The positional magnetic resonance imaging changes in the lumbar spine following insertion of a novel interspinous process distraction device

Study Design. Patients with symptomatic lumbar spinal stenosis underwent magnetic resonance imaging to study changes in the lumbar spine in various postures before and after implantation of the X STOP Interspinous Process Distraction Device (St. Francis Medical Technologies, Concord, CA). Objective. To visualize the effect of the device in vivo. Summary of Background Data. Previous studies have shown vertebral canal and exit foraminal area to reduce from flexion to extension. Recently, reports on improved kinematics in vitro at the implantation level of the X STOP device have also been published. Methods. Using positional magnetic resonance imaging, patients were scanned before and 6 months after surgery. Images were taken with the patient in sitting flexed, extended, neutral, and standing positions. The total range of motion of the lumbar spine and individual segments were measured, along with changes in disc height, areas of the exit foramens, and dural sac. Results. In 12 patients with 17 distracted levels, the area of the dural sac at these levels increased from 77.8 to 93.4 mm(2) after surgery in the standing position (P = 0.006), with increase in the exit foramens, but no change in lumbar posture. Conclusions. This study shows that the X STOP device increases the cross-sectional area of the dural sac and exit foramens without causing changes in posture.