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PubMed1993

Long-term stability of two different mandibular bridging systems.

To evaluate the benefits of narrow-beam roentgenography and spiral tomography for examination and monitoring of screw and plate fixation to bone we studied 22 rigid plate bridgings of mandibular defects. The plate reconstructions were of long duration or considered permanent. In 13 patients, AO-THORP (AO: Arbeitsgemeinschaft für Osteosynthesefragen; THORP: Titanplasma-beschichteten Hohl- und Vollkern-Rekonstruktionsplatten-Systems) reconstructions were used and in nine classic AO stainless steel plate bridgings. With the AO-THORP system, good bone apposition to the screws was evident in 96% (73/76 screws) of the cases. Fixation using the classic AO screws, however, was inadequate in 30% (20/66 screws) of the cases. Plate loosening was noted in 56% (5/9 plates). Examination using narrow-beam roentgenography and spiral tomography provided detailed information about bone resorption around the screws and provided a reliable tool for deciding on a follow-up regimen. When complications occur, they can be detected and treated early, reducing patient morbidity. In our opinion, classic AO plate bridging should always be considered temporary.

Bone Plates↗
PubMed1996

The last generation of pericardial valves in the aortic position: ten-year follow-up in 589 patients.

BACKGROUND: The first generation of pericardial valves has been withdrawn from the market because of excessively high rates of premature failure. With its original design, the Carpentier-Edwards pericardial valve has promised improved results. METHODS: In our institution, 589 patients underwent an isolated aortic valve replacement with a Carpentier-Edwards pericardial bioprosthesis between July 1984 and December 1993. The patients' mean age was 67.5 +/- 11.2 years, and 49% of the patients were in New York Heart Association clinical class III or IV. The operative mortality rate was 2.3% (14 of 595). All patients but 4 were followed up for an average of 4.1 years after their operation, and total follow-up was 2,408 patient-years. RESULTS: At the time of the study, more than 85% of the patients were in New York Heart Association class I or II. There were 79 late deaths. After 10 years, the actuarial survival rate was 71% +/- 7%. Nineteen patients died of valve-related causes (3 endocarditis, 7 thromboembolic complications, 1 structural failure, and 8 sudden deaths). The actuarial rate of freedom from valve-related death was 94% +/- 3% at 10 years. Valve-related complications included 23 thromboembolic episodes (0.9% per patient-year), 14 endocarditis (0.5% per patient-year), 9 reoperations (0.4% per patient-year), and 4 structural valve failures with calcification and stenosis (0.2% per patient-year). After 10 years, freedom from valve-related complications was 84% +/- 6%, from reoperation 97% +/- 2%, and from valve failure 96% +/- 4%. CONCLUSIONS: Because of its low rate of valve-related events at 10 years and low rate of structural deterioration with no leaflet tears, this prosthesis is an outstanding choice for patients who need tissue valves and for patients aged 60 years or older.

Age Distribution↗
PubMed2001

Cement penetration in the proximal femur does not depend on broach surface finish.

In a cadaver study, we prepared 29 paired human cadaver femora using 3 different broaches of identical geometry but different surface characteristics. In one group of 20 pairs, preparation with chipped-toothed broaches was compared to diamond-shaped broaches; in the other group of 9 pairs, polished tamps for compaction of cancellous bone were compared with chipped-tooth broaches. Cancellous bone was irrigated with 1 liter pulsed lavage. The specimens were embedded in specially-designed pots. Palacos R and Simplex bone cements were used. After vacuum mixing, the cement was applied in a retrograde manner and subjected to a standard pressure protocol with a constant force of 3,000 N. Radiographs were taken and horizontal sections were obtained at predefined levels using a diamond saw. Microradiographs were taken, digitized and analyzed to assess cement penetration into cancellous bone. In 6 of 9 femora prepared using smooth tamps, femoral fractures occurred despite careful preparation technique. The microradiographic evaluation showed no significant morphometric differences between diamond and chipped-tooth or between polished and chipped-tooth broaches with regard to cement penetration into cancellous bone. Therefore, in the presence of pulsed lavage, one finds no significant effect of broach surface characteristics on cement penetration into cancellous bone of the proximal end of the femur.

