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At least 1,387 records · Page 77Linked to original sources
PubMed2003

Reciprocal walking orthosis with composite material body brace: initial development.

Reciprocal walking orthoses are routinely used by thoracic lesion patients for ambulation using crutches. A primary reason for their prescription is to provide therapeutic benefit and improved independence. To achieve this, maximum efficiency of walking and acceptance of the device is necessary to promote long-term compliance. Lateral rigidity in the orthosis influences walking efficiency, but the structural properties of conventional techniques for producing a sufficiently rigid body brace makes them unattractive. Currently patients and clinicians are forced to choose between greater efficiency or cosmesis of the orthosis. Composite materials have the potential to permit the required rigidity in a structure that is less obtrusive. However, their material properties could lead to unsafe forms of failure unless suitable manufacturing methods are devised. It is therefore inappropriate to supply prototypes to patients for field evaluation until laboratory investigation of innovative production methods has ensured that the orthosis is safe. A production technique has been devised that is ostensibly suitable. Prototype body braces have been tested and have been shown to have improved structural properties and safe failure modes. A test programme implemented on a complete concept orthosis has confirmed that improved lateral rigidity can be achieved with a less obtrusive body brace, and that it will behave safely for long enough to permit field evaluation.

Braces↗
PubMed2005

Engineering properties and performance of dental crowns.

Dental crowns are used to replace damaged natural crowns of teeth and are fixed to prepared teeth with luting cements, which should provide an adhesive bond to the tooth structure giving reliable retention and minimal microleakage. Mechanical testing of crowns in vitro gives failure load distributions that are well described by Weibull models, comparing probabilities of survival and reliability. Fatigue testing of crowns is time consuming, but regression analysis to interpolate functions through data points quoting probability limits or applying Weibull analysis is achievable. A complementary approach is to conduct materials tests with appropriate interfacial geometries. Luting cements are used in thin layers of 40-150 microm. Contraction during polymerization is restrained by adhesion to substrates, allowing little relaxation of stresses. Conventional and resin-modified glass ionomer cements create thin zones of interaction with dentine and fail cohesively. The chevron notch short rod technique has been used to measure fracture toughness and rank cements. A development of this method, using chevron notch short bar specimens, permitted fracture toughness to be determined for luting cement--dentine substrate interfaces. Representative fracture experiments need to be developed to apply mixed mode conditions. The basic challenge to predict long-term performance from short-term laboratory tests remains.

Biomedical Engineering↗
PubMed2005

Wire tension in the Ilizarov system: accuracy of the wire-tensioning device.

The Ilizarov fixator consists of tensioned wires that attach bone segments to a modular frame. The aim of this study was to establish the accuracy and precision of the wire-tensioning device supplied with the Ilizarov external fixation system. The device was used to tension a wire in direct opposition to a calibrated load cell. Five subjects tested three devices, at each of their four tension settings, in two separate sessions. Subjects could not see the true tension during the test. There were significant differences between the results for different subjects (p < 0.01) and instruments (p < 0.01) but not for different tension settings or between the two sessions. Overall mean measured tensions were 4.9 per cent (standard deviation, 4.4 per cent) below intended values. Tensions obtained at the maximum edge (completely occluded) on the scale markings were significantly (p < 0.001) closer to the nominal values (mean discrepancy, 3.6 per cent) than those at the minimum edge (mean discrepancy, 17.6 per cent). Several factors influence wire tension. Tensioning devices are not identical and the results obtained with them depend on the user. If the scale markings are completely occluded, the discrepancy between intended and actual tensions of around 5 per cent is likely to be adequate for clinical practice since surgeons do not select the most suitable tension following quantitative data assessment, but rather it is a judgement based on surgical experience and consideration for the patient weight and expected level of activity.

Bone Wires↗
PubMed2005

Near-surface damage--a persistent problem in crowns obtained by computer-aided design and manufacturing.

Robust dental systems obtained by computer-aided design and manufacture (CAD/CAM) have been introduced and, in parallel, the strength of the ceramic materials used in fabricating dental crowns has improved. Yet all-ceramic crowns suffer from near-surface damage, limiting their clinical success, especially on posterior teeth. Factors directly associated with CAD/CAM fabrication that contribute to the degree of damage include material selection and machining parameters and strategies. However, a number of additional factors also either create new damage modes or exacerbate subcritical damage, potentially leading to catastrophic failure of the crown. Such factors include post-fabrication manipulations in the laboratory or by the clinician, fatigue associated with natural occlusal function, and stress fields created by compliance or distortion within the supporting tooth structure and/or adhesive material holding the crown to the tooth. Any damage reduces the strength of a crown, increasing the probability of catastrophic failure. The challenge is to understand and manage the combination of competing damage initiation sites and mechanisms, limitations imposed by the demand for aesthetics, and biologically related constraints.

