A BIOMECHANICAL STUDY OF A CERVICAL-SPINE STABILIZATION DEVICE - ROY-CAMILLE PLATES

Study Design. Three-hole Roy-Camille posterior plates (Howmedica, Inc. , Rutherford, NJ) were used to fix severely destabilized fresh cadaver ic cervical spines. Fixed spine constructs were tested mechanically in flexion-extension and torsion, and the results were compared with the same characteristics in the intact spine before destabilization. Stai nless steel and titanium plates and screws were evaluated. Objectives. To determine if the application of Roy-Camille posterior plates provi ded suitably strong and rigid fixation of a severe, surgically created three-column instability. Summary of Background Data. Controversy sti ll remains regarding the exclusive use of posterior cervical plating i n the face of three-column instability. Posterior plating has been eva luated biomechanically in severely destabilized calf spines; however, posterior plating of similarly destabilized human cadaveric cervical s pines using the Roy-Camille system has not been examined. Methods. The authors chose to lest the main motions of the neck (flexion, extensio n, and torsion) in the intact and the plated state using a servohydrau lic materials testing system. Testing the surgically altered spine bef ore fixation proved to be futile because of drastic instability, which is characteristic of the chosen defect. Once fixed, the spines were t ested, and the rigidity of the constructs were compared with that of t he intact slate. Strength and failure mechanisms were evaluated. Resul ts. The rigidity of the plated spine constructs surpassed that of the intact spines; the stainless steel and titanium systems were mechanica lly equivalent. Thus, application of the Roy-Camille plates of either type dramatically reduced the motion of the unstable spine. Strength o f the fixed spine constructs was limited by screw pull-out at theoreti cally predictable levels of force. Conclusions. Posterior application of Roy-Camille plates can fix cervical spines with severe destabilizin g defects rigidly. Screw pull-out of the most proximal or distal screw was always the mechanism of failure.