Effective emissions reduction of high-mileage fleets through a catalytic converter and oxygen sensor replacement program.

High-mileage vehicles such as taxis make disproportionately large contributions to urban air pollution due to their accelerated engine deterioration rates and high operation intensities despite their small proportions of the total fleet. Controlling emissions from these high-mileage fleets is thus important for improving urban air quality. This study evaluates the effectiveness of a pilot repair program in reducing emissions from taxis in Hong Kong which account for about 2 % of the total licensed vehicles. The emission factors of a large sample of 684 in-service taxis (including 121 for an emission survey program and 563 for a pilot repair program) were measured on transient chassis dynamometers. The results showed that 63 % of the sampled taxis failed the driving cycle test before the pilot repair program. Most of failed taxis were NO related and 91 % of failed taxis exceeded the emission limits of at least two regulated pollutants simultaneously. After the pilot repair program by replacing catalytic converters and oxygen sensors, the failure rate was significantly reduced to only 7 %. In addition, the fleet average NO, HC and CO emission factors were reduced by 85 %, 82 % and 56 %, respectively. In addition, on-road remote sensing measurements confirmed the real-world emission reductions from the taxis that participated in the pilot repair program. These findings led to the implementation of a large-scale replacement program for all taxis in Hong Kong during 2013-2014, which was estimated to have reduced the total HC, CO and NO emissions by about 420, 2570 and 1000 t per year, respectively (equivalent to 5-8 % emission reductions from the whole road transport sector). Therefore, reducing emissions from the small high-mileage fleets is a highly cost-effective measure to improve urban air quality.

Rapid detection of high-emitting vehicles by on-road remote sensing technology improves urban air quality.

Vehicle emissions are the most important source of air pollution in the urban environment worldwide, and their detection and control are critical for protecting public health. Here, we report the use of on-road remote sensing (RS) technology for fast, accurate, and cost-effective identification of high-emitting vehicles as an enforcement program for improving urban air quality. Using large emission datasets from chassis dynamometer testing, RS, and air quality monitoring, we found that significant percentages of in-use petrol and LPG vehicles failed the emission standards, particularly the high-mileage fleets. The RS enforcement program greatly cleaned these fleets, in terms of high-emitter percentages, fleet average emissions, roadside and ambient pollutant concentrations, and emission inventory. The challenges of the current enforcement program are conservative setting of cut points, single-lane measurement sites, and lack of application experience in diesel vehicles. Developing more accurate and vertical RS systems will improve and extend their applications.

Tackling nitric oxide emissions from dominant diesel vehicle models using on-road remote sensing technology.

Remote sensing provides a rapid detection of vehicle emissions under real driving condition. Remote sensing studies showed that diesel nitrogen oxides emissions changed little or were even increasing in recent years despite the tightened emission standards. To more accurately and fairly evaluate the emission trends, it is hypothesized that analysis should be detailed for individual vehicle models as each model adopted different emissions control technologies and retrofitted the engine/vehicle at different time. Therefore, this study was aimed to investigate the recent nitric oxide (NO) emission trends of the dominant diesel vehicle models using a large remote sensing dataset collected in Hong Kong. The results showed that the diesel vehicle fleet was dominated by only seven models, accounting for 78% of the total remote sensing records. Although each model had different emission levels and trends, generally all the dominant models showed a steady decrease or stable level in the fuel based NO emission factors (g/kg fuel) over the period studied except for BaM1 and BdM2. A significant increase was observed for the BaM1 2.49 L and early 2.98 L models during 2005-2011, which we attribute to the change in the diesel fuel injection technology. However, the overall mean NO emission factor of all the vehicles was stable during 1991-2006 and then decreased steadily during 2006-2016, in which the emission trends of individual models were averaged out and thus masked. Nevertheless, the latest small, medium and heavy diesel vehicles achieved similar NO emission factors due to the converging of operation windows of the engine and emission control devices. The findings suggested that the increasingly stringent European emission standards were not very effective in reducing the NO emissions of some diesel vehicle models in the real world.

