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Biomedical subjects

Andrew J Hamer

Publications and source records attributed to Andrew J Hamer.

8 recordsLinked to original sources
PubMed2005

Polyethylene wear rate and osteolysis: critical threshold versus continuous dose-response relationship.

We studied the relationship between polyethylene wear and osteolysis in 230 subjects after cemented Charnley total hip arthroplasty in order to examine the validity of the wear rate threshold concept. Polyethylene wear measured using image analysis (EBRA) software was compared in 115 subjects with osteolysis versus 115 control subjects that were individually matched for age, sex, and follow up period. Subjects with osteolysis had almost twice the mean annual wear rate versus the controls. The incidence of osteolysis increased in a linear manner with each quintile increase in wear rate throughout the range 0.01-0.54 mm/year. The odds-ratio for osteolysis approximately doubled with each quintile increase in wear rate above the middle quintile (wear rate 0.08-0.11 mm/year), and decreased at a similar rate with each quintile decrease in wear rate below the middle quintile. Our data suggests that the association of osteolysis with polyethylene wear rate represents a continuous dose-response relationship and does not support the concept of a discrete critical wear rate threshold above which the risk of osteolysis is disproportionately increased.

Aged↗
PubMed2005

Effect of pamidronate on bone turnover and implant migration after total hip arthroplasty: a randomized trial.

In this trial we studied the effect of pamidronate on periprosthetic bone turnover and pelvic implant migration over 2 years after hybrid total hip arthroplasty (THA). Twenty-two patients received 90 mg of pamidronate and 22 received placebo at randomization 5 days after surgery. Rapid periprosthetic bone loss occurred in the placebo group over the first 6 months and was accompanied by transient increases in biochemical markers of bone turnover. Partial recovery in bone mass occurred in most regions after this period. No recovery of bone mass occurred at the femoral calcar or the medial wall of the acetabulum. Femoral calcar bone loss at 2 years was strongly predicted by acute biomarker changes at week 6. Pamidronate therapy reduced femoral bone loss in the region of the femoral calcar (P = 0.01), but did not affect pelvic bone loss. Pamidronate therapy also inhibited the transient rise in biochemical markers of bone turnover during this period. Pamidronate therapy did not affect acetabular cup migration. Cup migration was inversely related to subject age, but unrelated to initial post-operative bone mineral density, or subsequent bone loss. In summary, early periprosthetic bone loss is associated with a transient expansion of the bone remodeling space. Bisphosphonate therapy reduces femoral calcar bone loss and bone turnover after THA, but did not influence cup migration in this study. Acute changes in biochemical markers predict femoral periprosthetic bone loss.

Adult↗
PubMed2004

Consequence modeling using the fire dynamics simulator.

The use of Computational Fluid Dynamics (CFD) and in particular Large Eddy Simulation (LES) codes to model fires provides an efficient tool for the prediction of large-scale effects that include plume characteristics, combustion product dispersion, and heat effects to adjacent objects. This paper illustrates the strengths of the Fire Dynamics Simulator (FDS), an LES code developed by the National Institute of Standards and Technology (NIST), through several small and large-scale validation runs and process safety applications. The paper presents two fire experiments--a small room fire and a large (15 m diameter) pool fire. The model results are compared to experimental data and demonstrate good agreement between the models and data. The validation work is then extended to demonstrate applicability to process safety concerns by detailing a model of a tank farm fire and a model of the ignition of a gaseous fuel in a confined space. In this simulation, a room was filled with propane, given time to disperse, and was then ignited. The model yields accurate results of the dispersion of the gas throughout the space. This information can be used to determine flammability and explosive limits in a space and can be used in subsequent models to determine the pressure and temperature waves that would result from an explosion. The model dispersion results were compared to an experiment performed by Factory Mutual. Using the above examples, this paper will demonstrate that FDS is ideally suited to build realistic models of process geometries in which large scale explosion and fire failure risks can be evaluated with several distinct advantages over more traditional CFD codes. Namely transient solutions to fire and explosion growth can be produced with less sophisticated hardware (lower cost) than needed for traditional CFD codes (PC type computer verses UNIX workstation) and can be solved for longer time histories (on the order of hundreds of seconds of computed time) with minimal computer resources and length of model run. Additionally results that are produced can be analyzed, viewed, and tabulated during and following a model run within a PC environment. There are some tradeoffs, however, as rapid computations in PC's may require a sacrifice in the grid resolution or in the sub-grid modeling, depending on the size of the geometry modeled.

Computer Simulation↗
PubMed2004

Accuracy and precision of peripheral quantitative computed tomography measurements at the tibial metaphysis.

The ability of 29 peripheral quantitative computed tomography (pQCT) software analysis modes at defining cortical from trabecular bone at three tibial metaphyseal regions was evaluated using five cadaveric tibiae. The accuracy of pQCT was determined by comparing the bone mineral content (BMC) with the ash weight. The precision of the pQCT scanner was calculated using repeated measurements. All the analysis modes had a good accuracy when measuring total bone area and a poor accuracy when measuring cortical bone area at the proximal 5% and distal 4% regions. For trabecular bone measured at all three regions and cortical bone area measured at the proximal 10% region, the Stratec peel mode 5 was the most accurate analysis mode. Highly significant correlations (r = 0.71-0.98) and a moderate accuracy error (coefficient of variation [CV] = 5-22%) was found between ash weight and BMC when using this mode. The precision of bone mineral density (BMD) measurements was good (total, CV = 2-5%; trabecular, CV = 2-5%; cortical, CV = 4-6%). pQCT is a moderately accurate, precise method of measuring trabecular and total BMD at the tibial metaphysis. The authors recommend caution when interpreting results for cortical BMD, as cortical area measurements at the metaphyseal region are less accurate and less precise.

