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PubMed1982

The direct fixation system of total hip prosthesis. Research of the possibilities of fixing total hip prosthesis directly to bone.

There are two methods for the fixation of prostheses to bone; one is a method using bone cement and another is the direct fixation of the prostheses to bone. Four types of animal experiments were performed to compare the two methods of fixation. A small pyramid shaped test piece was used to compare the fixation capacity of the socket spike. Also, a special test piece was used to study the time of bone formation, to check the fixation capacity of bone bar formation occurring in the hole in the based part of the prosthetic component. furthermore, models of prosthetic stem and socket were made and attached to the femur and ilium of dog to perform fixation tests and fatigue tests. As a result, any of the tests proved that the direct fixation method without the usage of bone cement was superior to the fixation method using bone cement.

Acetabulum↗

PubMed1984

Evaluation of nine different fixatives. 2. Preservation of IgG, IgA and secretory component in an artificial immunohistochemical test substrate.

An artificial substrate was developed for quantitative testing of the ability of various fixatives to preserve the reactivity of IgG and IgA isotypes (gamma and alpha chains) and the secretory component (SC) of secretory IgA as model antigens. Polymerized normal rabbit serum was used as matrix and defined amounts (10-0.1 g/l) of antigen were incorporated into it by diffusion before fixation and paraffin embedding. The various fixatives comprised alcohol, routine formalin, glutaraldehyde(1%)-formalin, Baker's formol calcium, formol sublimate, acetic acid(2%)-formol saline, Bouin's fluid, Susa fixative, and carbodiimide. The detection sensitivity afforded by these fixatives was defined as the immunofluorescence staining end point. Compared to the reference value obtained with alcohol (gamma and alpha chains, 0.06 g/l of IgG and IgA; SC, 0.12 g/l of colostral IgA), an antigen concentration at least 8 times higher was necessary for detection with most of the cross-linking fixatives. Bouin's and Susa fixatives were peculiar in that they required more than 150 times higher antigen concentration for detection of IgG but only 3-8 times higher for IgA. The determined sensitivities were compared with the immunofluorescence performance results obtained on human tissues prepared with the same fixatives; excepting carbodiimide (which produced unacceptable autofluorescence of the substrate matrix) a remarkably good correlation was found with regard to IgG- and IgA-producing cells (especially of the former isotype) and secretory epithelium (IgA and SC). However, the latter result depended on pronase treatment of the tissue sections to unmask epithelial antigens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2005

[ACL reconstruction with bone-patellar tendon-bone graft and proximal fixation with the EndoButton: a 2- to 5-year follow-up].

BACKGROUND: Interference screw fixation in ACL reconstruction with bone-patellar tendon-bone graft (BPTB) is a potential source of intraoperative complications such as graft laceration. Further problems are artifacts on MRI and screw removal in revision surgery. These problems can be avoided by using distant fixation with the EndoButton. We designed this study to evaluate the clinical as well as the subjective outcome of ACL reconstruction with BPTB graft and femoral fixation with the EndoButton. METHODS: A total of 51 patients (7 female, 44 male) were examined 2-5 years after ACL reconstruction with BPTB graft and femoral fixation with the EndoButton. We used the IKDC form, Lysholm score, Tegner activity score, and digital radiographs (AP, lateral, axial) for the evaluation. RESULTS: Of all the patients included in the study, 87% showed a "normal" or "nearly normal" knee function according to the IKDC score, Lysholm score 94.2+/-7.9, Tegner score 6.4+/-1.2, and subjective IKDC 89.9+/-11.9. Radiological signs of arthritic changes could be seen in ten cases. CONCLUSION: The clinical outcome of ACL reconstruction with EndoButton fixation is comparable to other studies on ACL reconstruction with interference screw fixation. However, since the EndoButton avoids potential problems of the interference screw fixation, we recommend this fixation technique for ACL reconstruction with BPTB graft.

Adolescent↗

PubMed2003

Active eye fixation performance in 940 young men: effects of IQ, schizotypy, anxiety and depression.

