Y. Baril, M. Chartrand, V. Brailovski, P. Terriault, Ecole de technologie superieure, Montreal, QC, Canada; R. Cartier, Montreal Heart Institute, Montreal, QC, Canada
Bone binding using cable or wire-like components made of stainless steel or Co-Cr alloys are subject to fixation loosening resulting in fracture dehiscence. A tubular braided structure made of superelastic Ti-Ni alloy, which tends towards a flat form when bent around the bone can solve this problem. The superelastic tubular component maintains positive pressure on the closure site throughout the healing process, even after an abrupt relative movement of the connected bones, thus increasing the overall stability of the fixation. Furthermore, the new device reduces the interface pressure between the bone and the binding component by increasing the contact area. Given the superelastic nature of the new binding component, a metallic sleeve is crimped to retain both ends of the cable with a specially designed installation device. The new bone binding component is also fatigue-resistant. As an example, binding component made of 24 x 0.1 mm filaments can sustain about 1000 cycles of the strain-controlled fatigue testing between 4 and 8% of relative elongation. In-vitro comparative testing of the new binding component and conventional wire suture is performed on a customary testing bench where sutures are installed directly by a surgeon. The bench can apply complex planar loading imitating real conditions of the sternum healing. The results of the comparative testing show that the new system gives an important gain in the residual compressive force between sternum halves following either a disruption event (coughing), or a long-term closure (deep breathing). Finally, the metallic sleeve is found capable of sustaining one and a half time the maximum theoretical force applied on a sternum site during a coughing fit.
Summary: Bone binding using stainless steel or Co-Cr cable or wire components are subject to fixation loosening resulting in fracture dehiscence. A new tubular braided structure made of superelastic Ti-Ni alloy, which tends towards a flat form when bent around the bone is proposed and in-vitro tested. It is shown that the new bone binding component maintains positive pressure on the closure site throughout the healing process, while reducing the interface pressure between the bone and the binding component, thus increasing the overall stability of the fixation.
