PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Prosthesis Design”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed1999

Haemodynamic performance of aortic pericardial bioprostheses and bileaflet prostheses at rest and during exercise: implications for the surgical management of patients with small aortic roots.

OBJECTIVE: To determine the haemodynamic behaviour, at rest and during exercise, of aortic valve pericardial bioprostheses and different sizes of bileaflet prosthesis. DESIGN: Observational study. SETTING: Tertiary medical centre. PATIENTS AND INTERVENTIONS: 74 patients (33 women, 41 men; mean age 64 years) in whom 40 pericardial bioprostheses and 34 bileaflet prostheses sized 19, 21, or 23 mm had been implanted to replace aortic valves. MAIN OUTCOME MEASURES: Doppler echocardiography at rest and at peak exercise, between 12 and 47 months after surgery. RESULTS: All patients achieved a significant increase in heart rate, systolic blood pressure, and cardiac output with exercise. Transvalvar pressure fall, valve area, and left ventricular systolic and diastolic function indices also underwent significant changes with exercise. Reductions in peak and mean transvalvar pressure, at rest and at peak exercise, were greater in patients with small valves (p < 0.05). Valve areas and effective area index were greater in the patients with larger valves (p < 0.001). There were no significant differences between patients with mechanical and biological prostheses with regard to transvalvar pressure fall and valve areas at rest and at peak exercise. CONCLUSIONS: 19 mm and 21 mm aortic prostheses and bioprostheses continue to create significant obstruction, particularly with exercise.

Aged↗
PubMed1998

Morbidity and mortality of reconstructive surgery of noninfected false aneurysms detected long after aortic prosthetic reconstruction.

OBJECTIVE: To determine the morbidity and mortality of surgical treatment of false (anastomotic) aneurysms, we analyzed the results of 158 consecutive surgical procedures for repair of false aneurysms that were detected as a result of a surveillance program after aortic reconstruction with a prosthesis. DESIGN: Retrospective analysis of patient data from a vascular registry that included information on the long-term follow-up of our patients. SETTING: A university hospital (tertiary referral center) in the Netherlands that has been performing vascular reconstructive surgery since 1958. PATIENTS: We performed 158 surgical procedures on 135 patients with 220 noninfected false aneurysms. Using a yearly surveillance program, the false aneurysms were detected at a mean interval of 8 years after the initial reconstruction. Most patients (60%) were asymptomatic. The operation was performed as an emergency in 25 instances (16%). RESULTS: The mortality rate of patients receiving nonsurgical treatment was very high (61%) owing to documented rupture (11 of 18 patients). The intraoperative death rate was 7.6% per procedure. This was higher for emergency (24%) than for elective procedures (4.5%). CONCLUSIONS: Conservative follow-up carries a very high mortality rate, as does emergency surgery for a false aneurysm. However, the intraoperative mortality rate of elective reconstruction of a false aneurysm can be in the same range as that of elective primary aortic reconstruction. Therefore, we advocate a surveillance program, including yearly ultrasound studies, after prosthetic aortic reconstruction for the timely detection and elective repair of all false aneurysms.

Adult↗
PubMed2003

Direct comparison of calculated hip joint contact forces with those measured using instrumented implants. An evaluation of a three-dimensional mathematical model of the lower limb.

Characterisation of hip joint contact forces is essential for the definition of hip joint prosthesis design requirements. In vivo hip joint contact force measurements have been made using instrumented hip joint prostheses. However, to allow determination of the range of values of joint contact force and their directions relative to anatomical structures in a range of subject groups sufficient to form an agreed data base it is necessary to adopt a different approach without the use of an implanted transducer. The use of mathematical models of the lower limb to examine the forces in soft tissues and at the joints has provided valuable insight into internal loading conditions. Several authors have proposed mathematical musculo-skeletal models. However, there have been only limited attempts at validation of these models. It is possible to use the results of in vivo force measurements from instrumented prostheses to validate the results calculated using the mathematical models. In this study two subjects with instrumented hip joint prostheses were studied. Forces at the hip joints were calculated using a three-dimensional model of the leg. Walking at slow, normal and fast speeds (0.97-2.01m/s), weight transfer from two to one leg and back again, and sit to stand were studied. Direct comparisons were made between the 'gold standard' measured hip joint contact forces and the calculated forces. There was general agreement between the calculated and measured forces in both pattern and magnitude. There were, however, discrepancies. Reasons for these differences in results are discussed and possible model developments suggested.