A total of 940 young men performed a task in which they actively maintained fixation for 50 s in three conditions: a). on a visual target, b). on a visual target while distracting targets appeared briefly on the periphery and c). with no visual target present. The same individuals completed psychometric evaluation tests measuring IQ, schizotypy and current state-dependent psychopathology. The proportion of fixation time decreased and saccade frequency increased in condition b compared wih condition a, and sequentially in condition c compared with condition b. A trend towards a decrease in proportion of fixation time and increase in saccade frequency was found as the subjects maintained fixation during the task and this time-dependent deterioration of performance was again most pronounced in condition c, less so in condition b and absent in condition a. Psychometric test scores were significantly correlated with fixation performance in the population. Worse performance in all three fixation conditions was observed for individuals with lower IQ scores. A deterioration of fixation performance with time in condition b was correlated with disorganization characteristics of schizotypy, suggesting that these individuals had difficulty maintaining active fixation in the presence of increased inhibitory load. A connection of such a difficulty with the frontal lobes and their role in the control of voluntary inhibitory functions is discussed.

Adolescent↗

PubMed1998

Visual responses with and without fixation: neurons in premotor cortex encode spatial locations independently of eye position.

The ventral premotor cortex (PMv) of the macaque monkey contains neurons that respond both to visual and to tactile stimuli. For almost all of these "bimodal" cells, the visual receptive field is anchored to the tactile receptive field on the head or the arms, and remains stationary when the eyes fixate different locations. This study compared the responses of bimodal PMv neurons to a visual stimulus when the monkey was required to fixate a spot of light and when no fixation was required. Even when the monkey was not fixating and the eyes were moving, the visual receptive fields remained in the same location, near the associated tactile receptive field. For many of the neurons, the response to the visual stimulus was significantly larger when the monkey was not performing the fixation task. In control tests, the presence or absence of the fixation spot itself had little or no effect on the response to the visual stimulus. These results show that even when the monkey's eye position is continuously changing, the neurons in PMv have visual receptive fields that are stable and fixed to the relevant body part. The reduction in response during fixation may reflect a shift of attention from the visual stimulus to the demands of the fixation task.

Animals↗

PubMed2005

Biomechanical evaluation of a bioabsorbable expansion bolt for hamstring graft fixation in ACL reconstruction: an experimental study in calf tibial bone.

INTRODUCTION: The purpose of our study was to evaluate and compare the primary fixation strength of a novel bioabsorbable two shell expansion bolt (EB) with that of a well-established interference screw-fixation technique in hamstring reconstruction of the anterior cruciate ligament. MATERIALS AND METHODS: Thirty calf tibia plateaus (age 5-6 months) were assigned to three groups: In group I (n = 10) triple-stranded hamstring grafts were fixed with titanium interference screws (7 mm thread / 8 mm head x 25 mm). Specimens of group II (n = 10) received bioabsorbable poly-L-lactide interference screws (8 x 23 mm). In group III (n = 10), the grafts were fixed using bioabsorbable poly-D,L-lactide expansion bolts (5.8/8.5/10 mm x 35 mm). The tensile axis was placed parallel to the bone tunnel. The construction was then loaded until failure under a displacement rate of 1 mm per second. RESULTS: There were no significant differences concerning the maximum pullout force (group I: 357 N +/- 61; group II: 326 N +/- 92; group III: 343 N +/- 55). In case of the expansion bolt, we found the stiffness to be higher (61 N/mm) when compared to group I (48 N/mm), and group II (52N/mm) (P < 0.01 I vs. III). Using interference screws, we were able to demonstrate a strong correlation between torque and pullout forces (group I: r2 = 0.7; group II: r2 = 0.92). Ruptures of the suturing material occurred only in groups I and II. CONCLUSION: We conclude that hamstring graft fixation, using the presented expansion bolt, demonstrates fixation strength similar to the established screw fixation and can therefore be regarded as a reasonable alternative fixation method. Especially, since some specific disadvantages of screw fixation can be prevented by application of the bolt fixation.

Animals↗

PubMed2005

External fixation in comminuted, displaced intra-articular fractures of the distal radius: is it sufficient?

