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At least 973 records · Page 54Linked to original sources
PubMed2001

Influence of polyethylene and femoral head surface quality on wear: a retrieval study.

Thirty-two polyethylene sockets and 22 femoral heads were retrieved because of aseptic loosening more than 9 years after total hip arthroplasty. The volumetric wear rates of the retrieved polyethylene sockets were significantly greater in those coupled with an alumina head (P < 0.05). The retrieved alumina heads showed significantly better surface roughness and roundness than heads of Co-Cr and of stainless steel (P < 0.05). However, no significant difference was found in polyethylene quality demonstrated as fusion defects among the three different groups. The present study suggests that maintaining better surface roughness and roundness of the femoral heads does not always result in an in vivo reduction of polyethylene wear.

Adult↗
PubMed2003

Closing behavior of the mechanical heart valve in a total artificial heart.

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. The cause of cavitation in mechanical heart valve was investigated in both 25-mm Björk-Shiley and 25-mm Medtronic Hall valves. The closing events of these valves in the mitral position were simulated in an electrohydraulic total artificial heart with a stroke volume of 85 ml. The tests were conducted under physiologic pressures at heart rates of 60, 70, 80, and 90 beats/min with cardiac outputs of 4.5, 5.5, 6.4, and 7.5 l/min, respectively. The disk closing behavior was measured by a laser displacement sensor. The closing behaviors were investigated under various atrial and aortic pressures. In both valves, the duration of closing decreased with an increase in the cardiac output. The greater the amount of atrial pressure, the shorter the closing duration of both valves. The maximum closing velocity of the Medtronic Hall monostrut valve ranged from 0.8 to 0.9 m/s, and that of the Björk-Shiley monostrut valve ranged from 0.73 to 0.78 m/s. In both valves, the maximum closing velocities were less than the reported cavitation thresholds. This suggests that there should be no possibility of occurrence of cavitation in an electrohydraulic total artificial heart with mechanical heart valve.

Biomechanical Phenomena↗
PubMed2004

Edge loading in third generation alumina ceramic-on-ceramic bearings: stripe wear.

Alumina ceramic-on-ceramic bearings perform exceptionally well under standard hip simulator conditions, but in vivo some retrieved bearings have shown an unusual stripe pattern of wear. We studied 16 bearings retrieved from a series of 1,588 cementless hip arthroplasties with third generation alumina ceramic-on-ceramic bearings to characterize the mechanism of stripe wear formation. None of these bearings were retrieved for bearing failure. The average wear volume was 0.4 mm(3) per year in the heads and 0.3 mm(3) per year in the liners. Mapping of wear stripes on the heads and liners showed that the majority do not occur with normal walking; instead they probably occur with edge loading when the hip is flexed, such as with rising from a chair or with climbing a high step.

Adult↗
PubMed2004

Knee-simulator testing of conventional and cross-linked polyethylene tibial inserts.

We compared the resistance to delamination and to adhesive/abrasive wear of conventional and highly cross-linked polyethylene tibial inserts of a cruciate-retaining total knee design using a knee simulator. Both groups were tested after aggressive, accelerated aging, and 1 set of conventional inserts was studied without aging. Aging oxidized the conventional, but not the highly cross-linked, inserts. The simulated normal gait testing lasted for 5 and 10 million cycles for the conventional and highly cross-linked inserts, respectively. Aged conventional inserts showed delaminations, whereas none were observed in the unaged conventional and aged cross-linked inserts. Wear rates measured by the gravimetric method were 9 +/- 2 mm3, 10 +/- 4 mm3, and 1 +/- 0 mm3 per million cycles; by the metrologic method, they were 8 +/- 1 mm3, 9 +/- 2 mm3, and 3 +/- 0 mm3 for the unaged conventional, aged conventional, and aged highly crosslinked inserts, respectively. In the test model used, oxidation led to delamination, whereas increased cross-link density resulted in reduced adhesive/abrasive wear of tibial inserts.

Equipment Failure Analysis↗
PubMed2005

In vivo wear and migration of highly cross-linked polyethylene cups a radiostereometry analysis study.

In 50 cemented hip arthroplasties, wear and migration of the polyethylene (PE) cups were measured with radiostereometric analysis for a period of 2 years. Twenty had a normal gamma-in-air-sterilized PE, another 20 had a PE sterilized with 30000 Gy followed by heat stabilization (Duration; Stryker Orthopaedics, Mahwah, NJ), and 10 had highly cross-linked PE cups irradiated with 100000 Gy (Crossfire; Stryker Orthopaedics). In the initial 2 months, head penetration (creep) was 63 microm on average for the 3 groups. From 2 to 24 months, the mean proximal head penetration (wear) was 156 microm for standard PE, 138 microm for stabilized PE (P = .45), and 23 microm for highly cross-linked PE (P < .001; analysis of variance). The low in vivo wear rate for highly cross-linked cups was not at the expense of higher migration or less favorable clinical outcome and looks promising.

