Deramond H

Temperature elevation caused by bone cement polymerization during vertebroplasty

Percutaneous vertebroplasty (PVP), whereby polymethylmethacrylate cement is injected into the vertebral body (VB), has been used to successfully treat various spinal lesions. The mechanism responsible for the palliative effect of PVP is unknown, but it may be the result of neural damage caused by heat liberated during polymerization of the polymethylmethacrylate. The purpose of the current study was to measure in vitro temperature histories at three key locations (anterior cortex, center, spinal canal) in VBs injected with one of two different bone cements (Simplex P and Orthocomp) to determine the role temperature plays in PVP. Twelve VBs (T11-L2) from three elderly female spines were instrumented with thermocouples and injected with 10 cc of one of the two cements. Temperatures were measured with the VBs in a bath (37 degrees C) for 15 min after injection. A Students paired t-test was used to determine differences in peak temperature and time above 50 degrees C between the two cement groups. Peak temperatures and temperatures above 50 degrees C were significantly higher and longer, respectively, at the center of VBs injected with Simplex P (61.8 +/- 12.7 degrees C; 3.6 +/- 2.1 min) than those injected with Orthocomp (51.2 +/- 6.2 degrees C; 1.3 +/- 1.4 min). There was no significant difference in peak temperature between cements at the spinal canal location; temperature there did not rise above 41 degrees C. Although thermal damage to intraosseous neural tissue caused by cement polymerization cannot be ruled out as a potential mechanism for pain relief experienced by patients subsequent to PVP, it seems unlikely based on the worst-case conditions tested in the current study.

The effect of monomer-to-powder ratio on the material properties of cranioplastic

Percutaneous vertebroplasty consists of injecting polymethylmethacrylate cement into the cancellous bone of vertebral bodies for the treatment of various lesions of the spine, including osteoporotic compression fractures. Clinicians practicing vertebroplasty commonly alter the mixture of monomer-to-powder recommended by the manufacturer in an effort to decrease viscosity and increase the working time. The purpose of the current study was to measure the effect that varying the monomer-to-powder ratio has on the compressive material properties of a cement (Cranioplastic) commonly used in vertebroplasty. Cylindrical specimens were prepared varying a monomer-to-polymer ratio of 0.40 to 1.07 ml/g and tested per the American Society for Testing and Materials standard F451. Specimens prepared at 0.53 mL/g, which is near the manufacturers recommended monomer-to-polymer mixture of 0.57 mL/g, exhibited the greatest mean values for ultimate compressive stress, yield stress, and elastic modulus. Specimens prepared at higher or lower ratios exhibited diminished strength, in some cases by as much as 24%. Although altering the monomer-to-powder ratio affects the cements material properties, it is as yet unknown if the decrease is clinically significant.

Vertebroplasty for Pain Relief

767 tion under fluoroscopic control away from the primary x-ray beam are recommended. The approach of the vertebral body can be either bilateral or unilateral. At the beginning of the experience a bilateral transpedicular approach is recommended. The pedicle is well seen under frontal or slightly oblique frontal fluoroscopy and it is easy to insert safely the needle into the lateral and anterior part of the vertebral body. But such an approach allows the injection of only half of the vertebral body and inserting a needle in the other part of the vertebral body will be needed for a complete injection of the whole vertebral body. Unilateral approaches have been developped to allow a complete injection with only one puncture. The oblique transpedicular route has been proposed by Jacques Dion. A slightly oblique frontal fluoroscopic view is obtained and the needle is inserted obliquely into the pedicle from its superoexternal part towards its inferomedial part. At the end, the needle is inserted on the midline and far anterior into the vertebral body. Faced to small pedicles, mainly at the thoracic level, or invisible peIntroduction