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PubMed1978

A methodological study for the quantification and the control of the physico-chemical processes occurring during cell fixation. I. The development of a new technology.

Fixation in a traditional sense means the immersion of biological material into a chemical fluid. For permanent preservation the fixative is always "offered" (1) in excess of the cell sample, and the process of fixation is influenced by (2) chemical impurities of the fixative fluid. Both factors influence the succeeding dyeing of cells. In order to avoid these uncontrolled criteria, a new technology for controlled cell fixation has been developed, whereby freshly prepared formaldehyde and methanol gas in an "inert" gas-flow of helium was applied to thin membranes by aid of a capillary flow-in technique. The instrumental equipment consists of (1) an ultra-high vacuum flow-apparatus with a total-pressure measuring unit, (2) a gas-supply device, (3) a mass spectrometer including a pump system, and (4) a Teflon and/or glass-gas chamber for the treatment of synthetic (Hostaphan foils) or biological membranes (mesenterium) with formaldehyde as the fixative gas. The amount of "offered", adsorbed, absorbed, diffused, and desorbed fixative gas could be absolutely estimated after the saturation of the membranes with an "on-line" operating "inert" mass spectrometer of the Omegatron type. The gas treatment of the Hostaphan foils with formaldehyde showed that nearly all adsorbed gas molecules could be desorbed. In contrast to native membranes the greatest proportion of the gas molecules adhered to the biological surface, and only a small quantity were desorbable. Physisorption or physisorption and chemisorption occured depending on the adsorber surface property. A monolayer of formaldehyde of 5.10(14) to 1.10(15) molecules per 10(16) A2 surface area can be postulated on the basis of these preliminary results. This value corresponds to a mass of about 5.10(-8) g CH2O. It resulted in an area-coverage ratio of CH2O molecules per cell of 10(9):1. The membrane surface facing the gas side always amounted to 1 cm2. A fixative gas concentration of 10(6) molecules/cm3, and therefore a degree of coverage of less than 1/1000 monolayer can be estimated absolutely. For a precise determination of the degree of fixation, further experiments and the evaluation of additional physico-chemical parameters are necessary.

Adsorption↗
PubMed1992

Orthopedic prosthesis fixation.

The fixation of orthopedic implants has been one of the most difficult and challenging problems. The fixation can be achieved via: (a) direct mechanical fixation using screws, pins, wires, etc.; (b) passive or interference mechanical fixation where the implants are allowed to move or merely positioned onto the tissue surfaces; (c) bone cement fixation which is actually a grouting material; (d) biological fixation by allowing tissues to grow into the interstices of pores or textured surfaces of implants; (e) direct chemical bonding between implant and tissues; or (f) any combination of the above techniques. This article is concerned with various fixation techniques including the potential use of electrical, pulsed electromagnetic field, chemical stimulation using calcium phosphates for the enhancement of tissue ingrowth, direct bonding with bone by glass-ceramics and resorbable particle impregnated bone cement to take advantages of both the immediate fixation offered by the bone cement and long term fixation due to tissue ingrowth.

Bone Cements↗
PubMed2005

The contribution of microsaccades and drifts in the maintenance of binocular steady fixation.

BACKGROUND: The eye performs three types of eye movements during fixation: fast microsaccades are interrupted by slow drift movements, and tremor is superimposed on the drifts. The contribution of the microsaccades and drifts in maintaining fixation has been discussed since the late 1950s. Initially, microsaccades were thought to correct the misalignment from the optimal fixation locus induced by the drift movements, a theory still postulated in more recent work. The present study aimed to uncover to what extent each fixation movement contributes to maintain steady binocular fixation. METHOD: Binocular fixation during a 40-s fixation task was recorded using an infrared recording technique for ten normal test persons. Start and end point of each microsaccade and drift were superimposed on a fixation map, and the distance to the preferred retinal location of fixation (PRL) was measured. RESULTS: It was found that 32.6% of the microsaccades corrected the previous drift movement towards the PRL, whereas 53.1% of the drifts corrected the endpoint of the previous microsaccade towards the PRL. The overall mean post-microsaccadic and mean post-drift distance to the PRL for the ten normal test persons were 0.46 degrees and 0.41 degrees , respectively; the difference was not statistically significant. Interindividually, the mean post-microsaccadic distance to the PRL ranged between 0.21 degrees and 0.91 degrees and the mean post-drift distance to the PRL ranged between 0.20 degrees and 0.72 degrees . CONCLUSION: Neither the endpoints of the microsaccades nor the drifts bring the visual line to coincide with the centre of the PRL. Consequently, it must be the eye movements performed during the drifts ("slow control") that keep the visual line in the centre of the foveola.

