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At least 1,333 records · Page 74Linked to original sources
PubMed2003

Comparison of different distal radius dorsal and volar fracture fixation plates: a biomechanical study.

PURPOSE: To compare the biomechanical properties of 6 dorsal and volar fracture fixation plate designs in a cadaver model. METHOD: Six different plating techniques were used on surgically simulated, unstable, extra-articular distal radius fractures in fresh-frozen cadavers. Specimens were tested to failure in axial compression with the Materials Testing System machine, and were analyzed with a motion analysis system. The 6 different fixation systems studied included an AO stainless steel Pi plate (group 1), an AO titanium Pi plate (group 2), a Forte plate (group 3), a dorsally placed Symmetry plate (group 4), a volarly placed Symmetry plate (group 5), and a volarly placed SCS/V plate (group 6). RESULTS: All dorsal plates (groups 1, 2, 3, 4) failed in apex dorsal angulation and all volar plates (groups 5, 6) failed in apex volar angulation. No group developed an average angular deformity greater than 5 degrees with a load of 100 N, which compares with the physiologic loads expected with active wrist motion. Only the volarly placed SCS/V plated specimens (group 6) resisted deformation of 5 degrees or more at loads up to 250 N, which compares with the physiologic loads expected with active finger motion, and was significantly stronger and more rigid than the other 5 plate groups. CONCLUSIONS: The SCS/V plate fixation system is the most rigid of the systems tested and may offer adequate stability for the treatment of the distal radius fracture in which the anterior and/or posterior metaphyseal cortex is comminuted severely.

Adolescent↗
PubMed2003

[Sacral neuromodulation in patients with nonobstructive, chronic urinary retention: relevance of the carbachol test and influence of associated nerve lession].

OBJECTIVE: Aim of this study was to evaluate whether the carbachol test and the nerve lesions responsible for bladder dysfunction possess predictive value in patients with chronic urinary retention who undergo temporary sacral neuromodulation (PNE test). MATERIAL AND METHODS: In 1999 and 2000, PNE tests were performed in 24 patients with chronic urinary retention and acontractile detrusor previously assessed by urodynamics. In 18 patients, a carbachol test was performed during urodynamics. The diagnosis related to the acontractile detrusor was additionally assessed and compared to the successful outcome of the PNE test. RESULTS: The PNE test was successful in 8 of the 24 patients (33.3 %). The bladder was completely emptied during the PNE test in 3 of the 10 patients with negative carbachol test and in 3 of the 8 patients with positive carbachol test. The highest success rate (80 %) was observed in patients after hysterectomy, whereas after lumbosacral pulposal prolapse or with a CNS tumor, it was only 20 - 33.3 %. CONCLUSIONS: We conclude that sacral neuromodulation is an effective treatment option in patients with nonobstructive urinary retention. The carbachol test does not possess any definitive predictive value with respect to the success rate of sacral neuromodulation in patients with chronic urinary retention. The success rate more likely depends on the localisation of the nerve lesion. PNE tests should be performed in all patients with therapy resistent nonobstructive urinary retention, as no other predictive factors exist.

Adult↗
PubMed2004

Nitinol in magnetic resonance imaging.

Surgical and interventional instruments as well as implants can cause significant magnetic resonance image (MRI) artifacts. The artifacts can be used to visualize instruments, cannulae, guide wires, catheters during interventional MRI and Nitinol devices have proven to be useful for MRI procedures. Diagnostic imaging is often compromised in the area of an implant. Complete vanishing of signals occurs in close proximity or inside implants. The paper presents a fundamental evaluation of MRI artifact of Nitinol devices such as Stents, Vena Cava Filter, heart defect closure devices, cannulae, guide wire, localizer, anastomosis device, etc. in a 1.0 Tesla magnetic field. The American Society for Testing Materials (ASTM) recommendations for selection of sequences and test setup were used but the results of this paper are not sufficient for FDA approval.

Journal Article↗
PubMed1998

Importance of the critical-size bone defect in testing bone-regenerating materials.

A substantial interest exists in developing substitute materials and human recombinant bone-inducing factors to enhance bone regeneration both in the craniofacial complex and in other parts of the skeleton. A persistent problem has been to find an animal model that allows for the comparison of different osteopromotive materials. The purpose of this investigation was 1) to determine whether a 5-mm calvarial defect in adult rats fulfilled the requirements of a critical-size bone defect and 2) to discuss the use of this animal model in assessing bone repair in the craniofacial region. Bilateral full-thickness calvarial defects were trephined in the calvarial bone of 56 5- to 6-month-old Wistar rats. Except for minor amounts of bone formation limited to the margins of the defect, none of the defects revealed any signs of spontaneous bone regeneration 6 and 12 months after surgery. The full-thickness 5-mm calvarial defects thus fulfill the criteria for a critical-size bone defect. This animal model allows for an experiment with a paired design, it avoids inclusion of the sagittal suture in the osseous defect, and it thereby minimizes morbidity by reducing the risk of damaging the midsagittal sinus. An adequate experimental model has been developed to evaluate the efficiency of osteopromotive materials in the healing of bone defects in the craniomaxillofacial region.