Computer Simulation↗
PubMed1986

A self-sealing dialysis prosthesis. Coaxial double PTFE-silicone graft.

The performance of a new dialysis prosthesis designed to self-seal after puncture was tested ex vivo and in vivo. It consists of two coaxial polytetrafluoroethylene tubes (PTFE), the space between them filled with silicone rubber sealant (PTFE-sil). Ex vivo: Three PTFE-sil, three double PTFE (without silicone), and three single PTFE grafts were placed sequentially between scribner shunts in the hind limb of four dogs. Bleeding on puncturing with an 18-gauge needle was measured for 30 seconds. PTFE-sil bled less than the controls (g): PTFE-sil; 16 +/- 18; double PTFE: 32 +/- 10; single PTFE: 52 +/- 19 (p less than 0.001). In vivo: Six PTFE-sil and five single PTFE grafts were interposed between the carotid artery and jugular vein of dogs and were punctured with a 16-gauge needle on days 1, 3, and 7. Bleeding was measured through an incision over the puncture site at 5 minutes. In 11 punctures of PTFE-sil, there was no bleeding; three bled less than 20 g. In 13 control punctures, none bled less than 70 g. Patency: Grafts were studied for patency in arteriovenous (AV) fistulas in 34 dogs. Each dog received a PTFE-sil graft in one groin and a single PTFE control graft in the other. At 4 months, patency rates were: PTFE-sil, 84%; single PTFE, 87% (NS). Four months after implantation, hemostasis after puncture in PTFE-sil grafts required 70 +/- 49 seconds versus 207 +/- 48 seconds for PTFE grafts (p less than 0.005). In conclusion, PTFE-sil grafts are self-sealing, can be used immediately after implantation, and need minimal compression after needle removal.

Animals↗
PubMed2004

Subretinal implantation and testing of polyimide film electrodes in cats.

BACKGROUND: Progress in the field of microelectronics has led to the development of visual prostheses for the treatment of blinding diseases. One concept under investigation is an electronic subretinal prosthesis to replace the function of lost photoreceptors in degenerative diseases, such as retinitis pigmentosa. METHODS: In the subretinal prosthesis design concept, an array of stimulation electrodes is placed in the subretinal space. To test the feasibility of the concept and to determine basic stimulation parameters, wire-bound stimulation devices were used in acute trials for up to 12 h in three eyes in anaesthetised cats. These wire-bound stimulation elements were based on strips of polyimide film. The film strips were introduced through a sclerostomy into the vitreous cavity and via a retinotomy into the subretinal space during a modification of the standard three-port vitrectomy procedure. On entry through the retinotomy, the film was advanced mechanically to the desired position in the area centralis. Perfluorocarbon liquid (PFCL) was used to establish close contact between the electrode array and the outer retina. Stimulation was performed with computer-generated sequences of current waveforms in acute trials immediately after surgical implantation of the stimulation film. Cortical recordings in the primary visual cortex were performed with electrodes placed in locations corresponding to the retinal stimulus site. RESULTS: All three implantations were carried out successfully with the stimulation array implanted beneath the outer retina of the area centralis of the operated eye. The retina was attached over the stimulation array in all cases. No cortical responses were recorded in one of the stimulation sessions. The results from another session revealed clear intracortical responses to subretinal stimulation with polyimide films. Following single-site retina stimulation, the estimates of spatial cortical resolution and temporal resolution were approximately 1 mm and 20-50 ms, respectively. DISCUSSION: Our results indicate that focal subretinal stimulation evokes localised spatio-temporal distribution of cortical responses. These findings offer hope that coarse restoration of vision may be feasible by subretinal electrical stimulation.

Animals↗
PubMed2003

Prosthetic rehabilitation of an amputated thumb.

