal-spanning 2.4-mm locking plate, which acts as an internal distal radius fixator, versus a standard distal radius external fixator. The number of locking screws necessary for adequate fracture fixation was also assessed. METHODS: Ten cadaveric specimens were mounted in a loading fixture with cables attached to the 2 flexor and 3 extensor wrist tendons. A 1-cm osteotomy was created to simulate an unstable distal radius fracture. The radiocarpal-spanning locking plate was fixed to the radius and index metacarpal with 4 screws proximally and 4 distally. The specimen was incrementally loaded through the tendons. Motion at the fracture site was determined. Screws were sequentially removed from the construct, the specimen was again incrementally loaded, and fracture motion was measured. The fixation was then changed to an external fixator, and the loading tests were repeated. RESULTS: Fracture fixation with the radiocarpal-spanning 2.4-mm locking plate was significantly more stable with 4 screws proximally and 4 screws distally (4 x 4) and with the 3 x 3 configuration than with the external fixator in both flexion and extension. The 4 x 4 screw configuration was not significantly different from the 3 x 3 screw configuration. The 4 x 4 screw configuration was significantly more stable than the 2 x 2 and 1 x 1 screw configurations in both flexion and extension. All internal fixator configurations and the external fixator showed more fracture displacement at increasingly higher loads. CONCLUSIONS: Fracture fixation with the new internal radiocarpal-spanning 2.4-mm locking plate is more stable than with a standard distal radius external fixator. Only three 2.4-mm locking screws proximally and three 2.4-mm locking screws distally are required for adequate fixation of the locking spanning plate.

Aged↗
PubMed2003

Biomechanical comparison of posterior pelvic ring fixation.

OBJECTIVE: To determine relative stiffness of various methods of posterior pelvic ring internal fixation. DESIGN: Simulated single leg stance loading of OTA 61-Cl.2, a2 fracture model (unilateral sacroiliac joint disruption and pubic symphysis diastasis). SETTING: Orthopaedic biomechanic laboratory. OUTCOME VARIABLES: Pubic symphysis gapping, sacroiliac joint gapping, hemipelvis coronal plane rotation. METHODS: Nine different posterior pelvic ring fixation methods were tested on each of six hard plastic pelvic models. Pubic symphysis was plated. The pelvic ring was loaded to 1000N. RESULTS: All data were normalized to values obtained with posterior fixation with a single iliosacral screw. The types of fixation could be grouped into three categories based on relative stiffness of fixation: For sacroiliac joint gapping, group 1-fixation stiffness 0.8 and above (least stiff) includes a single iliosacral screw (conditions A and J), an isolated tension band plate (condition F), and two sacral bars (condition H); group 2-fixation stiffness 0.6 to 0.8 (intermediate stiffness) includes a tension band plate and an iliosacral screw (condition E), one or two sacral bars in combination with an iliosacral screw (conditions G and I); group 3-fixation stiffness 0.6 and below (greatest stiffness) includes two anterior sacroiliac plates (condition D), two iliosacral screws (condition B), and two anterior sacroiliac plates and an iliosacral screw (condition C). For sacroiliac joint rotation, group 1-fixation stiffness 0.8 and above includes a single iliosacral screw (conditions A and J), two anterior sacroiliac plates (condition D), a tension band plate in isolation or in combination with an iliosacral screw (conditions E and F), and two sacral bars (condition H); group 2-fixation stiffness 0.6 to 0.8 (intermediate level of instability) includes either one or two sacral bars in combination with an iliosacral screw (conditions G and I); group 3-fixation stiffness 0.6 and below (stiffest fixation) consists of two iliosacral screws (condition B) and two anterior sacroiliac plates and an iliosacral screw (condition C). DISCUSSION: Under conditions of maximal instability with similar material properties between specimens, differences in stiffness of posterior pelvic ring fixation can be demonstrated. The choice of which method to use is multifactorial.

Fracture Fixation↗
PubMed2004

The use of a circular external skeletal fixation device for the management of long bone osteotomies in large ruminants: an experimental study.

