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Characteristics of titanium-coated polyester prostheses in the animal model.

Commercially available polyester vascular prostheses (n = 6) in the control group (CG) and titanium-coated vascular prostheses (TP; n = 7) were interposed within the infrarenal aorta of pigs. The respective healing characteristics and patency rates were compared after 3 months. For evaluation purposes, macroscopic, histological, and immunohistochemical criteria were applied. The macroscopic evaluation revealed complete healing of the TP in comparison with the CG. Extraluminal inspection revealed prominent firm cicatricial tissue in the prosthesis bed of the TP group. All TP were occluded. In the CG, occlusion of the prostheses occurred in n = 1 (16 %). On average, neointimal hyperplasia (NIH) in the proximal part of the anastomosis was not significantly different to the CG. The extraluminal proliferation index (Ki67) was reduced in the TP group (p = 0.002). The immunohistochemical analysis of intraluminal changes revealed no significant differences between CG and TP. All of the titanium-coated polyester vascular prostheses were found to be occluded. The additional coating of polyester prostheses with titanium would not appear to be of any particular benefit.

Animals↗

Three years experience with experimental implantation of fibrous polyurethane microvascular prostheses in the rat aorta.

The results of a 3-year study in which a series of 355 implantations of 1-cm-long fibrous polyurethane microvascular prostheses into the infrarenal aorta of the rat (group A) were evaluated with respect to patency and formation, structure, and fate of the neo-intima. Rats were sacrificed at various intervals from 1 day to 2 years in order to obtain a time-related impression of the re-endothelialization and stability of the neo-intima. A second series of 51 implants was done with prostheses 10 cm in length, placed in a 1.5-cm loop in the abdominal aorta (group B). An overall patency rate of 92.7% was achieved in group A. Initially, eight technical failures caused early thrombosis of the prostheses. Sixteen prostheses became infected and subsequently occluded. The overall patency in group B was 52.9%, due to kinking from adhesion formation and normal growth of the rat. In both the long and short prostheses, a continuous multilayered neo-intima developed, growing from the aortic stumps into the prosthesis from both sides. According to the growth rate of 0.3 mm/day, a 1-cm prosthesis was re-endothelialized after +/- 20 days and a 10-cm prosthesis after +/- 9 months. Once developed, the neo-intima, consisting of myofibroblasts and smooth muscle cells covered with a flat endothelium, remained stable and continuous, throughout the observation period. The neo-intima was firmly anchored onto the prosthetic wall by means of cellular protrusions extending between the polyurethane fibres. The significance of rapid healing of an implanted prosthesis is emphasized with respect to preventing (late) hematogenous, endogenous infection of the prosthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

[PTFE prostheses in infrarenal aneurysms of the abdominal aorta].

Postoperative dilatation of Dacron vascular grafts can lead to aneurysms and rupture of the prosthesis making it necessary to change the graft by operation. Therefore, 15 patients at Lübeck University Hospital underwent replacement of the aorta with PTFE prostheses due to infrarenal aortic aneurysms. Ultrasound measurements 2-12 months postoperatively revealed a dilatation of 11.6% concerning tubular grafts, 11.5% for the shafts and 14.6% for the limbs of bifurcation grafts compared to the higher dilatation rate of Dacron prostheses described in the literature. There was no evidence of anastomotic false aneurysms, thrombosis of the limbs of bifurcation grafts, peripheral embolization or perigraft reaction. In conclusion, PTFE prostheses seem to be a means of preventing patients from having secondary complications as a result of graft dilatation. Based on our early results and the results described in the literature, PTFE prostheses can be regarded as an alternative to dacron prostheses.

Aged↗

In vitro antistaphylococcal activity of collagen-sealed Dacron vascular prostheses bonded with rifampin, vancomycin, or amikacin.

