Biomechanical alterations in intact osteoporotic spine due to synthetic augmentation: finite element investigation.

A three-dimensional nonlinear finite element model (FEM) was developed for a parametric study that examined the effect of synthetic augmentation on nonfractured vertebrae. The objective was to isolate those parameters primarily responsible for the effectiveness of the procedure; bone cement volume and bone density were expected to be highly important. Injection of bone cement was simulated in the FEM of a vertebral body that included a cellular model for the trabecular core. The addition of 10% and 20% cement by volume resulted in an increase in failure load, and the larger volume resulted in an increase in stiffness for the vertebral body. Placement of cement within the vertebral body was not as critical a parameter as cement amount. Simulated models of very poor bone quality saw the best therapeutic benefits.

Biomechanical effects of unipedicular vertebroplasty on intact vertebrae.

STUDY DESIGN: To assess the biomechanical effects of unipedicular vertebroplasty on nonfractured vertebrae. OBJECTIVES: To evaluate the potential benefits of vertebroplasty as a preventative treatment. To evaluate the effects of cement volume and bone mineral density on the mechanics of augmented intact vertebral bodies. SUMMARY OF BACKGROUND DATA: Many studies have been undertaken to examine the effects of augmentation procedures such as vertebroplasty or kyphoplasty on fractured vertebral bodies. However, the role of such procedures as a prophylactic or interventional tool has not been well studied. This approach may be of clinical interest due to the high occurrence of secondary compression fractures and potentially altered biomechanics following an isolated vertebroplasty procedure. METHODS: Nonfractured osteoporotic vertebrae were measured to calculate volume and DEXA scanned to obtain bone mineral density information. Randomly selected specimens were injected with 10% and 20% bone cement by volume or left unfilled to serve as controls. After radiographs and noted cement leakage, specimens were subjected to destructive compression testing. RESULTS: It was found that the injection of 20% bone cement by volume in the lumbar levels resulted in a statistically significant 36% strength increase as compared with the unfilled controls regardless of density levels. However, in the upper thoracic vertebrae there was no significant difference between the strengths of the three groups. Additionally, injection of 20% bone cement frequently resulted in extravasation through vascular channels or into the spinal canal. CONCLUSIONS: The introduction of 20% bone cement by volume results in a significant increase in the compressive strength of intact lumbar vertebrae, however upper thoracic vertebrae do not demonstrate a similar strength improvement. There was no difference in the stiffness of the vertebrae injected with cement regardless of location. Bone mineral density (BMD) may play a role in the magnitude of the strength increase, with lower BMD specimens realizing a relatively greater strength improvement. Cement leakage was frequently noted with 20% cement injection, especially in the specimens with higher BMD. The location of the cement did not appear to have an effect on the loading behavior of the bone but should be controlled to minimize the chance of cement escaping into the spinal canal.