Adult↗
PubMed2005

Anterior C2-C3 fixation with screws: proposal of a new technique and comparative mechanical assays.

The technical difficulties involved in the anterior fixation of the C2-C3 vertebral segment by means of plates and screws, related to retraction of the structures around the vertebral segment, appropriate exposure of the site and positioning of the screws and plate, motivated the development of a new modality of fixation of this segment using only screws. Fixation of the C2-C3 vertebral segment according to the technique proposed requires less exposure of the vertebral segment and does not involve the technical difficulties of standard fixation with plates and screws. In order to study the mechanical properties of this new modality of vertebral fixation, mechanical tests were performed comparing the proposed technique (fixation solely with screws positioned in the craniocaudal direction) and routinely used fixation (H plate and screws). The tests were performed using 80 cervical spine segments from Landrace pigs aged 5 months. The vertebral segments fixed by the two techniques were divided into experimental groups of ten specimens each and submitted to mechanical tests of flexion, extension, lateral bending and rotation in a universal testing machine. The mechanical properties used to compare the results were the load necessary to produce a pre-established deformation and stiffness. No significant differences were observed between the values obtained for the production of the pre-established deformation in the flexion and rotation tests. In the extension and lateral bending tests, the mean values obtained for vertebral segments fixed only with screws were significantly higher. Analysis of stiffness showed no significant difference in the flexion, rotation and lateral bending tests, whereas in the extension tests, the mean values for the group fixed only with screws were significantly higher. The results of the mechanical tests performed showed that fixation of the C2-C3 segment only with screws was not inferior from a mechanical point of view when compared to fixation with H plates of the Orozco type.

Animals↗
PubMedDate not supplied

How spatial orientation of Japanese text affects fixation points in patients with bilateral macular atrophy.

PURPOSE: To ascertain the retinal area used by patients with bilateral macular atrophy when reading Japanese text of different character sizes written horizontally or vertically. In addition, to determine fixation points as part of the first of a series of studies designed ultimately to enhance the quality of life of these patients through the improvement of reading acuity. METHODS: Seventeen patients (34 eyes) with bilateral macular atrophy were tested to determine the retinal area employed for reading (R fixation point). Sentences were arranged either horizontally or vertically and projected onto the retina using a scanning laser ophthalmoscope. We also determined the fixation point using microperimetry (M fixation point). The positional relationships between these two fixation points and the scotoma were examined. RESULTS: The R and M fixation points were the same in 20 of the 34 eyes. Multiple R fixation points were found in 11 eyes. The R fixation point was frequently positioned above the lesion when reading horizontally (nine eyes), while it was often positioned in the area nasal to (eight eyes) or temporal to (six eyes) the lesion when reading vertically. CONCLUSIONS: Fixation points changed frequently in these patients with bilateral macular atrophy depending on the spatial orientation of the text. These data should be used in the future to help patients learn how to use the preferred retinal locus to improve their reading skills and enhance their quality of life.

Adolescent↗
PubMedDate not supplied

A microperimeter that provides fixation pattern and retinal sensitivity measurement.

