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PubMed2001

The influence of design on bioprosthetic valve durability.

Bioprosthetic heart valves have evolved over the years into remarkably useful and predictable devices. A number of specific designs have come and gone, and a few have remained. Many design changes were successful and many were not. This article describes the successes and failures of the various bioprosthetic valve designs and details the specific reasons why a particular design change succeeded or failed to improve bioprosthetic valve performance.

Animals↗
PubMed2000

Velocities, shear stresses and blood damage potential of the leakage jets of the Medtronic Parallel bileaflet valve.

Even nowadays, the essential problem of mechanical heart valve prostheses is the risk of thromboembolic events mainly caused by unnatural hemodynamics, e.g. just a few years ago the Medtronic Parallel (MP) showed unsatisfactory clinical results caused by thrombi. Therefore, in vitro investigations of the whole leakage jets were performed at the MP in mitral position by means of a pulse duplicator using a two channel laser Doppler anemometer. From the measured data, mean velocity profiles and the distribution of Reynolds shear stresses, as a function of the location within the jet, were calculated. From this data the potential of blood damage is evaluated computing a Blood Damage Index (BDI) of hemolysis and platelet damage. Four regurgitant free jets right above the hinges were observed during systole at the inflow side of the MP. The peak velocities at the origin of the jets were in the order of 1.6-2.1 m/s. Two jets experienced maximum turbulent shear stresses around 100 N/m2 within this area. The BDI for platelets of the MP is around ten times higher than the BDI of the St.-Jude-Medical. The study shows that besides the flow structure within the hinges of a mechanical heart valve, the whole regurgitant jet has a large blood damage potential. This potential is measurable, respectively calculable and seems to be (on account of it's support of the clinical outcome) one piece of the puzzle that explains the negative trials of the MP.

Blood Flow Velocity↗
PubMed2003

Fretting corrosion behaviour of ball-and-socket joint on dental implants with different prosthodontic alloys.

The fretting corrosion of five materials for implant suprastructures (cast-titanium, machined-titanium, gold alloy, silver-palladium alloy and chromium-nickel alloy), was investigated in vitro, the materials being galvanically coupled to a titanium ball-and-socket-joint with tetrafluoroethylene under mechanical load. Various electrochemical parameters (E(corr), i(corr), Evans diagrams, polarization resistance and Tafel slopes) were analyzed. The microstructure of the different dental materials was observed before and after corrosion processes by optical and electron microscopy. It can be observed that the mechanical load produces an important decrease of the corrosion resistance. The cast and machined titanium had the most passive current density at a given potential and chromium-nickel alloy had the most active critical current density values. The high gold content alloys have excellent resistance corrosion, although this decreases when the gold content is lower in the alloy. The palladium alloy had a low critical current density due to the presence of gallium in this composition but a selective dissolution of copper-rich phases was observed through energy dispersive X-ray analysis.

Biocompatible Materials↗
PubMed2003

Complications in primary total hip arthroplasty: avoidance and management: wear.

Many factors, including polyethylene processing, sterilization method, counterface material, femoral head size, femoral offset, acetabular component position, implant design, and patient activity level, affect the rate of wear in total hip arthroplasty. For patients with life expectancy that exceeds the longevity of the conventional implant materials, an alternative bearing surface (highly cross-linked polyethylene, metal-on-metal, or ceramic-on-ceramic) may be considered. Although laboratory wear tests with these materials are very favorable, clinical outcomes have not been clearly established. When osteolysis does develop in response to particulate debris, the location and progression of the lesions may be quite variable. Asymptomatic stable lesions can be followed clinically and radiographically while symptomatic or enlarging lesions or those that may compromise the integrity of the periprosthetic bone stock require surgery. If acetabular component revision is necessary and an adequate rim of host bone is maintained to support a revision acetabular component, defects can be filled with particulate bone graft. Large segmental defects generally require structural allografts. If the acetabular shell is well fixed in good position and the osteolytic defects are accessible, treatment with curettage and bone grafting of the lesions with liner revision is appropriate to avoid use of a structural allograft. Proximal femoral defects around a well-fixed stem can be managed in a similar manner with curettage and bone grafting. Distal lesions associated with risk of periprosthetic femur fracture or implant loosening require stem revision. Osteoclastic resportion of bone in response to particulate debris can be impaired with use of some drugs such as alendronate. However, the safety and efficacy of alendronate in the clinical management of osteolysis associated with total hip arthroplasty has not been established.

