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Biomedical subjects

G Scott

Publications and source records attributed to G Scott.

At least 145 records · Page 8Linked to original sources
PubMed1997

The size and shape of particulate polyethylene wear debris in total joint replacements.

Osteolysis induced by wear particles has been recognized as one of the major causes of long-term failure in total joint replacements. However, little is currently known about the exact nature of particles, as the particles are too small to be characterized by light microscopy. In this study, ultra-high molecular weight polyethylene (UHMWPE) particles retrieved from ten cases (six cemented and four uncemented) for Freeman type conforming tibiofemoral total knee replacements (TKRs), three Charnley total hip replacements (THRs) and five Imperial College/London Hospital double cup surface hip replacements for aseptic loosening were extracted using a high-performance method with ultracentrifugation and characterized by scanning electron microscopy. The equivalent circle diameter (ECD) of all 18 cases ranged from 0.40 to 1.15 microns (Mean +/- SE = 0.70 +/- 0.05 micron, median = 0.67 micron). The aspect ratio was 1.50 to 2.04 (Mean +/- SE = 1.75 +/- 0.04, median = 1.73), and roundness was 1.24 to 2.34 (Mean +/- SE = 1.61 +/- 0.07, median = 1.65). The numbers of particles were 5.2 x 10(8) to 9.17 x 10(10)/g tissue (Mean +/- SE = 1.42 x 10(10) +/- 5.41 x 10(9)/g tissue, median = 7.04 x 10(9)). The number of polyethylene (PE) particles/g tissue in TKRs was significantly larger than that in THRs (1.04 x 10(10)/g tissue and 2.16 x 10(9)/g tissue respectively, median, p = 0.03, Mann-Whitney U test). Unstable fixation of the tibial PE component might account for the accumulation of a large number of PE particles in the interface tissue.

Biocompatible Materials↗
PubMed1997

Radiological and survival comparison of four methods of fixation of a proximal femoral stem.

We compared the radiological appearances and survival of four methods of fixation of a femoral stem in 538 hips after follow-up for five or ten years. The fixation groups were: 1) press-fit shot-blasted smooth Ti-A1-V stem; 2) press-fit shot-blasted proximally ridged stem; 3) proximal hydroxyapatite (HA) coating; and 4) cementing. Survival analysis at five to ten years showed better results in the HA-coated (100% at five to six years) and cemented stems (100% at 5 to 6 years) than in the two press-fit groups. There was a higher mean rate of migration in the smooth and ridged Ti-A1-V shot-blasted press-fit groups (0.8 mm/year and 0.6 mm/year, respectively) when compared with the HA-coated and cemented prostheses (both 0.3 mm/year). More radiolucent lines and osteolytic lesions were seen in the press-fit groups than in either the HA-coated or cemented implants, with a trend for a lower incidence of both in the HA compared with the cemented group. Proximal osteopenia increased in the press-fit and cemented prostheses with time, but did not do so in the HA group. There was a higher incidence of resorption of the femoral neck with time in the cemented group than in the other three. We conclude that the HA and the cemented interfaces both provide secure fixation with a trend in favour of HA. The cemented prosthesis meets the suggested National Institutes of Health definition of 'efficacious' at ten years.

Adult↗
PubMed1997

Early radiological observations may predict the long-term survival of femoral hip prostheses.