Prosthetic rehabilitation of any defect or abnormality of any part of the body must be as indiscernible as possible from the surrounding natural tissues in terms of cosmesis as well as function. Surgical procedures are more likely to meet the requirements of absolute function but the patients' involvement and willingness to undergo extensive and costly procedures like micro-surgical grafting and implants may preclude these procedures. This paper presents an alternative method of prosthetic rehabilitation of an amputated thumb with a heat cured silicone material.

Adolescent↗
PubMed2005

Effect of decentration of wavefront-corrected intraocular lenses on the higher-order aberrations of the eye.

OBJECTIVE: To evaluate the theoretical effect of decentration of aspherical intraocular lenses (IOLs) and wavefront-corrected IOLs up to the sixth order on higher-order aberrations (HOAs) (third through sixth order) of the eye. METHODS: An aspherical IOL with HOAs of fourth-order spherical aberrations only (-0.287 microm with a 6-mm pupil) and a wavefront-corrected IOL with HOAs of equal magnitude and opposite from the corneal HOAs were created and laterally shifted up to 1 mm to simulate decentered IOLs. The residual HOAs for pupils of 3 to 6 mm were calculated by combining the HOAs from the cornea and the decentered IOL. Based on the residual HOAs, optical quality was rated by 3 criteria: the Marechal criterion, a diffraction-limited optical system with an aberration less than lambda/14; P(10), the lower 10th percentile of the corneal HOAs in this study group; and decreased HOA, residual ocular HOAs less than the corresponding corneal HOAs. RESULTS: Simulated implantation of the aspherical IOLs and wavefront-corrected IOLs was performed in 154 eyes of 94 patients aged 40 to 80 years. For a centered aspherical IOL and a 6-mm pupil, no eyes met the Marechal criterion, and the P(10) and decreased-HOA criteria were met by 46% and 93% of eyes, respectively. For a 6-mm pupil, the required centration was 0.47 mm to meet the decreased-HOA criterion in 50% of eyes. With a wavefront-corrected IOL and a 6-mm pupil, the centrations required to meet the criteria for 90% of eyes were 0.04 mm for the Marechal criterion, 0.36 mm for P(10), and 0.48 mm for the decreased-HOA criterion. CONCLUSION: Excellent centration is required to maximize the visual outcome of wavefront-corrected IOLs. CLINICAL RELEVANCE: With current surgical techniques, implantation of aspherical IOLs and wavefront-corrected IOLs will reduce total ocular HOAs below corneal HOAs in approximately 45% and 86% of eyes (6-mm pupil), respectively.

Adult↗
PubMed1997

Failure mechanisms of anterior cruciate ligament prostheses: in vitro wear study.

Previous retrieval studies analyzing the cause of failure of anterior cruciate ligament (ACL) prostheses identified a wear mechanism. However, the relative importance of yarn on bone compared to yarn on yarn wear has not been clearly understood. Therefore, the objective of this study was to elucidate which type of wear is the dominant cause of clinical failure. A variety of ACL prosthetic structures were exposed to two in vitro tests: one for yarn on yarn and the other for a novel yarn on bone wear test system. The latter included the use of both smooth (uncut) and rough (cut) bone surfaces to simulate the conditions around the condyle and at the exit of the tibial tunnel, respectively. The damaged textile structures were viewed by SEM. The various fiber fracture morphologies were identified and classified for the two types of wear tests; for the smooth and rough bone surfaces; for the braided, knitted, woven, and twisted textile structures; and for the three types of fibers that were included: polyethylene terephthalate, polypropylene, and ultrahigh molecular weight polyethylene. The results confirmed that yarn on bone and yarn on yarn wear phenomena are associated with significantly different failure mechanisms. While the more aggressive rough (or cut) bone causes more rapid and intense fiber damage and faster ACL failure than the smooth (uncut) osseous surface, both abradants cause the same type of abrasive wear phenomenon. Differences in failure mechanisms were identified between the different textile structures and the different fiber types. By interpreting the damaged fiber images from clinically failed and retrieved ACL prostheses, we are now able to confirm that the predominant cause of synthetic ACL failure is yarn on bone abrasion. Improvements in future ACL prosthesis designs will only be possible by eliminating or minimizing the effect of this type of abrasive wear.

