Effects of a cervical compression plate on graft forces in an anterior cervical discectomy model.

Abstract

An ex vivo biomechanical study using an instrumented distractor and load cells in a cadaveric multilevel discectomy construct was conducted. To demonstrate that a dynamic cervical plate can be used to increase compressive load on interbody grafts in a multilevel discectomy specimen. Cervical plating is used to decrease pseudarthrosis, graft extrusion, and graft subsidence in multilevel anterior discectomy procedures. Plating may shield a graft as it resorbs and may reverse normal loading mechanics. Preoperative disc height was measured in five cadaveric spines. A three-level discectomy was performed. The disc spaces were opened with a distractor instrumented with strain gauges to allow the introduction of spacers fixed rigidly to subminiature load cells. Distraction was removed, and immediate compressive forces were measured by the load cells. An external compressor was applied followed by a cervical plate. The specimen then was placed in a loading frame, and final compressive forces were measured. A mean 116.5 N distractive force was required to insert grafts into all three levels. No significant relation between preoperative disc height and distractive or compressive forces was noted. Release of the distractor yielded an immediate compressive load on each graft. The compressor significantly increased graft compression. After plate application, the external compressor was removed. Graft compression did not significantly decrease. In the loading frame, an increase in compressive load was noted. Preoperative disc height was not related to the compressive force on the graft. Compressive force can be increased and maintained with a dynamic plating system.