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PubMed1992

Evoked potential evidence for human brain mechanisms that respond to single, fixated faces.

The influence of visual fixation position and stimulus size on the scalp-recorded "vertex positive peak" (VPP) evoked by images of faces was studied in three subjects. Responses were recorded, in turn, for line-drawn, frontal-view faces of approximately 8, 4, 2, and 1 deg length, fixated at the centre (bridge of the nose), and at points 1, 2, 3, and 4 deg to the left and right, and above and below, centre. The results showed that central fixation produced VPPs of similar, maximal amplitude for all face sizes. By comparison, "on-face" eccentric viewing yielded attenuated and delayed responses, and the degree of response attenuation as a function of eccentricity was directly related to the face size, with similar amplitude responses being evoked for corresponding fixation locations on each face. Very small or no VPPs were recorded for most "off-face" fixations. Similar results were observed for profile faces, except that the maximal VPP was recorded for fixations near the eyes and not in the centre of the head, and almost identical VPPs were evoked by a centrally fixated face presented with and without an adjacent face or object. These response properties, which correspond to the subjective perception of the facial stimuli, suggest that the VPP reflects brain mechanisms optimized to respond to single, fixated faces, irrespective both of facial image size and of the presence of neighbouring figures.

Adult↗

PubMed2006

The effect of bone tunnel dilation versus extraction drilling on the initial fixation strength of press-fit anterior cruciate ligament reconstruction.

INTRODUCTION: Serial dilation of the bone tunnel has been reported to create a tighter graft-tunnel fit. It was hypothesized that a serial dilation of the femoral bone tunnel would increase the initial fixation strength in press-fit anterior cruciate ligament (ACL) reconstructive surgery. MATERIALS AND METHODS: Initial fixation strength of the femoral press-fit fixation technique was investigated in 72 porcine specimens in an ex vivo study by varying the femoral tunnel preparation technique. Extraction-drilling, tunnel dilation by 1 mm and dilation by 2.5 mm were assessed. Initial fixation strength of press-fit fixated patellar tendon-bone grafts was tested within each preparation group conducting a single cycle (and cyclic) load to failure protocol. The resulting tunnel diameter and the porcine femoral bone mineral density were determined using microradiographs and peripheral quantitative CT scans, respectively. RESULTS: Dilating a previously extraction-drilled femoral bone tunnel by 1 mm significantly enhances initial press-fit fixation strength in both single cycle and cyclic load to failure testing when compared to extraction-drilling and tunnel dilation by 2.5 mm. Due to an initial spring-back effect the resulting diameter of the femoral tunnel was underestimated by 3.3% with drilling and 6.7 and 12.2% with dilation by 1 and 2.5 mm, respectively. Volumetric trabecular bone mineral density at the site corresponding to the area of tunnel placement averaged 318 mg/cm(3). CONCLUSION: Dilating a femoral tunnel that is underdrilled by 1 mm appears to be a reasonable technical procedure in order to enhance initial fixation strength of press-fit ACL graft fixation.

Analysis of Variance↗

PubMed2004

Biomechanical comparison of anterior cervical spine locked and unlocked plate-fixation systems.

Three different anterior plate-fixation systems are available for the stabilisation of the cervical spine: (1) the cervical spine locking plate (CSLP), (2) dynamic plates allowing vertical migration of the fixation screws, and (3) various types of plates that are secured with either monocortical or bicortical unlocked screws. Unicortical screw purchase does not involve the risk of posterior cortex penetration and possible injuries to the spinal cord. The development of locking plates with unicortical screw-fixation and intrinsic stability of the screw-plate interface, via an angle-stabilised connection, was an attempt to increase the stability of unicortical screw-fixation systems. The aim of the study was to compare the biomechanical properties of a non-locking, anterior-plate system with 4.5 mm screw fixation and a locking anterior-plate system, in a single destabilised cervical spine-motion segment. Using fresh cadaveric cervical spine specimen C3-C7, multidirectional flexibility was measured at the C4-C5 level in an unconstrained test system, before and after destabilisation and fixation with an anterior plate with either locked or unlocked screw purchase. Direct comparison of the fixed cervical spine segments with unlocked and locked anterior-plate fixation did not demonstrate significant differences. This in vitro study documented that neither locked nor unlocked anterior-plate fixation can increase stability in all modes of testing. H-plate spondylodesis with unlocked screws seems to provide sufficient mechanical integrity in most cases of monosegmental lesions.