Absorption↗
PubMedDate not supplied

Novacor left ventricular assist system long-term performance: comparison of clinical experience with demonstrated in vitro reliability.

Since the first implant of the Novacor wearable left ventricular assist system (LVAS) in 1993, median implant duration worldwide has increased from 93 days (max 2.2 years) to 202 days (max 4.1 years) in May 2001. In vitro reliability/durability testing of the Novacor LVAS has previously demonstrated a mean time to failure of 4.2 (3.04-5.59) years. These tests revealed a single failure mode--main bearing wear--with measurable symptoms gradually appearing before degradation of pump function. An ongoing clinical study of 37 recipients implanted for more than 1 year has shown that a simple noninvasive method of pump surveillance, derived from the in vitro experience, is well tolerated in the clinical setting. The overall clinical experience is consistent with in vitro reliability/durability tests that demonstrated 99.9%, 98.5%, and 87.4% freedom from wear at 1, 2, and 3 years (80% confidence). So far, the clinical study has shown 99.4%, 91.5%, and 91.5% freedom from wear at the same 1, 2, and 3 year intervals (95% confidence). Furthermore, the clinical findings have corroborated the in vitro experience that the wear mechanism is generally measurable and gradual, enabling elective clinical LVAS replacement or transplantation. Clinical valve performance was also monitored, using an exercise protocol and collecting comparative data on peak flows across the valves. It was determined that developing valve dysfunction could be diagnosed early and, in the failures that did occur (n = 2), these were related to the patient's disease state. In conclusion, although clinical conditions exposed the LVAS to a wide range of different environmental and hydraulic stresses, the surveillance program described appears practical and reliable, and its findings broadly parallel those of the earlier in vitro study. Additional data needed to complete formal validation continue to be collected.

Adult↗
PubMed2003

Elastohydrodynamic lubrication analysis of a functionally graded layered bearing surface, with particular reference to 'cushion form bearings' for artificial knee joints.

Elastohydrodynamic lubrication of a functionally graded layered (FGL) bearing surface, whose elastic modulus increases with depth from the bearing surface, was investigated in this study. The finite difference method was employed to solve the Reynolds equation, simultaneously with the elasticity equation of the bearing surface, under circular point contacts. The finite element method was adopted to solve the elasticity equation for the FGL bearing surface. The displacement coefficients thus obtained were used to calculate the elastic deformation of the bearing surface, required for the elastohydrodynamic lubrication analysis. Good agreement of the predicted film thickness and pressure distribution was obtained, between the present method and a previous study for a single layered bearing surface with a uniform elastic modulus. The general numerical methodology was then applied to an FGL bearing surface with both linear and exponential variations in elastic modulus, with particular reference to the 'cushion form bearing' for artificial knee joints. The predicted film thickness and pressure distribution were shown to be quite close to those obtained for a single layer under typical operating conditions representative of artificial knee joints, provided that the elastic modulus of the single layer was chosen to be the average elastic modulus of the graded layer.

Coated Materials, Biocompatible↗
PubMed2000

Proximal femoral bone loss and increased rate of fracture with a proximally hydroxyapatite-coated femoral component.

We performed a retrospective analysis of the clinical and radiological outcomes of total hip replacement using an uncemented femoral component proximally coated with hydroxyapatite. Of 136 patients, 118 who had undergone 124 primary total hip replacements were available for study. Their mean age was 66.5 years (19 to 90) and the mean follow-up was 5.6 years (4.25 to 7.25). At the final follow-up the mean Harris hip score was 92 (47.7 to 100). Periprosthetic femoral fractures, which occurred in seven patients (5.6%), were treated by osteosynthesis in six and conservatively in one. We had to revise five femoral components, one because of aseptic loosening, one because of septic loosening and three because of periprosthetic fracture. At the final follow-up there were definite signs of aseptic loosening in two patients. Radiologically, proximal femoral bone loss in Gruen zones I and VI was evident in 96.8% of hips, while bone hypertrophy in zones III and V was seen in 64.7%. In 24 hips (20.2%) the mean subsidence of the stem was 3.7 mm which occurred within the first 12 postoperative weeks. This indicated poor initial stability, which might have been aggravated by early weight-bearing. The high rate of failure in our study suggests that proximal femoral bone loss affects the long-term survival of the replacement.