INTRODUCTION: External fixation has been extensively used to treat the intra-articular fractures of the distal radius and it has several distinct advantages over conventional POP cast and plate fixation. However, the limitation of external fixation to achieve articular congruity in the comminuted intra-articular fractures of the distal radius has been documented in the literature. This could be because external fixation alone does not expand crushed cancellous bone and cannot work without soft tissue hinges. This prospective study was conducted to look at the results of comminuted, displaced intra-articular fractures of the distal radius treated exclusively by external fixation. MATERIALS AND METHODS: A 2-year follow-up of 27 patients with comminuted, displaced intra-articular fractures of distal radius that were treated exclusively by external fixation is presented. The radiological results, functional results and complications were analyzed according to the scoring system given by Jakim et al. RESULTS: Anatomical reduction could not be achieved in 12 patients (44%) and reduction was lost in two patients (7%). Excellent and good results were seen in 59.3%, fair results were seen in 22.2% and poor results were seen in 18.5% of the cases. Outcome scores of patients without articular step were significantly better as compared to the patients with articular step at healing. There was a positive correlation between the restoration of normal anatomy (radiological results) and the functional outcome (r=0.775). Overall nine patients (33%) had complications. CONCLUSION: We conclude that although the external fixation is reliable in maintaining the reduction in displaced comminuted intra-articular fractures, it is inadequate in restoring articular congruity in many cases. The complications of external fixation are frequent and may be potentially serious in nature.

Adolescent↗

PubMed2006

Fixation of nondisplaced scaphoid fractures: making treatment cost effective. Prospective controlled trial.

INTRODUCTION: Nondisplaced scaphoid waist fractures treated with prolonged plaster immobilisation often lead in transient joint stiffness and to a delay in return to sport and work activity. The long time off work increases the work off compensation costs. Internal fixation of scaphoid fractures has resulted in a shorter time to union and to return to work and sports. This prospective study compares cast immobilisation with screw fixation and the direct cost with indirect cost of conservative and minimally invasive treatment of undisplaced scaphoid fractures. MATERIALS AND METHODS: Forty-seven patients with an acute nondisplaced waist fracture of the scaphoid were allocated into either cast immobilisation or internal screw fixation for this study. Cost data concerning the groups of nonoperated and operated patients were analysed. Range of wrist motion, grip strength, DASH-score, time to fracture union, return to work time and the needed physiotherapy at the final follow-up at 6 months were evaluated. RESULTS: Twenty-one patients were included in the group of screw fixation and 23 patients were included in the group of cast immobilisation. At final follow-up there was no significant difference in the range of motion of the wrist or in grip strength. The operatively treated group had a better mean DASH-score than the conservative group. Fracture union was seen in the screw fixation group at a mean of 43 days and in the cast immobilisation group at a mean of 74 days (P < 0.5). The average time of return to work was 8 days for patients who had an internal screw fixation, while those treated with a cast returned to work at a mean of 55 days (P < 0.5). In total the internal fixation of undisplaced scaphoid fractures is less expensive than conservative treatment. CONCLUSION: Internal screw fixation of nondisplaced scaphoid fractures had a shorter time to bony union and the patients returned earlier to work compared with cast immobilisation. Although it is assumed that operative treatment is more expensive, in this study the cost was not found to be higher.

Adult↗

PubMed1998

The role of supplemental translaminar screws in anterior lumbar interbody fixation: a biomechanical study.

The immediate stabilization provided by anterior interbody cage fixation is often questioned. Therefore, the role of supplementary posterior fixation, particularly minimally invasive techniques such as translaminar screws, is relevant. The purpose of this biomechanical study was to determine the immediate three-dimensional flexibility of the lumbar spine, using six human cadaveric functional spinal units, in four different conditions: (1) intact, (2) fixed with translaminar screws (TLS), (3) instrumented with anterior interbody cage insertion with the BAK system and (4) instrumented with BAK cage with additional TLS fixation. Flexibility was determined in each testing condition by measuring the vertebral motions under applied pure moments (i.e. flexion-extension, bilateral axial rotation, bilateral lateral bending) in an unconstrained manner. Anterior fixation with the BAK alone provided significant stability in flexion and lateral bending. Additional posterior TLS significantly reduced the motion in extension and axial rotation. TLS fixation alone resulted in smaller rotations than BAK fixation in all loading directions. Based on these results, it seems that interbody cage fixation with the BAK system stabilizes the spine in some, but not all, loading directions. The problematic loading directions of extension and axial rotation can be substantially stabilized by using translaminar screw fixation. However, one should emphasize that the degree of stability needed to achieve solid fusion is not known.