Anterior Cruciate Ligament↗
PubMed2000

Fluid sorption of orthopedic grade ultrahigh molecular weight polyethylene in a serum environment is affected by the surface area and sterilization method.

It is shown in this work that lubricant sorption in ultrahigh molecular weight polyethylene (UHMWPE) increases with available surface area of the component. This has clinical relevance, because sliding and articulation experienced in simulator studies can result in changes in surface roughness and the creation of new surfaces. This study compares the fluid sorption of orthopedic grade UHMWPE with different surface areas (but equivalent volume) for different sterilization methods. For both the gamma radiation and nonsterile control samples, the gain in total fluid absorbed scaled proportionately with surface area. For the EtO sterilization treatment, the fluid gain was nonlinear and substantially less than the radiated and control groups. The findings from this study clearly indicate that the sterilization and surface area affect the fluid uptake and weight gain of UHMWPE.

Adsorption↗
PubMed2000

Effects of fatigue loading and PMMA precoating on the adhesion and subcritical debonding of prosthetic-PMMA interfaces.

Debonding of clinically relevant CoCrMo-polymethylmethacrylate (PMMA) interfaces is shown to occur subcritically under fatigue loading, implying that debonding may occur at loads much lower than those required for catastrophic failure. Interface fracture mechanics samples containing precoated and uncoated grit-blasted CoCrMo substrates and a PMMA layer were constructed and quantitatively evaluated in terms of their critical interface adhesion and subcritical debond behavior. The precoat surfaces had markedly enhanced adhesion and fatigue resistance in both air and simulated physiological environmental conditions compared to the uncoated samples. Constraint of the PMMA layer does not significantly affect the debond process for thickness between 2- and 5-mm. In addition, wear particles were collected and shown to be consistent with particle sizes reported in vivo and are on the scale of the metal surface roughness. Life prediction methods using the subcritical debond-growth data are discussed.

Microscopy, Electron, Scanning↗
PubMedDate not supplied

Endoprosthetic replacement following limb-sparing resection for bone sarcoma.

Prosthetic replacements are widely used in the reconstruction of deficits created by surgical resection for bone sarcomas. The longevity, complications, and functional outcome of these reconstructions vary by anatomic location, prosthesis type, and mode of fixation. Distal femoral replacement appears to be the most reproducibly successful prosthetic reconstruction, particularly when utilizing a cemented rotating-hinge device. Expandable prostheses may be the only alternative to rotationplasty or ablation in the young skeletally immature patient. Aseptic loosening and bone resorption are frequently noted complications of prosthetic replacement for which successful revision is nearly always possible. The incidence of infection has been reduced by use of better soft tissue coverage. The concept of extracortical bone bridging continues to evolve while enhanced tendon attachment emerges as a new development.

Bone Neoplasms↗
PubMed1999

Unexpanded, irretrievable stent in the proximal right coronary artery: successful management with stent graft implantation.

Stent loss and failure of retrieval are rare; nevertheless, complications have to be taken into account during percutaneous coronary intervention. Here we report a case of an unexpanded, irretrievable Palmaz-Schatz stent in the proximal right coronary artery near to the ostium and the successful management by implanting a synthetic stent graft.

Angioplasty, Balloon, Coronary↗
PubMed2001

Physicochemical study of plasma-sprayed hydroxyapatite-coated implants in humans.