Adult↗
PubMed1998

Inferior performance of Boneloc bone cement in total knee arthroplasty: a prospective randomized study comparing Boneloc with Palacos using radiostereometry (RSA) in 19 patients.

We compared Boneloc bone cement with conventional cement (Palacos) in fixating the tibial component during 2-5 years in 19 patients with gonarthrosis undergoing total knee arthroplasty in a prospective randomized study. Boneloc displayed significantly larger migration, subsidence and lift-off than Palacos. The difference was identifiable already within 3 months postoperatively, but became significant at 12 months. In the Boneloc group, all components showed subsidence of the posterior part and lift-off of the anterior part of the tibial component, whereas in the Palacos group, the locations of subsidence and lift-off were evenly distributed about the edge of the implant. At 5 years, both Boneloc knees so far investigated were clinical failures with high migration rates. We conclude that, even in total knee arthroplasty, there is a substantial risk that Boneloc leads to inferior clinical results, but later than in hip replacements.

Aged↗
PubMed1999

Extramedullary fixation of 107 subtrochanteric fractures: a randomized multicenter trial of the Medoff sliding plate versus 3 other screw-plate systems.

We compared the efficacy of a load-sharing device, the Medoff sliding plate (MSP), with that of 3 other load-bearing screw-plate devices for the fixation of subtrochanteric fractures in a randomized multicenter trial of 107 elderly patients. 55 fractures were operated on with the MSP, and 52 with the dynamic hip screw (DHS) with or without a trochanteric stabilizing plate (TSP) or with the dynamic condylar screw (DCS). The patient material in the groups was similar regarding age, domestic situation, preinjury walking ability and fracture types. We followed the patients clinically and radiographically for a minimum of 1 year. There was no significant difference in walking ability or return rate to the home at follow-up. Fixation failure occurred in 1/55 fractures operated on with the MSP, in 3/32 with the DHS, in 3/12 with the DCS and in 2/8 with the DHS/TSR The difference in the rate of fixation failure was statistically significant, when the MSP group was compared to the 3 load-bearing devices in the other group (1 vs 8). On the basis of this experience, we think that the load-sharing principle of the MSP, which seems to facilitate fracture impaction and stability, appears to be a good alternative in extramedullary fixation of subtrochanteric fractures.

Aged↗
PubMed1999

[Complications associated with the use of first generation Harris-Galante porous-coated acetabular component after a mean follow-up of 7 years].

MATERIAL AND METHODS: Hundred and twelve hip were studied in 107 patients with a mean follow-up of 7 years (range, 6-9 years). Harris and Postel-Merle d'Aubigné clinical hip scores were used. The prosthetic components were evaluated using radiographic criteria. RESULTS: The mean Harris score was 91 (range, 34-100). The incidence of proximal pain was 3.7 p. 100 in anterior area and also 3.7 p. 100 in posterior area. Radiolucent lines were present in one acetabular zone in 28.5 p. 100 of cases, in two zones in 26 p. 100, in all three zones in 5.5 p. 100. No statistical significant corelation was identified relating pain and radiolucent lines. The mean rate of linear wear per year was 0.1 millimeter. A statistically significant corelation was identified relating a linear wear per year above 0.12 millimeter and the presence of radiolucent lines. A major polyethylene wear (from 2.75 to 3.5 millimeters) was found in 5 cases. One of them had an acetabular osteolysis. One acetabular liner was found unstable in the metal shell during a hip revision for a major wear. Two patients had a dislocation of the liner in the metal-back. Eight hips needed a revision surgery, always for a failure of the polyethylene liner, never for a loosening between the socket and the acétabulum. DISCUSSION AND CONCLUSION: The acetabular component bone fixation of this Harris-Galante prosthesis appears optimum. The polyethylene wear and the unstability between the polyethylene cup and the metal socket need to stop using this component. The fixation between his two parts have to be improved.

Acetabulum↗
PubMed1990

Clinical report on the success of 47 consecutively placed Core-Vent implants followed from 3 months to 4 years.