Adult↗

PubMed1984

Perturbation of ribosome subunit interaction by glutaraldehyde fixation.

Ultracentrifugal analysis of ribosomal purity is complicated by the rapid reequilibration of ribosomes with their subunits, and this is further enhanced by the effects of hydrostatic pressure. Fixation of the ribosome system prior to ultracentrifugal analysis supposedly freezes the reequilibration, and thus tends to obviate these difficulties. However, no redistribution of the ribosome-subunit population must be allowed to occur during fixation. Thus, it is necessary that fixation be extremely rapid compared to the ribosome-subunit reequilibration, in order to avoid errors in analysis. It was the purpose of this investigation to make a direct experimental comparison of the rates of these two processes, fixation and ribosome-subunit reequilibration, using the stopped-flow technique with a light-scattering detector, under a variety of buffer environment readjustments. The following findings resulted from this study: (1) Fixation in Tris buffers could not be followed by light scattering because of interaction of glutaraldehyde with Tris, leading to continuous production of high molecular weight contaminants. (2) Polymerization of glutaraldehyde leads to increased ultraviolet absorption, which must not be confused with scattering changes. (3) Undialyzed ribosome solutions prepared by dissolving stock suspensions stored at high levels of magnesium and univalent electrolyte into a known standard buffer produced solutions having free Mg2+ levels lower than those of original buffer, complicating kinetic observations and threatening ribosome stability. (4) Addition of malonic acid as a buffer for Mg2+ largely eliminated this problem. (5) The kinetics of glutaraldehyde were measured quantitatively by studying the perturbation of ribosome association and dissociation kinetics produced during shifts of Mg2+ levels. (6) At fixative levels not producing coagulation, fixation kinetics can be competitive with those of association-dissociation. (7) Mass action effects like those of dilution can be caused by fixation, and can give rise to excess subunits, which may be mistaken for loose couples in original ribosome preparations.

Aldehydes↗

PubMed1988

Stability of the mandible following advancement: a comparison of three postsurgical fixation techniques.

This study examines short-term stability of the mandible following mandibular advancement surgery by means of three standard techniques of postsurgical fixation. Twenty-two adult female rhesus monkeys (Macaca mulatta) underwent sagittal ramus advancement osteotomy of approximately 4 to 6 mm. Six animals had dental maxillomandibular fixation alone. Six animals had dental plus skeletal maxillomandibular fixation with circummandibular wires connected to pyriform aperture wires. Ten animals had rigid internal fixation with bicortical bone screws between the proximal and distal segments without maxillomandibular fixation. Radiographic cephalograms with the aid of tantalum bone markers and dental amalgams were analyzed during the first 6 postoperative weeks to evaluate skeletal and dental stability. Rigid internal fixation and the use of dental plus skeletal maxillomandibular fixation were both equally effective in the prevention of postsurgical relapse. However, in the animals in which only dental maxillomandibular fixation was used, statistically significant changes (relapse) occurred when compared with either of the other groups.

Animals↗

PubMed2006

Changes in the inferior alveolar nerve following sagittal split ramus osteotomy in monkeys: a comparison of monocortical and bicortical fixation.

We aimed to observe the changes in the inferior alveolar nerve (IAN) after bilateral sagittal split ramus osteotomy (SSRO) using monocortical or bicortical screw fixation. Bilateral SSRO for setback of the mandible was done in 12 monkeys, and monocortical or bicortical fixation was applied on opposing sides of each mandible. Sensory nerve action potentials were tested before and immediately after operation, and at 2, 4, 8, and 12 weeks. Six animals selected randomly were killed at 4 and 12 weeks after the operation. Specimens of nerve were harvested and processed for histological examination and electron microscopic analysis. Obvious prolongation of latency and diminution of amplitude in the IAN were found postoperatively. At 4 weeks after operation, Wallerian degeneration was apparent, and there were signs of axonal regeneration in the nerves. The IAN had more abnormalities of evoked potentials and pathological changes after bicortical than after monocortical fixation. Although considerable recovery was found after both forms of fixation at 12 weeks, the function of the nerve after plate fixation was better than after screw fixation. Our results suggest that the nerve damage during SSRO could be temporary and reversible, and monocortical fixation may result in restoration of the nerve function sooner than bicortical fixation.