The goals of this study were to evaluate the in vitro antistaphylococcal activity of vascular Dacron prostheses to which a type I collagen and an antibiotic had been bonded. Collagen was fixed to the prosthesis either by an original grafting procedure or by impregnation. The antibiotics used included rifampin, vancomycin, and amikacin. They were bonded to the prosthesis either at the same time as the collagen or by soaking the prosthesis in an antibiotic solution at the beginning of the experiment. Each prosthesis was sliced into 6 mm diameter circles and preserved in a solution of saline and albumin, which was changed every day. Three disks were retrieved from each prosthesis at the beginning of the experiment and then every 24 hours; these were placed in gelose smeared with Staphylococcus aureus. The diameter of the inhibition area of each disk was measured at 24 hours. The initial inhibition area (So), the time at which the inhibition area was equal to 50% of So, and the time at which the activity was nil were used to characterize the activity of the prostheses and to calculate a beta coefficient of decreasing activity. The prostheses bonded with vancomycin or amikacin did not show adequate activity. Those bonded with rifampin were effective for at least 4 days. When rifampin was grafted to the prosthesis, the So was 278.6 mm2, 50% of So was reached within 10.4 days, the duration of effective activity was 25.7 days, and the beta coefficient was 0.067. The two prostheses soaked in rifampin had a significantly more rapid decrease (beta = 0.19 and 0.56) and a shorter duration of effective activity (12.4 and 4.5 days). Both collagen-coated prostheses, whether impregnated or soaked with rifampin, have a sufficient duration of activity to be tested in an animal model.

Amikacin↗

The biologic fate of Dacron double velour vascular prostheses--a clinicopathological study.

Thirty-one Dacron double velour prostheses removed from 16 patients were studied microscopically in order to elucidate the changes they underwent following implantation. The process of incorporation was divided into three phases. In the initial phase, immediately following the implantation, the prostheses became surrounded by a fibrin meshwork. In the organizing phase, which sets in 10 weeks after the implantation, there was an external fibrous capsular formation around the initially fibrin-infiltrated grafts. There was also fibroblastic ingrowth and granulation formation among the interstices and the prostheses showed firm adhesion to the surrounding tissues. One year following the implantation, after most of the luminal surfaces had been covered with collagen tissues, the cellular infiltration subsided and the graft passed into the stable phase. Foreign body giant cells and lymphocytes were seen throughout the study period. These prostheses were then compared with other prostheses which do not have velour structures. The nonvelour grafts showed less adhesion to the surrounding tissues. Microscopically, cellular reaction and collagenous ingrowth were also less. The velour surface thus seems to stimulate granulation ingrowth and to contribute to the firm adhesion of the graft to the surrounding tissues. This firm adhesion enhances resistance to infection and is considered safer in case of suture aneurysm formation.

Aorta↗

[Treatment of per- and subtrochanteric femoral fractures by gamma nails and modular hip prostheses. Differential indications and results].

From January 1997 to August 1998 all stable and nonstable trochanteric femoral fractures (n = 72) were treated routinely by gamma nail using the correct operative technique. Patients showing additional osteoarthritis of the hip in radiographs hip replacement was performed by a cementless modular femoral hip prostheses from January 1996 to August 1998 (n = 28). Follow up period was 6 to 18 months. Operation time and blood loss were higher using the prostheses. However complications and lethality (< 5%) were not different during postoperative course. In each group three operative technical complications occurred. Using a modified Harris Hip Score (without range of motion, contractions) the score was decreased non significant comparing both groups first of all in unstable fractures until follow up. In each group one revision (loosening of prostheses, excessive shortening of femoral neck) was necessary. Using the correct operative technique, the gamma nail proved to be a save device with good outcome. Outcome using modular prostheses is comparable to gamma nail. Therefore the use of modular prostheses is justified in case of osteoarthrosis and in some cases of very unstable fracture.

Adult↗

[Tibial malalignment of mobile-bearing prostheses--a simulator study].