Animals↗
PubMed2002

Biomechanical analysis of humeral diaphyseal segmental defect fixation.

With disseminated malignancies, segmental defects of the humeral diaphysis may occur from surgical resection or as a complication of failed prior internal fixation. This study directly compared the biomechanical properties of a second generation titanium modular intercalary humeral spacer (segmental defect replacement prosthesis) with those of a modern locked humeral nail combined with methylmethacrylate (intramedullary nail) or with an intercalary allograft spacer (allograft nail composite) for fixation of segmental defects of the humeral diaphysis. Eighteen matched pairs (36 specimens) of fresh-frozen humeri were prepared in a standard fashion to create a 5-cm middiaphyseal defect and were divided randomly into three groups of 12 specimens each, using three different reconstructive methods. Specimens were tested in external torsion to failure on a Materials Testing System machine. The segmental defect replacement specimens had statistically greater peak torque (mean, 41.4 N-m) and stiffness (mean, 2.1 N-m/ degrees) than the intramedullary nail specimens (mean peak torque, 23.1 N-m) (mean stiffness, 1.6 N-m/ degrees) or the allograft nail composite specimens (mean peak torque, 12.4 N-m) (mean stiffness, 0.6 N-m/ degrees). The intramedullary nail specimens also had a statistically greater peak torque at failure and stiffness than the allograft nail composite specimens. For segmental defects of the humeral diaphysis, reconstruction with a cemented metallic intercalary spacer provides significantly greater immediate stability than interlocked intramedullary nail fixation supplemented with segmental methylmethacrylate or intercalary allograft reconstruction.

Biomechanical Phenomena↗
PubMed2002

Development of speech perception and production in children with cochlear implants.

The purpose of the present study was twofold: 1) to compare the hierarchy of perceived and produced significant speech pattern contrasts in children with cochlear implants, and 2) to compare this hierarchy to developmental data of children with normal hearing. The subjects included 35 prelingual hearing-impaired children with multichannel cochlear implants. The test materials were the Hebrew Speech Pattern Contrast (HeSPAC) test and the Hebrew Picture Speech Pattern Contrast (HePiSPAC) test for older and younger children, respectively. The results show that 1) auditory speech perception performance of children with cochlear implants reaches an asymptote at 76% (after correction for guessing) between 4 and 6 years of implant use; 2) all implant users perceived vowel place extremely well immediately after implantation; 3) most implanted children perceived initial voicing at chance level until 2 to 3 years after implantation, after which scores improved by 60% to 70% with implant use; 4) the hierarchy of phonetic-feature production paralleled that of perception: vowels first, voicing last, and manner and place of articulation in between; and 5) the hierarchy in speech pattern contrast perception and production was similar between the implanted and the normal-hearing children, with the exception of the vowels (possibly because of the interaction between the specific information provided by the implant device and the acoustics of the Hebrew language). The data reported here contribute to our current knowledge about the development of phonological contrasts in children who were deprived of sound in the first few years of their lives and then developed phonetic representations via cochlear implants. The data also provide additional insight into the interrelated skills of speech perception and production.

Age Factors↗
PubMed2004

Thermal microdebridement does not affect the time zero biomechanical properties of human patellar tendons.

BACKGROUND: Thermal microdebridement for the treatment of chronic tendinopathy has recently been introduced. The effect of thermal microdebridement on the biomechanical properties of human tendons, however, remains unknown. HYPOTHESIS: Thermal microdebridement does not affect the biomechanical properties of human patellar tendons in a cadaveric model at the time of initial treatment. STUDY DESIGN: Controlled laboratory study. METHODS: The central 15 mm of 12 matched, human (mean age, 71 years; 8 male, 4 female), fresh-frozen patellar tendons was divided into 3 equal 5-mm specimens. The treatment group (n = 12) underwent thermal microdebridement with a radiofrequency probe. A sham treatment group (n = 12) underwent insertion of a deactivated probe. The control group (n = 12) underwent no treatment. After treatment, each specimen was tested to failure in a servo-hydraulic materials testing machine at an elongation rate of 3 mm/s. One-way repeated measures analysis of variance was used to determine differences between groups. RESULTS: No significant difference in ultimate stress at failure, elastic modulus, strain energy density, or strain at maximum load was found between the groups. The ultimate stress at failure for the treatment, sham, and control groups was 61.0, 66.7, and 63.0 MPa, respectively (P = .653), and the strain at maximum load was 0.12, 0.11, and 0.09, respectively (P = .279). CONCLUSIONS: Thermal microdebridement does not affect the biomechanical properties of cadaveric human patellar tendons at the time of initial treatment. CLINICAL RELEVANCE: It may be safe to proceed with aggressive rehabilitation after thermal microdebridement of the patellar tendon. However, the results in this cadaveric model should be interpreted with caution. Additional studies using an in vivo model will be required to completely assess the effects of thermal microdebridement on the biomechanical properties of human patellar tendons.