Action Potentials↗

PubMed2006

Assessment of the fixation stiffness of some femoral stems of different designs.

BACKGROUND: Appropriate contour design of a femoral stem is important for the secure primary fixation. Although the relationship between the contour and stress or micro-motion at the fixation site has been analyzed, guidelines on stem design have not been established. METHODS: Different kinds of finite element models of three femoral stems were constructed for computer simulation. These models had the contour designs that head for the tight mechanical fixation by the different ways, respectively. Boundary and initial conditions were (i) rigid contact of the distal end of the model femur with the rigid base. (ii) Stepping load of 800 N or 1800 N was applied to the proximal top of the stem. (iii) Stepping load of 640 N or 1440 N was pulled from the greater trochanter of the femur as muscle force. The ratio of displacement to the vertical load, which was defined as fixation stiffness, was calculated. FINDINGS: The mean displacement of the intra-medullary cruciate stem was 27.6 nm. For the VerSys stem with sharp fins, the mean displacement was 32.9 nm. For the PerFix SV stem with a flange, the mean displacement was 52.8 nm. Vertical fixation stiffness estimated on the intra-medullary cruciate stem, the VerSys stem, and the PerFix SV stem was 461, 264, and 313 MN/mm, respectively. INTERPRETATION: Contour design of a femoral stem is important for achieving secure fixation, which prevents loosening. We introduce fixation stiffness as a measure to theoretically evaluate the primary fixation of femoral stems.

Adhesiveness↗

PubMed2005

Experimental ossicular fixations and the middle ear's response to sound: evidence for a flexible ossicular chain.

A human temporal-bone preparation was used to determine the effects of various degrees of artificial ossicular fixation on the sound-induced velocity at the input-side (the umbo of the malleus) and the output-side (the stapes) of the ossicular chain. Construction of various degrees of attachment between an ossicle and the surrounding temporal bone provided a range of reduction in ossicular mobility or "fixations". The results demonstrate different effects of the fixations on the umbo and stapes velocity: fixations of the stapes or incus produce larger reductions in sound-induced stapes velocity (as much as 40-50 dB with extensive stapes fixation), than reductions in umbo velocity (typically less than 10 dB). Fixations of the malleus produce similar-sized changes in both umbo and stapes velocity. These differential effects are consistent with significant flexibility in the ossicular joints (the incudo-malleolar joint and the incudo-stapedial joint) that permits relative motion between the coupled ossicles. The existence of flexibility in the ossicular joints indicates that joints in the ossicular chain can effect a loss of sound-induced mechanical energy between the umbo and the stapes, with a concomitant reduction in the sound-induced motion of the stapes. The introduction of such losses in sound transmission by the joints raises questions concerning the utility of three ossicles in the mammalian ear. The consequences of ossicular flexibility to ossicular-chain reconstruction is discussed. Also, as examined in a more clinically directed paper [Laryngoscope 115 (2005) 147], the different effects of the various ossicular fixations on the motion of the umbo and malleus may be useful in the diagnosis of the site of fixations in humans with conductive hearing losses caused by such pathologies.

Aged↗

PubMed2004

Medial rectus pulley posterior fixation: a novel technique to augment recession.

