discussion

The different properties of injectable cements will be analysed and we will try to propose how to choose the most appropriate cement for each indication.

All cements need to have some properties to be indicated in percutaneous vertebroplasty:

• Injectability
• Easy and safe injection (viscosity, appropriate injection set)
• Long setting time
• Sufficient radio-opacity
• Adapted mechanical properties.

The three categories of cements we have described share these properties.  Each cement has some specificities which could be used and adapated to each pathological case.

As PMMAs are the most widely-used and were the first cements available for vertebroplasty, they combine the advantages of long trial experience, low cost, good radio-opacity with some drawbacks.  The major drawback of the PMMAs is their toxicity and their non-biocompatibility.  This toxicity, due to a significant exothermic effect, is  an inconvenience in the treatment of vertebral bodies without any malignant component (osteoporotic or post-traumatic vertebras).

We have seen, however, that this thermal effect will provoke a cell necrosis (coagulation) that could be an interesting property in the malignant vertebral body lesions.

The recent development of new radio-opaque PMMA (osteopal V®) makes the preparation and the injection of the cement inside the vertebral body easier and safer.  Malignant tumors which sometimes present large osteolysis of the cortical bone, particularly on the posterior wall, require very accurate and careful injection of the cement.  To avoid leakage, particularly difficult cases would be better treated with such a radio-opaque cement combined with an appropriate injection set.

The Composite Cements ( Cortoss®) combine biocompatibility and easy handling (“mix-on- demand system”).  The initial clinical results show that pain relief occured in a percentage near that for PMMAs.  This effect obtained on pain at a low curing temperature cement seems to support the theory of the mechanical effect of the injection of cement as the major reason of pain relief in opposition to the exothermic effect. 

With composite cements, the consequences of leakage are offset by the non-toxicity of the cement.  However, the system of syringes and catheters for the injection of the cement is not ideal.  The snap-set could also be dangerous and could lead to a blockage of the needle inside the vertebral body.  In our opinion, an optimized product would include a modified injection system designed for greater safety.

Because of the low curing temperature and the mechanical properties of these composite cements, the treatment of osteoporotic compression fractures should be, in our opinion, the best indication for this category of cements.

Calcium Phosphate Cements are the most biocompatible.  For that reason, CPCs should be the best cements.  The composition of this cement makes it a “bone-like” cement that could avoid problems of toxicity inside and outside the bone (if a leakage occurs in the soft tissues).

However, the difficulty of injection in bone, the low radiopacity of some of those cements (Norian®) and the high cost make it a cement that should be limited to some specific indications.

The recent cement Calcibon® seems promising in percutaneous vertebroplasty because of its greater radio-opacity than Norian® SRS.

Biocompatibility, as major advantage, predisposes this cement to be used in the treatment of recent burst fractures in young patient.  

In osteoporotic cases, the bioresorption could be a drawback if it  occurred too early before any new bone formation.

The next figure will summarize the advantages and drawbacks of the different cements and specify, according to our experience, which indication we propose for each of them.