Aged↗
PubMed1991

The stability of fixation of first metatarsal osteotomies.

Five different types of osteotomies for the correction of the hallux valgus deformity were performed on dried human first metatarsal bones. These included the step-cut Mitchell osteotomy, a distal transverse osteotomy, a distal biplanar osteotomy, the Chevron osteotomy, and a basilar osteotomy. Each type of procedure was then fixed using a variety of clinically appropriate techniques including single K-wires, crossed K-wires, a single A-0 cancellous screw, a single A-0 cortical screw, and three different types of sutures. Specimens were placed in a test jig and physiological loads applied with a Materials Testing Systems servohydraulic testing machine (Minneapolis, Minnesota). No difference in stability was observed between the various types of osteotomies, except for the Chevron osteotomy, which did possess greater inherent stability. Fixation by screws or multiple K-wires provided the most stable configuration when compared to other methods. The postoperative regimen following first metatarsal osteotomy should take into account the relative stability of fixation. Cast immobilization and a nonweight-bearing status may be preferable after procedures characterized by less mechanical stability.

Bone Screws↗
PubMed1995

[Biomechanical properties of the anterior and posterior longitudinal ligament in the cervical spine].

The purpose of this study is to investigate the biomechanical properties of the anterior longitudinal ligament (ALL) and the posterior longitudinal ligament (PLL) of the human cervical spine. Twenty C3-C4 and twenty C5-C6 motion segments are dissected from the spines of human cadavers. Experimental specimens of the bone-ligament-bone complex are prepared for mounting on a testing jig. Static tensile tests are performed with an Instron-type material test system. Dynamic biomechanical properties were tested with a biomechanical spectrometer. The failure load and failure stress of the PLL tend to be higher than those of the ALL, but there are no statistically significant differences between them. The tan delta of the ALL is higher than that of the PLL (p < 0.01). The dynamic stiffness of the PLL is higher than that of the ALL (p < 0.01), but there was no statistically significant difference in the dynamic elastic modulus between the ALL and the PLL. These results imply that the PLL has better biomechanical properties as a stabilizer for cervical motion than the ALL in the lower cervical spine.

Adult↗
PubMed1993

The use of Weibull statistics in mechanical testing of brittle dental materials.

The mean strength that has traditionally been taken as a measurement of the strength of a material does not reflect the true strength, and therefore it cannot be used as a design parameter. This explains why many brittle materials fail at unpredictable stress, either below or above the mean strength. By using Weibull statistics, the prediction and assessment of strength can be made more sensibly. The performance of a material can be predicted by considering a stress at a lower level of failure probability.

Dental Materials↗
PubMed1998

The surgical gowns and drapes of tomorrow. Specifying material performance and test methods.

A mandatory European standard is being developed to establish basic requirements and test methods for disposable and reusable materials used for surgical gowns and drapes. Once this standard has been adopted, the continued use of cotton textiles and conventional cotton-polyester-mixed textiles will become questionable. This article outlines the proposed requirements and looks at alternative methods that use liquid-repellent micro-filament textiles or liquid-proof textile laminates.

Equipment Reuse↗
PubMedDate not supplied

Progressive worsening of idiopathic pulmonary fibrosis. High resolution computed tomography (HRCT) study with functional correlations.

