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Biomedical subjects

B M Wroblewski

Publications and source records attributed to B M Wroblewski.

At least 19 recordsLinked to original sources
PubMed1999

Low-friction arthroplasty of the hip using alumina ceramic and cross-linked polyethylene. A ten-year follow-up report.

We report the results of our continued review of 14 hip arthroplasties using alumina ceramic femoral heads with cross-linked polyethylene cups. There have been no complications and a very low rate of penetration. This was 0.02 mm per year after an initial 'bedding-in' period of two years. There has been no change in the mean rate between our earlier study at six years and the current results at 10 to 11 years. The use of these bearing surfaces appears to reduce the potential amount of polyethylene debris and may provide the next logical stage in the development of the Charnley low-friction arthroplasty.

Adult↗
PubMed1998

Prevalence of impingement in explanted Charnley acetabular components.

: Impingement of the femoral neck against the rim of the socket bore has often been cited as one of the contributory factors in the acetabular loosening process. However, there has been little research on its clinical prevalence or on the effects of both linear wear and the diameter of the femoral neck. With this aim in mind, 74 Charnley prostheses were examined after being removed at revision surgery and the sockets interrogated for evidence of impingement. The probability of impingement was assessed using logistic regression analysis. A strong positive association was observed between penetration depth and impingement (chi2 = 12.8; P = 0.0004) regardless of differences in the femoral neck diameter. Further, the introduction of femoral components which comprised a reduced diameter neck had a positive effect, in that the 50% probability of impingement occurred at approximately 2 mm of penetration. For those components with standard necks, the 50% probability of impingement occurred at zero mm of penetration. If impingement is a problem then a reduced diameter neck would appear to be a solution in cutting rates of long-term loosening. However, whether or not this reduction in rim damage, and therefore impingement, is clinically significant in terms of loosening can only be fully assessed from long-term survival analysis and comparison with autopsy retrieved specimens.

Acetabulum↗
PubMed1998

Polyethylene particles of a 'critical size' are necessary for the induction of cytokines by macrophages in vitro.

Particulate wear debris from total hip prosthetic components can stimulate macrophages to produce mediators of osteolysis which may cause aseptic implant loosening. This study evaluated the in vitro response of murine peritoneal macrophages to polyethylene particles of definitive size distributions at varying volume doses. Ceridust 3615 polyethylene particles with a mean size of 0.21, 0.49, 4.3 and 7.2 microm and GUR 120 polyethylene resin with a mean size of 88 microm were co-cultured with C3H murine peritoneal macrophages at volume (microm)3 to cell number ratios of 100:1, 10:1, 1:1 and 0.1: 1. The secretion of IL-6, IL-1beta and TNF-alpha was determined by ELISA. Significantly elevated levels of TNF-alpha and IL-1beta were determined at 100:1 ratios when the macrophages were challenged with particles with a mean size of 0.49, 4.3 and 7.2 microm, and at 10:1 ratios for particles with a mean size of 0.49 and 4.3 microm. IL-6 production was significantly elevated at 100:1 ratios for mean particle sizes of 0.49 and 4.3 microm. Particles outside this range produced considerably less cytokine suggesting that both the size and volume (or number) of polyethylene particles are critical factors in macrophage activation. Therefore particles in the phagocytosable size range of 0.3-10 microm appear to be the most biologically active.

Animals↗
PubMed1998

Differences in the rates of penetration determined from radiographic and shadowgraphic measurements of acetabular sockets.

A number of previous studies have observed a marked difference in the penetration depths recorded between direct and radiographic measurement, although no assessment of how these discrepancies affect the rates of penetration has been undertaken. In this report, the penetration depth of 95 sockets was determined from both prerevision radiographs and casts of the retrieved sockets using the uniradiographic and shadowgraphic techniques, respectively. It was observed that the mean discrepancy between the penetration rates derived from the two measurement methods was 0.046 (SE 0.017) mm yr(-1), which was significantly different from zero at P = .007. It was concluded that the penetration rates derived from this method of radiographic assessment seriously underestimated the true value as measured by a direct method by approximately 20%. As a consequence, the discrepancy in penetration rates between those sockets that are loose at revision surgery (direct measurement) and the general population of acetabular components (radiographic measurement) may not be as large as previously thought.

Acetabulum↗
PubMed1998

Wear and fracture of the acetabular cup in Charnley low-friction arthroplasty.