Ceramics↗
PubMed1999

Evaluation of a hip joint simulator.

To evaluate the functioning of the Durham hip joint wear simulator, the wear rates of ultra high molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE) acetabular cups articulating against 22 mm diameter cobalt-chromium-molybdenum (CoCrMo) femoral heads were studied. A wear test was conducted in a lubricant of distilled water at 37 degrees C for a duration of 4.8 million cycles. The average penetration rate for the CoCrMo femoral heads against UHMWPE acetabular cups was 0.03 mm/10(6) cycles, while penetration rate for PTFE cups was some twenty times greater. These results are of a similar order of magnitude to other simulator studies in distilled water and are in a similar ratio to clinical data.

Acetabulum↗
PubMed1999

Analysis of debris from brushing the femoral canal with a plastic brush--a potential cause of loosening in total hip replacement.

The generation of submicrometre sized polyethylene particles has been shown to be one of the major causes of osteolysis, loosening and failure of total replacement joints. It has been reported that intramedullary brushing of the femoral canal with polymer brushes prior to total hip arthroplasty results in the release of polymer particles into the femoral canal. The aim of this study was to isolate and characterize these particles on the basis of morphology and size and to determine whether these particles may play a role in osteolysis and loosening of the total hip prostheses. It was found that the majority of the particles shed by the polymer brushes were submicrometre in size and were similar in morphology to UHMWPE wear particles isolated from periprosthetic tissues. In addition, the majority of the particles released by the brushes were in the biologically active size range (0.1-10 microns), and may contribute to osteolysis and loosening of hip prostheses.

Arthroplasty, Replacement, Hip↗
PubMed1995

Experimental and theoretical study of the contact mechanics of five total knee joint replacements.

The tibio-femoral contact area in five current popular total knee joint replacements has been measured using pressure-sensitive film under a normal load of 2.5 kN and at several angles of flexion. The corresponding maximum contact pressure has been estimated from the measured contact areas and found to exceed the point at which plastic deformation is expected in the ultra-high molecular weight polyethylene (UHMWPE) component, particularly at flexion angles near 90 degrees. The measured contact area and the estimated maximum contact stress have been found to be similar in magnitude for all of the five knee joint replacements tested. A significant difference, however, has been found in maximum contact pressure predicted from linear elasticity analysis for the different knee joints. This indicates that varying amounts of plastic deformation occurred in the polyethylene component in the different knee designs. It is important to know the extent of damage as knees with large amounts of plastic deformation are more likely to suffer low cycle fatigue failure. It is therefore concluded that the measurement of contact areas alone can be misleading in the design of and deformation in total knee joint replacements. It is important to modify geometries to reduce the maximum contact stress as predicted from the linear elasticity analysis, to below the linear elastic limit of the plastic component.

Anthropometry↗
PubMed2004

T.120 application sharing for the remote configuration of prostheses.

We conducted a study to determine whether application sharing and desktop videoconferencing using the Internet constituted a viable method for remotely configuring a microprocessor-controlled lower-extremity prosthesis. A DSL broadband connection (operated at 256 kbit/s) was used to connect two prosthetic care facilities over the public Internet. PC-based videoconferencing was used with application sharing for the remote configuration of the prosthesis and to view information on the load and angle of the prosthetic knee. Fifteen people with trans-femoral amputations had the settings for their prosthesis scrambled before a specialist at another site remotely configured the device. There were no significant differences between the original and online settings. Clinicians at both sites considered that 14 out of 15 sessions were successful (one trial involved technical problems with the knee unit that were unrelated to the telemedicine trial). The clients rated their satisfaction with the technique as excellent (47%), above average (33%) or average (20%). The present study shows that a combination of desktop videoconferencing and T.120 application sharing can be used for the remote configuration of assistive devices.

Adult↗
PubMed1976

Ossicular chain reconstruction.

This study represents a review of 121 patients who underwent ossicular chain reconstruction during a five-year period. They depict a general cross section of the sequelae of chronic otitis media. There was no selection of "favorable" cases. Ninety have been followed for one year or more. Hearing results in the most favorable cases (malleus handle and stapes arch present), were improved by the employment of a sculptured, fitted incus prosthesis between the handle and capitulum. Postoperative hearing was improved to within 10 db of the postoperative bone level in about half of the cases. Hearing was 20 db or better in more than 80 percent.

Audiometry↗
PubMed1983

Ossicular chain reconstruction: the TORP and PORP in chronic ear disease.

