In vitro, biomechanical comparison of an anterior lumbar interbody fusion with an anteriorly placed, low-profile lumbar plate and posteriorly placed pedicle screws or translaminar screws

Study Design. An in vitro biomechanical comparison of anteriorly placed lumbar plates, pedicle screws, and translaminar screws in the anterior lumbar interbody fusion ( ALIF) setting. Objectives. To determine whether an anteriorly placed lumbar plate reduces the flexibility in terms of neutral zone and range of motion of a simulated ALIF, and to compare this reduction in flexibility to that provided by posteriorly placed pedicle screws and translaminar screws. Summary of Background Data. Pedicular and translaminar facet fixation add stability and increase fusion rates, compared with ALIF alone. An anteriorly placed lumbar plate has been introduced to provide stability without the need for a secondary approach. However, this plate has not been evaluated biomechanically. Methods. Seven intact, cadaveric lumbar motion segments were tested to +/- 7.5 Nm in flexion-extension, lateral bending, and axial torsion. Specimens were retested after ALIF, and after subsequent instrumentation with pedicle screws, translaminar screws, and anterior lumbar plates. The range of motion and neutral zone were measured from resulting flexibility curves. Results. Mean ( +/- standard deviation) flexion-extension range of motion for intact segments ( 9.9 degrees +/- 3.1 degrees) was significantly reduced to 7.7 degrees +/- 1.8 degrees after ALIF ( P = 0.02), and was further reduced to 3.0 +/- 0.9 with lumbar plates ( P < 0.001), 1.5 degrees +/- 0.6 degrees with pedicle screws ( P < 0.001), and 0.9 degrees +/- 0.4 degrees with translaminar screws ( P < 0.001). All 3 devices also reduced flexion-extension neutral zone and torsion neutral zone and range of motion, compared with ALIF alone ( P < 0.05). Lumbar plates did not decrease lateral bending range of motion or neutral zone ( P > 0.05), whereas pedicle and translaminar screws did ( P < 0.05). Conclusions. Although not as rigid as pedicle or translaminar screws, anterior lumbar plating does add significant stability to an ALIF and may provide a valuable, single-approach alternative to supplemental posterior fixation.