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Enhanced primary stability through additional cementable cannulated rescue screw for anterior thoracolumbar plate application.

OBJECT
The authors conducted a study to investigate the biomechanical in vitro influence of a new anchorage system for fixation of anterior stabilization devices and the possibility of using additional cement after screw insertion to compensate for poor bone quality. The incidence of osteoporosis-related fractures has increased nearly twofold in the last decade. Because of problems associated with anterior screw fixation such as loosening, mechanical failure, and the weakness of osteoporotic bone, current surgical treatments of vertebral body (VB) fractures are problematic. This is due to poor fixation strength of anterior screws in the adjacent segments. The aim of this study was to determine whether a new cemented and uncemented VB screw provides improved primary stability following placement of anterior instrumentation in cases of fracture.


METHODS
The primary stability-related parameters of a new uncemented/cemented screw were compared with those of conventional monocortical screw fixation in a burst fracture model in which strut graft and anterior overbridging instrumentation were used. The use of the new uncemented screw improved the range of motion (ROM) of the stabilized spine in flexion-extension by approximately 22%, in rotation by 20%, and in lateral bending by 15%. Additional cementation improved the ROM by approximately 41% in flexion-extension, 32% in rotation, and 30% in lateral bending compared with conventional monocortical screw fixation.


CONCLUSIONS
The new cannulated screw improves fixation strength and primary stability parameters. It is useful in the initial treatment of fractures in cases of poor bone quality and as a rescue device if previously inserted screws do not remain securely in place.