Clinical performance of an elastomeric lumbar disc replacement: Minimum 12 months follow-up.

BACKGROUND: Elastomeric disc replacements have been developed to restore normal shock absorption and physiologic centers of rotation to the degenerated disc. The Physio-L Artificial Lumbar Disc is an elastomeric disc which uses a compliant polycarbonate-polyurethane core with enhanced endurance properties. The objective of this study was to evaluate the safety and efficacy of the Physio-L through a 12-month follow-up period in a prospective, nonrandomized clinical trial. METHODS: Twelve patients who met the inclusion/exclusion criteria were enrolled in the study. Eight patients received a single implant (L5-S1) and 4 received a 2-level implantation (L4-5 and L5-S1). Patients were assessed preoperatively and postoperatively at 6 weeks and 3, 6, and 12 months. Primary outcomes included the VAS, ODI, a radiographic analysis of implant condition, incidence of major complications, and reoperations. Secondary outcomes included SF-36, ROM at index and adjacent levels and disc height. RESULTS: All patients completed the 12-month follow-up evaluations. Through 12 months, the Physio-L devices have remained intact with no evidence of subsidence, migration, or expulsion. VAS low-back pain and ODI scores improved significantly at all follow-up periods compared to preoperative scores. The range of motion of 13.3° ± 5.5° at the index level was considered normal. Overall, patients were satisfied with an average score of 83.5 ± 26.8 mm. When comparing the device to other artificial discs, the current device showed a clinically relevant improvement in both ODI and VAS scores at all follow-up time points. Statistically significant improvements in both scores were observed at 12 months (P < .05). CONCLUSION: The Physio-L is safe and efficacious, as demonstrated by improved pain relief and functional recovery without any implant failures, significant device related complications, or adverse incidents. The clinical results for VAS and ODI were superior to other marketed artificial lumbar discs such as the Charité and ProDisc-L at the same follow-up timeframes.

Osteopenia and total disc prosthesis subsidence: inclusion/exclusion criteria for total disc replacement.

BACKGROUND: Prosthetic subsidence is an adverse event of disc arthroplasty with a total disc prosthesis. Factors affecting prosthetic subsidence are (1) the size of the prosthetic endplate (footprint), (2) amount of load applied to the spine, and (3) compressive strength of the vertebral bone. The size of the prosthetic endplate has been addressed adequately in the development of the current generation of total disc prostheses. However, little information is available on the relation between osteopenia (low bone mineral density [BMD]) and prosthetic subsidence. We evaluated the relation between osteopenia and compressive strength of vertebral bone and propose an inclusion/exclusion guideline for disc arthroplasty in the presence of osteopenia. METHODS: This study was based on previously published data by C.K. Lee on bone mineral density, contact surface area, and applied load that emphasized the critical contact surface area required to prevent subsidence. The study included 35 cadaveric vertebral bones (representing ages 38-68) that were evaluated via quantitative computed tomography for BMD and subjected to nondestructive and destructive tests for compressive strength of the vertebral bones. The relationship of osteopenia to prosthetic subsidence was evaluated from the data. RESULTS: Patients with average BMD (0.137 g/cm(3)) require a minimum contact surface area of 6.5 cm(2) for the physiologic load of 2500 N. Patients with a BMD of up to 1 SD below the average will require 9.1 cm(2) of contact area for the same load. Patients with a BMD of up to 2 SD below the average will require 13 cm(2) of contact area. DISCUSSION: The average endplate surface area of small disc prostheses is about 6.5-8 cm(2), which is enough to tolerate normal physiologic load for patients with normal BMD. Patients with BMD of 2 SD below the average will require a disc prosthesis with an endplate surface area greater than 12.75 cm(2) to tolerate normal physiologic load. The largest size of prosthetic endplate of the currently available disc prostheses is about 11 cm(2); therefore, patients with BMD below 2 SD will have a high risk of subsidence, and these patients should be excluded for disc arthroplasty. Patients with BMD between -1.5 SD and -2.0 SD may be included for disc arthroplasty only when they can receive the large size of prosthesis with greater than 10.5 cm(2) prosthetic endplates. CONCLUSIONS: All patients should be evaluated preoperatively with BMD measurement. Patients with a BMD of up to 1.5 SD below the average can be included for total disc arthroplasty. Patients with BMD of 2 SD below the average should be excluded for total disc arthroplasty, and patients with BMD of 1.5-2 SD below the average should be carefully evaluated for the appropriate size of the prosthesis prior to the surgery.