Arthroplasty, Replacement, Hip↗
PubMed2003

Bubble formation on St. Jude Medical mechanical heart valves: an in-vitro study.

BACKGROUND AND AIM OF THE STUDY: Bubble formation in blood, which has been observed during valve closure in patients with mechanical heart valves (MHVs), raises concern because of cognitive changes and potential activation of blood elements associated with thromboembolic phenomena. Bubble formation in the vicinity of MHVs has been described previously; the present in-vitro study was undertaken to quantitate bubbles leaving the heart and entering the systemic circulation, and to gain a closer perspective of this phenomenon and its potential clinical implications. METHODS: Experiments were performed in a left heart pulsed flow simulator with 29 mm mitral and 23 mm aortic St. Jude Medical MHVs; mitral and aortic bioprosthetic valves were used as controls. De-aerated water was pumped through the left heart pulsed flow simulator at a fixed rate of 70 beats/min and at different cardiac outputs. Bubble numbers and sizes were monitored photographically at the simulator exit. RESULTS: Numbers of bubbles per frame generated in MHVs in the mitral position ranged from 8 to 14 at cardiac outputs of 3 to 6.5 1/min; this corresponded to gas volumetric flow rates of 330 to 830 mm3/min. The number of bubbles per frame for the aortic MHV was 3 to 7, reflecting the less severe flow conditions and milder valve closure impact. The diameter of bubbles generated by the mitral valve was almost uniform (0.45 mm), while bubble diameters in the aortic valve ranged from 0.36 to 0.69 mm. CONCLUSION: Bubble formation was found to be an inherent flaw of the present generation of MHVs, and this problem should be addressed in future valve designs.

Aortic Valve↗
PubMed2003

Good news and bad news: the cost of mending a broken heart.

The approval of a new treatment protocol known as "destination therapy" highlights the realities of today's health economics. This article discusses the technology, the economics and the philosophy of the newly approved left-ventricular-assist systems.

Cost-Benefit Analysis↗
PubMed2004

Postmortem retrieved canine THR: femoral and acetabular component interaction.

Dogs are the preferred animal model for testing of human total hip replacements (THRs). A postmortem retrieval program for clinical, cemented, canine THR was established to analyze the long-term performance of THRs in dogs and to compare that performance to postmortem retrievals of human THRs. The purpose of the present study was to analyze the interaction between the femoral and acetabular components. Thirty-eight postmortem retrievals from 29 dogs were donated and analyzed. The acetabular components (ACs) were measured for volumetric wear and graded for articulating surface damage. Femoral and acetabular components were mechanically tested for implant stability. Digital image analysis was performed on contact radiographs of transverse femoral slices. Of 14 cases with a firmly implanted femoral component (FC). 6 articulated against loose ACs. Of 24 cases with a loose FC, 16 articulated against loose ACs. Only 4 specimens had both components firmly implanted, and 14 specimens had both components loose. There was a significant positive correlation between AC volumetric wear and FC loosening; however, there was no evidence of osteolysis or wear debris induced osteolysis as seen in human postmortem retrieval studies. There was a significant but weak negative correlation between FC loosening at the cement/bone interface and AC scores reflecting damage to the rim and creep across the entire AC. Although implant-on-implant damage to the AC was expected to positively correlate with FC loosening, this was not found. Researchers need to look at interactions between AC and FC to understand how the failure of one component affects performance of the other.

