Minimum 5-Year Outcomes of a Multicenter, Prospective, Randomized Control Trial Assessing Clinical and Radiological Outcomes of Patient-Specific Instrumentation in Total Knee Arthroplasty.

BACKGROUND: Patient-specific instrumentation (PSI) was developed to produce more accurate alignment of components and consequently improve clinical outcomes when used in total knee arthroplasty. We compare radiological accuracy and clinical outcomes at a minimum of 5-year follow-up between patients randomized to undergo total knee arthroplasty performed using PSI or traditional cutting block techniques. METHODS: This multicenter, randomized control trial included patients blinded to the technique 1used. Outcome measures were coronal alignment measured radiologically, Euroqol-5D, Oxford knee score, and International Knee Society Score measured at 1- and 5-year follow-up. RESULTS: At a minimum 5-year follow-up, there were 38 knees in the PSI group and 39 in the conventional instrumentation group for analysis. Baseline demographics and clinical outcome scores were matched between groups. Overall, there was no significant difference in the coronal femoral angle (P = .59), coronal tibial angle (P = .37), tibiofemoral angle (P = .99), sagittal femoral angle (P = .34), or the posterior tibia slope (P = .12) between knees implanted using PSI and those implanted with traditional cutting blocks. On the measurement of coronal alignment, intraobserver reliability tests demonstrated substantial agreement (k = 0.64). Clinical outcomes at both 1-year and 5-year follow-up demonstrated statistically significant and clinically relevant improvement in scores from baseline in both groups, but no difference could be detected between the Euroqol-5D (P = .78), Oxford knee score (P = .24), or International Knee Society Score (P = .86) between the 2 groups. CONCLUSION: This study has shown no additional benefit to PSI in terms of improved alignment or functional outcomes at minimum 5-year follow-up over traditional techniques.

Multi-species occupancy modeling provides novel insights into amphibian metacommunity structure and wetland restoration.

A fundamental goal of community ecology is to understand species-habitat relationships and how they shape metacommunity structure. Recent advances in occupancy modeling enable habitat relationships to be assessed for both common and rare species within metacommunities using multi-species occupancy models (MSOM). These models account for imperfect species detection and offer considerable advantages over other analytical tools commonly used for community analyses under the elements of metacommunity structure (EMS) framework. Here, we demonstrate that MSOM can be used to infer habitat relationships and test metacommunity theory, using amphibians. Repeated frog surveys were undertaken at 55 wetland sites in southeastern Australia. We detected 11 frog species from three families (Limnodynastidae, Myobatrachidae, and Pelodryadidae). The rarest species was detected at only one site whereas the most common species was detected at 42 sites (naive occupancy rate 0.02-0.76). Two models were assessed representing two competing hypotheses; the best-supported model included the covariates distance to the nearest site (connectivity), wetland area, presence of the non-native eastern mosquitofish (Gambusia holbrooki), proportion cover of emergent vegetation, an interaction term between Gambusia and emergent vegetation cover, and the proportion canopy cover over a site. Hydroperiod played no detectable role in metacommunity structure. We found species-habitat relationships that fit with current metacommunity theory: occupancy increased with wetland area and connectivity. There was a strong negative relationship between occupancy and the presence of predatory Gambusia, and a positive interaction between Gambusia and emergent vegetation. The presence of canopy cover strongly increased occupancy for several tree frog species, highlighting the importance of terrestrial habitat for amphibian community structure. We demonstrated how responses by amphibians to environmental covariates at the species level can be linked to occupancy patterns at the metacommunity scale. Our results have clear management implications: wetland restoration projects for amphibians and likely other taxa should maximize wetland area and connectivity, establish partial canopy cover, and eradicate Gambusia or provide aquatic vegetation to mitigate the impact of this non-native fish. We strongly advocate the use of MSOM to elucidate the habitat drivers behind animal occupancy patterns and to derive unbiased occupancy estimates for monitoring programs.

Stay Short or Go Long? Can a Standard Cemented Femoral Prosthesis Be Used at Second-Stage Total Hip Arthroplasty Revision for Infection Following an Extended Trochanteric Osteotomy?