PURPOSE: Medial rectus (MR) pulley posterior fixation, a technique of suturing the pulley to its muscle without scleral sutures, may be as effective as traditional scleral posterior fixation in primary treatment of acquired esotropia (ET) with a high AC/A ratio. This study examines the effectiveness of MR pulley posterior fixation for other variants of ET. METHODS: We retrospectively analyzed the pre- and postoperative alignment of 16 patients: 9 previously operated patients with excess near ET, 4 patients with sensory ET with excess near ET, and 3 patients with large-angle infantile ET. Surgeries involved extraocular muscle recessions and resections in standard doses combined with MR pulley posterior fixation. RESULTS: All 9 reoperated patients were between 0 and 10 prism diopters of distance ET postoperatively. The excess near ET decreased from an average of 12.1 prism diopters preoperatively (range 6-20) to 1.3 prism diopters postoperatively (range, 0-4). Two of the 4 patients with sensory ET were overcorrected at distance (exotropia of 10 and 15 prism diopters, respectively). The excess near ET of these 4 patients decreased from an average of 13.5 prism diopters preoperatively (range, 10-20) to 2.5 prism diopters postoperatively (range, 0-8). In patients with large-angle infantile ET, the addition of pulley posterior fixation resulted in a greater effect than would be predicted for standard MR recessions, particularly at near. Pooling data for all groups, pulley posterior fixation was associated with a highly significant reduction of excess near esotropia postoperatively (P < 0.00001). DISCUSSION: MR pulley posterior fixation augments MR recession with relatively greater effect at near. Surgical dosage for unilateral recessions and resections combined with MR pulley posterior fixation should be reduced in patients with poor potential for postoperative fusion.

Adolescent↗

PubMed2006

Endovascular aneurysm repair with suprarenal vs infrarenal fixation: a study of renal effects.

OBJECTIVES: Although suprarenal fixation may be of benefit during endovascular aneurysm repair (EVAR), its safety with regards to renal effects remains uncertain. To date, there has been no controlled study of the topic, with most reports relying upon single-center experiences that use heterogeneous patient populations and devices from different manufacturers. The purpose of this analysis was to evaluate the effect of suprarenal fixation on renal function by comparing homogeneous patient populations receiving EVAR grafts from a single manufacturer that are identical in design and delivery method, except for utilizing either suprarenal (SR) or infrarenal (IR) fixation. METHODS: During two pivotal US Food and Drug Administration trials, 283 patients underwent EVAR with the Powerlink bifurcated graft. The trials' inclusion and exclusion criteria and grafts were identical except for fixation scheme. Clinical, laboratory, and computed tomographic (CT) data were retrospectively reviewed. A comparison of preoperative, perioperative (1 to 7 days), and postoperative (>7 days) alterations in serum creatinine (SCr), creatinine clearance (CrCl), and blood pressure was performed. Renal adverse events were determined by CT scan and clinical chart review and included renal infarction, renal artery stenosis (either progressive or requiring renal stent placement), and renal artery occlusion. RESULTS: Both SR and IR groups demonstrated a significant increase in SCr and a decrease in CrCl over time. No significant difference in SCr or CrCl existed between groups during any time period. There were no differences in postoperative renal impairment (IR, 10.2%; SR, 7.6%, P = .634), the need for hemodialysis (IR, 0.7%; SR, 0%, P = 1.00), or systolic and diastolic blood pressure during subsequent follow-up between treatment groups. There was no significant difference in the number of renal adverse events detected by CT between the IR (10, 6.8%) and SR (3, 3.8%) groups (P = .550). CONCLUSION: Suprarenal fixation does not lead to a significant increase in acute renal events, renal impairment, or alteration in blood pressure compared with infrarenal fixation. Patients undergoing aneurysm repair with devices that use either suprarenal or infrarenal fixation develop progressive renal dysfunction over time. Further studies are needed to determine the long-term effects of suprarenal fixation on renal function and progression of renal artery stenosis.

Aged↗

PubMed2004

A randomized controlled trial of resorbable versus titanium fixation for orthognathic surgery.

