Spinal MRI changes in 25 patients treated with dynesys stabilization

Francis W. Smith, M.D., Efthimios Karadimas, M.D., Malcolm Nicol, MRCS, Manal Siddiqui, FRCS, Waseem Bashir, MRCP, Douglas Wardlaw, FRCS

Purpose
It is claimed that the advantage of Dynesys spinal stabilization allows some motion, in all directions, at the operative levels. In vitro laboratory biomechanical studies show that the movement permitted is similar to rigid fusions. To assess this, patients with symptomatic low back pain underwent MRI to study changes in the lumbar spine in various postures before and after implantation of the Dynesys device.

Methods & Materials
Using Upright positional MRI, 25 patients were scanned before and nine months after Dynesis stabilization operation. MR Images were and the measures were made standing in neutral, flexion and extension as well as in lateral bending positions. Measurements were made from midline sagittal T2 images,
a) L1-S1 inter-endplate angle in full flexion & extension,
b) Flexion & extension at instrumented level,
c) Flexion & extension at levels adjacent to instrumented level,
d) Disc height at instrumented levels.
e) From the Coronal T2 images, Flexion angles to left & right.

Results
There is a statistically significant difference in flexion-extension range of movement of the whole lumbar spine (Mean=-11.79)(p<0.05), but it wasnt significant in the level above (mean=0.41)(p=0.930) The changes in the anterior disc height was (mean= -1.15)(p<0.05) and to the posterior (mean=0.34)(p= 0.12).

Conclusion
This study shows that in the Dynesys stabilizing system allows small range of movement at the instrumented levels, with no increased mobility in the adjacent/transition levels. Also our results show that the device alters spinal geometry by acting to compress the anterior annulus.

References
Research supported by: Scottish Higher Education Funding Council, ZIMMER

American Society of Spine Radiology
2005 Meeting abstracts