Background: After thoracolumbar corpectomy, standard anterolateral instrumentation may consist of dual rods with cross-connectors. However, when the vertebral bodies are small or involved with disease, only one rod may be possible.

Objective: To compare the biomechanics of an in-vitro L1 corpectomy model using one rod, two rods, or two rods with two cross-connectors.

Methods: Eight fresh frozen human cadaveric spines were potted from T9 to L3. Pure moments of 1.5, 3, and 4.5 Nm were applied, and motion of the spine measured using three infrared cameras. Loads were applied in flexion and extension, right and left lateral bending, and right and left axial rotation. Each spine was first tested in the intact state. After performing an L1 corpectomy and replacement with a carbon fiber reinforced polymer cage, three constructs were tested: single rod (1R), dual rod (2R), and dual rod with two transverse connectors (CC).

Results: ANOVA suggests significant main effects of load (p<0.0001), axis (p=0.022), construct (p=0.0019), and individual spine (p<0.0001). Overall, the single-rod construct is significantly less rigid than the intact spine in axial rotation. There is no significant difference between the intact spine and either the dual-rod construct or the dual-rod-cross-connector construct.

Conclusion: In our in-vitro model of anterior spinal stabilization following corpectomy and grafting, a single rod construct is significantly less rigid than the intact spine. Addition of a second rod returns the rigidity of the spine to the intact state. A dual rod cross-connector construct is significantly more rigid than a single rod construct.

From: An In-Vitro Biomechanical Comparison of Single Rod, Dual Rod, and Dual Rod with Transverse Connector in Anterior Thoracolumbar Instrumentation by Reddy et al

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