Deborah Jane Annesley-Williams FRCR, Presenter: Research support, Stryker Corporation Research support, Kyphon Inc Research support, Quadrant Medical Ltd

Jin Luo MD, Abstract Co-Author: Nothing to Disclose

Phill Pollintine MD, Abstract Co-Author: Nothing to Disclose

Michael Adams MD, Abstract Co-Author: Nothing to Disclose

Patricia Dolan MD, Abstract Co-Author: Nothing to Disclose

Kyphoplasty is a modification of the basic vertebroplasty technique used to treat osteoporotic vertebral fracture. This study evaluated whether kyphoplasty conferred any short-term mechanical advantage when compared with vertebroplasty.

Pairs of thoraco-lumbar “motion segments” were harvested from nine spines (42–84 yrs). Specimens were compressed to failure in moderate flexion to induce vertebral fracture. One of each pair underwent vertebroplasty, the other kyphoplasty. Specimens were then creep loaded at 1.0kN for 2 hours to allow consolidation. At each stage of the experiment, motion segment stiffness in bending and compression was determined, and the distribution of compressive “stress” was measured in flexed and extended postures by pulling a pressure- sensitive needle through the mid-sagittal diameter of the disc whilst under 1.5kN load. Stress profiles indicated the intradiscal pressure (IDP), stress peaks in the posterior annulus (SPP), and neural arch compressive load-bearing (FN).

Vertebral fracture reduced bending and compressive stiffness by 37% and 55% respectively (p<0.0001), and IDP by 55%-83%, depending upon posture (p<0.001). SPP increased from 0.188 to 1.864 MPa in flexion, and from 1.139 to 3.079 MPa in extension (p<0.05). FN increased from 13% to 37% of the applied load in flexion, and from 29% to 54% in extension (p<0.001). Vertebroplasty and kyphoplasty partially reversed these changes, and their immediate mechanical effects were mostly sustained after creep-loading. No differences were found between vertebroplasty and kyphoplasty.

Kyphoplasty and vertebroplasty are equally effective in reversing fracture-induced changes in motion segment mechanics. In the short-term, there is no mechanical advantage associated with kyphoplasty.

Kyphoplasty is a more invasive, expensive and technically demanding vertebral augmentation technique than vertebroplasty. This study indicates that it confers no significant biomechanical advantage.

Annesley-Williams, D, Luo, J, Pollintine, P, Adams, M, Dolan, P, Does Kyphoplasty Have Mechanical Advantages When Compared with Vertebroplasty?.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5011343.html