This report presents the clinical outcome of 47 consecutively placed Core-Vent implants inserted in 35 patients followed for 2 to 4 years by clinical and 3 to 48 months by radiographic examination. The implants were used in mandibles and maxillae to support single crowns, overdentures, and fixed prostheses splinted to natural teeth as recommended by the manufacturer. Of the 47 implants, 43 could be examined. A total of 11 implants was removed, nine because of progressive vertical bone loss and two because of fractures. The vertical bone loss was calculated for the 32 remaining implants. Twenty-eight implants demonstrated a bone loss of more than 2 mm and 16 showed a loss of more than one-third of the implant height. According to the criteria proposed by Schnitman and Shulman in 1979, the total success rate was 37.2%. When using the criteria suggested by Albrektsson et al in 1986, the total success rate was calculated to be 9.3%.

Adult↗
PubMed1986

Long-term results of low-friction arthroplasty performed in a community hospital, including a radiologic review.

This report is a prospective review of 450 low-friction arthroplasties (LFAs) performed by a single surgeon from 1972 to 1983 in a community hospital. The clinical results show sustained quality of the result over a maximum follow-up period of 11 years. The radiologic review shows a slight increase in the number and size of radiolucent lines with time. Bacteriologic studies confirm that clean-air technology reduces the bacteriologic contamination of the operating room and the wound. Deep infections occurred in 1.6% of cases. The most notable complication was failure to obtain bony union of the osteotomized trochanter in 14% of cases. The revision rate for aseptic loosening of the cup was 0.7% and of the femoral prosthesis 0.0%.

Adult↗
PubMed1993

Long term follow-up of Mitroflow pericardial valve prostheses in the small aortic annulus.

Between January 1985 and April 1992 we implanted 477 Mitroflow pericardial bioprostheses in 476 patients in our clinic. All except one valve prostheses were implanted in the aortic position. There were 160 male and 316 female patients, with a mean age of 74.1 years (range 30-89 years). Combined cardiac procedures were performed concomitantly with aortic valve replacement in 45 patients (9.5%): coronary artery revascularisation (n = 38), endarterectomy of the internal carotid artery (n = 4) and multiple valve replacement (n = 3). The sizes of the implanted Mitroflow prostheses were 100% in 19 mm, 70% in 21 mm, 60% in 23 mm and 8% in more than 25 mm. The hospital mortality was 1.3% (n = 5). During the mean follow-up period of 47.6 months valve failure requiring reoperation occurred in 7 patients (1.2%). The actuarial freedom from tissue failure is 89.9 +/- 2.5% and the actuarial survival rate is 90.3 +/- 1.7% (27 deaths) at 7 years. These findings corroborate our policy to continue to implant a pericardial prosthesis in the aortic position, especially in elderly patients with a smaller aortic annulus.

Adult↗
PubMedDate not supplied

Determination of cantilever length-anterior-posterior spread ratio assuming failure criteria to be the compromise of the prosthesis retaining screw-prosthesis joint.

The maximum cantilever length-anterior-posterior spread (CL-AP) ratio is often used as an indication of the ability to cantilever in completely implant-supported prostheses. The CL-AP ratios were determined assuming that failure occurs when the prosthesis retaining screw-prosthesis joint was compromised by either compressive (exceeding the pretorque value) or tensile (opening of the joint via plastic deformation) vertical forces using the Skalak model. Geometric arrangements of three, four, five, and six implants were analyzed. Force variables were 143, 200, and 400 N for the applied force, the pretorque value, and the joint tensile yield strength, respectively. The pretorque value was always exceeded before the yield strength. Allowable CL-AP ratios were (1) lower than those previously reported and (2) found to be 0.5 to 1.8, 0.7 to 1.6, 1.1 to 1.7, and 1.8 for three, four, five, and six implants, respectively. Although implant distributions with the highest AP often provide adequate occlusion, the results of this study indicate that the use of a single CL-AP ratio alone is not necessarily a good indicator of the ability to cantilever.

Algorithms↗
PubMed1999

Mixed oxides prosthetic ceramic ball heads. Part 1: effect of the ZrO2 fraction on the wear of ceramic on polythylene joints.