Adult↗
PubMed2006

Fracture of Colvin-Galloway Future band causing a tear in the anterior mitral leaflet.

The first case of a fracture of a semi-rigid annuloplasty device is reported. A 56-year-old man presented with recurrence of severe mitral and tricuspid regurgitation 10 months after proper implantation of a Colvin-Galloway Future band (Medtronic Inc, Minneapolis, MN). During redo surgery we made the unexpected finding that its metal skeleton was fractured near the posterior segment. A tear in the anterior mitral leaflet was also found. It is speculated that the device fracture may have put additional strain on the native annulus.

Aortic Aneurysm↗
PubMed2004

Effect of glenoid component inclination on its fixation and humeral head subluxation in total shoulder arthroplasty.

OBJECTIVE: To investigate the effect of glenoid component inclination angle on the fixation of cemented glenoid-bone structures and humeral head subluxation. BACKGROUND: Results of shoulder replacements, in terms of glenoid component fixation and joint functionality, are bad and must be improved. Repeated glenoid component tilting, a result of eccentric contact forces harms glenoid component fixation. However, the effect of glenoid component inclination is unknown. METHODS: Keeled glenoid components are cemented into bone substitutes and positioned under inclination angles varying between -4.5 degrees and +4.5 degrees . For each inclination angle 5 glenoid specimens are loaded by a horizontal, constant joint compression force (725 (SD 10) N) and a vertical, superior directed subluxation force (shear force), cyclically varying between 0 and 350 (SD 1) N. After 200,000 load cycles, the upper and lower glenoid component rim-displacements are measured during 1500 additional load cycles by custom made displacement sensors. RESULTS: The maximal superior rim-displacement significantly increased and the minimal inferior rim-displacement dramatically decreased for increasing glenoid component inclination angles up to +4.5 degrees . Maximal ratio of subluxation force over compression force significantly decreased for increasing glenoid component inclination. CONCLUSIONS: According to this study, decreasing glenoid component inclination angle decreases glenoid component tilting and humeral head subluxation and the results can be used to improve total shoulder replacements. RELEVANCE: Better understanding of the effect of glenoid component inclination on glenoid component tilting and humeral head subluxation may be useful information for the surgeon to improve results of the total shoulder arthroplasty, when replacing the glenoid surface.

Arthroplasty↗
PubMed1987

Heyde's syndrome: failure of a mechanical prosthesis and the possibility of a coagulation defect.

Recent data indicate that the gastrointestinal bleeding due to angiodysplasia associated with aortic stenosis (Heyde's syndrome) can be alleviated by aortic valve replacement with a bioprosthesis. This report details a situation in which valve replacement with a mechanical prosthesis and the subsequent anticoagulation promoted gastrointestinal bleeding from angiodysplastic lesions. Only when the mechanical prosthesis was replaced with a porcine prosthesis and the anticoagulation discontinued did the gastrointestinal bleeding stop.

Anticoagulants↗
PubMed2003

Cancellous and cortical morselized allograft in revision total hip replacement: A biomechanical study of implant stability.

To restore femoral intramedullary bone stock loss in revision surgery of failed total hip arthroplasties, impacted morselized cancellous allograft is recommended. This study investigated the mechanical properties of both impacted cortical (group A) and cancellous (group B) morselized bone graft for reconstruction of femoral bones. Ten matched pairs of fresh frozen human femora were prepared by over-reaming to create a smooth-walled cortical shell. Each pair had one cortical and one cancellous impacted morselized allograft and cement. Stem subsidence was evaluated by a cyclic axial load, which was applied by a servohydraulic test. The stem subsidence was measured for initial subsidence (subsidence at the first 1000 cycles), the total axial subsidence (subsidence at the end of cycles under load) and the final axial subsidence (subsidence after the unloading phase). Torque test was measured by torsional loads through the prosthetic femoral heads. Total axial subsidence was significantly higher in group B (mean: 1.32+/-0.32 mm) compared to group A (mean: 0.94+/-0.26 mm) (P<0.01). There was no significant difference between the two groups in terms of initial subsidence (P=0.09) and final axial subsidence. The mean maximum torque before failure was 39.5+/-22.2 N-m for the cortical morselized allograft and 32.5+/-18.1N-m for cancellous. We concluded that impacted morselized cortical bone graft used for reconstruction of contained femoral bone loss in revision hip arthroplasty, may reduce the stem subsidence. Further animal experimentation for mechanical and histological evaluation of in vivo application is warranted.

