Adrian Reist

Simulated joint and muscle forces in reversed and anatomic shoulder prostheses.

Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0 degrees to 150 degrees of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90 degrees of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.

Mathematical and numerical analysis of a three-dimensional fluid flow model in glaciology

The main goal of this article is to analyze a three-dimensional model for stress and velocity fields in grounded glaciers and ice sheets including the role of normal deviatoric stress gradients. This model leads to a nonlinear system of stationary partial differential equations for the velocity with a viscosity depending on the stress–tensor but which is not explicitly depending on the velocity. The existence and uniqueness of a weak solution corresponding to this model is established by using the calculus of variations. The approximation of this model is made by a finite element method with piecewise polynomial functions of degree 1 on a tetrahedral mesh and error analysis is performed. Numerical solutions show that the theoretical results we have obtained are almost optimal.

Rotator cuff deficiency associated to total shoulder arthoplasty

INTRODUCTION Glenohumeral osteoarthritis is frequently associated with some amount of degenerative changes in the rotator cuff tendons, especially in the supraspinatus. Consequently, a partial dysfunction of the cuff may be observed after prosthetic shoulder replacement. This situation could preclude the survival of the implant. The aim of this study was therefore to analyze the biomechanical consequences of the supraspinatus deficiency after an anatomic shoulder arthroplasty.

Joint force in reversed shoulder implants

Reversed shoulder implants are being used communly for glenohumeral joint arthritis combined with rotator cuff deficiency (Boileau et al. 2006). The biomechanics of these implants is however still poorly known. Due to the medialization of the rotation centre and the lack of rotator cuff muscles, the joint and muscles forces of the reversed implants are indeed expected to be very different from the classical anatomic implants. Therefore, the goal of this study was to determine the joint force of a reversed prosthesis during abduction, and to compare them with an anatomic one.