Mechanical stability of thoracolumbar pedicle screw fixation - The effect of crosslinks

Study Design. Pedicle screw fixation for unstable thoracolumbar spine injur ies is relatively new. The effect of one or two crosslinks on rotational an d lateral bending stiffness was studied. Objective. To determine the rotational and bending stiffness values of thor acolumbar fractures fixed by the. AO's internal fixation system with zero, one, or two crosslinks. Methods, Eight embalmed thoracolumbar spine segments. (T12-L2) were instrum ented at T12 and L2 with a pedicle screw-rod system. Rotational stiffness w as determined for 10 cycles to 2.5 degrees, 3.5 degrees, and 5 degrees of r otation, with and without one or two crosslinks, and lateral bending stiffn ess for 10 cycles to 0.25, 0.40, and 0.50 inch. The results showed a clear trend toward increased stiffness with crosslinks. Results. The stiffness values of the two-crosslink construct at 2.5 degrees and 3.5 degrees of rotation were significantly higher than those of the ze ro-crosslink system. Also, the bending stiffness of the two-crosslink const ruct was significantly higher than that of no-crosslink system at all of th e displacements. Conclusions. Rotational stiffness values of the two-crosslink construct wer e significantly higher than those of the zero-crosslink system, at 2.5 degr ees and 3.5 degrees of rotation. Lateral bending stiffness of the two-cross link system was higher than that of the zero-crosslink system at all levels of displacement.