Total knee replacement requires exact implantation in order to avoid long-term failure. Longitudinal in vivo studies of malaligned prostheses are problematic for ethical reasons. To assess the critical angle of tibial (varus/valgus) malalignment of knee prostheses in vitro, a simulator investigation was performed. Mobile-bearing prostheses were implanted in a simulator with 1-3 degrees valgus and varus malalignment as well as in a neutral position. More extreme malalignment caused unacceptable forces in the simulator. After each 500,000 cycles (ca. 0.5 years of walking) the replicas of the polyethylene inlay were examined and the extent of the tribocontact areas was measured until 1,500,000 total cycles. Finally the original polyethylene was examined with a scanning electron microscope. The polyethylene showed only abrasive wear without any fatigue effect. Tribocontact areas of 900-1500 mm(2) were observed under malalignment of mobile-bearing prostheses according to the manufacturer's specifications. With 1-3 degrees of malalignment, tribocontact areas were located at atypical polyethylene zones, but still showed abrasive wear only. Increasing malalignment due to a lift off of the femoral part of the prostheses with a strong torsional strength of the polyethylene made more extreme simulation impossible. Malalignment of 3 degrees could be suggested as maximum in vivo tolerability; perfect alignment with ideal implantation should be the goal. Soft tissue was given less consideration in this simulator study.

Bone Malalignment↗

Ultrastructural alterations of polytetrafluoroethylene prostheses implanted in abdominal wall provoked by infection: clinical and experimental study.

Infection of an expanded polytetrafluoroethylene (ePTFE) prosthesis after implant is a major drawback of its use in current clinical practice. The aim of the present study was to compare the behavior of such prostheses implanted into New Zealand rabbits with that of prostheses infected after clinical implant. Experimental implants of ePTFE Soft Tissue Patch were performed to repair defects (7 x 5 cm) created in the abdominal wall of 10 rabbits. Prior to implant the prostheses were contaminated with Staphylococcus aureus. Five animals implanted with noncontaminated ePTFE prostheses served as controls. All the animals were sacrificed at 30 days after implant. For the clinical study, specimens were taken from three ePTFE implants that had been found to be infected after intervention. The clinical and experimental implant specimens were processed for light microscopy and scanning electron microscopy. Macroscopic and microscopic examination of experimental and clinical implants revealed alterations to the ePTFE structure, such as areas of fragmentation, fracture lines, and detachment of fine layers of ePTFE that harbored numerous Staphylococcus colonies. Neoformed tissue around contaminated implants was arranged more loosely, and on occasion large spaces between fibers gave rise to an "unknitted" appearance with respect to the control implants. It may be concluded that microporous ePTFE prostheses show similar behavior following experimental or clinical implant in the presence of infection. Irreversible changes to the structure of the prosthesis are produced owing to colonization of the biomaterial by microorganisms, which in most cases necessitates total replacement of the prosthesis.

Abdominal Muscles↗

Dynamic behavior of the Provox and Staffieri prostheses for voice rehabilitation following total laryngectomy.

The present study evaluated the differences in aerodynamic behavior between the 1990 Provox and 1986 Staffieri voice prostheses for total laryngectomy patients. Both prostheses were submitted to in vitro laboratory testing to assess their aerodynamic behavior under different conditions of air flow through the valve and tracheal side pressure. In addition, six patients using the Provox and another six using the Staffieri prostheses were submitted to a dynamic study of phonation. This latter study evaluated the intratracheal pressure corresponding to the different intensities at which the vowel sound /a/ was pronounced. In vitro measurements revealed significant differences between the two prostheses, with the best results achieved with Provox. In contrast, the in vivo measurements did not reveal any significant differences between the two groups of patients in the 50-79 dBSPL range, although there was some difference at intensities equal to or greater than 80 dBSPL. Again, in this latter case the best results were achieved with the Provox. However, the ideal prosthesis has yet to be found. In some patients, the so-called low-resistance prostheses fail to maintain their aerodynamic performances, most likely because anatomic resistors interfere with the effort (i.e., pressure) required to produce a voice. At present the choice of prosthesis is best determined on an individual patient-to-patient basis.

Aged↗

Clinical performance of biological and mechanical prostheses.