The study was undertaken to evaluate the feasibility of a simple, inexpensive model of circular external fixator (CEF) for use in large ruminants. A simple model of CEF frames consisting of four full rings (13-19 cm diameter, 4 cm wide and 4 mm thick with 18-24 holes) connected by threaded rods (8 mm diameter, 10-15 cm long) and nuts was developed using mild (low carbon) steel and were nickel-plated. In the first phase of the study, three male cow calves were utilized to study the feasibility of application of the fixators in the metatarsus, tibia and radius, in reference of adaptation and tolerance by animals. In the second phase, the fixators were tested in osteotomized bones. Six bull calves of 1.5-2 years of age weighing about 200-250 kg were utilized for this purpose. After preparing the area for aseptic surgery, under xylazine (at 0.1 mg/kg, i.m.)-ketamine (i.v. till effect) general anaesthesia, the test bone (metatarsus, radius and tibia in two animals each) was approached through the medial surface and an osteotomy was created with a saw and chisel at the mid-diaphysis. The pre-constructed 4-ring CEF was mounted on the limb around the test bone in such a way that it formed a cylinder with the axis of the limb at the centre. Each ring was then fixed to the bone with a pair of beaded wires (316 SS) of 3.5 mm diameter. During the post-operative period, the animals were observed for any change in behaviour, tolerance of the fixators, the weight bearing on the test limb, the status of the fixator, and the level of reduction of the osteotomy, alignment and healing at different intervals. The fixation of CEF was easier in the metatarsus and radius than in the tibia. The inner ring diameters found adequate for metatarsus, radius and tibia were 13-15 cm, 15-17 cm and 17-19 cm, respectively. The fixators applied to different bones were well-tolerated, and the animals could lay down, stand and walk freely with the fixator without any problems. All the animals showed good weight bearing in the immediate post-operative period. Weight bearing, however, slightly reduced in the inflammatory period and showed improvement after about 4 weeks. Wire tract infection was seen in all the animals, which was more on proximal wire tracts on lateral aspect of limbs. Circular fixators were well-tolerated by all the animals, and there was no breaking/bending of connecting rods, slotted bolts or the rings at any stage of observation. Slight bowing of some wires was noticed in cases of tibia and radius (in phase II) and bending of some wires was noticed from first week in two animals one each in radius and tibia. Bone fragments were well maintained until healing occurred (appearance of bridging periosteal callus) at 60-70 days. The functional results were good in all but one case of tibia, where a mal-union was recorded. From this study, it can be concluded that CEF are well-tolerated by large ruminants and can be used to treat long bone fractures. The fixator assembly using mild steel is sufficiently strong to maintain fracture fixation and is inexpensive. The simple design of the CEF appears to be sufficient to treat simple diaphyseal fractures of the metatarsus and radius. Improvement in the technique of fixation and design-like coupling of linear and circular fixator components into hybrid constructs may help to provide greater rigidity in treating tibial and open long bone fractures.

Animals↗
PubMed1996

[Experimental study of the stabilization capability of upper metaphyseal tibial fractures by different types of external fixators].

PURPOSE OF THE STUDY: The major problem in external fixation of upper metaphyseal tibial fractures with a double-frame Hoffmann device is poor healing. With a dynamic fixation, it would be possible, with no change in technique, to compress the fracture site in a second phase, and therefore to facilitate the healing process. However, a new fixation device should not compromise the primary stability of the fixation. The aim of this experimental study on cadavers was to compare, in conditions very close to a clinical situation, the initial stabilization capability of five types of external fixation. MATERIAL: Five types of external fixators were tested on cadavers specimens: 1. a standard double-frame Hoffmann device; 2. a double-frame Hoffmann's device sagittaly reinforced with two additional anterior-posterior half-pins; 3. a type-1 axial dynamic fixation device using 6-mm conical pins; 4.a type-2 dynamic axial fixation device with 5-mm cylindrical pins; and 5. a mixed device including an lizarov-type epiphyseal fixation and a monoplane diaphyseal fixation. METHODS: The metaphyseal fracture was simulated by a transversal resection of a 20-mm segment. Specimens received by increments a load of up to 310 N, with which it was possible to determine stiffness components in valgus/varus, flexion/extension, rotation around the vertical axis and axial vertical displacement. The bone mineral content of the specimens was measured by Di Energy X-ray Absorptiometry. RESULTS: The stabilization characteristics of type-1 axial dynamic fixation were identical to those of the standard Hofmann's device in flexion/extension and in rotation as well as axially, but a greater mobility in valgus/varus was observed. The sagittal reinforcement of Hoffmann's device increased its rigidity in flexion/extension. The mixed lizarov fixation was stiffer than the standard Hoffmann's device in rotation; it was equivalent in valgus/varus and flexion/extension and less stiff in axial vertical displacement. In this study it was showed that the individual variability of bone mineral content is a negligible parameter. DISCUSSION: The experimental behaviour of the mixed Ilizarov device gives to assume that it may facilitate the healing process without endangering the primary stability of the fixation. However, this theoretical advantage should be validated in a randomized prospective clinical study.