PURPOSE: To investigate a microperimeter (MP-1) that can independently measure fixation status and microperimetry of retinal threshold sensitivity by comparing the results obtained by the MP-1 with those obtained by scotometry using scanning laser ophthalmoscopy (SLO). METHODS: Fourteen patients (15 eyes) with a macular disorder were examined by the MP-1 fixation test, MP-1 microperimetry, and SLO scotometry. The scotoma size seen in MP-1 microperimetry was compared with that observed in SLO scotometry. The location of the preferred retinal locus (PRL) and the fixation stability, which were obtained from the fixation test in MP-1, were also compared with those obtained in SLO scotometry. RESULTS: The scotoma size, which was not seen with 0 dB in MP-1 microperimetry, was larger than that in SLO scotometry in 8 of the 15 eyes. Retinal threshold sensitivity decreases were found using MP-1 microperimetry within a sensitive area of SLO scotometry in all eyes. The PRL in the MP-1 fixation test and in SLO scotometry agreed in all eyes. Fixation stability in the MP-1 fixation test significantly correlated with that in SLO scotometry (P = 0.0192). CONCLUSIONS: The results of MP-1 microperimetry do not completely agree with those of SLO scotometry owing to the difference in stimulus intensity. The MP-1 fixation test is useful for measuring PRL and fixation stability in a short time. MP-1 might be helpful to evaluate the foveal function in patients with macular disorders without severely damaged macular function.

Aged↗
PubMed1983

Selection of a fixative for identifying T cell subsets, B cells, and macrophages in paraffin-embedded mouse spleen.

Fixation techniques were investigated for their ability to preserve morphology, esterase activity and cell surface antigens in paraffin-embedded mouse lymphoid tissue. The avidin-biotin-peroxidase system was used to stain antigens Thy-1.2, Lyt-1, Lyt-2, RA32C2 and F4/80. Conventional fixatives were compared with fixatives containing periodate and lysine plus paraformaldehyde and/or glutaraldehyde. Conventional fixatives preserved esterase activity but not many cell surface antigens. Periodate-lysine fixatives allowed better preservation of membrane antigens, but esterase activity was often lost at antigen-preserving concentrations of paraformaldehyde or glutaraldehyde. However, a periodate-lysine fixative containing both paraformaldehyde and glutaraldehyde preserved esterase and showed good to excellent staining of Lyt-1, Thy-1.2, RA32C2, and F4/80. Lyt-2 could not be stained with any fixative, but was well preserved in frozen material post-fixed with periodate-lysine based fixatives. We conclude that with proper fixation immune cell surface markers can be identified in paraffin-embedded tissue.

Animals↗
PubMed2006

Comparison between different femoral fixation devices for ACL reconstruction with doubled hamstring tendon graft: a biomechanical analysis.

PURPOSE: The aim of the present study was to compare the mechanical behavior of some devices used for femoral fixation of doubled hamstring tendon graft in anterior cruciate ligament (ACL) reconstruction when included in a graft fixation complex (GFC). METHODS: An ACL reconstruction was performed on 90 porcine knees. The graft used was the doubled lateral extensor of toes (DLET). Nine different femoral fixation devices were tested and classified according to their fixation mechanism: compression (Bioscrew and RCI screw); expansion (Rigidfix); cortical suspension (Ligament Anchor, EndoButton-CL, and Swing Bridge); cancellous suspension (Linx-HT); and cortical-cancellous suspension (Transfix and Bio-Transfix). All GFC were subjected to a cyclic loading test, then to a load-to-failure test. Graft elongation after 1,000 load cycles, failure load, and stiffness were calculated for each device. RESULTS: Regarding graft elongation, Bioscrew and RCI screws showed the highest mean values. All the other GFC showed no significant differences between them when delta elongation (elongation(1,000 cycles) - elongation(20 cycles)) was considered. For failure load, the highest mean values were observed for Bio-Transfix, Transfix, and Swing Bridge; a homogeneous subset with the lowest mean values was formed by Ligament Anchor, RCI screw, Bioscrew, and Linx-HT. For stiffness, the greatest values were observed for Bio-Transfix, Transfix, and Swing Bridge; all other groups showed no significant differences between them. CONCLUSIONS: Cortical-cancellous suspension fixation seemed to offer the best and most predictable results in terms of elongation, fixation strength, and stiffness. For both compression and suspension, the weakest fixation was attained with cancellous fixation devices. Cortical suspension devices showed a greatly variable mechanical behavior, according to their design. CLINICAL RELEVANCE: Transcondylar devices offer the best structural properties for femoral fixation of doubled hamstring tendon graft in ACL reconstruction.