Acetabulum↗
PubMed2005

New polymer materials in total hip arthroplasty. Evaluation with radiostereometry, bone densitometry, radiography and clinical parameters.

AIMS: To evaluate the outcome of different types of polyethylene, bone cements and one design of uncemented fixation with porous and ceramic coating using radiostereometry, bone densitometry, conventional radiography and clinical parameters. MATERIALS AND METHODS: Study I: 201 patients were extracted from 5 prospective randomised studies to evaluate femoral head penetration at two years with radiostereometry in four basic designs, cemented Lubinus and Reflection cups, uncemented Trilogy and Reflection cups. Studies II and III: 60 patients (61 hips) were randomised to receive either highly cross-linked or conventional all PE cups. 32 patients with bilateral arthrosis received hybrid THA with highly cross-linked PE on one side and conventional on the contra lateral side. Femoral head penetration and the migration of the cups were evaluated with radiostereometry in the supine and standing positions. DEXA and conventional radiography were used to evaluate the bone mineral density and radiolucencies around the cemented acetabular component. Studies IV and V: 90 patients (97 and 96 hips respectively) were stratified depended on age, gender, diagnosis and preoperative BMD to create 3 main groups of socket fixation. In the first group fluoride containing cement was used, in the second group Palacos cum Gentamicin and in the third hybrid THA with porous coated HA/TCP cup. In the hybrid group the fixation of the femoral component was again randomised to either of the two cements. The results on femoral and acetabular sides are presented separately in studies IV and V, respectively. RESULTS: Study I: Cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates compared with gamma-sterilized polyethylene. Regression analysis showed that the type of sterilization, age and weight was the most important factors affecting the penetration rate. Studies II and III: In the cemented study the proximal penetration was lower in the study group independent of position at 3 years, while in the hybrid study the penetration was lower in the study group only in the supine position at 2 years. The migration of the cup did not differ between the plastics in both studies. At 2 years the periprosthetic radiolucency and BMD did not differ significantly between the 2 types of PE used in the cemented study. Study IV: The subsidence of the stem did not differ between the groups, but the periprosthetic BMD decreased more in fluoride cement group at 2 years. Conventional radiography revealed higher progression of radiolucent lines in the Palacos group, but only in one region. Study V: The proximal migration of the cup was almost similar in all three groups. The three dimensional migration was increased in patients with osteoporosis. Postoperative radiolucent lines tended to disappear with use of porous coating covered with HA/TCP. CONCLUSIONS: Study I: EtO sterilized polyethylene increased the femoral head penetration. Age and weight were also important predictors of the penetration rate. Studies II and III: The highly cross-linked polyethylene decreased the penetration rate mainly after one year probably reflecting less wear. The different mechanical properties of the two types of PE studied did not affect the early fixation of the cemented cup. Study IV: There were no obvious advantage of addition of fluoride to acrylic bone cement when used to fixate the femoral component. Study V: Use of fluoride containing cement or uncemented fixation did not improve the early stability of the socket compared to Palacos with Gentamicin.

Absorptiometry, Photon↗
PubMed2006

Glenoid loosening in response to dynamic multi-axis eccentric loading: a comparison between keeled and pegged designs with an equivalent radial mismatch.

Glenoid loosening is a common failure mode observed in total shoulder arthroplasty. In an effort to isolate the affect of differing fixation techniques on loosening, an edge displacement test was conducted using two, pear-shaped, UHMWPE glenoid designs: one keel and one peg, each having a glenohumeral radial mismatch of 4.3 mm. The susceptibility of each design to loosening was established by quantifiably comparing the maximum glenoid edge displacement before and after 100,000 cycles of eccentric loading by the humeral head along both the superoinferior (SI) and anteroposterior (AP) glenoid axes. Regardless of the axes tested, the results of this study indicate that no discernable difference in edge displacement (distraction and compression) occurred before or after cyclic, eccentric loading for either the keeled or pegged glenoid designs. Additionally, each keel andpeg glenoid remained firmly fixed after testing, suggesting that either fixation technique provides sufficient resistance to edge displacement.