Although mixed oxides ceramics have been indicated in the literature as a promising compromise between strength and wear, to the authors' knowledge no reports are available on the influence of the percentage of zirconia in ceramic femoral heads when sliding against polyethylene cups. Two types of mixed oxides ceramic ball heads (alumina plus, respectively, 60 and 80% of zirconia) were compared to pure zirconia and pure alumina heads in terms of wear behaviour against UHMWPE in a hip joint simulator. Polyethylene cups and ceramic femoral heads were fixed on a simulator apparatus with a sinusoidal movement and load in presence of bovine calf serum. The experimental results did not show significant difference between the two experimental ceramic materials or in comparison with pure materials. Considering that all specimens, regardless of the material, had the same level of surface roughness, this roughness factor seems to have a more relevant role than the mix of oxides used to manufacture the ceramic head. Wear tests are conducted on materials used in prosthetic hip implants in order to obtain quality control and to acquire further knowledge of the tribological processes that involve joint prostheses, therefore reducing the risk of implant failure of innovative prostheses.

Animals↗
PubMed1995

Position of the knee joint after total joint arthroplasty.

A method for assessing knee joint position after surgery using the preoperative long-leg radiograph and the postoperative knee radiograph is described. Assessment of the formula has shown a near perfect correlation between the calculated position on the long-leg radiograph compared with the measured position for 44 knees. Three hundred eighteen knees after total joint arthroplasty were retrospectively reviewed and the postoperative position was determined. The preoperative position of the mechanical axis was 14.5 +/- 37.3 mm medial to the knee joint center. Using the standing knee radiograph the postoperative position of the mechanical axis was 3.07 +/- 9.2 mm lateral to the knee joint center, while the portable radiograph placed the mechanical axis 4.5 +/- 12.4 mm medial to the knee joint center. There was a highly significant difference in the position of the knee joint center depending on the radiograph used for calculation (standing or portable). The difference between the two means was not due to opening of the knee joint, but likely due to change in the rotation of the knee in the presence of knee flexion. This series of the knee arthroplasties has a low projected rate of aseptic failure.

Femur↗
PubMed1999

Non-specific immunohistochemical responses in surgical tissue collected from total joint arthroplasty.

Tissues retrieved during revision arthroplasty (n = 25) were processed for routine immunohistochemical techniques to localize the presence of bone resorbing cytokines (IL-1, TNF alpha, and IL-6), and to identify areas of significant necrosis and metallic deposition. Tissues were processed and embedded according to standard laboratory techniques. Several tissue sections were prepared for each sample collected. Several sequential slides were used to demonstrate a thorough histopathological evaluation. Other slides of the same tissues were processed for immunohistochemical evaluation specifically for the localization of cytokines. To identify specific cytokine reactions, antibodies against cytokines were added in working dilutions overnight. Another set of slides were incubated overnight with nonspecific protein and served as negative controls. At the end of the incubation period, all slides were washed in buffer and a second antibody conjugated with peroxidase was added to both sets of slides for one hour. The slides were developed for peroxidase activity. The results revealed that there were several locations on the tissues that appeared highly reactive for cytokines. However, some of these areas turned out to be nonspecific when compared with negative controls and the Hematoxylin and Eosin stained slides. Areas of extreme necrosis or where metal debris was present demonstrated sites of nonspecific reactivity. Areas of necrosis have a high nonspecific affinity for antibodies and these areas of necrosis can be demonstrated on the Hematoxylin and Eosin sections, and were avoided in determining the amount of specific cellular reactivity. The results of this study strongly suggest that the aforementioned factors must be carefully controlled in determining true cellular responses that causes resorption of bone and eventually implant failure.

Arthroplasty, Replacement↗
PubMed2001

The failure modes of biological prosthetic heart valves.

Bioprosthetic heart valves have been used since the 1960s, starting with the use of homograft aortic valves obtained from human cadavers. Today prosthetic heart valves are used widely, and bioprostheses account for close to 40% of all heart-valve replacements. Although most bioprosthesis are still stented porcine aortic valves, the introduction of stentless valves and the increasing use of cryopreserved homograft valves has led to an upsurge of interest in bioprosthesis. There have been significant changes in the handling and fixation of porcine aortic valves; however, their modes of failure remain virtually unchanged, although many bioprosthetic valves now last for considerably longer periods. This article reviews the modes of failure of bioprosthetic heart valves.

Animals↗