Three-dimensional finite element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems

Glenoid component loosening is the dominant cause of failure in total shoulder arthroplasty. It is presumed that loosening in the glenoid is caused by high stresses in the cement layer. Several anchorage systems have been designed with the aim of reducing the loosening rate, the two major categories being "keeled" fixation and "pegged" fixation. However, no three-dimensional finite element analysis has been performed to quantify the stresses in the cement or to compare the different glenoid prosthesis anchorage systems. The objective of this study was to determine the stresses in the cement layer and surrounding bone for glenoid replacement components. A three-dimensional model of the scapula was generated using CT data for geometry and material property definition. Keeled and pegged designs were inserted into the glenoid, surrounded by a 1-mm layer of bone cement. A 90 deg arm abduction load with a full muscle and joint load was applied, following van der Helm (1994). Deformations of the prosthesis, stresses in the cement, and stresses in the bone were calculated. Stresses were also calculated for a simulated case of rheumatoid arthritis (RA) in which bone properties were modified to reflect that condition. A maximum principal stress-based failure model was used to predict what quantity of the cement is at risk of failure at the levels of stress computed. The prediction is that 94 percent (pegged prosthesis) and 68 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival in normal bone. In RA bone, however, the situation is reversed where 86 percent (pegged prosthesis) and 99 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival. Bone stresses are shown to be not much affected by the prosthesis design, except at the tip of the central peg or keel. It is concluded that a "pegged" anchorage system is superior for normal bone, whereas a "keeled" anchorage system is superior for RA bone.     

Design and validation of a machine for reproducible precision insertion of femoral hip prostheses for preclinical testing

Preclinical testing of orthopaedic implants is becoming increasingly important to eliminate inferior designs before animal experiments or clinical trials are begun. Preclinical tests can include both laboratory bench tests and computational modeling. One problem with bench tests is that variability in prosthesis insertion can significantly influence the failure rate; this makes comparison of prostheses more difficult. To solve this problem an insertion method is required that is both accurate and reproducible. In this work, a general approach to the insertion of hip prostheses into femoral bones is proposed based on physically replicating an insertion path determined using computer animation. As a first step, the seated prosthesis position is determined from templates and femur radiographs. Three-dimensional images of the prosthesis and bone are then imported into computer animation software and an insertion path in the coronal plane is determined. The insertion path is used to determine the profile of a cam. By attaching the prosthesis to a carriage, which is pneumatically moved along this cam, the required insertion motion of the prosthesis in the coronal plane can be achieved. This paper describes the design and validation of the insertion machine. For the validation study, a nonsymmetric hip prosthesis design (Lubinus SPII, Waldemar Link, Germany) is used. It is shown that the insertion machine has sufficient accuracy and reproducibility for preclinical mechanical testing.     

Bin2, a functionally nonredundant member of the BAR adaptor gene family

BAR family proteins are a unique class of adaptor proteins characterized by a common N-terminal fold of undetermined function termed the BAR domain. This set of adaptors, which includes the mammalian proteins amphiphysin and Bin1 and the yeast proteins Rvs167p and Rvs161p, has been implicated in diverse cellular processes, including synaptic vesicle endocytosis, actin regulation, differentiation, cell survival, and tumorigenesis. Here we report the identification and characterization of Bin2, a novel protein that contains a BAR domain but that is otherwise structurally dissimilar to other members of the BAR adaptor family. The Bin2 gene is located at chromosome 4q22.1 and is expressed predominantly in hematopoietic cells. Bin2 is upregulated during differentiation of granulocytes, suggesting that it functions in that lineage. Bin2 formed a stable complex in cells with Bin1, but not with amphiphysin, in a BAR domain-dependent manner. This finding indicates that BAR domains have specific preferences for interaction. However, Bin2 did not influence endocytosis in the same manner as brain-specific splice isoforms of Bin1, nor did it exhibit the tumor suppressor properties inherent to ubiquitous splice isoforms of Bin1. Thus, Bin2 appears to encode a nonredundant function in the BAR adaptor gene family.     

Analysis of the segmental stability of helical peptides by isotope-edited infrared spectroscopy

Isotope-edited infrared spectroscopy has the ability to probe the segmental properties of long biopolymers. In this work, we have compared the infrared spectra of a model helical peptide ((12)C) Ac-W-(E-A-A-A-R)(6)-A-NH(2), described originally by Merutka et al. (Biochemistry 1991;30:4245-4248) and three derivatives that are (13)C labeled at the backbone carbonyl of alanines. The locations of six isotopically labeled alanines are at the N-terminal, C-terminal, and the middle two repeating units of the peptide. Variation in temperature from 1 degrees to 91 degrees C transformed the peptides from predominantly helical to predominantly disordered state. Amplitude and position of the infrared amide I' absorption bands from (12)C- and (13)C-labeled segments provided information about the helical content. Temperature dependence of infrared spectra was used to estimate segmental stability. As a control measure of overall peptide stability and helicity (independent of labeling), the temperature dependence of circular dichroism spectra in the far-UV range at identical conditions (temperature and solvent) as infrared spectra was measured. The results indicate that the central quarter of the 32 amino acids helix has the maximal helicity and stability. The midpoint of the melting curve of the central quarter of the helix is 5.4 +/- 0.8 degrees C higher than that of the termini. The N-terminal third of the helix is more helical and is 2.0 +/- 1.4 degrees C more stable than the C-terminus.     

A model for multiexponential tryptophan fluorescence intensity decay in proteins.

Tryptophan fluorescence intensity decay in proteins is modeled by multiexponential functions characterized by lifetimes and preexponential factors. Commonly, multiple conformations of the protein are invoked to explain the recovery of two or more lifetimes from the experimental data. However, in many proteins the structure seems to preclude the possibility of multiple conformers sufficiently different from one another to justify such an inference. We present here another plausible multiexponential model based on the assumption that an energetically excited donor surrounded by N acceptor molecules decays by specific radiative and radiationless relaxation processes, and by transferring its energy to acceptors present in or close to the protein matrix. If interactions between the acceptors themselves and back energy transfer are neglected, we show that the intensity decay function contain 2N exponential components characterized by the unperturbed donor lifetime, by energy transfer rates and a probability of occurrence for the corresponding process. We applied this model to the fluorescence decay of holo- and apoazurin, ribonuclease T1, and the reduced single tryptophan mutant (W28F) of thioredoxin. Use of a multiexponential model for the analysis of the fluorescence intensity decay can therefore be justified, without invoking multiple protein conformations.     

Isoflavonoids of Dalbergia ecastophyllum

In addition to the known isoflavonoids formononetin and (±)-mucronulatol, the vine wood of Dalbergia ecastophyllum (L.) Taub. contains (R)-8-demethylduartin. The assigned structure (II) has been confirmed by synthesis. Its absolute stereochemistry is deduced from examination of the CD spectrum of its acetate.     

Blowing in the wind? Identity, materiality, and the destinations of human ashes

This article asks whether the recent UK-based practice of removing ashes from crematoria has led to entirely new, innovative rituals of disposal, or whether contemporary practice is an appropriation of late nineteenth-century Romantic values and beliefs. Drawing on findings from a major empirical study among both professionals and lay people involved in the removal of ashes, it explores the potentiality of ash remains as a mobile material residue of the corpse, and considers whether they enable disposal strategies which no longer reflect concerns with space and place – particularly those associated with traditional burial grounds.