The Biomechanical Advantage of Adding a Single Pair of Thoracolumbar Pedicle Screws to Luque-Galveston Construct Stability

· (a – Medtronic Sofamor Danek)

This study determined the increases in biomechanical stability of Luque-Galveston instrumentation when a single pair of L1 pedicle screws was added. Standard instrumentation was passed between L1 and the sacrum. Bilateral 6.5mm poly-axial pedicle screws were placed at L1 with cross links at L2 and L5. The proximal spine was attached via a cantilever apparatus for 20 cycle bending moments at +5Nm or an axially aligned fixture for torsional testing at at 1º per second between + 2Nm (MTS 858 machine). L1 screws were randomly tightened or left loosely connected to the rods to allow sliding. Construct stiffness was analyzed using a one-way ANOVA (p<0.05). Locked flexion-extension stiffness (1.45+0.49Nm/deg) was statistically greater (p<0.01) than for unlocked (0.88+0.15Nm/deg). Locked torsional stiffness (2.48+0.57Nm/deg) was statistically greater (p<0.01) than for unlocked (1.44+0.35Nm/deg). Thoracolumbar (L1) pedicle screws rigidly fix the length of the spine; which decreased axial motion due to flexion-extension and torsional loading, and increased the resultant

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