Measurement and analyses of the effects of adjacent end plate curvatures on vertebral stresses.

BACKGROUND: Vertebral end plates of the lumbosacral spine have various degrees of concavity and convexity. It is believed that the shape of the end plates alters the distribution of loads transferred along the spine, between the vertebrae. Animal models have been regularly used in the design and development of vertebral disc implants and cages; to date, very little information is known about the animal vertebral end plate curvature. PURPOSE: The purpose was to measure and analyze the end plate curvature in the cadaver human male-female, chimpanzee, and canine lumbar vertebral bones. STUDY DESIGN/SETTING: Nondestructive and nontouching scanning method was designed to obtain curvature in anterior-posterior and medial-lateral directions in the cadaver bones. Statistical analysis was performed on the data collected, and this data was then used to create a biomechanical model to evaluate the load transmission. METHOD: Measurements in anterior-posterior and medial-lateral directions were performed on human, canine, and chimpanzee cadaver lumbar bones to obtain accurate data for the end plate curvatures. Six sets of measurements (on human male-female L4 lower to S1 upper end plates) were performed. A parametric vertebral motion segment model (with and without posterior elements) that includes the experimental curvature information was developed. The characteristic kidney-shaped cross-sectional model was created using a parametric equation. This model was used to perform finite element analyses investigating the effects of the location of maximum curvature on the stress distributions. RESULTS: The measurements for different species showed that the canine and chimpanzees, the quadrupeds, have entirely different curvature of their upper end plates compared with those in humans, the bipeds. Also, the curvatures of the human S1 upper end plates are significantly different from the rest of the vertebrae. This is a very useful piece of information in the comparison of these species. The stress distribution varied as the location of the maximum curvature shifted from the center to a more posterior position. The stresses in the vertebral core were found to decrease, with the shell taking more loads. CONCLUSIONS: This provides essential information for rehabilitation and surgical techniques, including designs for various interbody devices such as fusion cages, bone grafts, and disc prosthesis.

The influence of subdiagnosis on radiographic and clinical outcomes after lumbar fusion for degenerative disc disorders: an analysis of the literature from two decades.

STUDY DESIGN: A critical review of published literature from 2 decades. OBJECTIVE: To critically analyze the literature from 1979 to 2000 in order to examine the influence of subdiagnosis on outcome after fusion for lumbar degenerative disc disorders. SUMMARY OF BACKGROUND DATA: Numerous diagnostic subgroups of degenerative disc disorders exist. Although it is commonly believed that surgical outcomes after lumbar fusion are influenced by these subdiagnoses, there is a paucity of literature demonstrating differences in clinical outcomes or fusion rates among them. As the indications for fusion have been under greater scrutiny recently, this information would be useful in prognosticating outcomes and optimizing patient selection. METHODS: A computer search of the English literature using the keywords "degenerative," "lumbar," and "fusion" was performed. Disorders were organized according to the following subdiagnostic groups: degenerative spondylolisthesis (DDDsp), herniated disc (DH), degenerative scoliosis (DDDsc), stable DDD (DDDs), dynamically unstable DDD (DDDu), and DDD that was not specified as either DDDu or DDDs (DDDn). For each group, the type of instrumentation, fusion location, fusion rate, clinical outcome, and complication rate were recorded in a computer database. Data were pooled by simple summation and statistically analyzed using a chi test or Fisher exact test. RESULTS: Of 244 articles identified, 78 satisfied inclusion criteria with data from 4454 patients recorded. The most common diagnosis was DDDn (50%), followed by DDDsp (25%), DH (14%), DDDu (6%), DDDs (3%), and DDDsc (2%). The DDDn group had a higher fusion rate than DDDsp (P = 0.025), but a lower clinical outcome (P = 0.051). Complication rates were highest in DDDsc, whereas this subdiagnosis also had the best reported clinical outcomes. In comparing individual subgroups, a trend towards higher fusion rate and better clinical outcome was noted in DDDsp cases with instrumentation compared to noninstrumented cases. This trend was reversed for patients in the DDDn group, in whom better clinical outcomes were noted after noninstrumented fusions regardless of a lower fusion rate. CONCLUSIONS: The present data indicate that clinical outcomes and fusion rates statistically differ among the various subgroups of degenerative disc disease. Concerning the use of instrumentation, it appears that it may have greater clinical benefit in patients with DDDsp than DDDn. These findings underscore the importance of delineating specific clinical diagnoses when documenting results of lumbar fusion. This information might also be useful for both selecting surgical candidates and discussing anticipated operative outcomes.

