A biomechanical analysis of decompression and reconstruction methods in the cervical spine. Emphasis on a carbon-fiber-composite cage.

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Abstract
Biomechanical analysis of three different patterns of instability--that created by fifth and sixth cervical anterior discectomy, that created by one-level (fifth cervical) anterior corpectomy, and that created by two-level (fourth and fifth cervical) corpectomy--was performed in eighteen calf spines. Three types of anterior reconstruction--anterior iliac strut bone-grafting, use of an anterior carbon-fiber-composite cage packed with cancellous bone graft, as well as use of polymethylmethacrylate anteriorly--were cyclically tested in axial compression, torsion, and flexion-extension. Each of these types of reconstruction was also tested with supplemental posterior wire stabilization (the triple-wire technique of Bohlman). Regardless of the type of anterior instability, the carbon-fiber-reinforced cage packed with cancellous bone graft was more rigid than the iliac bone graft alone. The cage resulted in good stiffness in the axial compression and rotation tests and was the most rigid construct in the flexion-extension tests. The superior aspect of the polymethylmethacrylate constructs loosened at the bone-cement interface in eight of the twelve specimens during flexion-extension testing. The addition of the supplemental posterior wiring to the anterior constructs provided additional rigidity in flexion-extension testing. In this study, the carbon-fiber-reinforced cage composite showed great biomechanical potential as an alternative to a bone strut alone or to polymethylmethacrylate in anterior cervical reconstruction. When a major amount of anterior decompression is indicated, supplemental posterior wiring should be considered.