Median sternotomy: comparative testing of braided superelastic and monofilament stainless steel sternal sutures.

A new device to reduce the risk of post-operative complications following median sternotomy is proposed, made of a superelastic shape memory alloy and called a braided tubular superelastic (BTS) suture. This study compares the viability of the BTS suture with that of the standard monofilament stainless steel (MSS) suture. A custom test bench was developed to perform comparative testing of the two sternal closure systems. Sternal models made of polyurethane were closed using common wiring configurations. Static and dynamic tensile separation forces, up to a maximum of 1200 N, were then applied to the closed sternums. The MSS and BTS sutures are compared in terms of the force required to open completely the sternum, the compression force at the sternum midline, and the permanent sternum opening. With a smaller sternum opening and a higher tensile separation force, the MSS suture showed greater rigidity than the BTS suture. The BTS suture, however, displayed a better capacity to reapply compression forces at the sternum midline following the repetitive application and release of tensile separation forces. These results confirm the potential of the BTS suture technology, but further studies using cadaveric sterna are needed to attest definitely to the benefits of using the BTS suture to improve bone healing.

Thermomechanical analysis of shape memory devices.

Shape memory alloys (SMA) are being increasingly used in various industrial applications as actuators, connectors, or damping materials. In the medical field, superelastic devices such as eyeglass frames, stents or guide catheters have come to market in the recent years. The design of SMA devices has usually been based on trial and error, since until recently no general simulation model was available to assist application engineers. The purpose of this article is to describe the computational methodology developed, validated and used for several industrial projects at Ecole Polytechnique of Montréal to simulate the thermomechanical behavior of shape memory materials. This new approach includes three main stages: experimental characterization, construction of a nonlinear material law based on dual kriging interpolation and finally, calculation of the thermomechanical response of SMA devices. For complex geometry, finite element analysis is used, but for simple devices such as springs or electrically activated SMA wires, simplified calculation methods are satisfactory. Validation results recently obtained will also be presented, and examples of industrial applications briefly reviewed.

[Traumatic tricuspid insufficiency with a right-to-left shunt and heart luxation]. / Insuffisance tricuspidienne traumatique avec shunt droit-gauche et luxation cardiaque.

Traumatic tricuspid insufficiency (TTI) with a right-to-left shunt through a patent foramen ovale associated with a cardiac herniation was identified in a 39-year-old man with severe hypoxemia. All reported cases of TTI with a right-to-left shunt are reviewed, the technical aspects of repair described and the physiologic mechanisms discussed.