Multi-disciplinary Psychiatric Case Management Model in Hong Kong: Service Coverage and Risk Stratification.

INTRODUCTION: Community mental health services in Hong Kong follow a multi-disciplinary case management model. We investigated whether at-risk patients received higher intensity care and whether risk stratification concorded between personalised care programmes and integrated community centres of mental wellness. METHODS: Records of all patients in North Lantau and Mongkok districts who received case management services (from personalised care programmes and/or integrated community centres of mental wellness) between 1 April 2014 and 30 June 2015 were reviewed. Patients' levels of risk, demographic data, and clinical characteristics were analysed. RESULTS: Identified at-risk patients received high-intensity care from personalised care programmes and integrated community centres of mental wellness. Case management was coordinated between the Hospital Authority and non-government organisations. However, risk stratification did not correlate with assessment rating scores of psychopathology or psychosocial functioning. Assessment rating scales appear unsuitable to provide any optimal cut-off scores for risk stratification. CONCLUSIONS: Risk stratification should be a structured clinical judgement based on comprehensive and accurate information of protective and risk factors, rather than relying on cut-off scores of assessment rating scales.

Analysis of a retrieved UHMWPE acetabular cup crosslinked in air with 1000 kGy of gamma radiation.

The oxidation and degradation that accompany high dose gamma irradiation in air for crosslinking and sterilization are important because they could affect the clinical performance of polyethylene total joint implants. We report a clinical case of a 1000 kGy gamma-irradiated, highly crosslinked ultra-high molecular weight polyethylene acetabular cup retrieved 24 years postoperatively. Performance evaluations included absorbed radiation dose, total wear penetration, average wear rate, crystallinity, oxidation, and equibiaxial tensile properties. A retrieved acetabular cup of the same grade of polyethylene but gamma-sterilized using a conventional dose was used as control. The highly crosslinked and control cups took in about 1300 and 30 kGy of radiation, respectively, as measured using a trans-vinylene index. Direct dimensional measurements revealed average wear rates of the highly crosslinked and control cups were 0.04 and 0.06 mm/year, respectively. The oxidation index of the highly crosslinked cup was very high (0.679), but equivalent to that of a 1000 kGy irradiated reference cup. The retrieved highly crosslinked cup showed much higher equibiaxial ultimate tensile strength than the retrieved control cup. Based on these observations, the increased wear resistance and equibiaxial tensile properties that resulted from extensive crosslinking in the presence of air were partially offset by the adverse effects caused by immediate oxidation during the process.

Accelerated aging studies of UHMWPE. I. Effect of resin, processing, and radiation environment on resistance to mechanical degradation.

The resin and processing route have been identified as potential variables influencing the mechanical behavior, and hence the clinical performance, of ultra-high molecular weight polyethylene (UHMWPE) orthopedic components. Researchers have reported that components fabricated from 1900 resin may oxidize to a lesser extent than components fabricated from GUR resin during shelf aging after gamma sterilization in air. Conflicting reports on the oxidation resistance for 1900 raise the question of whether resin or manufacturing method, or an interaction between resin and manufacturing method, influences the mechanical behavior of UHMWPE. We conducted a series of accelerated aging studies (no aging, aging in oxygen or in nitrogen) to systematically examine the influence of resin (GUR or 1900), manufacturing method (bulk compression molding or extrusion), and sterilization method (none, in air, or in nitrogen) on the mechanical behavior of UHMWPE. The small punch testing technique was used to evaluate the mechanical behavior of the materials, and Fourier transform infrared spectroscopy was used to characterize the oxidation in selected samples. Our study showed that the sterilization environment, aging condition, and specimen location (surface or subsurface) significantly affected the mechanical behavior of UHMWPE. Each of the three polyethylenes evaluated seem to degrade according to a similar pathway after artificial aging in oxygen and gamma irradiation in air. The initial ability of the materials to exhibit post-yield strain hardening was significantly compromised by degradation. In general, there were only minor differences in the aging behavior of molded and extruded GUR 1050, whereas the molded 1900 material seemed to degrade slightly faster than either of the 1050 materials.

Accelerated aging studies of UHMWPE. II. Virgin UHMWPE is not immune to oxidative degradation.

In Part I of this series, we showed that aging at elevated oxygen pressure is more successful at increasing the depth to which degradation occurs although it, too, generally causes greater degradation at the surface than at the subsurface. Therefore we hypothesized that thermal degradation alone, in the absence of free radicals, could be sufficient to artificially age UHMWPE in a manner analogous to natural aging. In the present study, virgin and air-irradiated UHMWPE (extruded GUR 1050 and compression-molded 1900) were aged up to 4 weeks at elevated oxygen pressure, and the mechanical behavior at the surface and subsurface was examined. All the materials were substantially degraded following 4 weeks of aging, but the spatial variations in the nonirradiated materials more closely mimicked the previously observed subsurface peak of degradation seen in naturally aged UHMWPE following irradiation in air. This aged material could provide a more realistic model for subsurface mechanical degradation, making it suitable for further mechanical testing in venues such as wear simulation.

Interlaboratory validation of oxidation-index measurement methods for UHMWPE after long-term shelf aging.