A review of spinal fusion for degenerative disc disease: need for alternative treatment approach of disc arthroplasty?

This article reviews the history of spinal fusion. The most common indication for fusion may be painful disc degeneration although the exact determination of this condition remains controversial. In the analysis of surgical fusion techniques, literature review has documented a higher rate of success in attaining successful fusion than in obtaining excellent clinical outcomes. Significant morbidity can be seen in the performance of spinal fusion. A limited number of patients presently undergoing spinal fusion will be candidates for disc arthroplasty, though indications for spinal arthroplasty are still evolving.

Artificial disc prosthesis: design concepts and criteria.

Clinical and biomechanical objectives of disc arthroplasty are reviewed in this paper. The available literature relative to these criteria for nucleus and total disc replacement where relevant is also reviewed. Clinical criteria include: pain relief, functional recovery, lower morbidity than spinal fusion, shorter recuperation, and ease of implantation and revision. Biomechanical criteria include: preservation of motion in compression-bending and compression-torsion, shock absorption, relief of abnormal stresses within and adjacent to the motion segment, stability, and alignment. A review of devices with these criteria in mind is reported.

Critical analysis of trends in fusion for degenerative disc disease over the past 20 years: influence of technique on fusion rate and clinical outcome.

STUDY DESIGN: Critical analysis of the results reported in published literature. OBJECTIVES: The purpose of this study was to evaluate whether various technical advancements have affected the outcome of lumbar spinal fusion for degenerative disease by critically analyzing the available literature from the past two decades. SUMMARY OF BACKGROUND DATA: To improve fusion rate and clinical outcome, various surgical options for lumbar spinal fusion for degenerative disc disorders have been introduced over the past 20 years. However, an important fundamental question still remains: What has been the impact of these new techniques and innovations on surgical results? METHODS: A comprehensive computer search of the English literature from 1979 to 2000 concerning lumbar/lumbosacral spinal fusion was performed using the keywords degenerative, lumbar, and fusion. RESULTS: Numerous deficiencies were noted in the reviewed literature. Nearly half of the studies failed to specify methodologic design, and documentation of brace use, graft source, fusion location, and fusion rate was missing in 38, 10, 2, and 4 of the 84 articles reviewed, respectively. From the data gathered, a noticeable trend toward the increasing use of internal fixation was noted, accounting for 23% of fusions in the 1980s versus 41% in the 1990s. Despite this trend, an improvement in overall fusion rate or clinical outcome could not be demonstrated. CONCLUSIONS: Numerous technologic advancements in lumbar spine fusion have been made over the past 20 years. Future advances in care are dependent on review of reported results. The numerous deficiencies detected in the analyzed literature herald the necessity for a uniform system of outcomes reporting containing a core of critical demographic, perioperative, and postsurgical information. Although a shift toward a greater use of technology was noted in the published literature, the clinical benefit of this trend remains unclear.