Arthroplasty, Replacement↗
PubMed1990

[The butterfly bridge: causes of debonding, 18 years clinical observation].

For 18 years, the acid-etched bridge has been put to good use. Clinical observations over this period of time allow us to take a step back and review this conservative technique. Using the results of clinical research, this article aims to evaluate the performance and basic principles relative to the acid-etched bridge. The primary and secondary causes of debonding are also identified.

Acid Etching, Dental↗
PubMed1988

Results of cementless revision for failed cemented total hip arthroplasty.

The goals of revision total hip arthroplasty (THA) are to reestablish and maintain stable implant fixation. Based upon promising early results in primary THA, porous-surfaced implants designed for bone ingrowth fixation are being increasingly used in hopes of more successfully achieving these goals than has been the case using cement. One hundred and sixty such revisions were followed for a mean of 4.4 years, with specific reference to implant fixation. Roentgenographic evaluation of implant fixation suggested four categories of femoral and acetabular components: (1) bone ingrown, (2) stable fibrous encapsulation, (3) questionable, with signs of impending instability, or (4) definitely unstable implant migration, indicative of the need for rerevision. Not surprisingly, success in achieving and maintaining stable implant fixation following revision THA is dependent upon component design, surgical technique, and preexistent bone stock damage. This classification according to bone stock damage should be borne in mind when critically evaluating the results from various revision series.

Acetabulum↗
PubMed1987

Results of reoperation for failure of cardiac bioprostheses.

A ten-year experience with reoperations for failure of cardiac bioprostheses is reported. 362 patients were operated for valve replacement with 412 bioprostheses. There were 35 (9.64%) reoperations for valve failure. Mean time between operation and reoperation was of 64.4 months. Operative mortality was 14.28%: 3 patients died for cardiac and 2 for extra-cardiac causes. Long-term mortality after reoperation was 6.25%. Morphological examination of the explanted bioprostheses confirmed the cause of bioprosthetic valve failure, due to calcific degeneration in 88.88% of case, to post-endocarditic rupture in 5.55% and to prosthetic thrombosis in 2.77%. The importance of timing reoperation is stressed in order to reduce the operative mortality. The conditions suitable for implantation of bioprostheses are listed.

Adolescent↗
PubMed2004

[Failure rate and revision surgery in ossiculoplasty with Kurz titanium prosthesis].

UNLABELLED: Despite its excellent biocompatibility, failures and in particular extrusion of the prosthesis have been described in ossiculoplasty with titanium prosthesis. OBJECTIVE: Report our experience with revision ossicular recontruction in ossiculoplasty with Kurz prosthesis. Identify causes of failure in ossiculoplasty using the titanium prosthesis. MATERIAL AND METHODS: Retrospective chart reviews were performed for 110 patients who had undergone titanium ossicular implants between November 1998 and 2002. All patients had undergone ossiculoplasty using titanium middle ear implants. Patients were divided into 2 groups: in group 1 patients underwent revision ossiculoplasty; in group 2 patients had a successful surgery at first stage. Anatomic and functional results have been studied in these two groups. Causes of failures were analysed. RESULTS: The overall failure rate was 20% (22/110). Twenty patients underwent revision ossiculoplasty. Nine primary failures were attributable to a short implant. Two extrusions were observed. At long term billow-up, the functional gain between the primary and revision ossiculoplasty was comparable. CONCLUSION: Revision ossiculoplasty is worthwhile for those patients who have failure of the titanium prosthesis in ossiculoplasty. A large cartilage graft interposition is necessary to prevent extrusion. The overall luxation rate observed in our series was mainly due to a too short prosthesis and we recommend now a reconstruction with longer prosthesis.

Adult↗