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Biomedical subjects

B M Wroblewski

Publications and source records attributed to B M Wroblewski.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1996

One stage revision arthroplasty of the hip for deep gram negative infection.

We describe the use of one stage revision arthroplasty of the hip for deep gram negative infections. We have followed up 15 patients for an average of 8 years following operation. Two procedures failed, one at two years due to aseptic loosening and another because of persistent infection. We attribute the low reinfection rate (1/15) to meticulous surgical technique, preoperative parenteral antibiotics and antibiotic loaded cement. Both failures occurred in the two operations performed without antibiotic loaded cement. We do not recommend the use of plain cement for exchange hip arthroplasty in the presence of gram negative infection.

Aged↗
PubMed1996

Outcome of revision for mechanical stem failure using the cemented Charnley's stem. A study of 399 cases.

Three hundred ninety-nine cemented stem revision total hip arthroplasties performed in cases with mechanical stem failure without infection and having a minimum follow-up period of 3 years were prospectively studied. Two hundred eighty-three were revised for aseptic stem loosening and 116 were revised for fractured stem. Bone-grafting was not performed in any of the cases. The average follow-up period was 7 years 5 months. At the last follow-up evaluation, 70.4% of the patients were pain free and 20.6% had only mild or occasional discomfort. On radiographic evaluation, 31 stems (7.8%) were loose. Thirty-five hips (8.8%) required a rerevision, of which only 20 (5.0%) were for recurrence of mechanical stem failure. Clinical survivorship of the revised stem was 93.9% at 10 years, whereas radiographic survivorship was 91.5% at 10 years. On radiographic analysis, the mechanical failure rate at the last follow-up evaluation was greater after revision for fractured stem than after revision for aseptic stem loosening. Prerevision femoral cortical bone stock did not appear to adversely affect the outcome of the procedure. The clinical and radiologic results achieved with cemented stem revision arthroplasty for mechanical stem failure are excellent.

Adult↗
PubMed1996

Ultra-high molecular weight polyethylene wear debris generated in vivo and in laboratory tests; the influence of counterface roughness.

The objective of this study was to investigate the effect of counterface roughness and lubricant on the morphology of ultra-high molecular weight polyethylene (UHMWPE) wear debris generated in laboratory wear tests, and to compare this with debris isolated from explanted tissue. Laboratory tests used UHMWPE pins sliding against stainless steel counterfaces. Both water and serum lubricants were used in conjunction with rough and smooth counterfaces. The lubricants and tissue from revision hip surgery were processed to digest the proteins and permit filtration. This involved denaturing the proteins with potassium hydroxide (KOH), sedimentation of any remaining proteins, and further digestion of these proteins with chromic acid. All fractions were then passed through a 0.2 micron membrane, and the debris examined using scanning electron microscopy. The laboratory studies showed that the major variable influencing debris morphology was counterface roughness. The rougher counterfaces produced larger numbers of smaller particles, with a size range extending below 1 micron. For smooth counterfaces there were fewer of these small particles, and evidence of larger platelets, greater than 10 microns in diameter. Analysis of the debris from explanted tissues showed a wide variation in the particle size distribution, ranging from below 1 micron up to several millimetres in size. Of major clinical significance in relation to osteolysis and loosening is roughening of the femoral components, which may lead to greater numbers of the sub-micron-sized particles.

Adult↗
PubMed1996

Wear in retrieved Charnley acetabular sockets.

One hundred and twenty-nine Charnley acetabular components were acquired at the time of revision surgery and a tribological investigation undertaken. The relative occurrence of pitting in the unworn and worn regions of the sockets suggest that most of the cement ingress occurs during the early part of the service life. The penetration depth of the explanted sockets was determined using the shadowgraph technique. Observation of the profiles in the wear planes suggest that, in general, the creep component was not a significant proportion of the overall change in the inner bore of the socket. Using weighted ordinary least squares regression, in which the intercept was not assumed to be zero, mean penetration and wear volume rates of 0.02 (SE = 0.02) mm/year and 55 (SE = 5) mm3/year, respectively, were recorded and are in agreement with other retrieval studies. In neither case was the intercept found to be significantly different from zero. A mean clinical wear factor, Kclinical, equal to 2.1 (SE = 0.2) x 10(-6) mm3/N m was calculated which is considerably larger than that found in laboratory experiments which purport to reflect in vivo conditions. In this analysis, a significant positive intercept was observed [96 (SE = 36) mm3] and may be evidence of the small initial penetration due to creep reported in simulator experiments. A strong positive association between kclinical and the arithmetical mean roughness, Ra, of the femoral head was also demonstrated although the rate of change was not as great as that cited for laboratory experiments.

Acetabulum↗
PubMed1996

An investigation into the origins of time-dependent variation in penetration rates with Charnley acetabular cups--wear, creep or degradation?

The total penetration of femoral heads into acetabular cups is achieved by a combination of long-term wear and early non-recoverable deformation or creep. The former is important in determining the total rate of production of polyethylene wear debris, recently implicated in the development of osteolysis and loosening, while the latter contributes to the overall penetration and the possibility of neck impingement in some designs of implants. Attention is drawn to the need to evaluate and to separate out these two physical processes in the assessment of clinical penetration rates. This is particularly important with more recent designs and combinations of materials, which are capable of operating with much reduced wear rates. Measurements of the penetrations of metallic femoral heads into polyethylene acetabular cups in 87 explanted Charnley hip arthroplasties from 85 patients are reported and assessed. The vast majority of the acetabular cups had been sterilized by gamma irradiation and the established shadowgraph technique was used to determine the penetrations. The average implantation time was 8.75 years, with a range from 0.2-18.6 years and the average age was 55 years, covering the span 19-73 years. The influence of sterilization procedure, implantation time and patient age are considered. Assessments of the relative magnitudes of wear and non-recoverable deformation are made by different statistical techniques and compared with previously reported data from clinical and laboratory studies.

