Elastic Anisotropy of Trabecular Bone in the Elderly Human Vertebra.

Knowledge of the nature of the elastic symmetry of trabecular bone is fundamental to the study of bone adaptation and failure. Previous studies have classified human vertebral trabecular bone as orthotropic or transversely isotropic but have typically obtained samples from only selected regions of the centrum. In this study, the elastic symmetry of human vertebral trabecular bone was characterized using microfinite element (µFE) analyses performed on 1019 cubic regions of side length equal to 5 mm, obtained via thorough sampling of the centrums of 18 human L1 vertebrae (age = 81.17 ± 7.7 yr; eight males and ten females). An optimization procedure was used to find the closest orthotropic representation of the resulting stiffness tensor for each cube. The orthotropic elastic constants and orientation of the principal elastic axes were then recorded for each cube and were compared to the constants predicted from Cowin's fabric-based constitutive model (Cowin, 1985, "The Relationship Between the Elasticity Tensor and the Fabric Tensor," Mech. Mater., 4(2), pp. 137-147.) and the orientation of the principal axes of the fabric tensor, respectively. Deviations from orthotropy were quantified by the "orthotropic error" (van Rietbergen et al., 1996, "Direct Mechanics Assessment of Elastic Symmetries and Properties of Trabecular Bone Architecture," J. Biomech., 29(12), pp. 1653-1657), and deviations from transverse isotropy were determined by statistical comparison of the secondary and tertiary elastic moduli. The orthotropic error was greater than 50% for nearly half of the cubes, and the secondary and tertiary moduli differed from one another (p < 0.0001). Both the orthotropic error and the difference between secondary and tertiary moduli decreased with increasing bone volume fraction (BV/TV; p ≤ 0.007). Considering only the cubes with an orthotropic error less than 50%, only moderate correlations were observed between the fabric-based and the µFE-computed elastic moduli (R2 ≥ 0.337; p < 0.0001). These results indicate that when using a criterion of 5 mm for a representative volume element (RVE), transverse isotropy or orthotropy cannot be assumed for elderly human vertebral trabecular bone. Particularly at low values of BV/TV, this criterion does not ensure applicability of theories of continuous media. In light of the very sparse and inhomogeneous microstructure found in the specimens analyzed in this study, further work is needed to establish guidelines for selecting a RVE within the aged vertebral centrum.

HCEC pearls and pitfalls: suggested do's and don't's for healthcare ethics consultants.

Members of the Clinical Ethics Consultation Affairs Standing Committee of the American Society for Bioethics and Humanities present a collection of insights and recommendations developed from their collective experience, intended for those engaged in the work of healthcare ethics consultation.

Acetabular polyethylene wear and acetabular inclination and femoral offset.

UNLABELLED: Restoration of femoral offset and acetabular inclination may have an effect on polyethylene (PE) wear in THA. We therefore assessed the effect of femoral offset and acetabular inclination (angle) on acetabular conventional (not highly cross-linked) PE wear in uncemented THA. We prospectively followed 43 uncemented THAs for a minimum of 49 months (mean, 64 months; range, 49-88 months). Radiographs were assessed for femoral offset, acetabular inclination, and conventional PE wear. The mean (+/- standard deviation) linear wear rate in all THAs was 0.14 mm/year (+/- 0.01 mm/year) and the mean volumetric wear rate was 53.1 mm(3)/year (+/- 5.5 mm(3)/year). In THAs with an acetabular angle less than 45 degrees , the mean wear was 0.12 mm/year (+/- 0.01 mm/year) compared with 0.18 mm/year (+/- 0.02 mm/year) in those with a reconstructed acetabular angle greater than 45 degrees . Reproduction of a reconstructed femoral offset to within 5 mm of the native femoral offset was associated with a reduction in conventional PE wear (0.12 mm/year versus 0.16 mm/year). Careful placement of the acetabular component to ensure an acetabular angle less than 45 degrees in the reconstructed hip allows for reduced conventional PE wear. LEVEL OF EVIDENCE: Level II, prospective study. See Guidelines for Authors for a complete description of levels of evidence.

"Like shining from shook foil". A "virtuous organization" is prepared to treat both the body and the soul.

The Catholic health care ministry is about mission, and the role of organizational ethical reflection is to encourage people in the ministry to think about the institutional performance and practice of medicine within a ministry of the Catholic Church. By engaging a creative process that identifies the needs of people served by Catholic health care, institutions are able to mediate the healing and redeeming power of Jesus, thereby creating virtuous organizations. To depict the mission of Catholic health care as an extension of the healing ministry of Jesus is to evoke explicitly Catholic theological language, and such language is appropriate because Catholic health care is a ministry of the Catholic Church. The church itself is the embodiment of the healing and redeeming ministry of Jesus, and the institutional ministries it has created over time need to bear witness to this fundamental reason for their existence.

Fulfilling institutional responsibilities in health care: organizational ethics and the role of mission discernment.

In this paper we highlight the emergence of organizational ethics issues in health care as an important outcome of the changing structure of health care delivery. We emphasize three core themes related to business ethics and health care ethics: integrity, responsibility, and choice. These themes are brought together in a discussion of the process of Mission Discernment as it has been developed and implemented within an integrated health care system. Through this discussion we highlight how processes of institutional reflection, such as Mission Discernment, can help health care organizations, as well as corporations, make critical choices in turbulent environments that further the core mission and values and fulfill institutional responsibilities to a broad range of stakeholders.