Biomechanical comparison of anterolateral plate, lateral plate, and pedicle screws-rods for enhancing anterolateral lumbar interbody cage stabilization

Study Design. A repeated measures in vitro flexibility experiment was performed in calf spines. Objectives. To determine the biomechanical differences among three techniques for augmenting stability of an anterolateral lumbar threaded interbody cage. Background. Stand-alone interbody cages are known to inadequately stabilize the spine. Surgeons often add supplementary instrumentation for a more stable construct. Methods. Six L2 - L5 calf spines (L3 - L4 level instrumented) were tested: 1) intact; 2) with a single anterolateral interbody cage; 3) with cage plus anterolateral plating; 4) with cage plus lateral plating; and 5) with cage plus pedicle screw fixation. Specimens were loaded in each anatomic plane quasistatically ( maximum 5.0 Nm). Angular motion was measured stereophotogrammetrically. Results. The stand-alone interbody cage allowed significantly less range of motion than normal during all loading modes except axial rotation. Addition of pedicle screws-rods, anterolateral plate, or lateral plate significantly further reduced range of motion in all planes. Pedicle screws slightly outperformed the anterolateral plate during extension and lateral bending and slightly outperformed the lateral plate during flexion, extension, and left axial rotation ( range of motion differences < 0.65 degrees, P < 0.05). The anterolateral plate outperformed the lateral plate during flexion and extension, whereas the lateral plate outperformed the anterolateral plate during lateral bending ( range of motion difference < 0.57 degrees, P < 0.05). Conclusion. Anterolateral or lateral lumbar plating increases stability significantly compared to stand- alone interbody cage fixation. These findings support anterolateral or lateral plate fixation as a potential clinical alternative to pedicle screws-rods in this role and may obviate the need for combined anterior and posterior approaches when spinal instability exists.