 This is a single-center, non-randomized study. 10 Subjects who are identified to receive the AST Stabilimax BAR device will be approached to participate in this study. All subjects will receive 10 RSA tantalum beads 5 in each vertebra at the time of their lumbar surgery. After surgery, subjects will have the biplanar xrays taken. The biplanar xrays will be taken from 5 standing positions: neutral, flexion bending forward, extension bending backwards, left side bending, and right side bending. RSA analysis will be completed to determine the amount of motion on sagittal and coronal planes. 