Prosthetic valve replacement remains the most viable alternative for the treatment of severely diseased heart valves. The cumulative experience of mechanical protheses and bioprostheses was evaluated for a 10-year performance comparison: Carpentier-Edwards standard porcine bioprosthesis (CE-S), 1,214 operations; Carpentier-Edwards supraannular porcine bioprosthesis (CE-SAV), 2,489; and mechanical prostheses, 1,364 operations (St. Jude Medical, Carbomedics, Duromedics, and Björk-Shiley Monostrut). The freedom from thromboembolism and hemorrhage at 10 years was 82% for CE-S, 78% for CE-SAV, and 65% for mechanical prostheses (p < 0.05). The relationship existed for major thromboembolism and hemorrhage, 91% (CE-S), 87% (CE-SAV), and 88% (mechanical) (p < 0.05), without clinical relevance. The freedom from structural valve deterioration and valve-related reoperation favored mechanical prostheses (p < 0.05) at 10 years (structural failure: 78% for CE-S, 81% for CE-SAV, and 99% for the mechanical group; reoperation: 74% for CE-S, 76% for CE-SAV, and 88% for mechanical prostheses). The freedom from fatal reoperation was not clinically different: 96% for CE-S, 99% for CE-SAV, and 99% for mechanical prostheses (p < 0.05) at 10 years. The freedom from valve-related mortality was not different (p = not significant) at 10 years: 87% for CE-S; 92% for CE-SAV; and 91% for mechanical. The freedom from permanent impairment or residual morbidity, primarily from thromboembolism, was 95% for CE-S, 92% for CE-SAV, and 95% for mechanical group (p < 0.05) but not clinically relevant.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗

Seeding of Dacron vascular prostheses with endothelium of aortic origin.

Seeding of autologous venous endothelium on Dacron vascular prostheses in dogs results in endothelial coverage of the prosthetic flow surface 4-6 weeks after implantation. Canine aortic endothelium, in contrast, usually fails to completely cover an unseeded prosthesis by pannus ingrowth even over much longer periods. To see if the success of endothelial seeding stems from a difference in the ability of venous and aortic endothelium to grow on prosthetic surfaces, we seeded freshly harvested autologous aortic endothelium on Dacron velour infrarenal aortic prostheses in dogs. Six weeks after surgery these prostheses showed the features reported to be typical of seeded prostheses. Scanning electron micrographs showed a luminal lining of flat polygonal cells without fibrin or adherent formed blood elements, and light microscopy showed an underlying layer containing aligned spindle-shaped cells with elongated nuclei and cell-lined subluminal channels. Control prostheses were covered with fibrin and platelet-rich thrombi everywhere except for limited pannus ingrowth at anastomotic sites. The results suggest that the success of autologous endothelial seeding cannot be ascribed to inherent differences in properties such as mitotic capacity or fibrinolysis between venous and aortic endothelium. The formation of complete endothelial linings by seeding must instead result from a more favorable condition for endothelial cell growth created by the cell harvesting or seeding process itself.

Animals↗

Validity of some methods of estimating circumferential elastance of vascular prostheses.

The two methods for tensile testing of vascular prostheses, cited in a Draft International Standard, have been compared on normal aorta, autologous vein, two knitted Dacron, expanded PTFE and elastomeric composite prostheses before and after implantation as an aorto-femoral bypass in the dog. With the exception of Gore-Tex expanded PTFE, tensiometric stressing and balloon distension are not equivalent techniques in 'as supplied' prostheses or in normal vessels, owing to the basic anisotropic properties of the different materials. The tensiometric method gave much lower estimates of circumferential elastance, ranging from 44.6% for CCV elastomeric to 80.4% for normal canine aorta of the elastance estimate using balloon distension. The differences between the two methods were much less marked on explant samples of synthetic prostheses, but remained for autologous vein. It is concluded that although the methods are equally valid for quality assurance purposes they are inappropriate to compare probable clinical performance, unless carried out on explant samples. The preferred method to cover all the prostheses studied, including autologous vein, should employ omnidirectional stressing. Manufacturers' specifications are, therefore, not necessarily related to clinical performance.

Animals↗

Evaluation of temporomandibular joint prostheses: review of the literature from 1946 to 1994 and implications for future prosthesis designs.

