The BSF construct showed stiffness similar to that of the regular construct, encouraging clinical investigation.

IntroductionDuring the last 40 years, surgical correction techniques applied to spinal deformity have progressed radically. Harrington [8], Luque [14], and then Cotrel and Dubousset [6] added successive contributions to these advances using different approaches. Harrington [8] chose a simple distraction, correcting deformation essentially in the frontal plane. Luque [14] obtained this same distraction by translating the spine toward the rods, which were fixed by laminar wires. Cotrel and Dubousset [6] introduced a threedimensional correction and fixation system using open hooks and rods. During the last few years, developments Abstract Disadvantages of thoracic posterior implants and developments in rod contouring in situ led to the design of a new spinal implant: the bipedicular spinal fixation device (BSF). The BSF is composed of two bifid hooks linked by a compression transverse connector and inserted into the costo-vertebral and costotransverse joints. The aim of this biomechanical study was to determine the loading tolerance of the BSF. Three strength tests -a pull-out test, a lateral load-to-failure test and a uniaxial transversal compression test to failure -were performed using six human thoracic spines on an Instron testing device. Specimen evaluation consisted of: bone mineral density (BMD) measurement with the dual-energy X-ray absorptiometry (DEXA) technique, cortical thickness measurements and a morphometric study. The mean values for load-to-failure in the posterior and lateral tests were 324 N and 400 N respectively. The mean value of the uniaxial compression was 988 N. The mean BMD estimated by DEXA was 0.557 g/cm 2 . The BSF loading tolerance was compatible with the in situ rod contouring technique requirements when we considered posterior and lateral pull-out tests. The transversal compression test determined the appropriate and efficient BSF tightening force.