Biomechanical Phenomena↗

PubMed1995

Stress protection due to external fixation.

Bone is sensitive to mechanical influences. The presence of an orthopaedic device will impose constraints on the mechanical environment that may influence subsequent remodelling and repair. An Oxford External Fixator was applied to six intact ovine tibiae. The strains engendered during normal walking were then recorded from strain gauges applied to the mid-shaft of the bone. The fixator configuration was then altered such that the intact fixator bar connecting the pins was replaced with a sectioned version that did not permit load transfer through the fixator, and the strain environment re-recorded. The peak strains recorded with the intact bar were significantly lower than those recorded with the sectioned bar. This showed that the use of a fixator with an intact bar resulted in significant stress protection of the underlying bone. A fixator was then applied to both the right and left tibiae of a further six animals and the resulting strain environment and corresponding remodelling response was observed over 16 weeks. In each case one fixator was configured with an intact bar (the stress protected limb), whilst the other utilised a sectioned bar (the unprotected limb). The results showed that over this period the bone mineral content fell by 9% in the stress protected limb compared to the unprotected limp. Quantitative assessment of the bones showed that this bone loss occurred as a direct consequence of resorption on the periosteal and endosteal surfaces. In addition, strain recordings at week 16 showed that the fixator was still stress protecting the tibia.

Animals↗

PubMed1995

The effect of red and neutral density filters on the degree of eccentric fixation.

The reported shift of fixation to a more central position when a red filter is placed before an eye which fixates eccentrically, has never been satisfactorily explained. To further investigate this phenomenon, 14 subjects with eccentric fixation were recruited. A Wratten No. 92 filter was placed before the eccentrically fixating eye, and any change of fixation was assessed by the after-image transfer test. A neutral density (ND) filter was then used, to mimic the reduced retinal illumination caused by the red filter. The results suggest that there is a significant reduction in the eccentricity of fixation, when placing the red filter before an eccentrically fixating eye, and also when placing the ND filter. No significant difference in the effects produced by either filter was found. This suggests that it is the reduction in retinal illuminance caused by the red filter which contributes towards such improvements in fixation.

Afterimage↗

PubMed2006

The initial safe range of motion of the ankle joint after three methods of internal fixation of simulated fractures of the medial malleolus.

BACKGROUND: Previous studies have demonstrated the safe passive range of ankle motion for inter-bone stiffness after internal fixation under load but there is a lack of information about the safe range of ankle motion for early rehabilitation in the absence of loading. The present study was designed to assess the effect of ankle movement on inter-bone displacement characteristics of medial malleolus fractures following three types of internal fixation to determine the safe range of motion. METHODS: Five lower legs obtained during autopsy were used to assess three types of internal fixation (two with Kirschner-wires alone; two with Kirschner-wires plus tension band wiring; and, one with an AO/ASIF malleolar screw alone). Following a simulated fracture by sawing through the medial malleolus the displacement between the fractured bone ends was measured during a passive range of movement with continuous monitoring using omega (Omega) shaped transducers and a biaxial flexible goniometer. Statistical analysis was performed with repeated measures analysis of variance. FINDINGS: Inter-bone displacement was not proportional to the magnitude of movement throughout the range of ankle motion as, when separation exceeded 25 microm, there was increasingly wide separation as plantar-flexion or dorsal-flexion was increased. There was no statistical significant difference between the small amount of inter-bone displacement observed with three types of fixation within the safe range of dorsal-flexion and plantar-flexion for early rehabilitation. However the inter-bone separation when fixation utilized two Kirschner-wires alone tended to be greater than when using the other two types of fixation during dorsal-flexion and eversion. INTERPRETATION: The present study revealed a reproducible range of ankle motion for early rehabilitation which was estimated to be within the range of 20 degrees of dorsal-flexion and 10 degrees of plantar-flexion without eversion. Also, internal fixation with two Kirschner-wires alone does not seem to provide stability achieved by the other two forms of fixation.