PURPOSE: This article describes the useful elements of applied temporomandibular joint (TMJ) prostheses and discusses the factors necessary to be addressed in an appropriate TMJ prostheses design. MATERIALS AND METHODS: Information about TMJ prostheses was gathered by a literature search. Only designs with the primary intention of true joint replacement were selected. The designs were divided in fossa-eminence, condylar, and total joint replacements, which are reviewed separately. RESULTS: A fossa-eminence prosthesis can be fixed by a metal plate screwed to the root of the zygomatic arch. A condylar prosthesis can be fixed by a metal plate screwed to the mandibular ramus and fitted by bending the plate or using different sizes. All reviewed designs resulted in a loss of translational movements of the mandible, especially in an anterior direction. Although the recent designs use the same materials as are used in hip and knee joint prostheses, the wear properties of the existing TMJ prostheses are still unknown. CONCLUSIONS: A future prosthesis must imitate the anterior movement of the mandible when the mouth is opened and also allow some mediolateral movement. The fitting to the skull is still a major problem, as is the combination of the required motions and low wear rates. To confirm good clinical performance of a new TMJ prosthesis, long-term follow-up studies are necessary.

Evaluation Studies as Topic↗

Mechanical heart valve prostheses: sound level and related complaints.

In a randomised study, we investigated the sound production of mechanical heart valve prostheses and the complaints related to this sound. The CarboMedics, Björk-Shiley monostrut and StJude Medical prostheses were compared. A-weighted levels of the pulse-like sound produced by the prosthesis were measured in 25 patients after aortic valve replacement. Additionally, 141 patients, 117 after aortic valve replacement, 20 after mitral valve replacement and 4 after double valve replacement were interviewed. The average sound pulse pressure levels were 46.0 +/- 2.9 dB(A) in the Carbomedics group, 55.4 +/- 1.2 dB(A) in the Björk-Shiley monostrut group and 44.1 +/- 4.4 dB(A) in the StJude Medical group, measured at a distance of 1 cm from the chest. The Björk-Shiley monostrut was louder than the other two prostheses (p less than 0.0005). Twenty (14.2%) of all patients had complaints related to the valve sound such as sleeping disturbances, irritation, nervousness or fear. Significantly more patients with a Björk-Shiley monostrut could hear their valve or had complaints when compared to the other two prostheses. Younger patients and patients with a mitral valve prosthesis could hear their valve more often than older patients or patients after aortic valve replacement. We conclude that sound characteristics and related complaints differ considerably among heart valve prostheses.

Aged↗

Hemolysis in mechanical bileaflet prostheses: experience with the Bicarbon valve.

BACKGROUND: Normal functioning mechanical heart valve prostheses are designed to have a certain degree of intrinsic structural regurgitation as a washout mechanism to avoid prosthetic thrombosis. However, intrinsic regurgitation leads to blood cell trauma and hemolysis. Information on hemolysis associated with mechanical bileaflet prostheses is scarce. This study evaluated factors influencing hemolysis in 197 Bicarbon mechanical bileaflet prostheses implanted in 164 patients. METHODS: Serial office interviews, laboratory studies, and echocardiography evaluations were done in the surviving patients. An assay for measuring lactate dehydrogenase activity was developed, and the presence and severity of subclinical hemolysis was determined using reported criteria and analyzed at 1 and 2 years. RESULTS: Hospital mortality was 5.5%. Follow-up was 98.1% complete. No patient had clinically significant or severe subclinical hemolysis. Serum lactate dehydrogenase levels were significantly higher when a paravalvular leak was documented (282 +/- 85 U/L versus 242 +/- 64 U/L; p = 0.0026). Subclinical hemolysis was significantly more frequent after mitral valve (p = 0.001) and double valve replacement (p = 0.001) than after aortic valve replacement, and was unrelated to prosthetic size or to geometric area index, even in those cases with effective orifice area index equal to or less than 0.85 cm2/m2 (p = 0.298). CONCLUSIONS: Mild subclinical hemolysis is frequently associated with normal functioning Bicarbon heart valves. Subclinical hemolysis was significantly influenced by valve position but not by valve size or effective orifice area index and remained stable through time. The magnitude of hemolysis in Bicarbon prostheses compared favorably with that reported for other bileaflet heart valve prostheses.

Adult↗

Clinical and functional comparison of bicondylar sledge prostheses retaining all ligaments and constrained total knee replacement.

