Biomechanical impact of vertebroplasty. Postoperative biomechanics of vertebroplasty.

OBJECTIVES To examine the biomechanisms underlying adjacent fractures following vertebroplasty, an emerging procedure to stabilize fractured vertebrae. In this procedure, bone cement is injected percutaneously into the vertebral cancellous bone. Once hardened, the cement offers mechanical reinforcement to the weakened vertebra. Recent clinical and biomechanical reports suggest that this procedure may cause new fractures adjacent to the one augmented. The cause and extend is unclear yet. The focus here is on the biomechanical hypothesis resulting from the rigid cement augmentation. METHODS A combination of experimental and numerical studies, in additional to a review of recent clinical reports. RESULTS The broader finding suggests that vertebroplasty changes the mechanical loading in adjacent vertebrae. Specifically, an increase in adjacent loading in the range of 17% has been found. The mechanism underlying this increase seemed to stem from the excessive cement rigidity that reduced the endplate bulge of the augmented vertebra, thereby reducing the local spinal joint flexibility. The reduction in joint flexibility seeks to reverse itself by creating an increase in the inter-vertebral disc pressure. The increased disc pressure seeks to relieve itself by increasing the load on the adjacent vertebra. The increased load on the adjacent vertebra relates directly to an increased risk of fracture. CONCLUSIONS Although an increasing amount of evidence exists to support this theory of the origin of adjacent fractures, one must be cautious. Vertebroplasty is a relatively new procedure and further observations and, ultimately, prospective clinical studies are required to conclusively determine the cause and extend of adjacent fractures.