BACKGROUND CONTEXT Low fusion rates and cage subsidence have been reported as the main drawbacks of lumbar fixation with stand-alone interbody cages. However, recent new cage placement techniques preserve the spinal structures that contribute to spinal stability. The biomechanical effect of the addition of posterior instrumentation to interbody instrumented segment was evaluated using cadaver spine and validated computational model. PURPOSE To evaluate the mechanical support/stability of different interbody fixation techniques in lumbar spinal segments and the effect of posterior instrumentation support on altering kinematics and load sharing of stand-alone cage instrumented segments. STUDY DESIGN/SETTING A combined cadaveric and finite element (FE) modeling study. PATIENT SAMPLE N/A OUTCOME MEASURES Segmental range of motion and load sharing on vertebral endplate. METHODS An in vitro experiment using seven fresh human cadaveric spines was performed to test intact versus instrumented spines instrumented with stand-alone lateral interbody cages (LIF) and cage instrumented spine supplemented with posterior pedicle screw-rod fixation (360 construct). A Finite element (FE) model of L4-L5 motion segment was also created and validated against cadaveric kinematic data then used to simulate different surgical setting as in the in vitro experiment. The validated model was then used to evaluate the stability of stand-alone lateral (LIF), transforaminal (TLIF) and anterior (ALIF) fixation constructs. The stand-alone cage models were then stabilized with posterior instrumentation and reassessed. To simulate anatomical loading, all FE models of were subjected to a 400N compressive pre-load followed by an 8Nm bending moment. The segmental kinematics and the load sharing at the inferior endplate were computed and compared among cases. RESULTS The segmental ROM for the intact cadaveric segment was 3.1±0.9(Ext), 7.1±2.8(Flex), 5.0±1.7(LB), 5.0±2.1(RB), 2.6±1.8(LR), 2.4±1.7(RR) degrees. The FE model predicted ranges of motion close to the average and within one standard deviation of the cadaver experiment. For the LIF instrumented in vitro cases the motion ranged from 1.7±1.3 (Ext), 1.8±1.0 (Flex), 1.7±1.1 (LB), 1.7±1.0 (RB), 0.9±0.5 (LR), 1.3±0.9 (RR) for cage alone and 0.8±0.5 (Ext), 0.8±0.7 (Flex), 0.9±0.5 (LB), 0.8±0.4 (RB), 0.5±0.4 (LR), 0.6±0.3 (RR) for 360 construct cases. The predicted reduction in motion for ALIF and LIF stand-alone cage cases in axial rotation (AR) and lateral bending (LB) were similar to those with the addition of posterior instrumentation (∼90%). The reduction in sagittal motion for ALIF and LIF ranged from 66% to 86% while the corresponding value for the 360 construct was ∼90%. The peak stresses in extension for the LIF stand-alone cage were somewhat higher than the posterior instrumented cases, but not significant. Stresses for the ALIF cages were similar to the 360 construct designs. Stresses for the ALIF and LIF cages in LB and AR were similar to the posterior instrumented constructs. CONCLUSIONS Our data suggest that stand-alone cages using ALIF and LIF techniques are effective in providing stability primarily in AR and LB, at least under the controlled conditions analyzed in the present study. Clinical data will further define the role and application of stand-alone cages. This data further supports, that 360° stabilization with cage and posterior instrumentation provides maximum construct stability, irrespective of the surgical technique used for cage placement. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.