BIOMECHANICAL COMPARISON OF SELF-STABILISING FORCEPS USED FOR POSTERIOR FIXATION OF THE SPINE: EVALUATION OF BILATERAL FORCEPS

Abstract

Purpose: As proposed by Marnay, posterior fixation of the spine with self-stabilising forceps facilitates the operative procedure. These forceps enable lamolaminal, pediculolaminal, or pediculotransverse fixations. We developed a method for posterior fixation of the spine where a self-stabilising forceps links the lateral forceps hook to a medial hook allowing a bilateral hold on the segment for better fixation and correction. The aim of this work was to evaluate the contribution of the self-stabilising forceps compared with standard hooks during reduction movements.

Material and methods: Pull-out tests were conducted on five different holds using a supratransversal hook, a sublaminal hook, a pediculotransversal forceps, and a pediculolaminal forceps (Spine-Evolution), and a bipediculolaminal hook mounted on two vertebrae (Sofamor-Danek). The tests were performed on anatomic specimens. The test procedure was a reduction of a kyphosis of the upper part to the tested segment. Fourteen measurements were made for each implant.

Results: Pull-out force (N) was (mean, range): supratrans-versal hook (24, 8-40) < pediculotransvers forceps (154, 80-280) < supralaminal hook (360, 120–560) < pediculolam-inal forceps (491, 440–550) < bipediculolaminal forceps on two vertebrae (711, 400–800). The differences were significant.

Discussion: These results must be considered under the experimental conditions. Fixation with a supratransversal hook did not produce a reliable hold. The pediculotransversal forceps failed in one case due to fracture of a weak transversal mass. The supralaminal hook exhibited more consistent pull-out resistance. In most of the cases, pull-out occurred by fracture of the posterior arch. The bilateral self-stabilising forceps demonstrated the greatest pull-out resistance. During the five tests made with this forceps, the test was limited by the weakness of the osteosynthesis rods used so the maximal resistance to pull-out could not be measured (> 800 N).

Conclusion: The self-stabilising pediculolaminal forceps provides greater pull-out resistance than hooks alone. The self-stabilizing bipediculolaminal forceps allows a new surgical strategy for segmentary fixation with promising potential.