Adult↗
PubMed1996

Revision of the acetabular component of a total hip arthroplasty with cement in young patients without rheumatoid arthritis.

The results for eighty-two young patients without rheumatoid arthritis who had had eighty-seven revisions of the acetabular component because of aseptic loosening were studied. The mean duration of follow-up was approximately six years (range, 1.9 to 18.1 years). The clinical result was excellent or satisfactory for seventy-nine hips (91 per cent). However, at the latest radiographic assessment, twenty-six sockets were loose. Of the fifty hips that had had good bone stock (only slight enlargement of the acetabulum or local defects involving only one wall) before the revision, seven (14 per cent) had loosening of the socket, compared with nineteen (51 per cent) of the thirty-seven that had had poor bone stock (massive or global collapse of the acetabulum and defects involving at least two walls). The relationship between loosening and the quality of the bone stock before the revision was highly significant (p = 0.0002, chi-square test). The results of revision of the socket with use of cement and without use of any bone grafts in young patients who have poor acetabular bone stock are not very encouraging. The need for regular follow-up of all patients who have had an arthroplasty cannot be overemphasized.

Acetabulum↗
PubMed1996

Prospective clinical and joint simulator studies of a new total hip arthroplasty using alumina ceramic heads and cross-linked polyethylene cups.

We report the findings from independent prospective clinical and laboratory-based joint-simulator studies of the performance of ceramic femoral heads of 22.225 mm diameter in cross-linked polyethylene (XLP) acetabular cups. We found remarkable qualitative and quantitative agreement between the clinical and simulator results for the wear characteristics with time, and confirmed that ceramic femoral heads penetrate the XLP cups at only about half the rate of otherwise comparable metal heads. In the clinical study, 19 hips in 17 patients were followed for an average of 77 months. In the hip-joint simulator a similar prosthesis was tested for 7.3 million cycles. Both clinical and simulator results showed relatively high rates of penetration over the first 18 months or 1.5 million cycles, followed by a very much lower wear thereafter. Once an initial bedding-in of 0.2 mm to 0.4 mm had taken place the subsequent rates of penetration were very small. The initial clinical wear during bedding-in averaged 0.29 mm/year; subsequent progression was an order of magnitude lower at about 0.022 mm/year, lower than the 0.07 mm/year in metal-to-UHMWP Charnley LFAs. Our results show the excellent tribological features of alumina-ceramic-to-XLP implants, and also confirm the value of well-designed joint simulators for the evaluation of total joint replacements.

Adult↗
PubMed1996

Polyethylene wear in the Charnley offset bore acetabular cup. A radiological analysis.

We studied wear in the ultra-high-molecular-weight polyethylene offset bore socket in 54 hips which had had Charnley low-friction arthroplasty. At an average follow-up of 8.1 years, the mean penetration rate was 0.04 mm per year. Correlation between the depth of socket penetration and the incidence of socket migration was confirmed, but socket migration occurred with lower penetration than had been previously reported.

Adolescent↗
PubMed1995

The clinical and radiological results of revision of low friction arthroplasty in the elderly.

We assessed 130 patients (138 hips) who were more than 70 years old at the time of revision arthroplasty and had a minimum follow-up of 4 years. The average follow-up was for 7 years 3 months. The clinical results were excellent or satisfactory in 95.6% of the cases. Systemic complications developed postoperatively in 47 patients (34.1%). Radiographically, 95.6% had a well-fixed, stable stem while 91.3% had a stable socket. Seven hips (5.1%) required re-revision. Analysis revealed a 96.5% survival of the arthroplasty at 8 years.

Aged↗
PubMed1995

Measurement of wear in retrieved acetabular sockets.

Twenty-eight standard Charnley sockets were retrieved at revision surgery. The penetration angle with respect to the cup coordinate system, beta, and penetration depth, d, of the sockets were measured using both the traditional shadowgraph technique and by analysing data obtained from a coordinate measuring machine (CMM). In addition, d was deduced radiographically from pre-revision X-rays. Limits of agreement between the three methods of measuring d were of the order of +/- 0.5 mm. Using the data obtained from the CMM it was possible to deduce the wear volume Vmeas directly. It was found that, in general, values of the wear volume calculated from d and beta using equations cited elsewhere (1, 2) were both imprecise and inaccurate. The direct measurement of the wear volume using the CMM depends on the location of reference points external to the wear surface. If such surfaces were damaged, then it was concluded that the shadowgraph technique provided the most suitable method for measuring the dimensional changes in the retrieved socket, due to its relative ease of use.

Bias↗
PubMed1995

One-stage revision of total hip arthroplasty for deep infection. Long-term followup.

One hundred eighty-three total hip arthroplasties were revised for deep infection in a 1-stage procedure using antibiotic containing acrylic cement and systemic perioperative antibiotics. At an average followup of 7 years 9 months, 154 (84.2%) patients were free of infection. The remaining 29 (15.8%) patients had evidence of persistent infection. The quality of pain relief immediately after a revision for deep infection often is a good predictor of success.

Adolescent↗