OBJECTIVES: To determine any differences in the intra- and postoperative morbidities and complications between resorbable and titanium plating systems for fixation in orthognathic surgery. STUDY DESIGN: This prospective randomized clinical trial was conducted in the Oral and Maxillofacial Surgery unit of the University of Hong Kong. Patients with dentofacial deformities were randomly assigned into the titanium and resorbable fixation groups. Intraoperative data such as the surgical procedures, time for fixing each plate, and number of broken plates and screws were recorded. Subjective and objective parameters related to clinical morbidities were assessed postoperatively. RESULTS: A total of 60 patients with 177 osteotomies were included in this study. Eighty-seven osteotomies fixated with 196 titanium plates and 784 titanium screws were performed in 30 patients, whereas 90 osteotomies fixated with 165 resorbable plates and 658 resorbable screws were done in another 30. The postoperative infection rate was 1.53% (3/196) and 1.82% (3/165) in the titanium and resorbable fixation groups, respectively. These infections were mainly due to loose screws and wound dehiscence. The plate exposure rate was 1.02% (2/196) for the titanium group and 1.21% (2/165) for the resorbable group. The plate removal rate in the titanium and resorbable groups was 1.53% (3/196) and 3.63% (6/165), respectively. Statistically significant difference was shown in the plating time of step (mandibular body) and Hofer (mandibular subapical) osteotomies. There was no significant difference in the subjective clinical parameters such as wound discomfort, clinical stability of the osteotomy segments, palpability of plate, and overall satisfaction of the results between the 2 fixation groups. Similarly, objective parameters including wound dehiscence, rate of infection, plate exposure, occurrence of sinus tract, and palpability assessed by surgeons in both groups also showed no significant difference. CONCLUSION: Bioresorbable fixation devices offer similar function as titanium in fixation for orthognathic surgery and do not impose an increase in the clinical morbidities.

Absorbable Implants↗

PubMed2006

Myopic shift from the predicted refraction after sulcus fixation of PMMA posterior chamber intraocular lenses.

BACKGROUND: To evaluate the refractive results of sulcus-fixated polymethylmethacrylate (PMMA) posterior chamber intraocular lenses (PC IOLs) after cataract surgery with and without posterior capsule complications. METHODS: The charts of patients who had undergone cataract surgery were reviewed, and eyes that had received sulcus-fixated PMMA PC IOLs were included in the study. Postoperative refraction, predicted postoperative refraction for in-the-bag IOL with the same diopter, intraoperative posterior capsular complications and vitrectomy, axial eye length, incision type (corneal or scleral), and surgery type were recorded and analyzed. The difference between actual postoperative refraction and predicted refraction for the in-the-bag lens was calculated for each patient. RESULTS: Of 143 patients (84 men and 59 women), 162 eyes with a sulcus-fixated posterior chamber intraocular lens were investigated. Mean age was 63.7 +/- 12.1 years. A mean myopic shift of -1.02 +/- 0.96 D from the predicted in-the-bag refraction was found. There were no significant differences between eyes with or without vitreous loss-vitrectomy (p = 0.8), eyes with scleral or corneal incisions (p = 0.11), and eyes having phacoemulsification or extracapsular cataract extraction (p = 0.93). In terms of axial length, there were no significant differences between long, normal, or short eyes (p = 0.85). INTERPRETATION: Sulcus fixation of a PMMA IOL originally planned for in-the-bag fixation caused approximately -1.00 D myopic shift in this study. We recommend that when sulcus fixation is necessary PMMA IOL power should be approximately 1.25 to 1.50 D less than the power for in-the-bag fixation. Axial length, incision type, vitreous loss and use of vitrectomy, and type of the surgery do not appear to alter the postoperative refraction significantly in eyes with sulcus fixation.

Adolescent↗

PubMed1996

Factors related to the time of fixation of the conceptus in mares.

The temporal relationships among day of conceptus fixation (cessation of mobility), conceptus diameter, uterine tone, uterine contractility, and myometrial and endometrial thickness of the middle and caudal segments of the uterine horns were assessed in 13 pony mares with fixation in the caudal segment of a uterine horn. The mean day of fixation (14.9 +/- 0.3) was established by 2-h mobility trials. Uterine tone increased (P < 0.0001) gradually over Days 11 to 21, whereas uterine contractility decreased (P < 0.0001) between Days 14 and 18. The diameter of the spherical embryonic vesicle increased (P < 0.0001) between Days 11 and 17. The day of fixation and vesicle diameter on Day 14 were negatively correlated (r = -0.9, P < 0.007); the larger the vesicle, the earlier fixation occurred. Each of 4 uterine-horn diameters (endometrium and endometrium plus myometrium of middle and caudal segments) decreased (P < 0.0001) correspondingly over Days 11 to 21. On the day of fixation conceptus diameter (21.5 +/- 1.0 mm) was similar to endometrial diameter (21.1 +/- 0.4 mm) at the caudal segment. The endometrial diameter represents the distance between the inner opposite walls of the myometrium. The percentage of change between the day before and day of fixation was greater for the conceptus (18.1% increase) than for the endometrial diameter at the caudal segment (1.0% decrease). The results suggest that fixation occurred when the mobile and growing conceptus attained, on the average, a diameter equivalent to the distance between opposite inner myometrial walls at the caudal segment. The uterus became turgid by this time and presumably did not expand adequately to accommodate continued mobility of the expanding conceptus.