Aged↗
PubMed1989

Eye fixations are influenced by the distribution of information within words.

Reader's eye movements were monitored while they inspected isolated words in preparation for a synonym judgement task. The 10-letter words appeared on a screen near the point of fixation, with the first fixation being imposed near the beginning, or the centre, or the ending of the word. The words themselves had uneven distributions of information, in that the beginnings or the endings contained common sequences of letters in English. Three types of words were used: those with very redundant endings (e.g., yearningly), with moderately redundant endings (e.g., varnishing), and with moderately redundant beginnings (e.g., contravene). Redundancy was defined in terms of the total number of words in English which possess that particular sequence of five letters as the beginning or the ending. The experiments asked whether the convenient viewing location within a word varied according to the distribution of information, and whether the extent of redundancy in a word ending is reflected in the distribution of visual attention given to the word. The results were analysed separately for those cases where the reader made just two fixations upon the word before moving to the synonym task, and for those cases where the reader made exactly three fixations. These were the dominant fixation patterns. Evidence for the notion of a convenient viewing position consisted of long first fixations (when there were just two fixations), when this fixation was near the centre of the word. The distribution of information within the words did not influence the duration of the first fixation, although the duration of the gaze within each half-word did increase when more informative letter sequences were being inspected. The extent of redundancy was also seen to influence the inspection patterns, when a comparison was made between the two types of words with redundant endings. Words with very redundant endings received fewer fixations when the first fixation was at the beginning, and for words gaining exactly two fixations, the second fixation was shorter if the word had a very redundant ending.

Adult↗
PubMed1996

Indications for anterior fixation of pelvic fractures.

From April 1982 to August 1995, the author treated 127 patients with pelvic ring injuries by open reduction and internal fixation within 3 weeks of injury. Fifty-five (43%) patients (none of whom had a symphysis dislocation) had posterior internal fixation without anterior pelvic internal or external fixation. In 37 patients (29%) anterior and posterior internal fixation was performed whereas 35 patients (28%) were treated by anterior internal fixation alone. Plates and screws were used for all anterior fixations. Bladder or urethral injury was not considered a contraindication to anterior internal fixation. Of 109 patients who were observed until union of their fractures, 3 required a repeat surgery because of loss of reduction or failure of fixation or both. All 3 patients maintained reduction and healed after the second intervention. Of 72 anterior internal fixations, 1 deep infection was the only surgical complication. A single plate is reliable for fixation of the symphysis pubis and when necessary, the superior pubic ramus. However, even in displaced and unstable pelvic ring injuries, most fractures of the pubic rami do not require stabilization by internal or external fixation. Eighty-eight of 105 fractures of the obturator ring were not internally fixed and none required subsequent treatment for nonunion or loss of reduction; nor did their initial instability cause failure of posterior fixation. Internal fixation of the anterior pelvic ring, though safe and reliable, should be reserved for symphysis pubis dislocations and only a minority of pubic ramus fractures.

Adolescent↗
PubMed2002

Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques.

STUDY DESIGN: Six different techniques for atlantoaxial fixation were biomechanically compared in vitro by nondestructive testing. OBJECTIVE: To evaluate the immediate three-dimensional stability of a new atlas claw combined with transarticular screws and alternative techniques for transarticular screw fixation in comparison with established techniques. SUMMARY OF BACKGROUND DATA: Posterior transarticular screw fixation in combination with wire-bone graft constructs is frequently used for C1-C2 fixation. Sublaminar wire passage carries the potential risk of neurologic complication. Transarticular screw fixation is technically demanding and, for anatomic reasons, not always feasible. METHODS: Six human cervical specimens were loaded nondestructively with pure moments, and unconstrained motion at C1-C2 was measured. The six specimens were instrumented with each of the following fixation techniques: Gallie fixation, transarticular screws and Gallie fixation, transarticular screws, transarticular screws and a new atlas claw, isthmic screws in the axis and the atlas claw, and lateral mass screws in the atlas and isthmic screws in the axis connected with rods. RESULTS: The transarticular screws restricted lateral bending and axial rotation best. The three-point fixations (transarticular + Gallie and transarticular + claw) additionally restricted flexion-extension, with lowest values for transarticular screws and the atlas claw. The alternative techniques were not as stable as the three-point fixations, but more stable than the Gallie fixation. CONCLUSIONS: Biomechanically, the three-point fixation with transarticular screws and the atlas claw provides a rigid internal fixation that is not dependent on bone graft and sublaminar wiring. In cases wherein transarticular screws are not feasible, the isthmic screws and claw or the lateral mass screws and isthmic screws are biomechanical alternatives with less immediate stability.