BACKGROUND: The aim of this study was to review the results of the use of a cemented, standard length, taper-slip femoral component at second stage following an extended trochanteric osteotomy (ETO). METHODS: We reviewed prospectively collected data from the hospital arthroplasty database, identifying and reviewing all patients who had undergone an ETO at first-stage revision for infection, who had subsequently undergone second-stage reimplantation. RESULTS: Over 17 years, 99 patients underwent 102 2-stage procedures with ETO at first stage, with a mean follow-up of 5.5 years; 70 of 102 patients received a standard prosthesis following ETO union and 32 of 102 patients received a long-stem prosthesis at second stage because of deficiencies in proximal femoral bone stock. There was a significant difference in the Paprosky classification between the 2 groups (P < .0001); 77% of the standard group and 52% of the long-stem group had no complications. A significant complication (infection, fracture, or dislocation) was observed in 12% patients in the standard group and 16% patients in the long-stem group. A number of radiographs were independently reviewed to assess for ETO union and complications and an intraclass correlation of 0.84 (P < .0001) was observed. CONCLUSION: A standard femoral prosthesis can be implanted at second stage following ETO union for Paprosky type I and some type II femora. There is no greater risk of complications, and distal bone stock is preserved for potential revision surgery in the future.

Hydrology is a major influence on amphibian abundance in a large European floodplain.

River-floodplain ecosystems play a crucial role in connecting landscape patches through hydrological connectivity, but they are among the most threatened ecosystems. Floodplains provide important habitat for amphibians by connecting aquatic and terrestrial habitats. Modifications to floodplain hydrology can impact amphibian communities, yet few studies have examined amphibian metacommunities in floodplain wetlands.In this study, we assessed patterns in amphibian breeding abundance in one of the largest floodplains of the Danube River, Hungary, relative to hydrological connectivity and multi-scale variables at 30 waterbody sites. Our aim was to determine whether these patterns aligned with the pond-permanence gradient hypothesis, where breeding amphibian abundance is predicted to be highest in ephemeral ponds without large predatory fish. We used Bayesian hierarchical modelling to estimate multi-species abundance from repeated survey (count) data collected over one breeding season.We detected the eggs and larvae of four amphibian species. The best model of abundance included covariates describing two principal component axes associated with waterbody hydrology and landscape composition within a 500-m radius of a site. There was a positive relationship between mean community abundance at a site and hydrological disconnection from the main river channel; however, the common toad (Bufo bufo) was associated with hydrologically connected waterbodies. There was a positive relationship between mean community abundance and a high proportion of forest cover and low cover of agricultural land within a 500-m radius around a site, although this relationship was clear for only two species. There was no support for models containing the number of large predatory fish species detected at a site.Although our results showed that amphibian abundance declined with hydrological connectivity, based on model selection we could not ascribe this relationship to an increased number of large predatory fish species detected in waterbodies close to the main river channel. Differences in life history and habitat requirements are likely to have explained interspecific responses to hydrological connectivity. Our results underscore the importance of addressing amphibian abundance at multiple spatial scales in floodplain wetlands, as landscape composition partly explained patterns in abundance.Application of multi-species abundance modelling allowed us to investigate environmental relationships for common and infrequently detected species. Habitat restoration programmes in floodplains should provide waterbodies disconnected from main river channels as potential amphibian breeding sites and protect or restore forest as terrestrial habitat.

Urbanisation generates multiple trait syndromes for terrestrial animal taxa worldwide.

Cities can host significant biological diversity. Yet, urbanisation leads to the loss of habitats, species, and functional groups. Understanding how multiple taxa respond to urbanisation globally is essential to promote and conserve biodiversity in cities. Using a dataset encompassing six terrestrial faunal taxa (amphibians, bats, bees, birds, carabid beetles and reptiles) across 379 cities on 6 continents, we show that urbanisation produces taxon-specific changes in trait composition, with traits related to reproductive strategy showing the strongest response. Our findings suggest that urbanisation results in four trait syndromes (mobile generalists, site specialists, central place foragers, and mobile specialists), with resources associated with reproduction and diet likely driving patterns in traits associated with mobility and body size. Functional diversity measures showed varied responses, leading to shifts in trait space likely driven by critical resource distribution and abundance, and taxon-specific trait syndromes. Maximising opportunities to support taxa with different urban trait syndromes should be pivotal in conservation and management programmes within and among cities. This will reduce the likelihood of biotic homogenisation and helps ensure that urban environments have the capacity to respond to future challenges. These actions are critical to reframe the role of cities in global biodiversity loss.

Local and landscape determinants of amphibian communities in urban ponds.

Urbanization is currently responsible for widespread declines of amphibian populations globally through the loss, isolation, and degradation of habitat. However, it is not clear how urbanization affects amphibian communities at both local (pond) and landscape scales. We assessed the breeding distribution of frogs in ponds along an urban-rural gradient in Greater Melbourne, Australia, and examined community relationships with habitat quality and landscape context. We sampled frog larvae at 65 ponds on four separate occasions and collected data on local pond and landscape variables. Using Bayesian Poisson regression modeling we found that species richness decreased at ponds surrounded by high densities of human residents and at ponds with high water conductivity, whereas species richness increased substantially at ponds surrounded by a high proportion of green open space. Ordination of individual species presence-absence data by canonical correspondence analysis largely confirmed these findings. Ordination also highlighted the negative influences of pond shading and density of predatory fish, and the positive influence of aquatic vegetation, on community composition. Individual species' responses to urbanization varied. Urbanization had strong negative effects on species that were associated with well-vegetated, sunny, fish-free ponds. Our study highlights the importance of strategic management actions in urban landscapes to improve terrestrial habitat and connectivity around ponds and other wetlands, and local management actions to improve water quality, remove predatory fish, and plant aquatic vegetation at breeding sites.