Animals↗
PubMed2006

Why fine-wire fixators work: an analysis of pressure distribution at the wire-bone interface.

Tensioned fine-wire external fixator systems have been used successfully for the treatment of fractures, mal-unions and for limb lengthening for many years. When used in metaphyseal bone, this type of fixator has a lower loosening rate than half-pin fixators. The differing mechanical properties of these fixator systems have been investigated extensively; however, most studies have centered on the mechanical properties of the fixator as a whole. Our knowledge of the interactions occurring at the interface between implant and bone remains sparse. In order to investigate this interaction, we devised a simple experimental model to characterise the distribution of pressure in cancellous bone surrounding a tensioned wire under loading conditions. Comparison was then made to a similar model of a half-pin fixator. Pressure was measured using pressure sensitive film at various distances away from the implant-bone interface. Static, single cycle loading of the model was performed with a Universal Testing Machine. Pressure distribution in the fine-wire model was found to occur in three regions: polar, beam loading and uniform. Polar patterns were seen closest to the wire with pressure concentrated at the entry and exit points of the wire. Beam loading was seen at a distance of 1.5 mm from the wire and pressure reached a uniform distribution at 4.0 mm. Most of the pressure measured was less than 2 MPa, which is less than the yield strength of cancellous bone (2-7 MPa). Higher loads produced higher stresses but the distribution pattern was similar. In contrast, the half-pin model showed far higher pressures (20 MPa), which were present deeper in the bone specimen. These results further our understanding of the biomechanics of fine-wire fixators and may explain the lower loosening rate of this type of fixator when compared to half-pin fixators used in metaphyseal bone.

Biomechanical Phenomena↗
PubMed2001

Distal femoral fracture fixation utilizing the Less Invasive Stabilization System (L.I.S.S.): the technique and early results.

The treatment of supracondylar femoral fractures in the past three decades has evolved from non-operative to operative treatment. While operative fixation utilizing either plate fixation or rigid intramedullary nail fixation has improved patient outcomes, the problems of malunion, nonunion, need for bone grafting, joint stiffness, and infection persist. An emphasis on maintenance of the soft tissue envelope around fractures has improved efficacy in increasing osseous healing and decreasing infection. Out of this movement grew the concept of submuscular plating for distal femoral fractures, and subsequently L.I.S.S. fixation (Less Invasive Stabilization System) for distal femoral fractures. The technique and early results utilizing the L.I.S.S. for distal femoral fractures is described. The technique of L.I.S.S. fixation first begins with traditional direct visualization and internal fixation of the articular surface. Closed reduction is then performed on the metaphyseal / diaphyseal component of the fracture, followed by submuscular fixation utilizing the L.I.S.S. fixation. The L.I.S.S. can best be thought as an "internal" external fixator.

Bone Screws↗
PubMed2000

Improved outcome after early fixation of acetabular fractures.

This study was done in order to evaluate the effect of the timing of fixation for acetabular and pelvic ring fractures on patient outcome. Demographic, clinical and outcome data for 5821 trauma patients admitted from January 1993 through January 1996 were retrospectively reviewed. Pelvic fractures were classified according to Young and Burgess. Patients who had fixation within 24 h of admission were compared with those who had later operation. Main outcome measures were Multiple Organ Dysfunction Score according to Moore, hospital and intensive care unit length of stay and discharge disposition. Out of 416 patients with pelvic fractures, one hundred patients had fracture fixation [90 open reduction and internal fixation, 10 external fixation]. There were 59 acetabular fractures and 41 pelvic ring fractures. The overall mortality was 4%. Early fixation of acetabular fractures was associated with lower MODS (p < 0.006) and decreased total length of stay (p < 0.026). Length of hospital stay was also less with early fixation of pelvic ring fractures (p < 0.04). Functional outcome was improved in early fixation of acetabular fractures with a greater proportion of patients being discharged home rather than to rehabilitation or skilled care (p = 0.05). Patients who underwent early repair of acetabular and pelvic ring fractures had a shorter length of hospital stay compared to those with late fixation. Patients with early repair of acetabular fractures had significantly less organ dysfunction and exhibited improved functional outcome.

