Biomechanical Characteristics of an Integrated Lumbar Interbody Fusion Device

Introduction We hypothesized that an Integrated Lumbar Interbody Fusion Device (PILLAR SA, Orthofix, Lewisville, TX) will function biomechanically similar to a traditional anterior interbody spacer (PILLAR AL, Orthofix, Lewisville, TX) plus posterior instrumentation (FIREBIRD, Orthofix, Lewisville, TX). Purpose of this study was to determine if an Integrated Interbody Fusion Device (PILLAR SA) can stabilize single motion segments as well as an anterior interbody spacer (PILLAR AL) + pedicle screw construct (FIREBIRD). Methods Eight cadaveric lumbar spines (age: 43.9 +/- 4.3 years) were used. Each specimen's range of motion was tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) under intact condition, after L4-L5 PILLAR SA with intervertebral screws and after L4-L5 360 degrees fusion (PILLAR AL+Pedicle Screws and rods (FIREBIRD). Each specimen was tested in flexion (8Nm) and extension (6Nm) without preload (0N) and under 400N of preload, in lateral bending (+/- 6 Nm) and axial rotation (+/- 5 Nm) without preload. Results Integrated fusion using the PILLAR SA device demonstrated statistically significant reductions in ange of motion of the L4-L5 motion segment as compared to the intact condition for each test direction. PILLAR SA reduced ROM from 8.9 +/- 1.9 to 2.9 +/- 1.1 degrees in FE with 400N follower preload (67.4%), 8.0 +/- 1.7 to 2.5 +/- 1.1 degrees in LB, and 2.2 +/- 1.2 to 0.7 +/- 0.3 degrees in AR. A comparison between the PILLAR SA integrated fusion device versus 360 degrees fusion construct with spacer and bilateral pedicle screws was statistically significant in FE and LB. The 360 degrees fusion yielded motion of 1.0 +/- 0.5 degrees in FE, 1.0 +/- 0.8 degrees in LB (p0.05). Conclusions The PILLAR SA resulted in motions of less than 3 degrees in all modes of motion and was not as motion restricting as the traditional 360 degrees using bilateral pedicle screws. The residual segmental motions compare very favorably with published biomechanical studies of other interbody integrated fusion devices.