Abstract
Introduction
Osteoporotic fracture reduces vertebral stiffness, and alters spinal load-sharing. Vertebroplasty partially reverses these changes at the fractured level, but is suspected to increase deformations and stress at adjacent levels. We examined this possibility.
Methods
Twelve pairs of three-vertebra cadaver spine specimens (67-92 yr) were loaded to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep-loaded at 1.0kN for 1hr. In 15 specimens, either the uppermost or lowest vertebra was fractured, so that compressive stress distributions could be determined in the disc between adjacent non-fractured vertebrae. Stress was measured in flexion and extension, at each stage of the experiment, by pulling a pressure-transducer through the disc whilst under 1.0kN load. Stress profiles quantified intradiscal pressure (IDP), stress concentrations in the posterior annulus (SPP), and compressive load-bearing by the neural arch (FN). Elastic deformations in adjacent vertebrae were measured using a MacReflex tracking system during 1.0kN compressive ramp loading.
Results
No differences were found between Cortoss and PMMA so data was pooled. Following fracture, IDP fell by 27% in extension (P=0.009), and SPP increased by 277% in flexion (P=0.016). FN increased from 17% to 30% of the applied load in flexion, and from 23% to 37% in extension (P<0.05). Vertebroplasty partially reversed these changes without inducing any increase in elastic deformation of the adjacent vertebrae.
Conclusion
Vertebral fracture increases stress concentrations acting on the vertebral bodies and neural arches of adjacent (non-fractured) vertebrae, and these increases can be partially reversed by vertebroplasty.
Conflicts of interest: None
Source of Funding: This work was funded by Action Medical Research. Vertebroplasty materials were provided by Stryker and by Orthovita.
We can confirm that this abstract has not been published previously in whole or substantial part and that they have not been presented previously at a national meeting.