Acetabulum↗
PubMed2005

[Pertrochanteric fractures: a randomized prospective study comparing dynamic screw plate and intramedullary fixation].

PURPOSE OF THE STUDY: The objective of this study was to compare the dynamic hip screw (Synthes) and intramedullary fixation (Targon PF, Aesculap) for the treatment of pertrochanteric fractures in terms of stability, complications and cost effectiveness. MATERIAL AND METHODS: This prospective randomized study included 60 patients hospitalized in an emergency setting for pertrochanteric fractures between December 2003 and June 2004. All surgeons in our unit participated in the study. Two fixation systems were used: the Targon proximal femoral nail (Aesculap) and the screw-plate dynamic hip screw (Synthes). We noted: patient status (ASA classification), operative data (type of implant, duration), postoperative data (blood loss, radiographic findings, early complications), and outcome (Harris score, time to walking, mortality). All patients were assessed three months after surgery. The series included 60 patients, 14 men (23%) and 46 women (77%). The Targon PF nail was used for 34 patients and the DHS for 26. In the intramedullary fixation group mean age was 81 years (SD = 12.8, range 23-96); it was 82 years (SD 9.8, range 47-97) in the screw-plate group. The AO classification was: intramedullary fixation 31A1 (n = 11), 31A2 (n = 20), 31A3 (n = 3); screw-plate 31A1 (n = 14), 31A2 (n = 11), 31A3 (n = 1). Thirty-one fractures were stable, 29 unstable. Unstable fractures were treated with the Targon PF nail (n = 18) and the DHS screw-plate (n = 11). Stable fractures were treated with the Targon PF nail (n = 15) and the DHS screw-plate (n = 15). RESULTS: Mean operative time was 35 minutes for intramedullary nailing and 42 mintues for screw-plate fixation. Mean blood loss was 410 ml for intramedullary nailing and 325 ml for screw-plate fixation (p = 0.07). Mean hospital stay was the same (11 days) in both groups. At three months, mechanical complications involved migration of the cervical screw outside the femoral head for three Targon PF fixations and for two DHS fixations. Screw migration was favored by fracture instability and presence of osteoporosis. There were two deaths in the intramedullary nailing group and one in the screw-plate group. Time to walking was 20 days on average in the intramedullary nailing group and 25 days in the screw-plate group. The mean Harris hip score was 60 in the intramedullary group and 59 in the screw-plate group. DISCUSSION AND CONCLUSION: Data in the literature report an advantage for intramedullary nailing, particularly a mechanical advantage, for the treatment of pertrochanteric fractures. Our findings show that good results are obtained with the screw-plate fixation using the DHS with less blood loss and at a lower cost.

Adult↗
PubMed1997

A novel use for a carbodiimide compound for the fixation of fluorescent and non-fluorescent calcium indicators in situ following physiological experiments.

The inability to determine the precise intracellular location of non-fluorescent organic calcium chelators such as BAPTA is a persistent problem which has precluded much detailed analysis of the chelators' spatial or temporal dynamics in live cells. Similarly, following physiological experiments with fluorescent indicators like Fura-2, it has often been desirable to maintain the dye within the cell for later analysis by additional histological techniques. Based on chemical considerations, and its prior use in tissue fixation, we examined the water soluble reagent 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) as a potential fixative for diverse calcium chelators. The utility of EDC, but not other common fixatives, was confirmed through electrophysiological means, through a novel ELISA, which exploits anti-BAPTA antibodies to assess the extent and kinetics of fixation; by autoradiography of neurons loaded with [14C]-BAPTA, and by immunocytochemistry and imaging of intracellular BAPTA or Calcium Green in neurons. At concentrations > 0.1 mg/ml, EDC caused virtually instantaneous, irreversible, fixation of > 95% of BAPTA free acid. Fixation of intracellular BAPTA was confirmed in hippocampal brain slices loaded with BAPTA/AM ester, and showed biphasic kinetics consistent with rapid loading and subsequent extrusion of the chelator. Immunocytochemistry on neurons microinjected with BAPTA free acid and the dye Lucifer Yellow showed BAPTA-specific staining which was distributed in the cell similarly to that of the accompanying marker dye. Application of EDC also efficiently fixed in situ analogs of BAPTA such as Calcium Green (a fluorescent Ca2+ indicator) as shown by confocal imaging of EDC-fixed brain slices loaded with this indicator. Taken together, these data show that EDC is an effective, inexpensive and versatile fixative for calcium chelators in diverse cells. The availability of a suitable fixative now makes it possible to determine the distributions of such chelators at both the light and, possibly, the electron microscope level. Two important features of EDC, arise from its specificity for free carboxyl groups. First, the ability to fix, selectively, the chelators but not their AM esters; and, second, its enormous potential as a fixative for the numerous other carboxyl-containing chelators, dyes and pH indicators currently available.