We reviewed a consecutive series of 527 uninfected hip replacements in patients resident in the UK which had been implanted from 1981 to 1993. All had the same basic design of femoral prosthesis, but four fixation techniques had been used: two press-fit, one HA-coated and one cemented. Review and radiography were planned prospectively. For assessment the components were retrospectively placed into two groups: those which had failed from two years onwards by aseptic femoral loosening and those in which the femoral component had survived without revision or recommendation for revision. All available radiographs in both groups were measured to determine vertical migration and examined by two observers to agree the presence of radiolucent lines (RLLs), lytic lesions, resorption of the neck, proximal osteopenia and distal intramedullary and distal subperiosteal formation of new bone. We then related the presence or absence of these features and the rate of migration at two years to the outcome with regard to aseptic loosening and determined the predictive value of each of these variables. Migration of > or = 2 mm at two years, the presence of an RLL of 2 mm occupying one-third of any one zone, and subperiosteal formation of new bone at the tip of the stem were predictors of aseptic loosening after two years. There were too few lytic lesions to assess at two years, but at five years a lytic lesion > or = 2 mm also predicted failure. We discuss the use of these variables as predictors of femoral aseptic loosening for groups of hips and for individual hips. We conclude that if a group of about 50 total hip replacements, perhaps with a new design of femoral stem, were studied in this way at two years, a mean migration of < 0.4 mm and an incidence of < 10% of RLLs of 2 mm in any one zone would predict 95% survival at ten years. For an individual prosthesis, migration of < 2 mm and the absence of an RLL of < or = 2 mm at two years predict a 6% chance of revision over approximately ten years. If either 2 mm of migration or an RLL of 2 mm is present, the chances of revision rise to 27%, and if both radiological signs are present they are 50%. If at five years a lytic lesion has developed, whatever the situation at two years, there is approximately a 50% chance of failure in the following five years. Our findings suggest that replacements using a limited number of any new design of femoral prosthesis should be screened radiologically at two years before they are generally introduced. We also suggest that radiographs of individual patients at two years and perhaps at five years should be studied to help to decide whether or not the patient should remain under close review or be discharged from specialist follow-up.

Adult↗
PubMed1997

Number of polyethylene particles and osteolysis in total joint replacements. A quantitative study using a tissue-digestion method.

Our aim was to analyse the influence of the size, shape and number of particles on the pathogenesis of osteolysis. We obtained peri-implant tissues from 18 patients having revision surgery for aseptically loosened Freeman total knee replacements (10), Charnley total hip replacements (3) and Imperial College/London Hospital double-cup surface hip replacements (5). The size and shape of the polyethylene particles were characterised using SEM and their concentration was calculated. The results were analysed with reference to the presence of radiological osteolysis. The concentration of polyethylene particles in 6 areas with osteolysis was significantly higher than that in 12 areas without osteolysis. There were no significant differences between the size and shape of the particles in these two groups. We conclude that the most critical factor in the pathogenesis of osteolysis is the concentration of polyethylene particles accumulated in the tissue.

Chromatography, High Pressure Liquid↗
PubMed1997

Application of the findings of the European Stroke Prevention Study 2 (ESPS-2) to a New Zealand ischaemic stroke cost analysis.

The aim of this study was to apply the findings of the European Stroke Prevention Study 2 (ESPS-2) to a paper that quantified and described the annual cost of ischaemic stroke in New Zealand, and to compare the cost of alternative drug regimens in the secondary prevention of ischaemic stroke. Comparisons were made between the costs of low-dosage aspirin (acetylsalicylic acid) monotherapy and a combination of modified-release dipyridamole and low-dosage aspirin. Differences in undiscounted costs were calculated over a 2-year period. The New Zealand cost per stroke event was multiplied by the ESPS-2 incremental reduction in stroke events to derive the cost of strokes avoided. As the focus of the paper was on direct medical costs, the primary perspective adopted was that of a healthcare provider or funder, but a societal perspective was also considered by evaluation of direct nonmedical and indirect costs. Compared with aspirin monotherapy, combination therapy generated incremental net direct costs of 18.22 New Zealand dollars ($NZ) per patient or $NZ18,223 per 1000 patients. However, individually, each treatment regimen resulted in direct cost savings when compared with placebo: combination therapy $NZ905.16 per patient; aspirin monotherapy $NZ923.39 per patient (a difference between the 2 regimens of $NZ18.22 per patient). Total direct and indirect incremental cost savings were $NZ40.96 per patient, and $NZ40,963 per 1000 patients, for the combination therapy. The analysis demonstrates that changing patients from low-dosage aspirin to a combination therapy of modified-release dipyridamole plus low-dosage aspirin would result in a small rise in incremental direct costs (using our conservative assumptions relating to hospital and continuing institutional care costs). If less conservative unit cost assumptions were adopted, a more likely outcome would be a saving in direct incremental costs of up to $NZ400 per patient treated.

Aspirin↗
PubMed1997

Multicenter evaluation of the Micral-Test II test strip, an immunologic rapid test for the detection of microalbuminuria.

