Effect of vertebral shell on injection pressure and intravertebral pressure in vertebroplasty

Study Design. An experimental biomechanical study conducted on osteoporotic cadaveric vertebrae. Objectives. 1) To measure the intravertebral shell pressure and injection pressure; and 2) to determine the effect of the vertebral shell on the intravertebral shell pressure and on the injection pressure. Summary of Background Data. Forces that govern cement flow are an essential component of the cement injection process in vertebroplasty. The vertebral shell may play a significant role in confining the flow of cement in the vertebral body and thereby affecting the intravertebral pressure and injection pressure. Methods. A small fenestration was created in the left lateral vertebral shell of 14 vertebrae. A valve to open and close the fenestration and a sensor to measure the intravertebral pressure were attached to the opening. A closed fenestration simulated an intact shell, whereas an open fenestration represented a vented shell. Injection pressure and intravertebral pressure at the shell were recorded during a controlled injection. Results. A closed fenestration resulted in a significant increase in the intravertebral pressure at the shell. During the injection, the shell pressure increased on average to approximately 3.54 +/- 2.91 kPa. Conversely, an open fenestration resulted in an instant relaxation of the shell pressure to the ambient pressure of 0 kPa. Additionally, the injection pressure was approximately 97 times higher than the shell pressure. Conclusion. The presence of vertebral shell seems to be important for intravertebral pressure. However, the intravertebral shell pressure adds very little to the injection pressure. Key words: vertebroplasty, injection pressure, intravertebral pressure, vertebral shell, cement injection process.