Animals↗
PubMed2000

Influence of different fixation procedures on the quantification of infarction and oedema in a rat model of stroke.

In pharmacodynamic studies using focal ischaemia models, the size of the infarct measured by quantitative histology is the most important outcome measure. Precise, unbiased and reproducible assessment of infarct volume is of foremost importance. A frequent problem in interventional stroke models is the evaluation of infarcts in animals found dead, where instant post-mortem fixation of the brain cannot be performed. The purpose of this study was to investigate possible bias from perfusion, immediate and 3-h post-mortem delayed immersion fixation on the measured volumes of cerebral infarction, oedema and hemispheres in a rat embolic stroke model. Thirty-six male Sprague-Dawley rats were thromboembolized into the internal carotid artery. After survival for 24 h, the animals were divided into three groups: group 1 - immediate perfusion fixation; group 2 - immediate immersion fixation of the brain; and group 3 - animals left dead for 3 h at room temperature before removal of the brain for immersion fixation. Following histological preparation and evaluation, the volumes of the hemispheres and infarction were measured by quantitative histology and planimetry. Brains fixed by immersion were 7% larger than the perfusion-fixed brains. Delaying the immersion fixation for 3 h may increase hemisphere volume by a further 12%. Independent of the fixation procedure, the size of infarction was approximately 40% of the ipsilateral hemisphere, and the oedema was approximately 11% of the size of the infarct. The used planimetric technique was accurate with measured values within +/- 2% of the factual value. In conclusion, sizes of hemispheres, infarction and oedema in absolute volume measures are influenced by the effect of unwanted variation of brain size caused by biological factors and artificial shrinkage caused by fixation, dehydration and heat treatment of the specimens. Infarction and oedema expressed relatively in per cent of hemisphere and infarct, respectively, are robust measures independent of the investigated fixation procedures.

Animals↗
PubMed1992

Plate fixation of premaxillomaxillary suture and compensatory midfacial growth changes in the rabbit.

It has been suggested that rigid fixation of the developing craniofacial skeleton may lead to altered craniofacial growth. However, recent experimental studies have shown that microplate fixation of slow-growing calvarial sutures resulted in regional growth disturbances but had little effect on overall craniofacial growth. The present study was designed to assess the effects of microplate fixation of the more rapidly growing facial sutures on compensatory midfacial growth in the rabbit. Twenty-two 1.5-week-old rabbits were randomly divided into 2 groups: sham controls (n = 11) and animals with bilateral premaxillomaxillary suture fixation (n = 11). Fixation was accomplished using an intraoral approach, a 6-mm straight Luhr microplate, and two 2-mm long self-tapping screws across each suture. Serial lateral head radiographs were collected at 1.5, 3.5, 6, 12, and 18 weeks of age. Results revealed that by 3.5 weeks, animals with rigid fixation showed significantly shortened premaxillary lengths (p < 0.05), class III occlusal relationships, decreased midfacial heights, and abnormal palatocranial base angles compared with sham control animals. By 12 weeks of age, "catch-up" growth was evident in most dimensions in animals with fixation compared with shams. Gross examination of the cleaned and dried skulls revealed bony bridging across the premaxillomaxillary suture and osseous fracture lines extending superiorly from the site of screw fixation. Results demonstrated that rigid fixation of a rapidly growing facial suture did not impair long-term midfacial growth in the rabbit model and suggest that compensatory changes may have occurred at fracture lines from the self-tapping screws in these animals.

