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Kyphoplasty may restore vertebral body shape more effectively than vertebroplasty
Fracture-induced vertebral wedging was reversed by nearly 80% in kyphoplasty-treated specimens.
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Biomechanical research comparing kyphoplasty and vertebroplasty as treatments for vertebral fracture suggests both procedures provide comparable benefits in restoring load sharing and stiffness to fractured vertebrae, but kyphoplasty may be better at restoring vertebral body shape.
Patricia Dolan, PhD, and her colleagues mechanically tested 15 pairs of cadaveric thoracolumbar motion segments taken from 11 donors between the ages of 42 and 96 years. The investigators subjected the specimens to preliminary creep loading, induced them to fracture, and then randomized one of each pair to undergo kyphoplasty and the other to receive vertebroplasty.
Following the surgical procedure, the investigators subjected the specimens to a final period of creep loading, she said during her presentation at the 36th Annual Meeting of the International Society of the Study of the Lumbar Spine, in Miami, Fla. U.S.A.
The investigators performed stress profilometry tests to determine the compressive stress distribution in the discs, and from these measurements calculated the intradiscal pressure, stress peaks in the posterior annulus and neural arch load-bearing. They also assessed compressive and bending stiffness. In addition, the investigators measured the vertebral body shape and wedge angle using radiographs.
Restoration
Following fracture, the investigators found that the intradiscal pressure dropped 61% to 88% from pre-fracture values. They also discovered that both techniques were equally effective in restoring pressure and the restoration was maintained after postoperative creep loading.
Similarly, they found that marked increases in annulus stress peaks and neural arch load-bearing post-fracture were significantly, but incompletely, restored with both procedures. However, they found no significant differences between the treatment groups for these measures.
“Compressive stiffness was reduced by about 55% following fracture,” Dolan said. “This was only partially restored following the treatments [and] the value was still significantly different from pre-fracture, but again, there was no significant difference between the two groups.”
Restoring the angle
The investigators found that fracture significantly increased the vertebral wedge angle by approximately 1·. However, they discovered that only kyphoplasty led to a significant reduction of the angle, which was restored by nearly 80%.
“In the vertebroplasty group, the wedge angle remained elevated even after a period of creep loading,” Dolan said.
To reduce measurement errors, Dolan said two blinded observers obtained the radiographic measurements in the study, and the specimens were placed precisely in the same position for each radiograph
“We achieved very high inter- and intra-observer reliability,” she said. – by Gina Brockenbrough
Reference:
- Luo J, Sangar D, Bertram W, et al. Comparison of the short-term mechanical outcomes of kyphoplasty and vertebroplasty. Paper #14. Presented at the 36th Annual Meeting of the International Society of the Study of the Lumbar Spine. May 4-8, 2009. Miami, USA.
- Patricia Dolan, PhD, can be reached at the Department of Anatomy, University of Bristol, Southwell Street, Bristol BS2 8EJ, England; +44-117-928-8363; e-mail: trish.dolan@bristol.ac.uk.