OBJECTIVE: Comparison of different total knee replacements regarding clinical and functional differences with respect to gait and electromyographic analyses. DESIGN: Retrospective, comparative, clinical and functional study. METHODS: Three groups (control group of 11 healthy subjects, 15 patients with bicondylar sledge prostheses retaining all ligaments (cemented unicondylar prostheses in both the medial and lateral compartment), 15 patients with constrained total knee replacement sacrificing all cruciate and collateral ligaments (cemented total knee prosthesis with intramedullary stems and a large intercondylar tibial post) were compared by clinical evaluation using a number of clinical evaluation scores, a pain scale, surface electromyographic examinations of the lower limb, and gait analysis. RESULTS: Clinical scores revealed significantly worse results for patients with constrained prostheses. Both patient groups had significantly lower clinical scores compared to the control group. Gait analysis and electromyographic parameters revealed no significant differences between both patient groups. Compared to the control group, patients revealed significantly impaired parameters. Electromyography also demonstrated significant differences between patients and controls: mean electromyographic activities were reduced in vastus medialis and lateralis, semitendinosus, tibialis anterior and gastrocnemius. Peak activities were reduced in all muscles but rectus femoris. CONCLUSION: Clinical scores demonstrated significantly better results in bicondylar sledge than in constrained prostheses. Nevertheless, gait and electromyographic analyses did not reveal significant differences. RELEVANCE: Retaining of ligaments in bicondylar sledge prostheses apparently improved the activities of daily living but is not reflected in gait and electromyographic parameters.

Arthroplasty, Replacement, Knee↗

Antibacterial activity of gentamicin-bonded gelatin-sealed polyethylene terephthalate vascular prostheses.

OBJECTIVES: To create an antibiotic-modified vascular prosthesis with a prolonged bactericidal activity, susceptible to endothelialisation. METHODS: We used a covalent method of gentamicin sulphate immobilisation to polyethylene terephthalate prosthesis sealed with gelatin. Antibacterial activity was assayed in Luria-Bertani medium against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa strains. Prosthesis endothelialisation was performed using bovine aorta endothelial cells (BAEC). RESULTS: Gentamicin was bound to vascular prostheses in the amount of 12g per kg of prosthesis. Ninety-seven percent of antibiotic bound in covalent way and remained on the biomaterial for at least 30 days during shaking in PBS solution. Gentamicin-modified prostheses exerted bactericidal or bacteriostatic effect on growth of clinical and reference bacterial strains, prevented biofilm formation and were highly susceptible to endothelialisation. BAEC viability exceeded 90%, which indicated that gentamicin-vascular prostheses were not toxic for these cells. CONCLUSIONS: Covalent gentamicin immobilisation resulted in effective antibacterial protection of vascular prostheses against clinical and reference strains of S. aureus, E. coli and P. aeruginosa and allowed for a strong adherence of endothelial cells to antibiotic-modified prostheses.

Anti-Bacterial Agents↗

A prospective controlled trial of St. Jude versus Starr Edwards aortic and mitral valve prostheses.

BACKGROUND: There is a paucity of controlled trials comparing the merits of different heart valve prostheses. In this prospective randomized trial we compared Starr Edwards and St. Jude prostheses in the aortic and mitral positions. METHODS: Two hundred sixty-seven patients and 122 patients undergoing aortic and mitral valve replacement, respectively, were allocated by minimization to receive either St. Jude or Starr Edwards prostheses. Patients (2 patients were lost to follow-up) were followed up in a special clinic. Event definition, recording, and reporting were in accordance with published guidelines. RESULTS: There were no demographic differences between patients receiving the two different valve models. With the exception of infective endocarditis, we found no differences in the rates of death or complication between patients receiving a Starr Edwards prosthesis or a St. Jude prosthesis in either position. Neither were there any differences between the two valve models in either position, in terms of symptomatic relief 5 years after surgery. CONCLUSIONS: We found no differences in rates of complication or of symptomatic improvement between the Starr Edwards and St. Jude valve prostheses in either aortic or mitral position. Left ventricular function had such a marked effect on long-term survival that it overwhelmed any differences that might exist between different prosthetic designs. This confirms that historical comparisons are of limited value in deciding the respective merits of heart valve prostheses. The most reliable method of assessing surgical procedures is through prospective controlled trials.

Aged↗