Adaptation, Physiological↗
PubMed2001

Treating forearm fractures using an internal fixator: a prospective study.

Some major complications of internal fixation with plates, such as infections and disturbance of healing, have been shown to be related to necrosis of bone and to the soft tissues immediately deep to the plate. This is attributable to plate contact. To deal with this phenomenon, an internal fixator, the Point Contact Fixator, was developed according to a new concept. The Point Contact Fixator resembles a plate but functions like a fixator, that is, the fracture is stabilized using a splint fixed to the bone by monocortical, angularly locked screws that are designed not to exert pressure between the splint and the bone, thereby minimizing implant-to-bone contact. Vascular damage to the osseous blood supply consequently is avoided. The new internal fixator is the first of a new family of implants in addition to nails, plates, and external fixators. To study the potential of the Point Contact Fixator in a prospective study, 79 forearm fractures in 55 patients were treated in a consecutive series by one surgeon using the same technique throughout. Followup to union is reported for 100% of the patients. Handling the fixator was simple; healing was uneventful; and the rate of complication was low.

Adult↗
PubMed2001

Comparative strength of three methods of fixation of transverse acetabular fractures.

With the advent of percutaneously placed lag screws for fixation of acetabular fractures, this study evaluated the strength of lag screw fixation compared with traditional fixation techniques of transverse acetabular fractures. Ten formalin-treated human, cadaveric pelvic specimens with bilateral, transtectal transverse acetabular fractures were used for this study. The right acetabular fractures were fixed with a five-hole plate and four screws with the central hole spanning the posterior fracture site. The left acetabular fractures were fixed with two lag screws, one each in the anterior and posterior columns, or with a screw and wire construct stabilizing both columns. The specimens were loaded to implant failure. Stiffness, yield strength, maximum load at failure, and site of failure was recorded. The plate and screw construct showed significantly greater yield and maximum strength when compared with the two lag screws. The stiffness of the lag screw method was 39% higher than that of the plating method, but this result was not statistically significant. In addition, the plate and screw method provided significantly greater maximum strength than the screw and wire technique. The quadrilateral plate seemed to be the weakest area of fixation because 83% of the implant failures occurred in this region. In patients in whom the risks of formal open reduction and internal fixation of acetabular fractures outweigh the possible benefits, such as in patients with burns or degloved skin, the advent of computer-assisted and fluoroscopically guided percutaneous surgical techniques have been instrumental. This study showed there is greater strength of fixation with a plate and screw construct, possibly secondary to supplementary fixation distal to the quadrilateral plate. However, lag screw fixation provided relatively greater stiffness, which may account for its clinical success. Percutaneous lag screw fixation of appropriate transverse acetabular fractures is a viable option.

Acetabulum↗
PubMedDate not supplied

Biomechanical comparison of hybrid external fixators.

OBJECTIVES: To determine the stiffness characteristics of the hybrid ring fixator in the treatment of (OTA 41-C) proximal metaphyseal and shaft tibial fractures. DESIGN: Five identical composite tibiae were fixed with a Synthes, ACE Fischer, Howmedica Monticelli-Spinelli, or Smith & Nephew Trauma Ilizarov hybrid external fixator or with the conventional Ilizarov wire fixator. The Synthes and Monticelli-Spinelli fixators were tested twice, the first time with the connectors on the outside of the ring and the second time with the connectors on the inside of the ring. MAIN OUTCOME MEASUREMENTS: A materials testing machine was used to apply pure compression, anterior and posterior bending, medial and lateral bending, and torsion. Stiffness values were calculated from the load deformation and torque angle curves. RESULTS: Overall, the Synthes and Monticelli-Spinelli fixators were the most rigid of the fixators when the wire-to-ring connectors were placed inside the ring. In general, the fixators were stiffest in axial compression and least stiff in posterior bending. Wire length had a significant effect on overall stiffness. CONCLUSIONS: This study suggests that the four hybrid external fixators in standard configuration have stiffness characteristics similar to those of the conventional Ilizarov fixator when used to treat proximal metaphyseal and shaft fractures of the tibia.

Biomechanical Phenomena↗