STABILITY OF DIFFERENT WIRING TECHNIQUES IN SEGMENTAL SPINAL INSTRUMENTATION - AN EXPERIMENTAL-STUDY

The pullout force of sublaminar and transspinous wires for segmental i nstrumentation which had been inserted into different segments of huma n cadaver spines were campared. Four different types of wiring were te sted: single and double sublaminar wires, button-wires according to Dr ummond's technique and button-wires with the additional use of two cri mps for each spinous process. A total of 50 tests were performed. In a ll attempts the bone proved to be the limiting factor. None of the 300 fixed wires failed. Typical types of fractures appeared with differen t wiring techniques. There was no statistically significant difference between the sublaminar wiring techniques tested. However, there were significant differences between sublaminar and transspinous wiring. Th e transspinous techniques achieved between 30% and 45% of the pull-out strength of sublaminar techniques. The forces decreased with increasi ng cranialisation. In all techniques the values in the upper segment ( D5-D3) were almost half those of the lower segment (L5-L3). The differ ences of the transspinous techniques increased cranially, in favour of the technique with additional crimps. Thus, the crimps have the stron gest effect on weak spinous processes. This study demonstrates that in non-dynamic testing, the stability of the bone and not the type of wi ring is the limiting parameter in segmental spinal stabilisation. As t he wires are inserted in different areas, the transspinous technique s hows significantly lower tension forces in comparison with sublaminar wiring.