Review of total hip arthroplasty in patients younger than 30 years: mid- to long-term results.

BACKGROUND: Data on the outcome of THA in patients under the age of 30 years is sparse. There is a perceived reluctance to offer surgery to young patients on the basis of potential early failure of the implant. The aim of this study was to review clinical and radiological outcomes of THA in patients under the age of 30 years in a high-volume specialist arthroplasty unit. METHODS: A retrospective review of patients between 1989 and 2009 was undertaken. 95 patients (118 THAs) were identified but 17 patients were excluded for lack of clinical records or for follow-up under 5 years. Clinical records were reviewed for demographics, underlying pathology, details of operation and failures. Radiographs were reviewed for evidence of loosening and wear of the components. Functional assessment was carried out using the modified Hip disability and Osteoarthritis Outcome Score, Oxford Hip Score and EQ-5D-5L. RESULTS: Mean age was 25 (16-30) years and 65% patients were females. The most common underlying pathologies were development dysplasia of the hip (29%) and juvenile rheumatoid arthritis (25%). Mean follow-up was 12.6 (5-24) years, during which 19 patients (25%) were revised. The majority of the revisions were for aseptic loosening of the acetabular component. CONCLUSIONS: Surgeons are cautious when considering THA in very young patients despite the significant documented improvement in function and quality of life after THA. This study reports on the mid- to long-term results of THA which will be valuable when advising young patients on the prospects of revision surgery at the time of primary THA.

Effect of denosumab on osteolytic lesion activity after total hip arthroplasty: a single-centre, randomised, double-blind, placebo-controlled, proof of concept trial.

BACKGROUND: Osteolysis causes recurrent pain and disability after total hip arthroplasty. We investigated the effect of the human monoclonal antibody denosumab on osteolytic lesion activity in patients undergoing revision total hip arthroplasty surgery to show the biological proof of concept for a non-surgical treatment for the disease. METHODS: We did a phase 2, randomised, double-blind, placebo-controlled, proof of concept superiority trial at Sheffield Teaching Hospitals, Sheffield, UK. Eligible patients aged 30 years or older and scheduled for revision surgery for symptomatic, radiographically confirmed osteolysis were randomly allocated (1:1) to subcutaneous denosumab (60 mg single-dose) or placebo by an independent pharmacist using a random number table. The primary outcome was the between-group difference in osteoclast number per mm of bone surface of biopsies taken from the osteolytic membrane-bone interface at surgery 8 weeks later, measured by quantitative histomorphometry in all patients who underwent revision surgery. Adverse events were analysed in all randomly assigned participants. This trial is registered with the EU Clinical Trials Register (EudraCT 2011-000541-20). FINDINGS: Between Dec 12, 2012, and June 24, 2018, 51 patients were assessed for eligibility, of whom 24 were randomly assigned to study treatment. Two patients had their revision surgery cancelled for unrelated reasons, leaving 22 patients (ten in the denosumab group) for analysis of the primary outcome. There were 83% fewer osteoclasts at the osteolysis membrane-bone interface in the denosumab versus the placebo group (median 0·05 per mm [IQR 0·11] vs 0·30 mm [0·40], p=0·011). No deaths or treatment-related serious adverse events occurred. Seven adverse events, including one severe adverse event, occurred in four (36%) of 11 patients in the denosumab group. In the placebo group ten adverse events, including three severe adverse events, occurred in five (38%) of 13 patients. INTERPRETATION: To our knowledge, this is the first clinical trial of an investigational drug for osteolysis that shows tissue-specific biological efficacy. These results justify the need for future trials that target earlier-stage disease to test for clinical efficacy in reducing the need for revision surgery. FUNDING: Amgen.

How noisy are total knee and hip replacements?

Orthopaedic theatre can be noisy. Fifty percent of orthopaedic theatre staff have features of noise-induced hearing loss (NIHL). In this study, decibel (dB) levels were recorded in 17 total knee replacements (TKRs) and 11 total hip replacements (THRs). Noise levels reached 105.6dB(A) using a hammer and 97.9dB(A) with an oscillating saw. Exposure to levels above 90dB (which occurred in every case) even for short time periods is proven to cause irreversible loss of hearing. Tools used in orthopaedic theatre produce impulse noises that can cause NIHL. Further investigation is required.