An international oxidation index standard would greatly benefit the orthopedic community by providing a universal scale for reporting oxidation data of ultra-high molecular weight polyethylene (UHMWPE). We investigated whether severe oxidation associated with long-term shelf aging affects the repeatability and reproducibility of area-based oxidation index measurement techniques based on normalization with the use of 1370- or 2022-cm(-1) infrared (IR) absorption reference peaks. Because an oxidation index is expected to be independent of sample thickness, subsurface oxidation was examined with the use of both 100- and 200-microm-thick sections from tibial components (compression-molded GUR 1120, gamma irradiated in air) that were shelf aged for up to 11.5 years. Eight institutions in the United States and Europe participated in the present study, which was administered in accordance with ASTM E691. On average, the 100-microm-thick samples were associated with significantly greater interlaboratory relative standard uncertainty (40.3%) when compared with the 200-microm samples (21.8%, p = 0.002). In contrast, the intralaboratory relative standard uncertainty was not significantly affected by the sample thickness (p = 0.21). The oxidation index method did not significantly influence either the interlaboratory or intralaboratory relative standard uncertainty (p = 0.32 or 0.75, respectively). Our interlaboratory data suggest that with the suitable choice of specimen thickness (e.g., 200 microm) and either of the two optimal oxidation index methods, interlaboratory reproducibility of the most heavily oxidized regions in long-term shelf-aged components can be quantified with a relative standard uncertainty of 21% or less. Therefore, both the 1370-cm(-1) and the 2022-cm(-1) reference peaks appear equally suitable for use in defining a standard method for calculating an oxidation index for UHMWPE.

Interlaboratory studies to determine optimal analytical methods for measuring the oxidation index of UHMWPE.

Fourier transform infrared spectroscopy has emerged as the technique of choice for the quantification of oxidation in ultra-high molecular weight polyethylene used in orthopedic implants. We initiated interlaboratory studies to determine the method of normalization, hence quantification, that provided the highest level of reproducibility across multiple institutions. The goal of this research was to identify optimal normalization methods that minimize the experimental uncertainties associated with interlaboratory reproducibility and intralaboratory repeatability of oxidation index measurements. Test samples were prepared from GUR 4150 HP, gamma irradiated in air, and had a shelf age of two years. Samples were analyzed according to ten oxidation index test methods during two interlaboratory studies, which were conducted in accordance with ASTM E691. Variations in reproducibility and repeatability were evaluated using analysis of variance (ANOVA). The basis of the test methods (peak area-based vs. peak height-based), as well as the normalization method, were both found to be associated with significant differences in reproducibility (p = 0.0006 andp < 0.0001, respectively). Normalization techniques based on the 1370 and 2022cm(-1) peaks areas were found to be the most reproducible methods, and were associated with mean interlaboratory uncertainties of 16.5% and 24.2%, respectively. Repeatability of the test methods was not sensitive to the normalization technique; the mean intralaboratory repeatability for all of oxidation index measurements was found to be 10.2%. The results of this interlaboratory research will be a useful basis for the development of a new oxidation index standard for the orthopedics community.

Interlaboratory reproducibility of standard accelerated aging methods for oxidation of UHMWPE.

During accelerating aging, experimental uncertainty may arise due to variability in the oxidation process, or due to limitations in the technique that is ultimately used to measure oxidation. The purpose of the present interlaboratory study was to quantify the repeatability and reproducibility of standard accelerated aging methods for ultra-high molecular weight polyethylene (UHMWPE). Sections (200 microm thick) were microtomed from the center of an extruded rod of GUR 4150 HP, gamma irradiated in air or nitrogen, and circulated to 12 institutions in the United States and Europe for characterization of oxidation before and after accelerated aging. Specimens were aged for 3 weeks at 80 degrees C in an air circulating oven or for 2 weeks at 70 degrees C in an oxygen bomb (maintained at 503 kPa (5 atm.) of O2) in accordance with the two standard protocols described in ASTM F 2003-00. FTIR spectra were collected from each specimen within 24 h of the start and finish of accelerated aging, and oxidation indices were calculated by normalizing the peak area of the carbonyl region by the reference peak areas at 1370 or 2022 cm(-1). The mean relative interlaboratory uncertainty of the oxidation data was 78.5% after oven aging and 129.1% after bomb aging. The oxidation index measurement technique was not found to be a significant factor in the reproducibility. Comparable relative intrainstitutional uncertainty was observed after oven aging and bomb aging. For both aging methods, institutions successfully discriminated between air-irradiated and control specimens. However, the large interinstitutional variation suggests that absolute performance standards for the oxidation index of UHMWPE after accelerated aging may not be practical at the present time.

Continuous family of finite-dimensional representations of a solvable Lie algebra arising from singularities.

A natural mapping from the set of complex analytic isolated hypersurface singularities to the set of finite dimensional Lie algebras is first defined. It is proven that the image under this natural mapping is contained in the set of solvable Lie algebras. This approach gives rise to a continuous inequivalent family of finite dimensional representations of a solvable Lie algebra.

Criterion for biholomorphic equivalence of isolated hypersurface singularities.

Two germs of complex analytic hypersurfaces with isolated singularities are biholomorphically equivalent if and only if they have the same dimension and their moduli algebras are isomorphic.

Index theory for the boundaries of complex analytic varieties.

A result of boundary p-index is presented for a vector bundle on a complex analytic variety with boundary. A characterization of which odd-dimensional, real submanifolds of [unk](N) are boundaries of complex subvarieties (respectively submanifolds) in [unk](N) is given.