Seven cases of progressive wear-out and fracture of the cemented high-density polyethylene cup in Charnley low-friction arthroplasty were identified in a group of 1,815 revisions of failed total hip arthroplasties. Normal function, rapid wear in the superolateral direction, and localized superolateral loss of bone-cement interface support with perfect medial cup fixation but, above all, asymptomatic nature of the problem until the moment of sudden failure were the characteristic features. The time to failure ranged from 11 to 20 years. Stem fixation remained unaffected. The findings suggest that the problem was wear-out without any changes that could have been attributed to the volume of high-density wear particles shed into the tissues.

Adult↗
PubMed1998

Discrepancy between penetration depths derived from radiographic and direct measurement of acetabular components.

The most common technique for assessing penetration due to wear in acetabular components is with the aid of the most recent serial radiograph. This approach, which is often termed the uni-radiographic method, has been shown to underestimate the more reliable value of the penetration depth deduced from direct measurement of explanted sockets. In this article the causes of the discrepancies between the two data sets are explored. Ninety-six sockets were available from revision surgery for which both the penetration depth and angle could be measured using the shadowgraphic technique in both the coronal and wear planes. Further, the penetration depth for each of the sockets was also assessed from pre-revision X-rays. A significant discrepancy was observed between the penetration depths measured in the wear plane of the replica delta Pw and that measured from the radiograph, delta PX-ray. The discrepancy was greatest for loose sockets as opposed to those that were still fixed at revision surgery. Using the corresponding data from the shadowgraph measurements, it was possible to deduce that the errors have arisen from the radiographic measurement of wear in the coronal plane and the formula used in calculating delta PX-ray. If these errors (which cannot be calculated from the X-ray data alone) were taken into consideration, then the systematic bias between radiographic and shadowgraphic measurement was greatly reduced. The largest portion of the discrepancy was accounted for by wear occurring out of the plane of the radiograph, and this, in general, coincides with the coronal plane. Overall, these results indicate that the accurate measurement of wear from serial radiographs is not possible and that improved performance in terms of accuracy can only be achieved when a three-dimensional system is used. An alternative method for deducing the radiographic penetration depth is proposed which, theoretically, negates the error arising from the inaccuracy of the formula.

Acetabulum↗
PubMed1998

The association between rates of wear in retrieved acetabular components and the radius of the femoral head.

Current evidence suggests that loosening of the acetabular socket is related to the volume of ultra-high molecular weight polyethylene wear debris generated at the articulating surfaces, through a process of bone resorption. Therefore it is important that the rate of volumetric wear is minimized in an attempt to extend the useful life of the procedure. Laboratory evidence indicates that a reduction in sliding distance would be beneficial in achieving this target and may be attained by a reduction in femoral head radius. To investigate the relationship between femoral head size and the rates of both volumetric wear and penetration, 200 acetabular components were retrieved at the time of revision surgery. The joints had femoral heads ranging in size from 11.1 to 19.8 mm radius. For those sockets that were loose at revision surgery, a significant correlation was observed, between the rate of volumetric wear and the radius of the femoral head. For this cohort an increase in radius of 1 mm resulted in an increased rate of volumetric wear of 5.1 (SE 1.4) mm3/yr. However, the explained variance in the regression was low and exemplifies the multifactorial nature of the wear process. In particular, it is anticipated that the activity of the patient will have a significant effect on the rate at which the debris is produced. No significant correlation was observed between the rate of linear wear and femoral head radius. These results would indicate a benefit in using head sizes of a smaller radius, which generate debris at a reduced rate, and therefore require more time to accumulate large volumes of wear products.

Aged↗
PubMed1998

Stem fixation in the Charnley low-friction arthroplasty in young patients using an intramedullary bone block.

We report a prospective study of the use of intramedullary bone blocks to improve the fixation of a matt-finish femoral stem in Charnley low-friction arthroplasties. There were 379 patients (441 hips), but at a minimum follow-up of ten years there were 258 arthroplasties in 221 patients including some which had been revised. The mean age at surgery was 41 years (17 to 51) and the mean follow-up was 13.4 years (1 to 20 including the early revisions). Nine stems (3.5%) had been revised for aseptic loosening, but there were no stem fractures. Survivorship of stems was 99.2% at ten years and 94.35% at 15 and 20 years. We found that the patient's gender, the position of the stem and the experience of the surgeon all influenced the outcome. Our findings suggest that using our method of stem fixation, follow-up of over 11 years was needed to reveal the effects of endosteal cavitation of the femur, and of over 13 years to assess any divergence between the clinical and the radiological outcomes of stem fixation.

Adolescent↗
PubMed1998

Quantitative comparison of wear debris from UHMWPE that has and has not been sterilised by gamma irradiation.

