Effect of reverse shoulder design philosophy on muscle moment arms

This study analyzes the muscle moment arms of three different reverse shoulder design philosophies using a previously published method. Digital bone models of the shoulder were imported into a 3D modeling software and markers placed for the origin and insertion of relevant muscles. The anatomic model was used as a baseline for moment arm calculations. Subsequently, three different reverse shoulder designs were virtually implanted and moment arms were analyzed in abduction and external rotation. The results indicate that the lateral offset between the joint center and the axis of the humerus specific to one reverse shoulder design increased the external rotation moment arms of the posterior deltoid relative to the other reverse shoulder designs. The other muscles analyzed demonstrated differences in the moment arms, but none of the differences reached statistical significance. This study demonstrated how the combination of variables making up different reverse shoulder designs can affect the moment arms of the muscles in different and statistically significant ways. The role of humeral offset in reverse shoulder design has not been previously reported and could have an impact on external rotation and stability achieved post‐operatively. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:605–613, 2015.     

Paxillin phosphorylation and integrin expression in osteoblasts infected by Porphyromonas gingivalis

OBJECTIVE: We investigated early biological events initiated by Porphyromonas gingivalis infection of human osteoblasts, focusing on tyrosine-phosphorylation and the expression of key components in focal adhesion and cell signalling. DESIGN: Human primary osteoblasts were challenged for 1h with Porphyromonas gingivalis. Tyrosine-phosphorylation of paxillin and focal adhesion kinase (FAK) was examined by Western blotting. Changes in alpha3- and beta1-integrin mRNA expression were quantified by RT-PCR. RESULTS: Tyrosine-phosphorylation of paxillin was proportional to the size of the Porphyromonas gingivalis inoculum. FAK, a potential kinase for paxillin, was not activated. The amount of alpha3- and beta1-integrins, determined by Western blotting, did not vary significantly, while the corresponding mRNA levels fell significantly when a large bacterial inoculum was used. CONCLUSIONS: These results indicate that Porphyromonas gingivalis infection of osteoblasts in vitro triggers tyrosine-phosphorylation of paxillin but not FAK and modify alpha3- and beta1-integrin mRNA expression. This infection thus appears to have different effects on components with essential roles in focal adhesion (paxillin) and cell signalling (FAK and integrins).     

Phenotype in girls and women with Turner syndrome: Association between dysmorphic features,karyotype and cardio-aortic malformations

Introduction

Turner syndrome (TS) is a genetic disorder characterized by the (partial) absence or a structural aberration of the second sex chromosome and is associated with a variety of phenotypes with specific physical features and cardio-aortic malformations. The objective of this study was to gain a better insight into the differences in dysmorphic features between girls and women with TS and to explore the association between these features, karyotype and cardio-aortic malformations.

Becoming an eCoach: Training therapists in online cognitive-behavioral therapy for chronic pain

Objective

Online cognitive-behavioral therapy (iCBT) is effective in supporting patients’ self-management. Since iCBT differs from face-to-face CBT on several levels, proper training of therapists is essential. This paper describes the development and evaluation of a therapist training based on theoretical domains that are known to influence implementation behavior, for an iCBT for chronic pain.

Tribonucleation of bubbles

We report on the nucleation of bubbles on solids that are gently rubbed against each other in a liquid. The phenomenon is found to depend strongly on the material and roughness of the solid surfaces. For a given surface, temperature, and gas content, a trail of growing bubbles is observed if the rubbing force and velocity exceed a certain threshold. Direct observation through a transparent solid shows that each bubble in the trail results from the early coalescence of several microscopic bubbles, themselves detaching from microscopic gas pockets forming between the solids. From a detailed study of the wear tracks, with atomic force and scanning electron microscopy imaging, we conclude that these microscopic gas pockets originate from a local fracturing of the surface asperities, possibly enhanced by chemical reactions at the freshly created surfaces. Our findings will be useful either for preventing undesired bubble formation or, on the contrary, for “writing with bubbles,” i.e., creating controlled patterns of microscopic bubbles.Elementary considerations show that a bubble will spontaneously disappear unless its radius r is larger than a critical value r_c = 2γ/ΔP, where γ is the surface tension of the liquid and ΔP is the difference between the pressure of the bubble contents and the surrounding liquid (1). Only bubbles larger than r_c can persist and grow by gas diffusion and liquid evaporation. The classical kinetic theory of nucleation (2) shows that, for water, the spontaneous formation of critical bubbles requires either superheats of 212 °C or negative pressures (i.e., tensions) of 140 MPa. Recent experiments have come close to the quantitative verification of these predictions (3, 4), but only at the cost of a great deal of sophistication and ingenuity. It must therefore be concluded that a different mechanism is responsible for the exceedingly commonplace occurrence of bubbles.The seed for the currently accepted explanation was planted by Gernez (5) who, in 1867, hypothesized that bubbles start from a preexisting gaseous nucleus lodged in solid impurities or the walls of the container. An explanation for the stability of these heterogeneous nuclei was later supplied by Harvey et al. (6) who pointed out that the curvature induced by contact with a hydrophobic solid surface would be able to stabilize a gas pocket even in an undersaturated liquid. This “crevice model” of bubble nucleation explains a large number of observations and has been applied to the development of so-called enhanced boiling surfaces (7, 8). Gas bubbles can be further stabilized by the formation of organic skins at their surface (9, 10).Despite these advances, the nucleation phenomenon still exhibits obscure facets, one of which—tribonucleation—is studied in this paper. It has been known for at least half a century that, as noticed by Hayward in 1967 (11), “extremely gentle rubbing” of two solid objects inside a liquid under tension, which is otherwise stable against most forms of mechanical action (e.g., knocking on the container wall or stirring), readily induces nucleation. This tribonucleation is often cited as a plausible source of the microbubbles found in the limbs of humans and animals after physical exercise (12, 13). Campbell (14) and Ikels (15) attributed the nucleation observed in these conditions to the pressure drop induced by the viscous flow in the space between two separating solid surfaces. Indeed, in highly viscous liquids, bubble formation compatible with this picture has been reported (16–18). However, this explanation cannot easily account for the nucleation observed in low-viscosity fluids like water and ethanol, because in many cases the theoretical gap between the solids would have to be smaller than the surface roughness. More strikingly, it cannot account for the key observation by Hayward that bubbles do not nucleate in the case of a rolling motion, but only in the case of a sliding motion between the solids (11), although for the same force and velocity the pressure drop is expected to be twice as large for rolling than for sliding (19). Another instance of bubble nucleation upon solid–solid contact in a low-viscosity liquid was reported by Theofanous et al. (20). These authors were able to reliably nucleate single bubbles by gently bringing into contact two stainless-steel wires in Freon superheated by up to 60 °C.In this paper, we present experiments in which we rub a bead against a wafer submerged in a low-viscosity liquid. We vary the rubbing force and velocity, the temperature, and the materials of the solids. Our approach is to combine macroscopic observations, revealing a threshold for the rubbing-induced nucleation, with microscopic observations at the smallest scales of the problem: that of the apparent (Hertz) contact between the solids and that of the roughness tips where the actual contact is realized.