Arthroplasty, Replacement, Hip↗
PubMed1999

Which manufacturing characteristics are predictors of outlet strut fracture in large sixty-degree Björk-Shiley convexo-concave mitral valves? The Björk-Shiley Study Group.

BACKGROUND: Identification of predictors of outlet strut fracture is important for recipients of large (>/=29 mm) 60-degree Björk-Shiley convexo-concave mitral valves when it comes to decision making on prophylactic explantation. An association between the manufacturing process of Björk-Shiley convexo-concave valves and the risk of fracture has been suggested. OBJECTIVE: The aim of this study was to determine which items from the manufacturing records, in addition to known risk factors, were predictive of fracture of large 60-degree Björk-Shiley convexo-concave mitral valves. METHODS: All Dutch recipients (n = 2264) of Björk-Shiley convexo-concave valves were followed up until fracture, death, reoperation, or end of the study (July 1, 1996). Information was abstracted from the manufacturing records of large 60-degree Björk-Shiley convexo- concave mitral valves (n = 655) in Dutch recipients and included items that described the manufacturing process and items for which an association with strut fracture had been suggested. Manufacturing records were available for 637 valves (97%), including 25 fractured valves. RESULTS: Multivariate analysis identified age at implantation (hazard ratio 0.95, 95% confidence interval 0.93-0.97), lot size (<175 valves versus >/=175 valves; hazard ratio 6.6, 95% confidence interval 2.2-20.1), number of hook deflection tests performed (0 or 1 versus >/=2; hazard ratio 4.7, 95% confidence interval 1.4-16.2), number of disks that were used (1 versus >/=2; hazard ratio 5.9, 95% confidence interval 1.9-18.5), and lot fracture percentage (hazard ratio 1.6, 95% confidence interval 1.4-1. 8) as independent predictors of fracture. Although the added predictive value of a model with these 5 variables was sizable compared with a model containing age only, it was only slightly better than a model with age, lot size, and lot fracture percentage. CONCLUSION: If the serial number of a large 60-degree Björk-Shiley convexo-concave mitral valve is known, manufacturing information can add significantly to the prediction of fracture. Information on lot size and lot fracture percentage should be made available to clinicians for risk assessment of prophylactic explantation.

Equipment Failure Analysis↗
PubMed2003

The relative influence of five variables on the in vitro wear rate of uncrosslinked UHMWPE acetabular cup liners.

The wear factors, k(exp)(in 10(-6)mm(3)N(-1)m(-1)), of two sets of hemispherical uncrosslinked ultra-high-molecular-weight polyethylene UHMWPE acetabular cup liners, when articulated against 28-mm-diameter Co-Cr alloy femoral heads, were determined in a hip joint wear simulator. All test conditions used were the same for both sets, with the exception that in one set (comprising six liners), the bovine serum concentration in the test lubricant (P) was 25vol%, while it was 90vol% for the other set (comprising seven liners). For each liner in each set, the values of the following independent or explanatory variables were determined: the tensile toughness (U, in MJm(-3)) of the UHMWPE; the degree of crystallinity (%C) of the UHMWPE; the mean surface roughness (R(a), in microm) of the liner; and the radial clearance between the femoral head and the liner (DeltaL, in mm). All the results in both sets were combined and correlational analyses were performed between k(exp), on the one hand, and various combinations of U, %C,R(a),DeltaL, and P, on the other hand. It was found that the strongest correlations were obtained when P was included, but that %C and U are also important variables. Within the range of values of the independent variables used, the recommended relationship isk(exp)=460U(0.72)%C(-5.29)P(-0.66)(adjustedr(2)=0.858). This relationship has many potential uses, such as for screening uncrosslinked UHMWPEs that are being considered as candidates for fabricating acetabular cup liners, and for conducting studies of the sensitivity of k(exp) to a change in a value of a specified independent variable (with the values of all the other independent variables held constant). These uses, as well as the study limitations, are discussed in detail.

Algorithms↗
PubMed2003

The effect of frictional heating and forced cooling on the serum lubricant and wear of UHMW polyethylene cups against cobalt-chromium and zirconia balls.