Ultra-high-molecular-weight polyethylene (UHMWPE) components for total joint replacement generate wear particles which cause adverse biological tissue reactions leading to osteolysis and loosening. Sterilisation of UHMWPE components by gamma irradiation in air causes chain scissions which initiate a long-term oxidative process that degrades the chemical and mechanical properties of the polyethylene. Using a tri-pin-on-disc tribometer we studied the effect of ageing for ten years after gamma irradiation in air on the volumetric wear, particle size distribution and the number of particles produced by UHMWPE when sliding against a stainless-steel counterface. The aged and irradiated material produced six times more volumetric wear and 34 times more wear particles per unit load per unit sliding distance than non-sterilised UHMWPE. Our findings indicate that oxidative degradation of polyethylene after gamma irradiation in air with ageing produces more wear.

Air↗
PubMed1998

Quantification of third-body damage and its effect on UHMWPE wear with different types of femoral head.

We examined stainless-steel, cobalt-chrome, titanium and alumina and zirconia ceramic femoral heads retrieved at revision surgery. All the heads had articulated against ultra-high-molecular-weight-polyethylene (UHMWPE) acetabular cups. We studied the simulation of third-body damage and the wear of UHMWPE against the various materials used for the heads. The surfaces of the retrieved heads were analysed using a two-dimensional contacting profilometer. Third-body damage was characterised by the mean height of the scratches above the mean line (Rpm). The alumina ceramic and zirconia ceramic retrieved heads were found to have significantly less damage. In laboratory studies the ceramics were also more resistant to simulated third-body damage than the metal alloys. We studied the wear of UHMWPE against the damaged counterfaces in simple configuration tests. The damaged ceramics produced less polyethylene wear than the damaged metal counterfaces. The wear factor of UHMWPE against the damaged materials was dependent on the amount of damage to the counterface (Rp). Our study has shown the benefit of using the harder and more damage-resistant ceramic materials for femoral heads.

Aluminum Oxide↗
PubMed1998

Observations on the direction of wear in Charnley sockets retrieved at revision.

The direction of wear in the acetabular socket has implications for the amount of debris that is generated during movement, for the magnitude of eccentric loading and for the incidence of impingement of the neck. We observed the direction of penetration with respect to a global co-ordinate system in 84 acetabular components retrieved at reoperation. The mean direction of wear relative to the open face of the sockets was found to be 37 degrees with a range from 0 degrees to 87 degrees. For those values determined using the inclination of the socket on the prerevision radiograph, the mean direction of penetration in the coronal plane had a lateral, rather than a medial, component. The mean angle was 84 degrees (SD 17 degrees) with respect to the horizontal. The angle of penetration was found to correlate significantly with the depth, in that the lateral component became larger as the wear progressed. There was also a significant correlation between the rate of penetration and the direction of wear. Despite the theoretical advantage of penetration in the superolateral direction, i.e., along the margin of the socket, in reducing the probability of impingement of the neck, no significant correlation was seen between the angle of penetration and the period of use in vivo. This may suggest that impingement of the femoral neck on the rim of the socket may not be the dominant factor in loosening of the socket but can still be important in a few cases.

Acetabulum↗
PubMed1998

Fatal pulmonary embolism after total hip arthroplasty: diurnal variations.

From 1970 through 1986, a total of 18,104 Charnley low-friction arthroplasties were performed; of these, 122 deaths occurred from pulmonary embolism within 1 year of surgery. Diagnosis was confirmed by postmortem examination in 71% of cases. The exact time of the onset of the complication was recorded in 90 cases. In 74 (82%) cases, the time of collapse occurred during the 7-hour period from 9:00 AM to 4:00 PM, and in 16 (18%) cases, it occurred in the 17-hour period from 4:00 PM to 9:00 AM. The patient's activity at the time of collapse was recorded in 73 cases. Sixty (82%) were mobile, 3 were in the bathroom, and 10 (14%) were in bed. Sixty-six (70.2%) patients died within 1 hour of the onset of symptoms.

Arthroplasty, Replacement, Hip↗
PubMed1997

Factors affecting socket fixation after cemented revision.

Factors influencing the radiographic outcome of revised cemented sockets have been investigated in 360 cases; 70 with radiological signs of failure were analysed. The acetabular bone stock at revision and preparation of the acetabular floor were the two factors which had a significant influence on the outcome. The thickness of the cement mantle around the socket also had an influence. Young patients were at a higher risk of failure. The use of a flanged socket and an acetabular cement pressuriser appeared to improve the radiographic result, but this was not statistically significant.

Acetabulum↗
PubMed1997

The effect of surface topography of retrieved femoral heads on the wear of UHMWPE sockets.