Ankle Injuries↗

PubMed2005

A biomechanical analysis of an instrumented spinal fixator under torsional loads.

The effect of design features of an internal spinal fixator on the loading of its individual components is paramount to the understanding of the interaction between the fixator and the instrumented spine. Using a corpectomy injury model, a strain gauge instrumented spinal fixation device was employed to investigate the role of clamp tightening torque and the inclusion of transverse bars on the distribution of bending and torsional moments acting on the fixator under torsional loading. The increase in clamp torque from 5 to 10 Nm caused a marked decrease (40%) in torsional moments acting on the vertical rods, an increase of 24% in torsional moments acting on the screws and an increase of 44% in bending moments acting on the rods along the sagittal plane of the fixator. The inclusion of transverse elements significantly increased (132%) the bending moment acting on the rods and decreased (92%) the bending moments acting on the screws along the sagittal plane. The change in both design parameters significantly reduced the response hysteresis and decreased the asymmetry of loading. A theoretical model, developed to elucidate the load path mechanisms underlying this response, successfully predicted the external response of the fixator. This model suggested both design parameters would affect the internal force and moment distribution across the fixator and the relative role of each load response mechanism in effecting this response. The changes in load patterns across the fixator will influence both its ability to augment the process of spinal fusion and the long-term performance of its components.

Biomechanical Phenomena↗

PubMedDate not supplied

Volar fixation for dorsally angulated extra-articular fractures of the distal radius: a biomechanical study.

PURPOSE: To compare the biomechanical properties of 10 volar plate-fixation designs in 2 fracture models (dorsal wedge osteotomy, segmental resection osteotomy models). METHODS: Forty-eight radiuses were used in this study including 8 pairs. In 40 specimens a 15-mm dorsally based wedge osteotomy was performed and the volar cortex was fractured manually. They were arranged into 10 fixation groups with 5 different fixation designs (test 1). In the contralateral specimens of 8 paired radiuses a 10-mm segment of bone was excised (test 2). Four of the 10 fixation systems were chosen for these specimens. Cadaver hands and the proximal radiuses were potted in polymethylmethacrylate and tested with a servohydraulic materials testing machine with 300 N of axial compression load at 1 N/s initially and after each 1,000 cycles up to 5,000 cycles. After cyclic loading the specimens were loaded to failure in axial compression at 2 mm/min. The stiffness, failure peak load, and failure mode of each specimen were recorded. RESULTS: In test 1 in the wedge osteotomy specimens the T plate was the stiffest and the Synthes titanium plate was the least stiff; however, all specimens completed the 5,000 cycles of loading with no failures. There was no significant difference between the 10 fixation groups in failure peak load and only 7 of 40 failed at the distal portion of the hardware in the final load to failure testing. In test 2 the resection osteotomy specimens were less stiff and failed at a lower failure peak load compared with the wedge osteotomy specimens. Failure at the distal portion of the fixation system was seen in 7 of 8 specimens; nonlocking screws loosened and tines compressed the surrounding bone, resulting in tine-hole enlargement. CONCLUSIONS: All of the plate-fixation systems delivered sufficient stability to permit the simulated postoperative regimen of 1 week of immobilization followed by 5 weeks of early mobilization until expected union at 6 weeks after surgery. Based on these results a preferable volar fixation system would appear to benefit from the following: (1) sufficient plate strength to support the distal fragment from the volar side, (2) a locking system with sufficient strength to remain locked during the healing process, and (3) a distal design that does not affect the bone adversely. The anatomic reduction of the volar cortex in the wedge osteotomy specimens added stability to the construct.

Adult↗

PubMed1978

The relationship between fixation disparity and heterophoria.