Journal Article↗

PubMed1993

A randomized trial of intraocular lens fixation techniques with penetrating keratoplasty.

PURPOSE: Pseudophakic corneal edema is the principal indication for penetrating keratoplasty in the United States. Currently, three techniques of intraocular lens (IOL) fixation during penetrating keratoplasty for this condition are commonly used--flexible anterior chamber IOL (AC IOL) implantation, iris suture fixation of a posterior chamber IOL (PC IOL), and transscleral suture fixation of a PC IOL. This study represents the first prospective, randomized comparison of these three techniques. METHODS: One hundred seventy-six consecutive patients with pseudophakic corneal edema who underwent penetrating keratoplasty with IOL exchange were randomized to one of the three implantation techniques. Standardized evaluations were performed at baseline and at 6, 12, and 18 months postoperatively. Life-table analysis provided cumulative risk estimates for specific complications. RESULTS: Randomization produced comparable groups at baseline. The cumulative risk of macular edema was significantly less for the iris fixation cohort than for either the AC IOL or scleral fixation group. A complications index was constructed based on the major adverse outcomes of glaucoma escalation, cystoid macular edema, IOL dislocation, and graft failure. A significantly lower risk of complication was found for iris compared with scleral fixation of PC IOLs. CONCLUSION: The authors conclude that transscleral fixation of the PC IOL at the time of penetrating keratoplasty for pseudophakic corneal edema is associated with a greater risk of adverse outcome than iris fixation of a PC IOL.

Aged↗

PubMed1997

A biomechanical study on five unilateral external fracture fixation devices.

OBJECTIVE: This study examines plastic, slip and fatigue failures in external fixator frames. DESIGN: Failure was examined in five commonly used unilateral external fixators using experimental models that simulated both stable and unstable diaphyseal fractures. BACKGROUND: Plastic failure arises from permanent deformation of a frame initiated by bending of frame components, while slip failure arises from slip at clamping interfaces. Such failure may lead to refracture or to malalignment of the bone (transverse or angular). Fatigue failure arises from the loosening or wear of components under long-term cyclic loading; this can lead to variable interfragmentary displacement and impairment of fracture stability. METHODS: Axial loads were measured at which plastic or slip failure occurred, as were changes in interfragmentary motion due to 10 000 load cycles simulating walking activity. RESULTS: In four fixators, plastic or slip failure initiated bone malalignment at only 50% of average adult weight bearing (650 N). Additionally, in three fixators a third screw at the clamp centre was found to reduce retention of the two adjacent screws, causing premature slip failure. Evidence of fatigue was found in all the fixators after only 10 000 load cycles. In one fixator, the amplitude of elastic interfragmentary motion increased progressively by 30% transversely, 15% angularly and 100% torsionally. In another fixator it increased by 10% in all directions while the column was locked (non-dynamizing), and it increased a further 10% while it was unlocked and able to slide telescopically (dynamizing). Clamp slip occurred at the column of a third fixator almost immediately after commencing the cyclic loading. CONCLUSION: Plastic or slip failure of frames may occur prematurely during routine weight-bearing on unstable fractures, and frame fatigue may affect long-term interfragmentary stability.

Journal Article↗

PubMed1997

The hybrid ring tubular external fixator: a biomechanical study.

