[Definition of pedicle malposition. Primary stability and loosening characteristics of pedicle screws in relation to position: spongious anchoring, cortical anchoring, perforation and malposition].

Totally misplaced pedicle screws will lead to major stability problems. There are no publications about the stability behavior of screws, which have no pure trabecular position and perforate the pedicle slightly. Since neurological problems are only described with screws perforating the pedicle medially by at least 4 mm, this question has great relevance concerning the definition of pedicular malposition. Sixty-eight pedicle screws were tested in human cadaveric lumbar spines. Their vertical path was measured at the beginning and end of 1000 sinusoidal cycles with a force amplitude of 160 N. They were divided into four groups according to their screw position as mentioned in the title. We found no significant differences in primary stability or loosening between the groups. The cortical contact and perforation groups had slightly better results, which were not significant in comparison to the other two groups.