Aged↗
PubMed1998

Shift of visual fixation dependent on background illumination.

Visual fixation, the act of maintaining the eyes directed toward a location of interest, is a highly skilled behavior necessary for high-level vision in primates. In spite of its significance, visual fixation is not well understood; it is not even clear what attributes of the visual input are used to control fixation. Here we show, in four Macaca fascicularis monkeys, that the position the eyes assume during fixation depends on the luminance of the background. Dark background yields fixation positions that are shifted upward with respect to the fixation positions obtained with a dimly illuminated, featureless background. This phenomenon was observed previously in a nutshell by Snodderly; here first we rigorously establish its existence by testing proper controls. We then study the properties of this upshift of the fixation position. We show that, although the size of the upshift varies between monkeys, for all monkeys the upshift is larger than the radius of the fovea. Hence, if the background is dim, the eyes are positioned during fixation so that the target does not fall on the fovea. The size of the upshift remains almost unchanged while the eyes fixate at different orbital positions; thus the upshift is not caused by orbital mechanics. The upshift clearly is present even at the first days of training, but with additional training in fixation with dark background, the upshift increases in size. The upshift rotates with the head. The upshift increases gradually with decreasing levels of background luminosity. Luminosity, not visual contrast, is indeed the primary variable determining the size of the upshift. The contribution of a unit area of the retina to the upshift decreases as inverse square root of distance from the target; therefore, it is the perifoveal region of the retina that mostly contributes to the upshift, while the far periphery has little influence. The upshift can be induced or be canceled in the midst of a fixation by changing the background illumination; hence, the upshift is indeed an attribute of the fixation control system. Finally, the fixation-upshift studied here is different from a previously reported upshift of the endpoints of memory-guided saccades with respect to their target locations. These two types of upshift add up to each other. In discussing the function of the upshift, we note a possible morphological analogue with the retinal rod distribution. The upshift moves the line of gaze to a point intermediate between the fovea and the "dorsal rod peak." The upshift thus may improve visual acuity in scotopic conditions. The brain structure in which the upshift is generated must be involved in both ocular control and visual sensation. We consider several possibilities, of which we regard as the most likely the cerebellum and superior colliculus.

Animals↗
PubMed2005

Unilateral external fixator in the treatment of lower third humeral shaft fractures.

OBJECTIVE: To retrospectively analyze the effect of unilateral external fixators in the treatment of lower third humeral shaft fractures. METHODS: From October 1997 to October 2003, 33 patients aged 15 -70 years (average 31 years) with lower third humeral shaft fractures were treated with unilateral external fixators. There were 9 spiral fractures (type A1), 1 oblique fracture (type A2), 3 transverses fractures (type A3) and 20 comminuted fractures (11 type B1, 9 type B2) according to AO classification. Fifteen cases were treated with open reduction and limited internal fixation and fixation with external fixators, 10 cases treated with open reduction and fixation with external fixators, and 8 cases treated with closed reduction and fixation with external fixators. Nerve exploration was undertaken in 9 cases with preoperative radial nerve injury. External fixators were removed after bone healing. The average follow-up was 18 months with a range from 8 to 24 months. RESULTS: The time of bone healing ranged 11-22 weeks (average 14 weeks). The latest follow-up showed the functions of 9 cases of preoperative radial nerve injury and of 2 cases postoperative radial nerve injury and the function of elbow were recovered to normal. There were only 7 cases of superficial infection at pin hole, which was subsided by using oral antibiotics and pin-hole care with mild disinfectants. CONCLUSIONS: Fixation with unilateral external fixators combined with open reduction and limited internal fixation has a good effect in the treatment of lower third humeral shaft fractures.

Adolescent↗