Twenty-five asymptomatic subjects with normal binocular vision underwent determination of the magnitude and direction of their heterophoria and their fixation disparity. Fixation disparity was measured at a 2-m fixation distance with the phase-difference haploscope under conditions simulating those of casual seeing. When combined with careful attention to symmetrical control of accommodation, this method eliminates several known technical artifacts. Examples of the normal fluctuation of the magnitude and direction of fixation disparity for individual subjects were demonstrated. Whereas only a slight preponderance of subjects were esophoric, many subjects had convergent fixation disparity (esodisparity). Linear regression analysis of the data revealed a coefficient of correlation between fixation disparity and heterophoria at 6 m of 0.61, and at 33 cm of 0.50. The results suggest that normal, small magnitude heterophoria does not necessarily produce fixation disparity and that fixation disparity does not necessarily sustain heterophoria.

Adult↗

PubMed1999

Open tibial fractures: faster union after unreamed nailing than external fixation.

Unreamed intramedullary nailing is an alternative to external fixation in the treatment of open tibial fractures. We compared a prospective series of thirty-one patients managed with a solid nail with static interlocking without intramedullary reaming, with a retrospective series of thirty-one patients managed by external fixation. The protocol for soft tissue treatment was the same throughout the study period. Most fractures were caused by high energy trauma and included Grade I to III B injuries. The fracture wound infection rate was equal in both groups; there were two deep and three superficial infections in the nail group and three deep and two superficial infections in the external fixation group. In addition, eleven patients in the external fixation group had severe pin track infections. The mean time to union was five months in the nail group and eight months in the external fixation group. The incidence of delayed union was twice as high in the external fixation group as in the nail group. The number of surgical procedures performed to promote union was three times higher in the external fixation group. The malunion rate did not differ between the groups. Although the treatment groups are not fully comparable, the results indicate that intramedullary nailing is superior to external fixation in the treatment of most open tibial fractures.

Adolescent↗

PubMed2002

A precise radiographic technique for the measurement of dimensional changes in heart valve biomaterials following fixation.

Accurate tissue thickness measurements are difficult to acquire by present techniques. Error is introduced by tissue compression during measurements or by tissue processing prior to measurement. In the field of valve replacement, tissue dimensional changes from fixation prior to implantation may predispose implants to premature tissue failure and it becomes important to have an accurate method for comparing cusp dimensions pre- and post-fixation. A new approach is to use high-resolution digital radiography to make thickness maps of entire specimens. For 25 matched porcine aortic valve cusps, we have evaluated this technique's ability to measure and compare thickness, surface area and volume before and after 7 days of aldehyde fixation. Digital radiographs were acquired pre- and post-0.5% glutaraldehyde (n=13) or 10% formaldehyde (n=12) fixation. Mean thickness, surface area, volume and four measurements to evaluate shape differences with fixation were obtained and compared pre- and post-fixation using paired t tests. The results demonstrate that this X-ray imaging technique can provide dimensions of matched fresh and fixed specimens and is sensitive enough to show statistically significant changes due to fixation. These findings also illustrate that aldehyde fixation can cause tissue contraction resulting in a significant overall increase in tissue thickness and a decrease in surface area. This technique could be used to gain further insights into tissue anatomy and mechanics.

Animals↗

PubMed1999

Fixation disparity and nonius bias.

Fixation disparity, i.e. the vergence error within Panum's area, can be measured psychophysically with two nonius (vernier) lines that are presented dichoptically, i.e. one to each eye. The observer adjusts these nonius lines to subjective alignment; the resulting physical nonius offset indicates the amount of fixation disparity. The present experiments investigate the relation between fixation disparity and the nonius bias, which is the physical offset of the nonius lines that is adjusted by the observer in order to perceive them as aligned when both nonius lines are presented to both eyes (binocular nonius bias) or both to the left or both to the right eye (monocular nonius bias). It was found that (1) the fixation disparity is correlated with the binocular nonius bias in the horizontal and vertical meridian and (2) the binocular nonius bias can be predicted from the average of the right eye and left eye monocular nonius bias. To remove the influence of the nonius bias on measured fixation disparity it is possible to calculate the fixation disparity relative to the individual binocular nonius bias, rather than to the physical coincidence of the nonius lines. This procedure tends to increase the correlation between fixation disparity and the tonic resting position of vergence. We discuss the clinical relevance of the dichoptic nonius method for measuring fixation disparity and its limitations as compared to physical recordings of eye position.

Convergence, Ocular↗