This study represents the first report of the physical and chemical changes occurring in coatings of failed hydroxyapatite (HA)-coated titanium implants obtained from a comprehensive, multicenter human dental implant study. A total of 53 retrieved samples were obtained and compared with unimplanted controls with the same manufacturer and similar manufacture dates. Forty-five retrieved implants were examined for surface characteristics and bulk composition. Implants were staged based on implantation history: stage 1 (implants retrieved between surgical placement and surgical uncovering), stage 2 (implants retrieved at surgical uncovering and evaluation), stage 3 (implants retrieved between surgical uncovering evaluation and occlusal loading), and stage 4 (implants retrieved after occlusal loading). Scanning electron microscopy showed progressive coating thinning with implantation time. At later stages, bare Ti metal was detected by energy-dispersive X-ray analysis and electron spectroscopy for chemical analysis. Increases in Ti and Al (2-7.5 atm % each) were detected at the apical ends of all stage 4 samples. In unimplanted coatings, X-ray diffraction analysis demonstrated the presence of amorphous calcium phosphate, beta-tricalcium phosphate, tetracalcium phosphate, and calcium oxide in addition to large hydroxyapatite crystals (c axis size, D002 = 429 +/- 13 A; a axis size, D300 = 402 +/- 11 A, a/c aspect ratio 0.92). The nonapatitic phases disappeared with increased implantation time, although there was a persistence of amorphous calcium phosphate. Bulk coating chemical analysis showed that Ca/P ratios for implant controls (1.81 +/- 0.01) were greater than stoichiometric HA (1.67) and decreased for implant stages 3 and 4 (1.69 +/- 0.09 and 1.67 +/- 0.09, respectively), explained by the dissolution of the non apatitic phases. Crystal sizes also changed with implantation times, being smaller than the control at all but stage 4. Fourier transform infrared analyses agreed with these results, and also indicated the accumulation of bone (protein and carbonate-apatite) in the retrieved coatings. The accumulation of bone was not stage dependent. These findings indicate that there was some biointegration with the surrounding bone, but the greatest changes occurred with the HA coating materials, their loss, and chemical change.

Absorptiometry, Photon↗
PubMed2001

In-depth morphological changes and embrittlement near the wear surface of UHMWPE inserts from uncemented hip systems.

Polyethylene hip cups were examined with optical and electron microscopy after permanganic etching, a technique that allows in-depth examination from the articulating surface downward. In addition to wear features present on the surface, novel defects were revealed in implants after retrieval from the body but not in as-manufactured controls. They were incipient cracks that indicated the existence of an embrittled layer extending 10 microm or more into the implant from the wear surface after exposure to the body environment. The lengths of the cracks, which were perpendicular to the tensile stresses responsible for their formation, were mostly more or less parallel to the wear surface. The embrittlement and cracking revealed are probably major contributors to the wear of polyethylene implants in the body. Poor particle consolidation may be a contributory factor, but it was not observed to be the primary cause of implant wear within the body.

Biocompatible Materials↗
PubMed2000

Transcatheter closure of membranous ventricular septal defects with a new nitinol prosthesis in a natural swine model.

Transcatheter closure of a membranous ventricular septal defect (MVSD) is much more difficult than closure of other intracardiac defects because of the proximity to the aortic and tricuspid valves and their relatively large size in small children. In this report, transcatheter closure of naturally occurring membranous VSDs was attempted in 12 Yucatan minipigs. The prosthesis is constructed from fine Nitinol wires in the shape of two buttons and a connecting waist filled with polyester fiber. Two kinds of prosthesis were used in this study: concentric and eccentric left-sided retention disks. A 6 or 7 Fr delivery sheath was advanced across the membranous VSD over a wire from femoral vein. The prosthesis was inserted through the sheath by pushing the delivery cable to deploy a button into left ventricle and the second button was then deployed into right ventricle by withdrawing the sheath. Successful implantation of the device was achieved in all animals except one. Complete closure rate was 58.3% immediately after placement, 100% at 1 week, 90.9% at 1 month and 3 months, and 100% at 6 months. An associated aneurysm of the membranous septum increased significantly in size in two of three animals using the concentric device, and in none of the animals using the eccentric device. A trace to mild aortic regurgitation was present in two of the three animals using the concentric device, and only in one of the eight animals using the eccentric device. Five animals developed a trace to mild tricuspid regurgitation. Pathologic examination showed all devices to be covered by smooth neoendothelium at 3 months. This report presents the first experimental study where closure of membranous ventricular septal defects in a swine model was attempted by specially constructed devices. Procedural success and occlusion rates are very encouraging but overall results cannot equal surgery. Further experimentation is needed with devices that are redesigned according to the experience gained from this study.

Alloys↗