A COMPARISON OF CERVICAL PLATING SYSTEMS UNDER PURE BENDING AND TORSIONAL LOADING

Abstract

Introduction: Various plating devices and screw systems are available for single and multi-level cervical fusions. Recent reports regarding screw migration under torsional load and a “windshield wiper effect” has brought to light the importance of plate and screw design as well as the choice of graft.

Aim: This study examined the relative stability of cervical plating systems under pure bending and axial-torsional fatigue using the Cloward type graft.

Methods: Five fresh-frozen human cervical and 10 porcine spines assessed by dual-energy x-ray absorptiometry (DEXA) scanning and then reconstructed at the C_2–3 and levels using the anterior Cloward technique. C_4–5 Two different plating systems (a solid plate and a hollow plate) were used and alternated between the C2–3 and C4–5 levels. Strain gauges placed on the plates themselves. The systems were subjected to pure bending and torsional loading.. Five kilogram loads were used to apply bending moments to the spine and did not differ between the two systems evaluated. Bending moments and displacement angles were recorded for the pure bending loading regime and torque versus time was recorded for the torsional fatigue loading.

Results: Strain gauge analysis revealed minimal strains on the plates under the loading conditions. Torque versus time was measured, and the decay constant was calculated from the decay curves. The hollow plating system decayed quicker than the solid plating system. Angular displacement under pure bending was minimal. The hollow system plate system resisted greater torque compared with the solid system. The decay curves eventually reached an asymptote for the both systems. This implied that the systems become stable under fatigue loading. The X-rays illustrated no failure at the screw/ bone interface (i.e. No “wiper” effect) after torsional fatigue.