Biomechanical Evaluation of Cervical Spine Stabilization Methods Using a Porcine Model

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Abstract
The biomechanical stability of three different methods of cervical spine stabilization was evaluated in a porcine model. Specimens were tested in flexion, extension, and axial rotation. Our goal was to determine if posterior lateral mass plating after anterior reconstruction provided more stability compared with unicortical or bicortical anterior plate fixation after a simulated corpectomy. Previous implant biomechanical evaluations use ligamentous and intervertebral disc disruption models under constrained and nonrepetitive loading. This study examines implant performance using a corpectomy model loaded for multiple cycles, allowing for unconstrained motion. Twenty-one porcine cervical spines were destabilized with a one-level cervical corpectomy and reconstructed with an anterior methacrylate graft. Each construct was stabilized with either an AO Morscher plate system with unicortical, self-locking screws; a Caspar plate with biocortical screws; or two posterior lateral mass plates. Testing with cyclic loads was performed on an MTS machine in flexion, extension, and axial rotation. There was no statistical difference between the two anterior forms of fixation in flexion, extension, or axial rotation. Posterior lateral mass plating was significantly more stable than either anterior construct. Screw loosening was seen more frequently with bicortical Caspar plating. After a single-level cervical corpectomy and idealized grafting, all three surgical constructs provided stability equal to or greater than the intact condition in flexion, extension, and axial rotation. In unstable cervical spine injury patterns involving anterior disruption, this study supports the use of anterior grafting combined with posterior lateral mass plating to achieve maximum stability.

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