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

STUDY

DESIGN

Pedicle screw fixation for unstable thoracolumbar spine injuries is relatively new. The effect of one or two crosslinks on rotational and lateral bending stiffness was studied.

OBJECTIVE

To determine the rotational and bending stiffness values of thoracolumbar fractures fixed by the AO's internal fixation system with zero, one, or two crosslinks.

METHODS

Eight embalmed thoracolumbar spine segments. (T12-L2) were instrumented at T12 and L2 with a pedicle screw-rod system. Rotational stiffness was determined for 10 cycles to 2.5 degrees, 3.5 degrees, and 5 degrees of rotation, with and without one or two crosslinks, and lateral bending stiffness 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 zero-crosslink system. Also, the bending stiffness of the two-crosslink construct was significantly higher than that of no-crosslink system at all of the displacements.

CONCLUSIONS

Rotational stiffness values of the two-crosslink construct were significantly higher than those of the zero-crosslink system, at 2.5 degrees and 3.5 degrees of rotation. Lateral bending stiffness of the two-crosslink system was higher than that of the zero-crosslink system at all levels of displacement.