Hip simulator tests of femoral balls of cobalt-chromium alloy or zirconia against acetabular cups of UHMW polyethylene were run with and without a coolant circulated inside the femoral balls. Without cooling, the wear of polyethylene against zirconia was about 48% lower than with cobalt-chromium alloy, but the steady-state temperature of the zirconia ball was higher (55 degrees C vs. 41 degrees C), and there was more precipitation of protein from the serum, which sometimes formed an adherent layer on the surface of the zirconia. Circulating coolant at 1-20 degrees C markedly reduced the bearing temperatures and the protein precipitation. With coolant at 4 degrees C, wear of the polyethylene against cobalt-chromium alloy was about 26% lower than against zirconia, but the macroscopic and microscopic appearance of the worn polyethylene surfaces were unlike that typically generated in vivo. With or without coolant, the morphology of the polyethylene wear debris was comparable to that generated in vivo, but the ratio of fibrillar to granular debris was higher at the reduced temperature. These results suggested that circulating coolant at an appropriate temperature could avoid overheating (due to non-stop running of the simulator), preventing excessive protein precipitation while providing wear surfaces and wear debris with morphologies closely comparable to those generated in vivo.

Artifacts↗
PubMed2003

Semi-quantitative analysis of cytokines in MM THR tissues and their relationship to metal particles.

Cytokines associated with osteolysis have been demonstrated in tissues surrounding failed metal-metal (MM) total hip replacements (THRs). The objective of the present study was to semi-quantify the amounts of inflammatory cytokines in tissues from 28 failed MM THRs, and determine their relationship with the quantity of metal particles. Paraffin sections were immunohistochemically stained with monoclonal antibodies: anti-IL-1-beta, anti-IL-6 and anti-TNF-alpha. Cytokines and metal particles were rated in 10 fields per tissue using standard light microscopy. Because of the use of light microscopy, only relatively large particles or agglomerations of particles were visible. Therefore, a polarized light and a semi-quantitative scheme based on the discoloration of cell cytoplasms induced by the presence of particles were used to evaluate the quantity of metal particles. Results showed an overall higher amount of IL-6 than IL-1beta while TNF-alpha remained at very low levels. For each patient, the average IL-1beta and IL-6 ratings decreased when the average particle rating increased, following a linear regression, with relatively high correlation factors (r=-0.69 for IL-1beta and r=-0.57 for IL-6). IL-1beta decreased about twice as fast as IL-6. TNF-alpha, remaining at very low levels, did not demonstrate any correlation with particle rating. When multiple tissues were available for the same patient, the correlation factors between the average cytokine and particle ratings were highly variable between samples, demonstrating the heterogeneity between the tissues from the same patient. At the cellular level, there was an even higher correlation between the quantity of metal particles and the production of IL-1beta and IL-6 (r=-0.99), while TNF-alpha did not demonstrate any correlation, remaining at very low levels. In conclusion, this study showed that tissues surrounding failed MM THRs with low to moderate quantities of metal particles can induce the production of potentially osteolytic cytokines. However, the overall number of cells producing these cytokines tended to be lower than that typically seen in tissues surrounding metal-polyethylene THRs.

Adult↗
PubMed2003

Early head penetration into cemented Hylamer Ogee socket.

The authors reviewed 18 consecutive cemented total hip arthroplasties with the Hylamer Ogee socket. The average follow-up period was 47 months. All Hylamer Ogee sockets were sterilized by gamma irradiation in air, and the average period from production to surgery was 12 months. Two-dimensional penetration of the femoral head into the Hylamer Ogee socket was determined from anteroposterior radiographs of the pelvis using a digitizer. The average head penetration rate of the present series was 0.36 mm/y. Osteolysis around both components was found in 6 cases (30%). Of 4 cases defined as aseptic loosening, 2 were revised during the follow-up period. To detect component loosening because of catastrophic high wear of the cemented Hylamer Ogee socket as early as possible, precise radiographic follow-up is essential.

Aged↗
PubMed2003

Four-angle radiographic assessment of cement mantle thickness in cemented total hip arthroplasty.

In this study, the cement mantle thickness of 57 hips undergoing primary cemented total hip arthroplasty (THA) were investigated with 4 angle radiographs. All surgeries were performed with a standardized posterolateral surgical approach. In addition to conventional anteroposterior and lateral radiographs, obturator oblique and iliac oblique radiographs were taken. In the evaluation of the cementing grade on the anteroposterior radiograph, the incidence of hips with thin cement mantles was 25%. In evaluating the cementing grade on the anteroposterior and lateral radiographs, we found an incidence of hips with thin cement mantles of 37%. From the evaluations with 4 angle radiographs, 10 hips were additionally assigned as being of a poor cementing grade (Mulroy's grade C-2). Thin cement mantles were mainly seen on the iliac oblique radiographs.

Adult↗