Biomechanical properties of Coflex and X-STOP in treatment of lumbar spinal stenosis / 医用生物力学

Objective To analyze different biomechanical properties between Coflex and X-STOP device in the treatment of lumbar spinal stenosis (LSS), and provide references for design improvement of interspinous process spacer. MethodsFour finite element models, i.e., the L2-5 healthy segment model, the mild degenerated L4/5 segment model, the X-STOP-fixed L4/5 segment model, the Coflex-fixed L4/5 segment model, were constructed based on the normal lumbar CT images of a volunteer, and the models under flexion, extension, lateral bending and axial rotation were simulated to compare range of motion (ROM) changes and stress distributions on the spinous process and interspinous process spacer. ResultsX-STOP and Coflex decreased extension ROM by -48.12% and -75.35%, respectively, and released disc pressure by -58.03% and -80.75%, respectively. Coflex even restricted flexion ROM by -59.58% and reduced flexion disc pressure by -52.84%. No distinct changes appeared in lateral bending and axial rotation ROMs and disc pressure. The largest Von Mises stress appeared at the U-shape place during flexion in Coflex and at connection between left wing and screw during torsion in X-STOP, respectively. The largest contact pressure between Coflex and spinous process was 31.38 MPa during bending, and that between X-STOP and spinous process was 46.86 MPa during torsion. Conclusions Both X-STOP and Coflex are an effective treatment for LSS, and can effectively restrict the ROM of extension and reduce the disc pressure, without affecting the adjacent segments.

A Morphometric Study of the Lumbar Interspinous Space in 100 Stanford University Medical Center Patients

OBJECTIVE: With the increased use of interspinous spacers in the treatment of lumbar stenosis, knowledge of the geometry of the interspinous space is important. To prevent dislodgment of an interspinous spacer, the accurate depth and width of the interspinous space needs to be established to facilitate the best intraoperative selection of correct spacer size. METHODS: To determine the depth and width of the interspinous space, two methods are available which utilize plain film and magnetic resonance imaging (MRI). Data analysis of the interspinous depth and width was undertaken in 100 patients. RESULTS: The standard deviations were variable, since skin thickness (zone 1) was altered by sex and age. The difference in the zone 1 distance between adjacent interspinous processes varied according to gender (p0.05). For zones 6 and 7, the interspinous distances at the narrowest and widest points, respectively, were found to decrease with the aging process, but the decrease was not statistically significant. There were no differences with regard to gender (p>0.05). CONCLUSION: This study provides additional information on the interspinous space. This statistical data are valuable for use in the design of interspinous spacers.

Preliminary Report on Usefulness of Adjacent Interspinous Stabilization using Interspinous Spacer Combined with Posterior Lumbosacral Spinal Fusion in Degenerative Lumbar Disease

OBJECTIVE: Posterior lumbar or lumbosacral spinal fusion in degenerative lumbar disease has the problems of adjacent level disease as well as surgical complications. An interspinous device used for dynamic stabilization can also be applied to the adjacent segment for spinal fusion to reduce the severity of these problems. The authors reviewed the adjacent interspinous stabilization using an interspinous spacer(CoflexTM paradigm spine,Germany) combined with posterior lumbar or lumbosacral spinal fusion in degenerative lumbar disease. Method: From January 2007 to July 2008, ten patients with degenerative lumbar disease underwent posterior lumbar or lumbosacral spinal fusion with adjacent interspinous stabilization using CoflexTM. The indications for this type were adjacent segmental disc protrusion, adjacent segmental degenerative changes or high surgical risk groups, such as elderly patients or osteoporotic patients undergoing multiple leveled fusions. CoflexTM was inserted into the adjacent segmental interspinous space. The control group consisted of fifteen patients, who underwent posterior lumbar or lumbosacral spinal fusion without interspinous stabilization. The radiological parameters and clinical outcomes were compared. All patients were followed-up for more than twelve months. RESULTS: The visual analogue scale(VAS) in both groups postoperatively and at the twelve month follow-up were improved. In the CoflexTM group, the postoperative and twelve month follow-up X-ray showed no significant change in posterior disc height, interpedicular height, segmental lordotic angle, flextion-extension angulation and translation and no significant segmental instability. The control group showed a higher level of segmental lordotic angle, translation and a lower posterior disc height, interpedicular height, flextion-extension angulation and three patients showed adjacent segmental instability. CONCLUSION: CoflexTM can be used to stabilize the adjacent segment of spinal fusion in degenerative lumbar disease and might be effective in preventing adjacent segmental degeneration. However, further study will be needed to confirm this observation.