Adult↗
PubMed2003

Biochemical markers of bone turnover and development of heterotopic ossification after total hip arthroplasty.

We studied biochemical markers of bone turnover markers in 20 men and women over 26 weeks after total hip arthroplasty (THA) in order to characterize the changes in bone metabolism associated with developing heterotopic ossification (HO). Transient increases in biochemical markers of both osteoclast and osteoblast activity occurred after surgery. Subjects developing HO (n=9) had greater rises in the osteoclast marker C-telopeptide of type-I collagen (CTX-I; ANOVA P=0.004), and the osteoblast markers N-terminal propeptide of type-I procollagen (PINP; ANOVA P=0.01) and osteocalcin (OC; ANOVA P=0.02) than those who did not develop HO. A rise of >42% in CTX-I at one week after surgery had a sensitivity of 89% and a specificity of 82% for predicting HO development at week 26 (P<0.05). Rises of >57% in PINP and >13% in OC at week 6 had sensitivities of 89% and 56%, and specificities of 82% and 91%, respectively for development of HO. Transient increases in osteoblast and osteoclast activity occur after THA. These changes are greater in patients developing HO than in those who do not develop HO. The potential applications of these markers are as a non-invasive, radiation-free tool for investigating the pathogenesis of HO, and as an early surrogate outcome marker for HO development in clinical trials of novel prophylaxis regimes for its prevention.

Adult↗
PubMed2003

Bone mineral density and biochemical markers of bone turnover in aseptic loosening after total hip arthroplasty.

The aims of this study were to determine whether subjects with aseptic loosening after total hip arthroplasty (THA) have regional differences in periprosthetic bone mineral density (BMD) and systemic biochemical markers of bone turnover compared to subjects with successful implants.Proximal femoral and pelvic BMD were measured by dual energy X-ray absorptiometry and bone turnover markers were assayed in 49 subjects 12.6+/-4.3 (mean+/-SD) years after cemented THA. Femoral BMD was lower in Gruen zones 2, 5, 6, and 7 in subjects with a loose femoral implant (n=17) compared to those (n=32) with fixed femoral implants (P<0.05 all comparisons). This BMD difference was greatest (-31%, P=0.02) in the proximal and medial region of the femur. Subjects with femoral loosening had higher levels of the bone resorption marker N-telopeptides of type-I collagen (P=0.02) than those with a fixed femoral implant. No differences in pelvic BMD or bone turnover markers were found between subjects with loose (n=18) versus fixed (n=31) pelvic implants. This study suggests that failure of femoral components after cemented THA is associated with region-specific decreases in BMD and an increase in urinary excretion of N-telopeptide cross-links of type-I collagen. These surrogate outcome markers may be of value in monitoring response to antiresorptive therapies used to treat periprosthetic osteolysis, although the diagnosis of aseptic loosening remains clinical and radiological.

Absorptiometry, Photon↗
PubMed2003

Variation in the TNF gene promoter and risk of osteolysis after total hip arthroplasty.

UNLABELLED: Genetic factors may influence implant failure caused by osteolysis after THA. In an association study of 481 subjects after THA, we found that carriage of the TNF-238A allele was associated with an increased incidence of osteolysis versus noncarriage (odds ratio, 1.7) and was independent of other risk factors. Genetic and environmental factors influence implant survival after THA. INTRODUCTION: Tumor necrosis factor (TNF) is thought to play a role in osteolysis, the major cause of implant failure after total hip arthroplasty (THA). Natural sequence variations at -238 and -308 in the TNF gene promoter are associated with differences in susceptibility to several TNF-mediated diseases. We tested whether these polymorphisms are associated with osteolysis after THA. MATERIALS AND METHODS: A total of 481 whites (214 with failed versus 267 with intact implants) were recruited 11.7 +/- 4 years after cemented THA. Genomic DNA was extracted from peripheral blood and genotyped for the -238 and -308 polymorphisms using the Taqman 5' nuclease method. Healthy controls (n = 500) from the background population were also genotyped to establish the local prevalence of these alleles. RESULTS: The carriage of -238A was 8.8% in the background population and 10.9% in the THA controls (p > 0.05). Carriage of -238A in the osteolysis group was 17.3% (odds ratio, 1.7; 95% CI, 1.0-2.9). Carriage was highest (20.5%) in patients with more widespread osteolysis (OR, 2.1; 1.2-3.8). The association of -238A with osteolysis was independent of other risk factors for osteolysis (logistic regression analysis: OR, 1.8; 1.0-3.2). Carriage of -308A was not associated with osteolysis. CONCLUSION: Genetic, as well as environmental factors, influence implant failure after THA. Whether the TNF-238 polymorphism causes a biological change that predisposes to loosening or is in linkage disequilibrium with such a locus is not yet known.

Aged↗