PURPOSE: To evaluate the usefulness of the high-resolution computed tomography (HRCT) visual score in idiopathic pulmonary fibrosis (IPF) and its correlation with respiratory function tests. MATERIAL AND METHODS: We studied the pulmonary function tests and HRCT scans of 42 IPF patients, at presentation (T0) and follow-up (T1: mean 13.7 months post-diagnosis). Of the 42 patients, 21 had been treated with steroid and immunosuppresion therapy. The pulmonary function tests considered were vital capacity (VC), diffusion lung capacity for carbon monoxide (D(L)CO) and arterial blood oxygen partial pressure (PaO(2)). The main HRCT parameters were type of lesion, and site and extent, the latter calculated by means of the visual score. RESULTS: Between T0 and T1, both mean HRCT score (from 43.57% to 50.64%) and lung function tests worsened (VC from 68.43% to 64.18%; D(L)CO from 36.31% to 28.97%; PaO(2) from 76.31 to 68.89 mmHg), without considerable differences between treated and untreated patients. At presentation (T0), the HRCT visual score had a significant correlation with lung function tests and these correlated with one another. Similar correlations were found at T1, but not for HRCT score and D(L)CO. In the interval between T0 and T1 the variations correlated significantly with each other, with two exceptions: HRCT score and D(L)CO, and D(L)CO and PaO(2). DISCUSSION AND CONCLUSIONS: IPF exhibited a progressive deterioration both in HRCT extent of disease and lung function impairment. There is a significant correlation between HRCT visual score and lung function tests both at diagnosis and at follow-up. The HRCT study is able to identify and quantify anatomic IPF and also to evaluate the progression of the disease. In clinical practice, the HRCT visual score of disease extent can be used in association with function tests to monitor IPF evolution, and to evaluate prognosis and therapy. In the future, helical CT with 3D model construction will provide a more precise IPF quantification with automatic score.

Aged↗
PubMed1989

Incisal and occlusal tooth wear and wear of some prosthodontic materials. An epidemiological and clinical study.

In the epidemiological studies of this thesis, the aims were to elucidate the prevalence of incisal and occlusal wear in a normal Swedish population, and to present factors related to incisal and occlusal wear in that population. In the clinical studies, the aims were to develop methods for and to perform in vivo studies of wear of prosthodontic materials and to present quantitative and qualitative data of occlusal contact wear in these materials. The epidemiological part of this study consisted of 585 randomly selected dentate individuals from the Community of Jönköping, Sweden, who in 1983 reached the age of 20, 30, 40, 50, 60, 70 or 80 years. The results showed that the severity and prevalence of incisal and occlusal wear increased with age. Men presented more teeth with occlusal wear than women. An individual tooth wear index (IA), with the potential to rank individuals with respect to incisal and occlusal wear, has also been introduced. Factors which were found to correlate significantly to increased incisal and occlusal wear were: number of teeth, age, sex, occurrence of bruxism, use of snuff and the saliva buffer capacity. From the in vivo studies, data of occlusal contact wear of gold, porcelain and some resin based materials in four different persons, with earlier histories of occlusal wear of teeth and/or restorations, were presented. The in vivo models combined two methods: removable segments or double crowns, and a replica technique. The combination of a polyvinylsiloxane impression material (President) and an epoxy resin (Metapox) was chosen for the replica model technique. All materials tested showed increased wear rate when the opposing material was porcelain. Gold and porcelain showed equal wear resistance when opposing porcelain. The resin-based materials showed at least a three to four times higher wear rate. No difference in wear resistance could be observed between gold type III and type IV. Gold showed a combined abrasive and fatigue type of wear and porcelain mainly a fatigue type of wear. The resin-based materials showed a fatigue type of wear, sometimes in combination with a tribochemical reaction.

Adult↗
PubMed1983

p-tert.-Butylphenol formaldehyde and other causes of shoe dermatitis.

Because p-tert.-butylphenolformaldehyde-free shoes are unavailable in the Dutch market we had to have shoes made of alternative materials for 13 patients reacting to this resin. These alternative materials consisted of leather samples prepared with various tanning agents, counters (heel stiffeners), stitching yarns, adhesives, etc. The composition of these alternative materials was kept a secret. New shoes were composed of materials to which the patient had shown negative reactions. These shoes are well tolerated. Only one patient reacted to virtually all materials tested. She may have an excited skin syndrome. She will be tested in the near future with the necessary materials applied one by one to find out whether this is true. Up to present we have encountered only a few shoe positive patients who have neither reacted to the resin, nor to a series of alternative adhesives. These patients will be studied in more detail as to the origin of their dermatitis.

Dermatitis, Contact↗
PubMedDate not supplied

Effect of various commercially available enzymes in the liquid chromatographic determination with external standardization of thiamine and riboflavin in foods.

The efficacy of various commercially available enzymes in the determination of thiamine and riboflavin in foods was studied by liquid chromatography (LC) using external standards. Different enzymes, as well as the same enzyme produced by different manufacturers, very strongly affected the determination of both vitamins. The recoveries for different foods ranged from 85 to over 100% for thiamine and from 80 to 100% for riboflavin. The present LC method was accurate and precise when tested on a food and a feed reference material, and coefficients of variation were 5.5% for thiamine and 10% for riboflavin in a rye flour reference material tested for 8 months.

Amylases↗