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 cadaveric 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. Stainless steel and titanium plates and screws were evaluated. Objectives. To determine if the application of Roy-Camille posterior plates provided suitably strong and rigid fixation of a severe, surgically created three-column instability. Summary of Background Data. Controversy still remains regarding the exclusive use of posterior cervical plating in the face of three-column instability. Posterior plating has been evaluated biomechanically in severely destabilized calf spines; however, posterior plating of similarly destabilized human cadaveric cervical spines using the Roy-Camille system has not been examined. Methods. The authors chose to test the main motions of the neck (flexion, extension, and torsion) in the intact and the plated state using a servohydraulic materials testing system. Testing the surgically altered spine before fixation proved to be futile because of drastic instability, which is characteristic of the chosen defect. Once fixed, the spines were tested, and the rigidity of the constructs were compared with that of the intact state. Strength and failure mechanisms were evaluated. Results. The rigidity of the plated spine constructs surpassed that of the intact spines; the stainless steel and titanium systems were mechanically equivalent. Thus, application of the Roy-Camille plates of either type dramatically reduced the motion of the unstable spine. Strength of the fixed spine constructs was limited by screw pull-out at theoretically predictable levels of force. Conclusions. Posterior application of Roy-Camille plates can fix cervical spines with severe destabilizing defects rigidly. Screw pull-out of the most proximal or distal screw was always the mechanism of failure.