Effect of friction and clearance on kinematics and contact mechanics of dual mobility hip implant.

The dual mobility hip implant has been introduced recently and increasingly used in total hip replacement to maintain the stability and reduce the risk of post-surgery dislocation. However, the kinematics and contact mechanisms of dual mobility hip implants have not been investigated in detail in the literature. Therefore, finite element method was adopted in this study to investigate dynamics and contact mechanics of a typical metal-on-polymer dual mobility hip implant under different friction coefficient ratios between the inner and the outer articulations and clearances/interferences between the ultra-high-molecular-weight polyethylene liner and the metal back shell. A critical ratio of friction coefficients between the two pairs of contact interfaces was found to mainly determine the rotating surfaces. Furthermore, an initial clearance between the liner and the back shell facilitated the rotation of the liner while an initial interference prevented such a motion at the outer articulating interface. In addition, the contact area and the sliding distance at the outer articulating surface were markedly greater than those at the inner cup-head interface, potentially leading to extensive wear at the outer surface of the liner

Biomechanical concept and clinical outcome of dual mobility cups.

Dual mobility cup systems in total hip arthroplasty consist of a metal back with a non-constrained liner, in which a constrained standard head articulates. While superior stability of such implants in comparison with standard total hip replacements is assumed, it is the purpose of this study to outline the biomechanical concept of dual mobility cups and to describe implant survival and dislocation rate based on the series published in the English-speaking and Francophone literature. A growing body of evidence indicates reduced dislocation rates in primary and revision total hip arthroplasty and in selected tumour cases. The limited availability of studies evaluating long-term implant survival and existing concerns with regard to increased wear rates and aseptic loosening, leads to the conclusion that such implants have to be used with prudence, particularly in standard primary hip arthroplasty and in young patients

Transport features in layered nickelates: correlation between structure, oxygen diffusion, electrical and electrochemical properties

Oxygen migration is increasingly acknowledged as playing an important role in the ionic transport in mixed conductors and influencing the electrode electrochemical performance. The aim of this work was to establish correlations between the structural and electrical properties of undoped (Ln2NiO4 + δ, Ln = La, Pr) and doped (La1.7M0.3NiO4 + δ, M = Ca, Sr, Ba, La0.85Pr0.85Ca0.3NiO4 + δ, Pr1.7Ca0.3NiO4 + δ) layered nickelates and the oxygen diffusion in these materials to determine what influences their electrochemical response. A new technique for temperature programmed isotope exchange of oxides with C18O2 in a flow reactor was applied to investigate oxygen mobility and surface reactivity in the polycrystalline powder samples which provided the means to experimentally demonstrate the appearance of two channels of oxygen migration in the doped materials via cooperative mechanism and via near-dopant position. The electrochemical performance of the electrodes based on the developed materials was found to exhibit a strong dependence on their oxygen transport characteristics