BRINGING BACK GRAVITY: THE USE OF POSITIONAL MRI IN THE EVALUATION OF SPINAL PROTHESIS

Abstract

Introduction Conventional MRI scanners require the patient to lie in a supine position within the bore of the magnet; positional MRI (pMRI) scanners allow patients to be scanned in any position. This is of particular value when patients have postural dependent symptoms.

Here we discuss the evaluation of two spinal devices: Dynesys, a spinal stabilisation system for back pain, and X STOP, an interspinous process distraction device for spinal stenosis.

Materials, Methods & Results For each device, patients underwent pre and post-operative scans in standing, lying and seated in neutral, flexed and extended positions and the ranges of movement at the operated levels and across the whole lumbar were measured.

For Dynesys, 30 patients with lower back pain were recruited. The first 20 patients have completed their 9 month scan, and the results show that the device reduces the range of movement at the operated segments, with a small increase in movement at adjacent segments and an overall reduction in the range of movement of the lumbar spine.

For X STOP, the first 10 of 45 have reached their second scan at 6 months post surgery. The scans demonstrate a net increase in the cross-section of the spinal canal of 21% when flexed to 35% whilst standing, and an increase in the surface area of the exit foramen of 23% flexed and 51% standing at operated levels.

Conclusion These studies demonstrate the value of pMRI for the evaluation of lumbar spine prosthesis. pMRI allows for the assessment of the devices in their functional (i.e. upright) position.