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The Positional Magnetic Resonance Imaging Changes in the Lumbar Spine Following Insertion of a Novel Interspinous Process Distraction Device

Siddiqui, Manal FRCS†; Nicol, Malcolm MRCS†; Karadimas, Efthimios MD†; Smith, Frank MD*; Wardlaw, Douglas FRCS (Ortho)†

Diagnostics

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 mm2 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.

This study shows changes in the cross-sectional area of vertebral canal and exit foramens by using positional magnetic resonance imaging in patients with lumbar spinal stenosis before and after X STOP implantation (St. Francis Medical Technologies, Concord, CA). The implant significantly improved the vertebral canal and exit foramens area without affecting overall movement of the lumbar spine.

From the Departments of *Radiology and †Orthopaedics, Woodend Hospital, Aberdeen, Scotland.

Acknowledgment date: November 10, 2004. First revision date: July 8, 2005. Second revision date: July 22, 2005. Acceptance date: July 23, 2005.

Grants have been received from St. Francis Medical Technologies Incorporated to fund the MRI scans.

The device(s)/drug(s) that is/are the subject of this manuscript is/are not FDA- approved for this indication and is/are not commercially available in the United States.

Corporate/Industry funds were received in support of this work. Although one or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript, benefits will be directed solely to a research fund, foundation, educational institution, or other nonprofit organization which the author(s) has/have been associated.

Address correspondence and reprint requests to Douglas Wardlaw, FRCS (Ortho), Consultant Orthopaedics, Woodend Hospital, Eday Road, Aberdeen AB2 4NA, Scotland; E-mail: Doug.Wardlaw@arh.grampian.scot.nhs.uk

© 2005 Lippincott Williams & Wilkins, Inc.