Devoted to diagnostic and interventional spine imaging and therapeutics


MRI Changes in the Lumbar Spine Following Insertion of X-Stop Inter-spinous Process Distraction Device 2005

Interventional Spine

Francis, W. Smith, MD
Manal Siddiqui, FRCS, Non ASSR Member
Malcolm Nicol, FRCS, Non ASSR Member
Efthemios Karadimas, MD, Non ASSR Member
Malcolm Pope, PhD, Non ASSR Member
Douglas Wardlaw, FRCS, Non ASSR Member


Patients with symptomatic lumbar spinal stenosis underwent MRI to study changes in the lumbar spine in various postures before and after implantation of the X-Stop Interspinous Process Distraction Device
Objective. To visualise the effect of the device in vivo and to measure the changes in the geometry of the spine and dimensions of the spinal canal after X-stop implantation.

Methods & Materials

In Twelve patients, age range 57 to 99 years 13 males and 4 females, diagnosed with LSS and neurogenic intermittent claudication who have not responded to non-operative treatment such as bed-rest, physiotherapy, anti-inflammatory/analgesic medication, were enrolled in the study. 17 treated levels were measured.Using Upright MRI,Images were taken in sitting flexed, extended, neutral, and standing positions. The total range of motion of the lumbar spine and of the individual segments were measured, along with changes in disc height, areas of the exit foramina, and dural sac.


In 12 patients with 17 distracted levels, the area of the dural sac at these levels increased from 77.8 mm2 to 93.4 mm2 postoperatively in the standing position (p=0.006), with increase in the exit foramina, but no change in lumbar posture.
Preoperatively, from flexion to extension, the left exit foramina decreased by 31.2% and the right exit foramina by 18.3%. The dural sac area decreased by 26.7% from flexion to standing, 20.3% from flexion to extension, and 16.5% from neutral to standing.
Postoperatively, from flexion to extension, the left exit foramina decreased by 14.1% and the right exit foramina by 9.4%. The dural sac area decreased by 18.1% from flexion to standing, 5.9% from flexion to extension, and 13.8% from neutral to standing. Hence, Xstop reduces the degree of encroachment on the exit foramina and dural sac.
Comparing areas before and after surgery, in extension, the left and right exit foramina increased by 34.2% and 25.4% respectively. Similarly, the increase in dural sac area by 20% in standing, 16.3% in neutral, and 26.9% in standing was statistically significant. This area also increased by 7.5% in flexion, but was not statistically significant. Furthermore, the net increase of spinal canal area after the insertion of the X Stop was maintained when the patient went from sitting in neutral to standing in extension. The reduction in the endplate angles was statistically insignificant and the range of lumbar flexion-extension was maintained.


This study demonstrates that the XStop device increases the cross-sectional area of the dural sac and exit foramina through the use of positonal MRI without affecting overall movement of the lumbar spine.


Scottish Higher Education Funding Council.
St. Francis Medical Technologies, Inc. Purchase of scanning time.