OBJECTIVE: To measure and compare the mechanical properties in bending of the four-ring, and three-ring/one-tube hybrid external fixation frames. DESIGN. IN VITRO: measurements of the mechanical behaviour of ring and ring-tubular external fixation frames. In the latter, one ring of the full circular frame was replaced by one tube and Schanz screws. BACKGROUND: The mechanical properties of the classical Ilizarov four-ring external fixation frames has been compared to those of other external fixation frames by various authors. However, in clinical practice the hybrid fixation frame is being used with increasing frequency. Therefore the mechanical properties of the latter are of immediate interest and clinical value. METHODS: On explanted sheep tibiae with single and double osteotomies, frame stiffness in the four-point bending mode was measured at different K-wire tensions, comparing the values obtained from four-ring frames, to those of three-ring-tubular hybrid frames. These measurements were made under conditions of (a) bone distraction (BD), and (b) segment transport (ST), both at the initial and final stages of this procedure. RESULTS: In circular frames, frame stiffness in bending for increasing K-wire tension showed a Gaussian distribution both in distraction and post-ST with an optimum at 1000 N. In ring tubular hybrid frames, however, frame stiffness showed a more linear relationship to K-wire tension. CONCLUSIONS: In the four-ring Ilizarov external fixation frame, the exchange of one ring with one tube and one Schanz screw both reduced frame stiffness in bending and converted to linear its relationship to K-wire tension. RELEVANCE: Under clinical conditions, the use of a similar ring tubular hybrid external fixator allows the adjustment of frame stiffness in a simple and practical way. This is not the case with the original ring fixation frame.

Journal Article↗

PubMed1998

Is the stability of a tibial fracture influenced by the type of unilateral external fixator?

OBJECTIVE: To examine whether the type of unilateral external fixator significantly influences the stability of a tibial fracture. DESIGN: Inter-fragmentary displacements were measured during walking while the fractures were stabilized, first with one type of fixator then with another. BACKGROUND: It is commonly claimed that one type of fixator exerts a different influence on mechanical stability at a fracture in comparison with another. METHODS: This study compares inter-fragmentary displacement, fixator displacement and weight bearing during walking, in four patients stabilized with an Orthofix DAF, which was replaced by a Howmedica International Monotube. RESULTS: The null hypothesis of no difference in fixator performance was unproved (P < 0.05) through insufficient data. Interpatient variability in inter-fragmentary displacement implies that anthropometry, gait and fracture type may influence fracture stability more than the type of fixator. CONCLUSIONS: Since weight-bearing and displacements were not substantially different, no basis was found for the claim that one fixator provides a mechanical environment substantially different to another. Sample size was not large enough to prove that a small but statistically significant difference exists. RELEVANCE: The influence on fracture stability of one type of unilateral fixator in comparison with another appears to be less than the influence of anthropometry, gait and the type of fracture.

Journal Article↗

PubMed2003

Complications of trapeziometacarpal arthrodesis using plate and screw fixation.

PURPOSE: This study was designed to determine the complications associated with plate and screw fixation of thumb trapeziometacarpal arthrodesis and to compare these results with a previous report from our institution using K-wire fixation. METHOD: We retrospectively reviewed 26 trapeziometacarpal arthrodeses that used plate and screw fixation. The most common diagnosis was primary osteoarthritis and the average follow-up evaluation was 40 months. Nineteen patients were available for a clinical follow-up examination and radiographs. These results were compared with the previously published K-wire fixation group that consisted of 59 arthrodeses with an average follow-up period of 84 months. RESULTS: There were 2 (8%) painful nonunions. There were 6 (23%) hardware malpositions, most frequently associated with a screw in the trapeziotrapezoid joint. Seven (27%) arthrodeses had a second procedure, most commonly hardware removal. Twenty-one (81%) of the patients were satisfied and reported they would have arthrodesis again. In the K-wire fixation group 4 of 59 (7%) arthrodeses went on to nonunion and 2 of 59 required a secondary procedure; patient satisfaction was high (98%). CONCLUSIONS: K-wire and plate and screw fixation have comparable union rates. In the plate and screw fixation group, however, the satisfaction rate was lower and a second surgery was more common. We now recommend pin fixation when performing trapeziometacarpal joint arthrodesis.

Arthrodesis↗