STUDY DESIGN: A biomechanical study using human cadaveric lumbar spinal motion segments and three different posterior stabilization devices. OBJECTIVE: To compare the range of motion, disc height, and foraminal area of a spinal motion segment intact, injured, and fixed with each of three posterior lumbar motion preservation devices. SUMMARY OF BACKGROUND DATA: Motion-sparing lumbar posterior dynamic stabilization devices are gaining increasing popularity, particularly for the treatment of degenerative disc disease. METHODS: The PercuDyn, the X-Stop, and the Isobar posterior stabilization devices were compared using an in vitro cadaveric model. First, pure moments of +/-8 Nm were applied in all three planes, then a follower load of 700 N was applied, and finally, sagittal bending tests were repeated. All tests were conducted using an 8-df servohydraulic load frame. Experiments were performed intact, with a simulated injury, and then with each of the three devices for a total of four specimens per device. Foraminal area and disc height (posterolateral and anterior surface) were measured under neutral and peak torques in all three planes and range of motion was recorded for all experimental conditions. RESULTS: Overall, the injury model successfully increased range of motion and decreased disc height and foraminal area. Once treated with one of the three implants, the PercuDyn was most effective at preventing hyperextension, decreasing extension with a follower load by a mean of 52% compared to injured conditions (P = 0.07). The X-Stop stabilized the posterior column, increasing foraminal area under all conditions, particularly extension with a follower load, by 27% compared to injured conditions (P = 0.01). The Isobar, the only device to stabilize the anterior column, increased anterior disc height under flexion with a follower load by 22% (P = 0.03). CONCLUSION: All three devices functioned as intended by their respective manufacturers, but each appeared to excel in different areas; therefore, each should be used for unique clinical applications.
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