Failure of the bone-metal interface in posterior spinal instrumentation systems is stili a problem in spinal sur-gery. The posterior pull-out of the upper hooks with or without loss of correction is a relatively common problem postoperatively. We have performed a serial of experiments on the human cadaver thoracolumbar spines for clari-fying the reasons of the upper hook pull-out phenomena. İn these tests, we compared the anatomical pedicie hooks with the non-anatomical pedicie hooks concerning the posterior pull-out strength with Instron Universal Test Machine. Finally, we were able to decide that contact surface width and depth of the hook blade are important fac-tors for the posterior pull-out strength. Because of the contact surface area of the anatomical pedicie hooks are greater than that of nonanatomical pedicie hooks, maximum had to failure of the anotomical hooks is also higher. Except from the effect of the contact surface area of the pedicie hooks on the pull-out strength, rod contouring, careful technique of the hook site preparation and insertion, preoperative evaluation of the patient and accurate selection of the fusion levels, avoidance from the overdistraction intraoperatively, usage of claw construct and supporting the upper hooks with sublaminar wiring are also effective against the postoperative failure of the upper hooks.
Keywords: biomechanics, pedicie hook, pull out strength