Prof Marc Bohner, Head of the Skeletal Substitute Group, Switzerland, corresponded exclusively with Spinal News International in an interview to share his views on why the brittleness of calcium phosphate cements has been their downfall in relation to being used for vertebroplasty and kyphoplasty.
Spinal News International: Do you think calcium phosphate cements (CPC) have been a failure in vertebroplasty/kyphoplasty?
Prof Marc Bohner: There are still very few reports on the use of CPC for vertebroplasty/kyphoplasty. However, the few I have heard in congresses have not been very positive: CPCs have been reported to fail mechanically and lead to partial bone loss and/or loss of height restoration. Therefore, one could say that the use of CPC for vertebroplasty/kyphoplasty is presently a failure.
Spinal News International: What are the reasons for failure?
Prof Marc Bohner: The main problem of CPC is their poor mechanical properties. The problem is not low compressive strength, but rather, their brittle nature. Another problem is their poor injectability: users have normally to hurry to proceed for the injection, which is certainly not a good thing.
Spinal News International: Is there scope for improvement?
Prof Marc Bohner: For the future, I don’t see much potential for improvement in terms of mechanical properties: CPC will remain brittle and hence not suitable for most cases of kyphoplasty/vertebroplasty. Even an increase of the compressive strength to 100-200MPa would probably not solve the problem because very small shear loads can completely destroy CPC.
Furthermore, compressive strengths are generally determined on geometrically perfect sample, whereas implanted samples are by far not perfect in terms of geometry. In terms of rheological properties, the next cement generation will be fine (I believe that one or two formulations – e.g. hydroset, biopex – are already fine).
Spinal News International: In your opinion, when it comes to kyphoplasty/vertebroplasty, is there a use for CPC?
Prof Marc Bohner: I believe that the use of CPC for kyphoplasty/vertebroplasty will remain limited to young patients who suffered from traumatic fractures and whose fractures were stabilised mechanically (so that there is no need to have a mechanical stabilisation through the use of the cement and no problem of cement failure under load). In other words, the market share of CPC compared to Polymethyl methacrylate will remain very small. Perhaps there is also a potential for CPC to be used for prophylactic vertebroplasty/kyphoplasty. In that case, there would only be a limited need for high mechanical properties because CPC are, mechanically speaking, not interesting due to their brittleness. They are only biologically interesting due to their potential to be replaced by new bone.
Spinal News International: What are your views on polymethyl methacrylate?
Prof Marc Bohner: Mechanically speaking, it is a very interesting material. The main problem is of biological nature, but so far, its use has been very successful. The only concern I could see at the moment is the long-term outcome of the use of PMMA, particularly for very young patients.
