Evaluation of the fixation and strength of a "rescue" revision pedicle screw.

One potential complication of pedicle screw instrumentation is long-term nerve root irritation, most commonly resulting from medial or inferior screw malpositioning. This study evaluated the pullout strength and fatigue strength properties of a novel "rescue" revision screw designed to reduce the sequelae of medial screw malpositioning by eliminating threads along the section of the screw corresponding to the pedicular region. The results of this study revealed that a rescue screw with threads eliminated from one half of its circumference provided comparable pullout strength to fully threaded pedicle screws in cadaveric specimens. In addition, mechanical testing of the rescue screw did not show a decrease in fatigue strength characteristics compared with controls. These results suggest that the rescue screw may offer a way to decrease nerve root irritation caused by canal impingement without jeopardizing the overall strength of the spinal construct.