Precision of periprosthetic bone mineral density measurements using Hologic Windows versus DOS-based analysis software.

Dual energy X-ray absorptiometry (DXA) is a precise tool for measuring bone mineral density (BMD) around total joint prostheses. The Hologic "metal-removal hip" analysis package (Hologic Inc., Waltham, MA) is a Microsoft DOS-based analysis platform that has undergone a change in the operating platform to a Microsoft Windows-based system that has also incorporated changes to DXA image manipulation on-screen. We evaluated the impact of these changes on instrument precision by analysis of sequential DXA scans taken on the same day using the Hologic QDR-4500A fan beam densitometer (Hologic Inc.) in 29 subjects after total hip arthroplasty. The coefficient of variation percentage (CV%) for the net pelvic region was 3.04 for Windows versus 2.36 for DOS (p>0.05). The CV% for the net femoral region was 1.75 for Windows versus 1.51 for DOS (p>0.05). Absolute BMD values for the net pelvic and net femoral regions were similar (Bland-Altman, Windows minus DOS; pelvic region mean=-1.0%; femoral region mean=1.3%; p>0.05 for both comparisons). Our results suggest that scans analyzed using each platform may be used interchangeably without the need for a calibration correction.

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.

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.

Genetic structure and diversity of the endangered growling grass frog in a rapidly urbanizing region.

Two pervasive and fundamental impacts of urbanization are the loss and fragmentation of natural habitats. From a genetic perspective, these impacts manifest as reduced genetic diversity and ultimately reduced genetic viability. The growling grass frog (Litoria raniformis) is listed as vulnerable to extinction in Australia, and endangered in the state of Victoria. Remaining populations of this species in and around the city of Melbourne are threatened by habitat loss, degradation and fragmentation due to urban expansion. We used mitochondrial DNA (mtDNA) and microsatellites to study the genetic structure and diversity of L. raniformis across Melbourne's urban fringe, and also screened four nuclear gene regions (POMC, RAG-1, Rhod and CRYBA1). The mtDNA and nuclear DNA sequences revealed low levels of genetic diversity throughout remnant populations of L. raniformis. However, one of the four regions studied, Cardinia, exhibited relatively high genetic diversity and several unique haplotypes, suggesting this region should be recognized as a separate Management Unit. We discuss the implications of these results for the conservation of L. raniformis in urbanizing landscapes, particularly the potential risks and benefits of translocation, which remains a contentious management approach for this species.

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.

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.

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.

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.

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.

Effect of sliding-taper compared with composite-beam cemented femoral prosthesis loading regime on proximal femoral bone remodeling: a randomized clinical trial.

BACKGROUND: This two-year randomized clinical trial was performed to examine whether the geometry of the cemented femoral prosthesis affects the pattern of strain-adaptive bone remodeling in the proximal aspect of the femur after primary total hip arthroplasty. METHODS: One hundred and twenty patients were randomized to receive a Charnley (composite-beam), Exeter (double-tapered), or C-Stem (triple-tapered) prosthesis. The change in proximal femoral bone mineral density over two years was measured by dual x-ray absorptiometry (DXA). Bone turnover markers were measured in urine and serum samples collected at the preoperative baseline and during the first postoperative year. N-telopeptide of type-I collagen was measured in urine as a marker of osteoclast activity, and osteocalcin was measured in serum as a marker of osteoblast activity. Clinical outcome was measured with use of the Harris and Oxford hip scores and prosthesis migration was measured with use of digitized radiographs during the first two postoperative years. RESULTS: The baseline characteristics of the subjects in each group were similar (p > 0.05). Decreases in femoral bone mineral density were observed over the first year for all prosthesis designs, with no further loss during the second year. The decreases were similar in regional distribution and magnitude between the composite-beam and sliding-taper designs (p > 0.05). Bone loss was greatest (14%) in the proximal medial aspect of the femur (Gruen zone 7). Transient increases in both N-telopeptide of type-I collagen and osteocalcin activity also occurred over the first year, and these increases were similar in pattern among the three prosthesis groups (p > 0.05). All prostheses showed migration patterns that were consistent with their design type, and similar improvements in clinical hip scores were observed over the two-year course of the study. CONCLUSIONS: Differences in the mechanism of load transfer between the prosthesis and host bone in composite-beam or sliding-taper cemented femoral prosthesis designs were not a major determinant of proximal femoral bone loss after total hip arthroplasty, and the design that included a third taper exhibited a remodeling profile that was similar to those of the double-tapered design.