The study was undertaken to investigate the association, if any, between the surface roughness of 35 explanted femoral heads and the clinical wear factors of the corresponding polyethylene sockets. The wear of the socket was measured using a shadowgraph technique. The surface topography was investigated using a Rodenstock RM 600 non-contacting profilometer, and six parameters were used to characterise the roughness. Further, qualitative inspections of the femoral surface were undertaken using both a Joel JSM-IC-848 scanning electron microscope and a Zeiss Axiotech microscope with a differential interference contrast facility. Two parameters were found to correlate with the clinical wear factor, namely the skewness of the amplitude distribution function, Sk, and the arithmetic mean roughness, Ra. Simple parameters describing the peak heights of the asperities were found not to have a significant association with the clinical wear factor. The exponent in the power relationship between the arithmetic mean roughness and kclinical was found to be equal to 0.5 (SE: 0.2). This value is significantly smaller than that found in laboratory experiments and may be due to the non-uniform nature of the roughening of the femoral head, three-body wear and the effect of other clinical factors on the wear process. Further, extremely strong correlations were detected between the differing roughness parameters, which would suggest that any attempt to deduce which one is the most important in affecting the wear of the polymeric counterface is fraught with difficulty. However, further investigation of those parameters, such as the reduced peak height or the material filled profile peak area, which may better describe the effect of the counterface on the wear of the UHMWPE surface would appear to be prudent.

Hip Prosthesis↗
PubMed1997

The friction of explanted hip prostheses.

Charnley prostheses, retrieved at revision surgery, were studied to assess the effects of friction on the total hip replacement procedure. Frictional resistance was measured using the Durham hip function simulator under both dry and lubricated conditions. The friction factor values (f) for the explanted prostheses were found to have a non-Gaussian distribution with medians of 0.13 [inter-quartile range (IQR) 0.10-0.16] and 0.06 (IQR 0.005-0.08) for dry and lubricated (n = 0.01 Pa s) regimes, respectively. New Charnley prostheses had values of f equal to 0.11 +/- 0.025 and 0.04 +/- 0.01 under the same conditions, and showed no large deviation from a Gaussian distribution. There was found to be a statistically significant difference in the medians of the friction factors for new and retrieved prostheses in the lubricated regime. Ingression of cement into the worn region of the cup was found to increase the friction factor significantly under dry conditions. There was no evidence of an increase in the friction factor or torque for those joints that had a loose socket with respect to those that were fixed at revision. A decrease in the frictional torque against number of cycles undergone by the joint in vivo may indicate that a fatigue-type process may have a role in the loosening of the socket. However, this relationship was found not to be significant for friction measured under lubricated conditions and it seems unlikely that the frictional torque generated in this type of prosthesis will contribute significantly to the long-term loosening of the socket.

Adult↗
PubMed1997

Wear of the high-density polyethylene socket in total hip arthroplasty and its role in endosteal cavitation.

High-density polyethylene (HDP) has been used in clinical practice in total hip replacement since its introduction by Charnley in November 1962. Fears are being expressed that this may be the weakest link and the ultimate cause of failure of the arthroplasty. Long-term clinical experience suggests that loosening may be the primary cause while the presence of HDP wear particles is secondary. Healing of endosteal cavities can take place in the presence of HDP wear particles.

Biocompatible Materials↗
PubMed1997

A study of the combined effects of shelf ageing following irradiation in air and counterface roughness on the wear of UHMWPE.

Damage to polished femoral heads in vivo can cause increased wear of acetabular cups. Oxidation and ageing after sterilisation by gamma irradiation in air, can also change the mechanical properties and wear resistance of ultra high molecular weight polyethylene (UHMWPE). This study investigated the combined effect of these changes in material properties on the wear of UHMWPE for different counterface roughnesses, representative of new femoral heads and those damaged in vivo. Wear rates were studied on a tri-pin-on-disc tribometer in a protein-containing solution. A comparison was made of the wear, using three different counterface roughnesses, of specimens that were manufactured from polyethylene acetabular cups of different shelf ages (3-120 months) after gamma irradiation in air but never implanted. These were compared to the wear of control specimens that were manufactured from cups that had not been sterilised. The wear surfaces were tested 1 mm below the initial articulating surface of the cup, the position of high degradation. The wear rate of UHMWPE which had been sterilised by gamma irradiation in air was shown to increase significantly with ageing time on the shelf for all counterface conditions. The wear rate of all materials increased markedly as the counterface roughness increased, but to different extents depending on the age of the material. The combined effect of ageing and increase in counterface roughness had a dramatic effect (as high as 2000 fold increase) on the wear rate. Both ageing of the polymer and damage to the femoral head have been cited as causing increased wear in vivo. The results of this study demonstrate that these variables can act synergistically to markedly effect UHMWPE wear rate.

Air↗