OBJECTIVE: To assess the performance of the Micral-Test II immunologic test strip for the detection of microalbuminuria, a multicenter evaluation in eight European study sites was performed. RESEARCH DESIGN AND METHODS: Using both the Micral-Test II test strip and the routine method for the determination of albumin concentration, we investigated 2,228 urine samples from diabetic patients. Additionally, interperson variability, color stability, and possible interfering factors (temperature, pH, leucocyturia, erythrocyturia, and drugs) were tested. RESULTS: For a cutoff concentration of 20 mg/l with respect to the routine methods, a sensitivity of 96.7% and a specificity of 71% were calculated for the Micral-Test II test strip. The negative predictive value was 0.95, and the positive predictive value was 0.78, with a prevalence of positive samples (laboratory method) of 52%. The interperson variability of color interpretation showed 93% concordant readings. The interference study showed an influence of oxytetracycline, leading to higher readings. There was no interference from pH. A sample temperature of < 10 degrees C led to lower readings. In the case of samples with massive leucocyturia and erythrocyturia that may delete the chromatographic process, waiting an additional 1-2 min is needed before reading. CONCLUSIONS: The results of the multicenter evaluation show that the Micral-Test II test strip permits an immediate and reliable semiquantitative determination of low albumin concentrations in urine samples with an almost user-independent color interpretation.

Albuminuria↗
PubMed1996

Reverse transcriptase mutations in HIV-1-infected children treated with zidovudine.

Human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) mutations were detected in DNA from peripheral blood mononuclear cells from 11 of 12 HIV-1-infected children after 11-20 months of zidovudine monotherapy. The number of children with mutations detected at each codon were as follows: codon 41, 4; codon 67, 2; codon 70, 7; codon 215, 7; codon 219, 0. Codon 41 mutations were found only in the presence of a codon 215 mutation and in the absence of a codon 70 mutation. The codon 41/215 mutant combination was associated with decline in weight-for-age z score during therapy, weight < 10th percentile, CD4+ cell counts < 3rd percentile, and immune-complex dissociated HIV-1 p24 antigen (ICD p24 Ag) levels > 100 pg/ml. Patients developing the codon 70 mutation tended to have body weight > 30th percentile, CD4+ cell counts > 25th percentile, and ICD p24 Ag < 100 pg/ml. The codon 41 mutation was associated with clinical deterioration during a 6-month followup period.

Anti-HIV Agents↗
PubMed1996

Tough talking.

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Economics, Nursing↗
PubMed1996

Man trouble.

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Adolescent↗
PubMed1996

Broken promises.

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Collective Bargaining↗
PubMed1996

Giving false hope?

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Abortion, Spontaneous↗
PubMed1996

On-going struggle.

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Economics, Nursing↗
PubMed1996

Bone formation and bone resorption in failed total joint arthroplasties: histomorphometric analysis with histochemical and immunohistochemical technique.

To elucidate the reactions of bone around aseptically loosened total joint arthroplasties, 24 interface tissues with adjacent bone were obtained in 17 revision operations (11 hips and six knees). The morphology of the bone surface next to the interface membrane was investigated with histochemical and immunohistochemical techniques and then histomorphometrically analysed. One-third of the total bone surface. 32.69 +/- 5.16% (mean +/- SE) (n = 24), showed positive alkaline phosphatase activity. The bone surface in contact with the cells positive for CD11b (a macrophage marker) amounted to 19.33 +/- 5.16% (n = 24). The proportion of the osteoclastic bone resorption estimated by vitronectin receptor expression was 7.67 +/- 1.82% (n = 21). Tissues retrieved from the sites where radiographic evidence of osteolysis was present (n = 12) had a significantly larger extent of the bone surface in contact with CD11b-positive cells than did the tissues from areas without osteolysis (n = 12, p = 0.0067, Mann-Whitney U test), whereas no significant difference was observed in the extent of osteoclastic bone resorption. These data demonstrate that active bone formation, regarded as a repair process, is the most common feature even in revised cases. They also highlight the role played by macrophages, not as cells producing inflammatory mediators that could activate osteoclasts, but as cells primarily responsible for the bone loss in osteolytic lesions.

Adult↗