A pedicle screw bridging device for posterior segmental fixation of the spine: preliminary mechanical testing results

Mechanical assessment of a new pedicle screw bridge device for spinal surgery is reported. Results are given for a series of single tests to failure and a fatigue cyclical loading test. Comparative testing of torsional and lateral bending resistance on three surgical spinal fixation systems was carried out: Luque, wired Hartshill rectangle and pedicle screwed bridge with Hartshill rectangle and pedicle screwed bridge with Hartshill rectangle. The results show the superiority of the bridged Hartshill in both rotational and lateral bending resistance. The new bridge device could also improve the versatility of the Hartshill system to cover a wider spectrum of spinal fixations. A test to determine the axial pull-out strength of three screw designs was undertaken. The differences between the forces needed were insignificant. At failure a cylinder of bone tissues greater than the major diameter of the screw was pulled out without breaking the bone.