The traditional objectives of tympanoplasty are infection control, closure of the ear by grafting techniques, and hearing rehabilitation via ossicular reconstruction. The multiplicity of contemporary prostheses and surgical options available would seem to underscore the magnitude of the ossicular reconstruction problem in the difficult chronic ear relative to all else. The success of stapedectomy has led to great expectations for all problems of ossicular reconstruction. The circumstances of the chronic ear is a milieu hostile in comparison and precludes any such comparison. Multiple sites of ossicular pathology, variations in mucosa health, inconsistent middle ear aeration and the overall complexity of the chronic ear present the otologist with a physiodynamic problem the solution of which is far from simplistic. The TORP and PORP have been enthusiastically endorsed in this regard, as a very suitable answer. Such enthusiasm, however, has been largely derived from data accumulated in the short term, often in less than a year's follow-up. This report reviews the authors' results in 141 patients in whom 86 TORPs and 55 PORPs were employed. For comparison, hearing data in 276 ears in which the fitted incus prosthesis, the authors' preferred reconstruction format, was used. Success for TORP reconstruction was assessed as air-bone gap closure to within 30 dB and for PORP, to within 20 dB. This was accomplished in 85% and 49% respectively. Extrusion rate, overall, was 10%. Relative advantages and disadvantages of the TORP and PORP are discussed and serve as a basis for the decision to continue to use this method of ossicular reconstruction. This data is put into perspective in acknowledging that the TORP and PORP are not the ultimate solution to this problem. When employed in combination with newer techniques in cartilage tympanoplasty, further improvement is expectant.

Chronic Disease↗
PubMed2002

A clinical overview of removable prostheses: 3. Principles of design for removable partial dentures.

Removable partial dentures (RPDs) should not be made for patients unless they are necessary. Most partial dentures have the potential to cause some damage to the teeth and supporting tissues, however well they are designed and constructed; the criteria for selecting such devices were described in a previous article. In general there is merit in, wherever possible, reducing tissue coverage as much as possible when RPDs are being planned. This article, the third in a series on the prescription of RPDs, discusses the design principles involved.

Dental Abutments↗
PubMed1999

Planar anteversion of the acetabular cup as determined from plain anteroposterior radiographs.

In total hip replacement, orientation of the cup is critical to the stability of the prosthesis. A new method to determine the angle of planar anteversion is described. A simple mathematical formula uses the measurements taken from anteroposterior radiographs to calculate the planar anteversion without reference to tables or charts. An experimental study in vitro has shown the efficacy of the formula in giving results which are within a clinically acceptable range.

Acetabulum↗
PubMed1999

Extensible endoprostheses of the humerus after resection of bone tumours.

We carried out extensible endoprosthetic replacement of the proximal or total humerus in 18 children aged between six and 12 years, after resection of primary bone tumours mainly for osteosarcoma and Ewing's sarcoma. In 11 patients we performed 44 lengthening procedures, with an average of two per child annually and a mean total extension of 29.9 mm per patient. We were able to achieve lengthening of the operated limb with few complications and a mean functional rating of 79.3% according to the Enneking system. Progressive lengthening of these prostheses does not adversely affect the overall function of the arm, and superior subluxation of the head of the prosthesis has not been a problem.

Bone Neoplasms↗
PubMed2003

Turn-up bone flap for lengthening the below-knee amputation stump.

When amputation just below the knee becomes necessary after extensive loss of bone from the tibia and of anterior soft tissue in the treatment of tumours, fractures or infection, the remaining proximal tibia may be too short for a below-knee prosthesis, although the knee may be normal. We have included the distal tibia or foot in a long posterior flap by turning it up thus increasing the length of a very short proximal tibial stump. The knee is thereby saved, allowing satisfactory use of a below-knee prosthesis. This technique is particularly applicable when the distal leg is normal and well vascularised. Five procedures have been undertaken. We present two illustrative cases.

Adolescent↗
PubMed2006

Assessment of reproducibility and accuracy in templating hybrid total hip arthroplasty using digital radiographs.

In 20 patients undergoing hybrid total hip arthroplasty, the reproducibility and accuracy of templating using digital radiographs were assessed. Digital images were manipulated using either a ten-pence coin as a marker to scale for magnification, or two digital-line methods using computer software. On-screen images were templated with standard acetate templates and compared with templating performed on hard-copy digital prints. The digital-line methods were the least reliable and accuracy of sizing compared with the inserted prostheses varied between -1.6% and +10.2%. The hard-copy radiographs showed better reproducibility than the ten-pence coin method, but were less accurate with 3.7% undersizing. The ten-pence coin method was the most accurate, with no significant differences for offset or acetabulum, and undersizing of only 0.9%. On-screen templating of digital radiographs with standard acetate templates is accurate and reproducible if a radiopaque marker such as a ten-pence coin is included when the original radiograph is taken.

Acetabulum↗